Lene Hau

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ORAL HISTORIES
Image of Lene Hau

Credit: Justin Ide, Harvard University News Office

Interviewed by
David Zierler
Interview date
Location
Video conference
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Interview of Lene Hau by David Zierler on August 12, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
www.aip.org/history-programs/niels-bohr-library/oral-histories/47139

For multiple citations, "AIP" is the preferred abbreviation for the location.

Interview with Lene Hau, Mallinckrodt Professor of Physics and Applied Physics at Harvard. Hau recounts her childhood in Denmark and her early interests in science, and she describes her education at the University of Aarhus. She describes her studies in math and physics and her determination to build something meaningful for experimentation. Hau describes her interest in using lasers to cool down atoms during her postdoctoral work at Harvard and at the Rowland Institute, and she describes the opportunities that led to her full-time work at Rowland. She describes her collaboration with Jene Golovchenko and the impact of the discovery of Bose-Einstein condensation in 1995. Hau details the experiments that initially slowed down and then ultimately stop light in a Bose-Einstein condensate. She explains her decision to join the Harvard faculty and she surveys some of the practical applications of her research. Hau describes her research in nanoscale systems and her interest in applying her research to create more energy efficient systems with the explicit goal of addressing climate change. She describes some of the difficulties and systemic biases that women have to deal with in the sciences, particularly when they achieve prominence. At the end of the interview, Hau explains her interest to promote diversity in physics and particularly to encourage students who are the first in their generation to go to college.

Transcript

Zierler:

Okay, this is David Zierler, oral historian for the American Institute of Physics. It is August 12th, 2020. It is my great pleasure to be here with Professor Lene Hau. Lene, thank you so much for joining me today.

Hau:

Well, thank you for having me, David.

Zierler:

Okay. So, to start, would you please tell me your title and institutional affiliation?

Hau:

Yeah. My title is Mallinckrodt Professor of Physics and Applied Physics at Harvard University.

Zierler:

Now, physics and applied physics suggests what? Is that a joint appointment?

Hau:

Yes, that’s correct. My physics appointment is in the physics department and applied physics is part of the School of Engineering and Applied Sciences. So, it’s actually 50/50. I’m in both places.

Zierler:

So, there is no department of applied physics?

Hau:

That’s correct. Because the School of Engineering and Applied Sciences has a very open structure. There are no departments. In recent years, we have started to talk about areas. So, there’s an area of applied physics. So, in that sense, you could say its sort of trending towards departments, without calling them departments.

Zierler:

Right.

Hau:

Then when we appoint people, for example, that’s also a new invention. Then we are in a cluster in terms of voting for whom to appoint, for example. So, there are areas, where areas kind of have to do with teaching. And then there are clusters. And the clusters can then be a different set of people. When we are voting for appointments that would be in a cluster vote. So, it’s split into clusters and it’s split into areas. It’s not one to one correspondence. It’s not…they’re not the same set of people. So, it’s actually a little bit confusing.

Zierler:

(Laughter) Now is a 50/50 appointment, in terms of your own research interests and the kind of classes that you teach, do you find yourself sort of naturally gravitating towards one or the other more? Or it really depends on the year?

Hau:

Yeah. That’s a good question. I think it depends on the year. I’m teaching in both. In physics, I was teaching there in the spring. And right now, in this coming semester I’ll be teaching in applied physics. The environment in a particular place can be different. But, of course, I should mention that physics and applied physics…most people in applied physics have a joint appointment with physics.

Zierler:

Right.

Hau:

So, in that sense you could say it’s in some sense, to a great extent, the same people in applied physics…most of them are also in physics. So, in that sense, it’s not so different.

Zierler:

Now, coming from the Danish system, are these basic categories, applied physics, experimental physics, theoretical physics, is that roughly the same way that it works in Denmark? Or no?

Hau:

Yeah. There are experimental physicists in Denmark. And there are theoretical physicists. So, that same split is there too. Yes.

Zierler:

Well, Lene, let’s take it back to the beginning. Let’s start first with your parents. Tell me a little bit about them and where they are from.

Hau:

Okay. They are from Jutland which is the peninsula of Denmark. You know, Denmark is basically a peninsula connected to the European continent. And then a bunch of islands. And of course, now, all the main islands are connected by bridges. And actually, if you think about Copenhagen, Copenhagen is actually on a rather eastern island. The eastern part of an eastern island. And Jutland is in the western part of the country. And of course, the country is small, right? So, it takes from my hometown, which is Vejle on the east coast of Jutland, it takes to Copenhagen…by train you can probably get there in- let me think, two and a half hours (laughter). If it’s a good, fast train.

Zierler:

And what were your parents’ professions?

Hau:

So, they were both from Jutland. My father, a little bit further north from my hometown. And my mother, from the western part of Jutland. In particular, my mom was from a very rural area. She grew up in this very rural area. Her parents had a store called Brugsen which was really a co-op. It was a general store in a small rural town where they carried everything from fine china to grain and seeds and fertilizer. And it was all surrounded by farms. It was a co-op, so the farmers actually owned cooperatively this store. So, it was really part of the co-op movement that started in Denmark. I believe actually around 1876 or so. The first co-op was a dairy farm. So, boy, they had this co-op store and of course, this was fantastic for me as a grandchild. Because as a child you love to play that you open a store. And here I had a real store to play around in. And also, the fact that it was so incredibly broad in terms of what they carried, you know? The farmers would come to the place where they’re delivering milk to the dairy farm. What is it called? Is it called a dairy farm?

Zierler:

Yeah.

Hau:

To this dairy where they would deliver their milk for processing. And my mom was a single child so- and only me and my brother- we were the only grandchildren. And I was the oldest one, so I had a particular close connection with my grandparents. And I spent huge amounts of time with my grandparents in this rural area in the co-op store. So, that’s really a great memory for me. And my father, he came from a little bit further north of my hometown. So, sort of middle part of Jutland. Also, not quite as- his town was a little bit bigger but again, he came from a rural town in Denmark. In terms of my mom, she was trained by my grandfather in the store. So, she always was much more on the business side of things. So, when me and my- she actually was a stay-at-home mom until my brother, who is three and a half years younger than me, until he was about sort of, school aged. Then she started work because she really liked to work. So, she started working part-time in a brand-new department store in my hometown. You know, at the time when the big department stores started. That was the first big department store in my hometown. So, she started working there part-time. And my father, he actually started out being a cheese and butter maker. But then, sort of in the fifties, he could sort of see the trend that the small dairies or dairy farms- Dairy farm, that’s really a farm, right?

Zierler:

Yeah.

Hau:

I’m really talking a place where they process the milk. Is that called a dairy?

Zierler:

Yeah, that’s right.

Hau:

Okay, good. So, he could see that the small, local dairies, they all had their own kind of cheese, their own kind of butter, their own recipes. And they were very proud of them, right? But then everything started to merge. He could see that there were going to be sort of a big merging going on and there would probably be a lot of layoffs. And it didn’t look like something with a great future. So, he actually went back to school and became a technician. An HVAC technician. So, then at that point, my parents moved to my hometown of Vejle, where I was born a year later. And Vejle’s a town in Denmark of 50,000 people at that time. No, 40,000 people at that time. It’s 50,000 now. He started working for the big pride of the town. One of two main businesses in town that was kind of the big pride. That was, I guess, a meat factory. A meat plant where they both had cattle coming in. Had pork coming in, or pigs coming in. That they would then slaughter and then produce the meat. Process the meat. And one of the famous products of this place was bacon. The place was called Tulip. One of the great products of that place was bacon that was sliced and vacuum packed. And later in my life, which of course we can come back to, I actually ended up working in that meat packing plant.

Zierler:

Really?

Hau:

But he was really an HVAC technician. He was in charge of the cooling of the plant. I remember as a five-year-old that on Sundays, when he went to the meat packing plant to take tours to check in on things, that everything was cooling correctly. He would take me along with him on this business to the plant and that was a fantastic experience for me. I mean, I could remember all the meat, all the sort of half pigs hanging there. And all the half cows hanging there. The cows were a little scary. The pigs looked really cute. But then the highlight of the walk through was that I was allowed to, he allowed me- they used forklifts. And he allowed me to- of course, he was really steering it, but I was there in his lap driving the forklift. That was the highlight of the trip. And later, I really loved cars and I loved to drive. So, this was just a fantastic, good experience. Driving the forklifts.

Zierler:

Lene, when did you first realize that you were interested in science and how the world works?

Hau:

I mean. I know I was a very curious kid who would ask a lot of questions. And I still am to the extent that it annoys people (laughter). I asked a lot of questions. So, I would say I was a very, very curious kid. And maybe just to stay with my father for a little bit. It’s probably not a good thing to put in the transcript, but I would ask so many questions. And then sort of pursue it. And if I didn’t feel I got a good answer, I would keep questioning. And in the end, if it got too much for my father he would say, “Okay. Why doesn’t the cow shit upward?” Then it was time to stop the questioning (laughter).

Zierler:

Lene, this is as much a cultural question about Denmark as it is specific to you, but growing up did you ever feel discouraged as a girl or as a young woman that science was not something for you to pursue?

Hau:

I think I have been very lucky in the sense that- let me say that I had a fantastic teacher in my elementary school and junior high. So, the way the school system is in Denmark is a little different from here. But, basically from first through ninth grade I was in one school. And then when I went to high school I went to another school. For three years. In the first school I was in, I was in there, it was sort of nominally ten years. But I left after nine years and skipped the tenth grade to go to high school in this other school. I had the same math teacher from first through ninth grade and-

Zierler:

Wow. Is that because the school was so small?

Hau:

No. It was much more based upon that you had the same teachers for a very long time. I also had, for example, my Danish teacher for nine years. And of course, that works great if you have a great teacher. It’s not so great if you don’t have a great teacher.

Zierler:

Right (laughter).

Hau:

But I was so lucky in that I had a fantastic math teacher. And I had him from first to ninth grade. I loved math. He was such a good teacher that…and my parents had actually only gone to school for seven years. And they of course, had had no math. They had had addition, subtraction, division, multiplication, that kind of thing. But they hadn’t had real math with equations and everything. And when we started that, like other parents of their generation, they didn’t know about that. But I loved that. And when I would bring my schoolbooks home the first day of school every year, my parents sometimes…they would look at them. And I had the sense that they thought, “Wow. This is going to be hard.” But I was very confident with this teacher that, okay, it might look incomprehensible looking forward in the book, but I was absolutely certain that I could learn this. You know? So, he kind of instilled in me to not be- if something is there, if it can be understood, I would be able to understand it by working with it. So, he instilled that confidence in me.

Zierler:

Wow. That’s wonderful.

Hau:

Yeah.

Zierler:

Lene, were your parents, despite their limited education- when they realized your academic talents, were they supportive and encouraging of you?

Hau:

Yeah. Very much. They totally- and of course, they grew up in rural areas. For that generation, growing up in a rural area, seven years of schooling was normal.

Zierler:

Right. So, it’s not that they were uneducated relative to their time. They just got the education that was standard.

Hau:

Exactly. Yes. That’s right. So, basically, I mean, they really believed in education. They believed that if you got a good education, the sky was the limit. That was simply the- enormously important. And they were very, very supportive of that.

Zierler:

When you were thinking about college, did you ever consider leaving Denmark for school?

Hau:

No. I never thought about that.

Zierler:

How was your English growing up? Did you learn English in school?

Hau:

At my time, we started learning English fifth year of school.

Zierler:

And can you give a little sense of, as a senior in high school, a good student looking to pursue a university degree. What are the options for you if you want to stay in Denmark and you want to be at the best place for math and science? What options are available to those students?

Hau:

There’s several main universities. I mean, there’s University of Aarhus that I went to. Aarhus is the next biggest city in Denmark. So, there’s University of Aarhus. There’s University of Copenhagen. And then, now it’s called University of Southern Denmark. I would say those are the three main universities.

Zierler:

And is there any distinction between public and private, like we have in the states?

Hau:

Education is really public. They are state universities. So, it’s really a public university. Which also meant that I didn’t have to pay tuition.

Zierler:

Wow (laughter). Life is good in Denmark. Why did you choose Aarhus?

Hau:

Well, that’s kind of a little bit of an interesting story. So, also my elementary and high school were public schools. So, why did I pick Aarhus? Well, when I was done with high school where I picked…you know, there were different branches you could pick. And I picked the mathematics physics branch. When you entered high school, you had to make a pick. And of course, a lot of that has changed since then, right? But I had to make a pick. If I wanted to be more on the humanities side or I wanted to do the math side, and I picked to do the math side upfront.

And then after one year in high school, we then had to branch out even more. And I picked the mathematics physics line. Which meant I had a lot of math and a lot of physics and some biology and some chemistry. In Denmark, the high school teachers actually have master’s degrees in the subjects that they teach. So, my high school experience was really, really great. Because it was sort of like- it became a different level. I felt a high academic level when we entered high school. So high school was a great experience for me, those three years. And I was also lucky, actually entering a high school that had just been built. And this was in 1975. And it was sort of that seventies style of building. One story. And we had a courtyard with a little pond. There were different branches of the building. The first-year students in high school, they would have their own branch of buildings around one pond. And then the second year, they had another sort of courtyard around their pond. And then there was sort of open access from the classrooms, with big open windows into the pond area. So, it was just this sort of place- the building had this- an architect makes a huge difference. So, it was just a building with a very open feel with big windows. Lots of light. And it was new. We were the first year there moving into the new buildings. So, we were- the high school had started two years earlier in sort of interim buildings. But we were sort of proud of creating the traditions for this high school. So, this was a very exciting time.

And the teachers, since they had just been hired, they were all sort of young. Right out of university. Full of energy. Full of enthusiasm. So, this was a fantastic experience. And then we had plenary meetings. They could be once every couple of weeks, once a month or so. Where we invited a speaker. It could be an author, or a politician. And those were great, great events. And then eventually I decided to- I was interested in so much. I thought about biophysics. Starting biophysics. But then I discovered there was only a small program at University of Copenhagen. And it looked like a little bit too small. And I was interested in physics and math and I was interested in medical stuff. I was interested in studying Danish. But then I eventually decided I wanted to be an engineer because I loved to build things.

Zierler:

And the forklift. You remember the forklift.

Hau:

And more so, during my whole childhood, I always built. I built with wood. It might have started out that I built a wooden house. Sort of a kid’s playhouse. With my father. We built it from scratch. We scrounged wood from- at that point, he actually worked as a refrigerator technician. So basically, we used wood from the wooden crates the refrigerators came in and then built this playhouse. And I think that very much- you know, I just loved to build. And that meant throughout my whole childhood, I would always try to scrounge wood and find wood where I could. And built an Indian village. Built a soapbox car. A very fancy one. And then of course I played with LEGO bricks. Like- just all the time. So, this whole idea of building was something I just was really, really interested in.

So, I decided I loved to build. I wanted to become an engineer. So, I actually started at the technical university in Copenhagen, to become an electrical engineer. But, at that time, it took four hours to travel to Copenhagen from my hometown. Because at that time there was not a bridge. I had to take a ferry and all of that. And we had no family whatsoever in Copenhagen and it just seemed so far from home. I only lasted three weeks. Then I had to go back to Jutland. So, then I went to University of Aarhus to study mathematics and physics.

Zierler:

And so there, why didn’t you continue on with engineering?

Hau:

Because the engineering I wanted to do was high level engineering. There were sort of three stages of engineering. And it was only, at that particular technical university in Copenhagen that you could study to become the highest-level engineer. Which was the one I was interested in. So, then the math and physics, which I was also very interested in. And that was the closest to that high-level engineering. So, they were sort of at par with each other in terms of the demands in mathematics and physics.

Zierler:

Did you think that with mathematics and physics you would be pursuing a different career, than had you stayed on with engineering?

Hau:

Um. Yeah, I probably would have. I’m sure I would have worked as an engineer, for example, in a company. But with that engineering degree, you also had the possibility of becoming a researcher. So, in that sense, I might have ended up working for a company with the engineering degree. But with that engineering degree, I could also have ended up becoming a researcher, for example, the technical university in Copenhagen would be a place where you could be a researcher. And there are researchers there that are essentially physicists. So, in terms of the intellectual level, you could say it could have led to both. So, having a technical university degree, I could have become a researcher. For example, at the technical university there. And I could actually then have built on that to get a PhD and then become a researcher at the university.

So, it was very much the same intellectual level in terms of math and physics, with that engineering degree. But then it would have had the more applied side to it. And that’s what I had in mind at the time. I mean, definitely in the back of my mind, I knew there was the possibility that I could become a researcher at that place. But the real reason that I picked wanting to be an engineer is that I wanted to build. So, I had in my mind to go out to a company and work as an engineer in a company. In particular, around building. I was just super, super interested in terms of building things. It could be building buildings. It could be building electronic devices. And in particular, the engineering degree I had signed up for was actually in electrical engineering.

Zierler:

Now, Lene, what’s the process? When you decided to stay on at university for graduate work, what is the process of connecting with a graduate adviser and developing a dissertation?

Hau:

Yes. Maybe I can even elaborate on what I was just saying. Because at the time, I thought if I went to do mathematics and physics, then I’ll end up as a teacher. And it seemed a little bit self-looping. Like you have a teacher, you get an education, and then you go back and become a teacher. It seemed to me that somebody had to break out of that loop and build something. That was sort of what I had in the back of my head. I wanted to build things. And I thought that somebody should break out of the loop of teacher, student, back to teacher. That somebody should break out of that loop and build something. So, that was very much in my mind in terms of picking the engineering field. But then of course, I got homesick (laughter). Then I picked the math physics. And then it turned out that I ended up being able to build anyway, in terms of being able to be an experimental physicist.

Zierler:

And how did you go about developing your dissertation topic? Was it something that was related to your adviser’s research?

Hau:

Yeah. So, basically the way it worked was when I entered university, I had to pick between- we picked two topics. I picked the two topics mathematics and physics. And you had to immediately decide to go for your master’s degree. After the bachelor’s degree, we would then pick either math or physics for the master’s degree. And mathematics and physics were essentially all we had. We didn’t have the humanities. I actually think that would’ve been good if it had been- here you sort of go into being an undergrad where if you’re in physics you also have maybe American history, for example. Right? You learn about that. But we would really only have mathematics and physics. And I think I actually missed having also the humanities. Sort of in hindsight, I think I really would have enjoyed having that.

So, it was really hard-core math and physics. And I actually first thought I would become a mathematician. It really had to do with the classes we had. The first year of university, the math classes were taught the best - we had a wonderful professor who taught us math. And he put what we were learning in the context of history. Like, why did these ideas develop? The physics classes seemed a little bit confused, like an incoherent mixture of classical mechanics, special relativity, and some thermodynamics. So, math was simply taught the best and I really thought I would become a mathematician. Until I started to have quantum mechanics.

Zierler:

Ah. That did it.

Hau:

That did it. And again, I mean I thought the topic was absolutely fascinating. And of course, it’s also very mathematical in terms of its language.

Zierler:

It’s also very Danish. I mean, it goes back to Niels Bohr.

Hau:

That’s true. But I don’t think I thought about that as much as it was just a very beautiful theory. And really counterintuitive. And you do an algebraic solution to find eigenvalues. And they turned out to be the energy levels of a physical system. A seemingly very mathematical model that you can actually relate to something in nature. That was fascinating. But again, there I had a fantastic teacher. He was actually a painter. A serious painter, as a hobby. And he was actually a student of Niels Bohr. And he would be telling us stories from when he was working with Bohr.

Zierler:

Oh wow (laughter).

Hau:

His lectures would be- he would be writing on the blackboard, and it was as if he was painting. But he was very clear in terms of his lectures and his explanations. So that again, I’m sure, had a big effect. The combination of the subject and the teacher. And that made me decide to go into physics.

Zierler:

And your thesis. What were you most interested in exploring with your thesis research?

Hau:

Um…

Zierler:

Was it spectroscopy that you were most interested in?

Hau:

I actually ended up- it was a little bit- it was kind of funny. Because I was sort of talking to my student friends. There was this guy who was considered one of the smartest guys in the department. I wanted to figure out what he was working on. That turned out to be really very interesting to me. It was in solid-state physics. He was really considered the whiz kid. The smartest guy. And he was on the boundary between experimental physics and theory which also appealed to me. That you’re sort of on the boundary and can do both. He was doing research on what is called channeling, which is part of solid-state physics. I like a good challenge. The fact that he was considered the smartest person at the institute appealed to me. To in some sense have to go toe to toe with this guy. I was actually advised against working with him because he had a reputation for not being a good adviser in the sense that he didn’t take care of his students. That he wasn’t interested in talking to them until he felt they were at the same level as he was.

But I ignored the advice. And decided to work with him anyway. He gave me a lot of freedom. And it meant that I very much picked the dissertation topic. Because I started discussing with him and during our discussions it became clear to me in terms of the discussions, we had what I was interested in. So that was something I picked to go after on my own. In that sense I had a lot of independence working with him. So, then it turned out he actually went on sabbatical for a year. And then I got a chance- actually that happened a little bit before, I got a chance to be a summer student at CERN.

Zierler:

Wow.

Hau:

You know, they pick a few summer students from each country who can go down and be there all summer.

Zierler:

Was this your first-time leaving Denmark, when you went to CERN?

Hau:

Let’s see now. Except- I had had a trip to England with my family. And a trip to Sicily in high school with my class. Apart from that and a little bit going down to the border of Germany. Apart from that, I guess it was the first time. And I was seventeen years old when I went to Sicily. And then going to CERN, that was in the summer of ’84 when I was twenty-four.

Zierler:

What were your impressions of CERN when you got there?

Hau:

I had a spectacular time.

Zierler:

Yeah?

Hau:

Yes. It was an amazing experience. We were a total of 120 summer students, you know, young kids or young people from all over. And this was just amazing. And we had these lectures and we worked in the research groups. I remember this enormous intensity of CERN really struck me. If you got beam time at one of the big accelerators for a week then you just ran your experiment 24/7 for that week. No questions asked. And then at that time we were writing the data to tape. And I remember driving up in the middle of the night in one of the old Renaults with the umbrella stick shift. Driving up to the computer center to hand in the tape so it could be stored there and then we could access the data remotely. That’s how you did it.

And it didn’t matter what time…in the middle of the night, at three a.m., there would always be people up there working. I was really struck by that intensity and loved it. You know, this idea of focusing on physics. Just completely immersed in it and this intensity. So, that really stayed with me. And I think it was also during my time at CERN that I really got this idea in my head that I wanted to go abroad to do physics. At some point I actually thought about that I would become a fellow at CERN after I was done with my PhD. But of course, that’s in high energy physics and I ended up taking a different route in terms of actually specializing in solid-state physics. But it was definitely by working at CERN that I got this taste for working abroad and wanting to do that.

Zierler:

Now you actually got to Cambridge- you got to the Rowland Institute before you completed your dissertation in 1989?

Hau:

Yes. I was actually done with my dissertation work. I was also almost done writing the dissertation. But then what happened is that I had a postdoc position that I had to start in August. I didn’t have quite enough time to finish the writing and hand the dissertation in. So then when I went back to Denmark for Christmas, the following Christmas, in ’89, I took a month there to finish my thesis and get it handed in. Then I was not back in Denmark until a year after. During Christmas of 1990. So, that’s when I then defended my dissertation. Because defending a dissertation there is a big public event. And there were people on the committee who had to come from abroad. There were two local committee members and then one coming from Germany. And this was a public event in the department. A big event. Since I wasn’t back in Denmark for that whole year from Christmas ’89 to Christmas ’90, I defended it in January ’91. So that’s why my official date is ’91. But the work was actually finished when I left for the U.S.

Zierler:

Now, Lene, when you were finishing up your graduate work, was your sense that you needed to leave Denmark for the best opportunities?

Hau:

I was extremely curious about the U.S. I had grown up watching American movies and being very influenced by American culture. And I was so curious about the U.S. And one of the things I really wanted to know was whether the cars were really as a big as they were in the movies. But I was very curious about the U.S. at many levels. I knew there was so much good research going on here. So, that’s how I decided I wanted to go to the U.S. to be a postdoc after my PhD.

Let’s see. So, the year before- that would be in the summer of ’88, so the year before I finished my PhD work, I travelled for one month in the U.S. to visit different places. To try to figure out where a good postdoc place might be. I wrote to a bunch of people over here, both in the U.S. and some in Canada. And then I figured out where I would visit. I gave seminars at the different places about my PhD work. And then to fund this, I had applied to the Danish analogue of the National Science Foundation. So, I got funding from them. And I got funding also from the Carlsberg Foundation. And then some from a private foundation. That was actually interesting, I didn’t quite have enough funding for the trip. But then literally the morning I was leaving for my trip, my phone rang. And it was this private foundation. They had decided to give me their whole annual distribution for my trip. So, that kind of closed the hole. And the department also chipped in a bit. So, getting that phone call was pretty astonishing. On the very day I was leaving.

And so, I travelled alone over that month and saw a tremendous amount of the U.S. I actually started out here in Boston. And went to Harvard. And then I went to a Gordon Conference, and then down to Washington DC, where the next stops were the Catholic University and the Naval Research Lab. And then I was up at University of Ontario. And then over to California. The University of California Irvine and Stanford and Berkeley. The professor I talked with at Harvard, my adviser had mentioned him, that I should be sure to visit him. He had much earlier worked as an associate professor at University of Aarhus. So, my adviser knew him. It was Professor Golovchenko at Harvard. And my adviser said I definitely should go visit him. And then he checked in with me later if I had written to him. “No.” I said. I hadn’t. Because Golovchenko was doing scanning tunneling microscopy and I really wanted to get into a new research field with ultra-cold atoms.

Zierler:

And what was your interest in that? What was so fascinating to you about that?

Hau:

Using lasers to cool atoms down to extremely low temperatures gave us access to parts of nature that one had never been able to probe before – those were just fascinating possibilities.

Zierler:

Tell me more about your CERN work.

Hau:

Oh yeah. I guess we talked about the CERN stuff before. As I said, my adviser went on sabbatical. And then I ended up going down to work with the same group that I had worked with when I was a summer student at CERN. Because while he was on sabbatical, they offered that I could come back and work with them. Then I was actually thinking of writing a double thesis. I was thinking about also writing a thesis about the CERN work, because that totally fascinated me too. But then I came to my senses and decided to focus and write up the work with my adviser. This ended up being a purely theoretical thesis. But I also loved experiments. And I loved doing theory. And there were just such good options that I was excited about. So, I spent quite a while at CERN. Actually, at some point, being the only one there representing the group.

And I really enjoyed the teamwork at CERN. But then, as I said, I did end up writing a thesis on the work with my adviser in Aarhus. I’m really glad. I learned a lot from that. So, my thesis ended up being really theoretical. And in solid-state physics. But then I was really interested in comparing what I was doing to what other groups were doing in different fields of physics. I remember spending a lot of time in the library. There was a Saturday that particularly stands out in my head. I was just roaming around in the library. And the way that the library system worked was that it was on an honor system. That we would just take a book and stick a slip in that we had the book. And then we had keys to all offices. So that meant if a professor had a book, had borrowed it, and I needed the book, I could see on the slip that this professor had it. And I could go into his office and find the book. And then I could read the part I needed to read right away. And then put it back. So, if you are following a train of thoughts, you can have an idea and then you pursue that idea by reading in some book and then getting a clue, then going to the next book. So, you could really pursue an idea and get access to the reading material right away. And the department had a fantastic library. As I said, it was this particular Saturday I remember where I was just pursuing an idea, and I wanted to compare what I was studying for my thesis work with other effects in physics to get a more unified view. And it was during that hunt that I came across that people were starting to use lasers to cool atoms down to really low temperatures. And I thought that was just the most fascinating, this was like pushing into a whole new realm of nature. So, I decided right there that that’s what I would like to do.

Zierler:

And Lene, who were some of the leaders in that field? Using lasers to cool down atoms?

Hau:

There was Steven Chu out of Stanford, who is s one who really stuck out. And then the Paris group, Ecole Normale Superieure with Dalibard and Cohen-Tannoudji. And Salomon. So, I would say those were the ones I sort of had in my mind. And I also got a chance to visit Paris and visit that group in December of ’88. Coming back to when my adviser suggested I should visit Professor Golovchenko at Harvard but didn’t write to him “because he’s doing STM and I want to do cold atoms.” He said, “Visit him anyway. He’s an interesting person.” So, I wrote to him. And that actually ended up- the trip ended up being segmented. Because I was going to a Gordon Conference in New Hampshire, so it made sense to land in Boston and then visit him first.

So, I gave a seminar to his group. And he asked really good questions. And I loved to get good questions that sort of spurred new thoughts. But then I went on and we didn’t talk about postdoc positions at that point because he was doing STM, etc. And then I went to the Gordon Conference and down to California and sort of did the whole loop like I mentioned. And then I had a stopover again in Boston. And he asked me what I was going to do for a postdoc. And I said, “I really want to do cold atoms.” I said, “This is what I’m really, really interested in.” And he said, “Oh. I’m real interested in that too. I don’t know anything about it. Why don’t you come here and do it?” And the thing is, I could also have gone to Paris, which was in some sense, the most natural thing to do. Because they were a group at the frontier of that field. But I felt a little bit that it would be too predictable. You kind of hop on a train that was already moving. And sort of hop on at station A and two years later hop off at station B. So, it seemed perhaps a little bit too predictable to me. Whereas the Harvard thing seemed- I wasn’t quite sure exactly what would come out of it. But I was sure there would be something exciting. Because it’s also like, given that I had got such good questions for my dissertation work, seemed like this would be an interesting person to work with. And I don’t like things to be too predictable. And I’m a very curious person. So, that’s how I actually ended up at Harvard as a postdoc.

Zierler:

Now was the appointment at the Rowland Institute, was that part of the postdoc? Or that was a separate endeavor?

Hau:

That was a part of the postdoc because at the same time as I visited Harvard, I also visited the Rowland. That was presented to me as a place for people with crazy ideas and I loved that idea because I sort of became aware that Land- Edwin Land who built Rowland Institute, right? Edwin Land from the Polaroid Corporation. He founded Polaroid. And when he sold his interests, most of his interests in Polaroid in 1980, he was one of the world’s richest people at that time. And he said, “Now I want to do what I always wanted to do. To build a place for basic research.” So, I visited that place. And he built this place. Beautiful building. And he made an endowment for the place, such that if you worked at the place you could apply for funding at Rowland. And they could make a decision and you could move if you got the green light. So, he believed that scientists were the best to make decisions as to what was interesting. So, that’s why he wanted to keep the funding locally.

Zierler:

Now did you tend to divide your research between the Rowland Institute and Harvard? Or it was all one, big project for you?

Hau:

It was all one, big project for me. And this whole idea- because Land wasn’t interested in making small steps. He wanted to take big steps. Therefore, it was phrased as, “This is a place for people with crazy ideas.” So, in that sense he didn’t want to sort of, as I say, make small steps. He wanted some big steps.

Zierler:

Yes. And what big steps were on your horizon? What were you thinking about accomplishing at that time?

Hau:

I really wanted to work with cold atoms. I also got a fellowship from the Carlsberg Foundation in Denmark that basically funded me for a year. So, it was really a combination of- so it was really a joint position, having Rowland, having my fellowship, and then working with this interesting person at Harvard. It was like this sort of triple combination that gave me an enormous amount of flexibility to move into a new field. So, even though my dissertation work was in solid-state physics, even in theoretical solid-state physics, it gave me the possibility to move into experimental cold atom physics.

Zierler:

And Lene, if you could explain, what was so exciting about cold atom physics at that time? What was on the cusp of discovery that would be relevant beyond the particular work that you were doing?

Hau:

It was very much- when you can cool atoms down to these very low temperatures, it’s really a new regime of nature.

Zierler:

What does that mean? New regime of nature?

Hau:

Yeah. It’s basically- you can push into a part of nature where you have never been before, you can probe nature with a completely new tool in a parameter space that’s just unexplored. So, I think it was very much- and I think that if you ask Steve Chu, I think he would probably say the same thing. It’s just a kind of thing where its curiosity driven. Here you have a whole new- you’re at the bottom of the temperature scale with these super cold atoms. It’s an absolutely clean system.

Zierler:

And so, you can see new aspects of atoms at these low temperatures? Is that the idea?

Hau:

Yeah. Atoms and new aspects of atom behavior. For single atoms, or it can be multiple atoms, interacting. And ultimately forming new states of matter. Like the Bose-Einstein condensate.

Zierler:

Now normally we associate lasers with heating things up. Can you explain the science a little bit about how you can use lasers to supercool atoms?

Hau:

Yes. So, basically lasers, it’s a really ordered system. And in many ways, heat is disorder. And a laser system is a very ordered system. So, in some sense you use the laser to take heat out. To take disorder out of the atomic system. And then sort of stick it somewhere else in the radiation field. So, the laser is a highly ordered system. So, it can be used to take disorder, heat out of the atomic system and put it somewhere else. That’s sort of the quick way of thinking about it. And then of course, you can work out the details of how it actually works. But it’s really the fact that a laser has a particular…you know, all the photons are exactly the same. It’s light with a very particular direction. With a very particular wavelength. So, the whole thing is one coherent system. All the photons are in lockstep.

Zierler:

At what point did you realize that you were going to stay on full time at the Rowland Institute?

Hau:

Well, I actually, when I came to the U.S. in ’89, I thought for sure that I would be a postdoc for two years and then return to Denmark. After the two-year period.

Zierler:

Right. Your intention was to go back. You were not thinking you were making a life for yourself in America.

Hau:

Right. That’s right. But then I just absolutely loved it here. And it was—

Zierler:

Now when you say “here,” how much of America had you seen at that point? Cambridge, Massachusetts is a very tiny part of the United States, of course.

Hau:

Sure, sure. I mean I loved the focus of the work that goes on here. It’s a very intense area to be in. And I love the focus and the intensity of this place. But I also love the American culture.

Zierler:

Interesting. What about it? What sticks out in your mind?

Hau:

Um. I find Americans to be very-

Zierler:

Is it less formal? Is it a less formal culture than Denmark, perhaps?

Hau:

I mean, in many ways, I would say- it’s funny. There’s a real resonance between American and Danish culture. They are, of course, in some ways, very different. But in some ways, very similar. And I, of course, did check out the cars. They were as big as they were in the movies. That I could certify. But I also found Americans to be very open. I mean, at the time, if you were standing on a corner. You couldn’t quite find your way- at that time you would stand with a paper map, right? And try to figure out how to get there. And I would only stand on the corner for about five seconds before an American would walk up to me and say, “Can I help you?”

Zierler:

A-ha (laughter).

Hau:

And then you would strike up a conversation. And I found them to be just really open. Like sort of people who have self-confidence. Like open. And sharing. I remember also, like I had to find a place to live. I started out looking for what I would do in Denmark. Looking out for a one-bedroom apartment. And I discovered, gee, that’s quite expensive. And then I discovered that people were using this- that there was a thing called roommates, which was a concept I didn’t know about. But then the Harvard housing office had lists of people who had an apartment, who were looking for a roommate. And I said, hmm, maybe actually, that might not be a crazy idea because I actually don’t know anybody here. So, then I started looking for, you know, roommates. And there was actually a Dane who was starting a postdoc position at Harvard in the chemistry department at the same time. And he would have liked to rent an apartment, so we could share an apartment. But I had this idea that I really wanted to move in with an American.

Zierler:

Sure.

Hau:

Because I wanted to learn American culture.

Zierler:

A-ha.

Hau:

So, I ended up moving in with two roommates. One was American. I mean, it was actually a couple. And he was from Holland. But she was American. And that turned out to be the best choice ever. Because she really took it upon herself of teaching me American culture. You know, not sit me down and give me lectures about where America is, but basically, you know, becoming a friend.

Zierler:

A-ha.

Hau:

And then I remember the first October. I was here. I moved in in September. And then she invited me to come down with them to her mom for Thanksgiving. And I said, “What is Thanksgiving?” And then it turned out- I was invited to be part of the family there for Thanksgiving. And discovering this important American holiday. So, really, this was the best choice ever. And they’re still my really close friends.

Zierler:

Lene, I’m curious, given your parents’ limited education, was it difficult to explain to them why you wanted to stay in the United States?

Hau:

Uh. Well, um. Not so much for education. But they had sort of said to me- they had friends where both of their kids had moved to America. And they always thought that they were so lonely. With the kids being so far away. And they sort of jokingly, half-jokingly, I guess, always said, “You can move anywhere. Just not to America.” In the sense that it’s so far away. Because they had these friends, right? With the kids.

Zierler:

Right.

Hau:

But then I ended up moving. Deciding to stay here. But then they took it really well. And my mother started to take- of course, it was hard for them, right? Because I was so far away. But my mother started taking English lessons. She had not had English ever in school. So, she started taking English lessons. And so, in that sense, their attitude was quite impressive, I thought. And then after I’d been here three years, they came to visit for the first time.

Zierler:

That must’ve been fun.

Hau:

Yes. And I remember at the end of that visit, my father said to me, “Gee. If I had been your age, I would have done the same thing.” He was here for a little more than two weeks, and then he sort of was quite- he was so excited about it. So, he said if he had been the same age, he would have done the same thing. That also really struck, that’s a very memorable thing for me. That he said that.

Zierler:

Now, at the end of your postdoc, you stayed on full time at the Rowland Institute. But did you also maintain an affiliation with Harvard during those years? From ’91 to ’99?

Hau:

Yes, I did maintain an affiliation with Harvard. I think it was called an associate with the department. And of course, the reason that I ended up staying was that I got a job offer I couldn’t say no to. And that was at the Rowland that they offered me, you know, after my two-year postdoc they offered that I could become member of scientific staff. Which basically meant, I could be a PI, right – that’s just another way we would phrase it today. And have my own lab and do exactly what I wanted to do. Namely, pursue cold atoms.

Zierler:

So that was something that you saw was important enough, and there was enough fundamental work to do for this to occupy your full attention?

Hau:

Yes. Yes. Yes.

Zierler:

And at Rowland, of course, there are no distractions with teaching or departmental service. You can really just be doing the science full time?

Hau:

Yeah. But then during those years, I actually, not the whole time, but I did end up teaching for some semesters at Harvard. Because I really liked that possibility. So, it wasn’t every semester. But I did teach even though I didn’t have to. I did teach during some semesters at Harvard. During that period.

Zierler:

Did you want to? Did you feel like that was important for your professional development? To keep up the teaching?

Hau:

Um. Well, I basically thought, I just really loved the opportunity. Basically.

Zierler:

And what were you teaching? Graduate and undergraduate classes?

Hau:

I was part of starting a freshman seminar. Where we would put these freshmen- this was actually a class I started up with Golovchenko that I mentioned before. That we started up this freshman seminar together, where we would pick twelve freshmen through interviews. And then we would split them into teams. And then they would pick a project. And then pursue that experimental project through the semester. And one of the things I did with them was to build a cooling setup. With a little vacuum chamber and everything. And they would be building lasers that we could use for manipulating atoms. So, this was one I was involved in. That was at the freshman level. And then I also taught a graduate class in solid-state physics. I did try both actually. Both working with freshmen and graduate students.

Zierler:

Now the Rowland Institute had an informally close relationship with Harvard. But at some point, it got sort of integrated formally into Harvard?

Hau:

Yes. That was after I left, actually. This was I guess three years after I left. Because that had been a completely independent research institute. And I actually consider it a bit of a loss that it didn’t stay independent. Because for me, it had given me the opportunity, you know, coming with a background in theoretical solid-state physics. And then giving me the opportunity to go in and do experimental physics in a completely different field. This was unusual.

And we talked about what made America special before? I felt that in America there were more paths you could take if you wanted to go from A to B. And a place like Rowland, that they would give me an opportunity to do this. To make such a change and let me, who was a theoretical solid-state physicist, give me a lab and do experiments in a whole new area. I felt that was sort of uniquely American. Somebody like Land, right? With crazy ideas. And give me an opportunity like that. I felt the Rowland was a uniquely American place. And it was a job offer I couldn’t refuse. So that’s why I ended up staying.

Zierler:

Lene, who are some of your most important collaborators during your Rowland years in the 1990s? Was it within the Institute? Would you work with people at other universities or organizations?

Hau:

I would say it was within the Institute. Collaborating with people at the Institute. And Michael Burns, in particular, come to mind. And also, for at least part of the time, collaborating with Jene Golovchenko who was at Harvard. And then later on, with Steve Harris at Stanford. I would sort of say those- in some sense, those are examples of collaborators that I had. So, it was both inside and outside. And the place was very open. And actually, encouraging collaborations on the inside.

Zierler:

Lene, looking back, given the fact that you were so focused on this particular area, what fundamental discoveries were made during these years that you were aiming for? What surprises were there along the way? And what mysteries remain from those years that you were not able to solve?

Hau:

Yeah. So, one of the things that I was very interested in was to basically make wave guides for cold atoms. You know you can guide light in optical fibers. How can you guide cold atoms? And we were very interested in creating a guide for cold atoms based on very, very, very small wires. And that was a thing. I mean, I’m just giving you an example of a thing we were interested in that I was working on, early on. And we actually succeeded later on to observe some of these interesting effects that we predicted. That was actually after I came to Harvard that we ended up doing these experiments where we took a nanotube that we could freely suspend in air. A long, freestanding nanotube where we could capture atoms. And of course, I can tell you more about that physics. But basically, captured cold atoms. And sort of have- what we have called a black-hole-like structure for cold atoms. So that’s something that we worked on early on. But then it came to fruition when I later came to Harvard. Because then in the meantime, Bose-Einstein condensation came along and that was something that I felt really excited about getting into. And I’m wondering, David, can we take a little break? So, I can get a coffee.

Zierler:

Absolutely.

Hau:

Cause, it’s hard to talk for so long.

Zierler:

Take your time. I’ll be here.

Hau:

Okay.

[Pause]

Hau:

So, I’m back.

Zierler:

We’re back. So, we were talking on the issue of the fundamental discoveries that you made. My question really comes from the idea that this was really a unique opportunity for you. You were intensively interested in this field of cold atoms. You were working in this amazing place where you had all the resources you needed to devote as much time that you wanted to. And so, it’s really- the question is about given these resources and given your talents and interests, what were you able to accomplish in terms of fundamental discovery? And what remained to be learned by the time you had left Rowland?

Hau:

Yes. So, to get back to that, it was really driven by curiosity in terms of getting into that system with cold atoms. And in particular, when Bose-Einstein condensates were discovered in the summer of ’95, I was just dying to get my hands on this state of matter. It required taking cold atoms further. It really required significant changes to the experimental setup. To be able to get a Bose-Einstein condensate. Which is this completely new state of matter that Bose and Einstein had predicted at that time, eighty years earlier. But it really was not until 1995 that it was possible to create it cleanly in the lab.

When I saw that, it was like, gee, I would love to take my cold-atom setup and really rebuild and change it significantly to be able to get my hands on this Bose-Einstein condensate. And why was that? Well, because again, this was such a completely new state of matter. It was known that it had properties similar to superfluid’s and superconductors. And for these Bose-Einstein condensates, we could now create a system very cleanly in the lab with these very cold atoms. Because if you take superfluid helium, for example, it’s only part of it that’s in a Bose-Einstein condensate. With these dilute gases we had in the vacuum systems, you could create a Bose-Einstein condensate where basically the whole cloud of atoms was in the condensate.

So, it was an extremely clean way of getting such a Bose-Einstein condensate and be able to probe it. And I was just dying to get my hands on one and start to poke at it to see how it would react. That was a case where I actually applied with the National Science Foundation for funding. This was shortly after that Eric Cornell and Carl Wieman at JILA and Wolfgang Ketterle at MIT had observed the first Bose-Einstein condensates. And immediately I thought, gee, I want to get my hands on that. And I submitted a proposal to the National Science Foundation, and I got five referee reports back that all said she’s a theorist. There’s no way she’s building a setup for Bose-Einstein condensation. It’s really hard. She’s a theorist. There’s no way she can ever do that.

Zierler:

Why not? Why would they assume a theorist could never do this?

Hau:

Yes.

Zierler:

First of all, Lene, aren’t you defying these divisions in the first place?

Hau:

I guess so (laughter). There’s a big conservatism in the system, right? So, I think it is a very conservative viewpoint, I guess. Is the best way of describing it. But then, within fourteen months of getting the rejection, we had the biggest, fattest condensates ever. So, basically, we managed to create Bose-Einstein condensation with big, fat condensates fourteen months after I got that rejection. Of course, at that time the world was really going gangbusters trying to make them. And I think it’s okay to say that we were kind of the first, or one of two being the first to get the condensate in this second wave.

Zierler:

Can you explain the significance of that?

Hau:

We got really big, fat ones with a lot of atoms in them.

Zierler:

And so, what’s the significance of that? If you can explain that a little bit?

Hau:

Getting a condensate- is that what you’re talking about?

Zierler:

Right. Yes.

Hau:

Yes. So, basically getting a condensate. It’s very similar to what I said about the laser before. So, a condensate is where the cloud gets so cold that all the atoms go into the same quantum mechanical ground state. So, every atom is in exactly the same quantum state as any other atom. So, the sort of popular way of saying it is all the atoms are in lockstep. From a physics point of view, all the atoms are described by the same wave function. So, in that sense, the atoms are phase locked. So again, every atom is doing exactly the same as every other atom. So, they’re in lockstep. They’re phase locked. They’re in the same quantum state.

So, what I wanted to do- I like to push things as hard as you possibly can without totally breaking it apart. What we did was we started to send laser beams in to poke at these Bose-Einstein condensates. And we picked to use laser beams that were resonant. Meaning, had a wavelength that would cause the laser beam to interact very, very strongly with the sodium atoms making up this condensate. And people thought we were crazy because they would say, I’m paraphrasing, that what we were doing would be like putting a bull in a china shop. Because if an atom in the condensate absorbs just one photon, that means when it absorbs a photon it gets a recoil. It gets a little momentum kick. The velocity from that momentum kick for the atom, from just absorbing one photon, is enough that it will then basically bang into the other atoms and it will escape the cloud and the whole cloud will heat up. And you will lose the condensate, ultimately. So, people thought we were crazy. Because again, the velocity that an atom would get from the recoil, by just absorbing one photon, is a velocity that’s so much higher than the mean velocity of the atoms in the condensate because they have been cooled so much to get into the Bose-Einstein condensate.

And now we shine a laser on and start giving these atoms very high velocities. It’s like, you’ll just blow the whole thing apart. And they thought we were crazy. But the reason that we wanted to use near-resonant light was precisely because you get very large interactions with atoms. And you’ll be able to, just before you blow the whole thing apart, you’ll be able to probe this condensate in novel regimes, so again you are pushing as hard as you can without totally breaking it apart initially. Just before it totally breaks apart, you might see some interesting new phenomenon.

And you also, by working with light very close to resonance, you have very, very high sensitivity. For example, to the atomic density distribution of these condensates. Because remember, at that time, nothing was known about these condensates and we wanted to know exactly what do they look like? Basically. And what are their properties? And then it was during our work with probing condensates with near-resonant light that we started to discuss with Steve Harris at Stanford that what if you have two resonant light beams? Then you might be able to slow light to very, very low velocities. And so, we set out with this work shortly after we had the condensates in ’97. And then the idea is that you use one resonant laser beam to manipulate the optical properties of the condensate. And then you can send another laser pulse in. And now this laser pulse will slow down to the speed of a bicycle. That’s ultimately what we ended up showing was possible. And I remember when we had the first little bit of slow down. In the lab, of course in the middle of the night. Then we had to be sure that somebody hadn’t pushed the knob on the oscilloscope. To be sure it was not a fake result. So, we had to double check that this effect was real. So, we had to do a control experiment. But we could only create a condensate once every two minutes. So, we had to wait for two minutes to be sure that this was real. And those two minutes seemed like an eternity. But then when we got the control experiment, we knew, gee, we are really starting to slow light down in this Bose-Einstein condensate.

Zierler:

And Lene, was the goal to stop light completely? Or just to slow it down?

Hau:

In this experiment to slow it down. But then we knew immediately that because of what we had done when we had the results that came out, when we had the results for the paper that came out in early ’99, we knew immediately that if you could slow it, you could also completely stop it.

Zierler:

Why? What is the theoretical basis for that? Why would it suggest that if you can slow light, you can stop it?

Hau:

Yes. So basically, the way we looked at it was that when you illuminate Bose-Einstein condensates with a laser beam that we call the coupling laser…we can also call it the control laser…but this coupling laser beam is the one that we use to illuminate the atom cloud, and then we send our light pulse in and slow the light pulse. And as the light pulse is slowing, the front-end edge goes into the condensate. So, you have a light pulse that initially might be a kilometer long in free space. The little condensate is only 100 microns or 0.1 millimeter long. So, as the front edge of the light pulse goes into the little condensate, it will start to slow down. But the back edge will continue in free space at the normal light speed and catch up to the front edge. And the whole pulse will spatially compress. And it compresses so much, that it’s actually completely contained within the atom cloud. And it creates a little imprint of itself in the atom clouds. That combination of coupling laser field and light pulse creates a little imprint in the atoms. Very much like a little holographic imprint. And so, it transfers the internal state of the atoms to a different state.

So, the holographic imprint is in the light pulse region. And it follows along with the light pulse, it’s slowly propagating through the atom cloud. And then when the front edge of the pulse comes to the edge of the condensate, it will move out in free space and accelerate back up to the normal light speed. And at the same time, the light pulse will then decompress and expand again and end up with exactly the same length it had before it entered the atom cloud. So now the thing is, when the light pulse is slowed, it is ultimately being compressed by the same factor as it is slowed down. That means by a factor of twenty to fifty million. So that means the light pulse, being one kilometer in free space, compresses to only twenty microns inside the atom cloud. So, it’s actually completely contained within the atom cloud. And it’s there with its little imprint. And I should also mention that the intensity of- if we lower the intensity of the coupling laser field, the light pulse will slow down further. The light-pulse speed is proportional to the intensity of the coupling laser field. So now, if we have this light pulse contained in the atom cloud, and if we now block the coupling laser intensity, this light pulse will come to a complete stop. And it will actually turn itself off. But its imprint was already imprinted in the atoms.

When we then, later, illuminate with a coupling laser beam, the system has all the information to recreate the light pulse. It’s basically the movie in reverse and the light pulse is revived. And then it moves on as if nothing had happened. So, it’s really important that you can contain the light pulse in the atom cloud. And the pulse gets so small you can contain it in the atom cloud. And it has already made its imprint in the atom cloud when it’s slowing down. Those combination of effects lead to that you can completely stop the light pulse. And that’s something we knew immediately. And talked widely about, that that would happen.

Zierler:

What are some of the fundamental understandings in physics that come as a result of these discoveries and capabilities?

Hau:

Sorry. Could you repeat that?

Zierler:

What are some of the fundamental things that we can understand about physics, generally, as a result of these experiments and discoveries?

Hau:

Yeah. I think there’s a bunch of applications of this. And of course, in some of our later work we have taken things further. Where we have stopped and extinguished the light pulse in one part of space and then regenerated it in a completely different location. We actually created two condensates, two independently created Bose-Einstein condensates. And then we can send the light pulse into the first condensate. Stop it. Extinguish it. And now we have that imprint in the first condensate. The holographic imprint that I mentioned. And that imprint actually consists of atoms in a different atomic state. And now, when we have extinguished the light pulse, that matter imprint can start moving because it got a little recoil from absorbing and emitting photons. So now, this little imprint has a recoil, so it will start moving. And it will exit the first condensate and move out in free space. So now what we have out in free space is actually a perfect copy of the light pulse we have extinguished. But now in matter form. And if we let this matter copy continue and then we make it overlap with a second condensate…if we don’t do anything else, it will move through the second condensate and come out on the other side. But, once the matter copy is embedded in the second condensate, if we now turn the coupling laser back on, we can regenerate the light pulse and it moves on.

So, in other words, we have stopped and extinguished the light pulse in the first condensate. We get a little matter copy moving across to the second condensate. And then we can turn that matter copy back to light and it moves on. This is kind of mind warping. We really believed, again from the beginning, that this would be possible because we are dealing with Bose-Einstein condensates where we have this coherence. All the atoms moving in lockstep. This matter copy that we create from the light pulse, it’s truly a perfect matter copy in the sense that it has the same shape as the light pulse we extinguished. It has the same phase distribution as the light pulse we extinguished.

And it has the same quantum statistics. So, in quantum mechanics there’s often an uncertainty and for example, in our original light pulse there will be an uncertainty in terms of the exact number of atoms. There’s a certain probability that you will have maybe 50,000 photons. There’s a certain probability you will have 50,001. And it’s only if you make measurement of the light pulse and count the photons that the system will kind of collapse and will pick, okay, I have 50,000 photons. So, there’s an initial quantum uncertainty in terms of the number of photons you have in the light pulse. And that same uncertainty will be in the matter copy. If you ask for the number of atoms, again there’ll be the same quantum uncertainty. There will be the same number of atoms in the matter copy as you had photons in the first light pulse. And the number of atoms will have the same quantum uncertainty. So, in other words, we also preserve the quantum statistics. And now you can imagine that you can start to- once things are in matter form, it’s easier to manipulate. So, you could now start to change the shape or the information content of this matter copy. You could also let it interact with another matter copy from another light pulse. And while photons don’t interact, atoms do. So, you can get very strong interactions between these matter copies.

And then once you are done with your manipulations, you can then take the matter copies and turn them back to light. So, this is a system that you can really use for creating new paradigms for information processing. Because as we know, we love to imprint information in light and carry it around in optical fibers. So, you can imagine you could have a system like ours in a node in the fiber-optical network and turn the light pulses into matter copies. Let them interact and then take them apart. Turn them into light and send them down other optical fibers. So, this could be really a new way of processing. This is really a new way of processing information. Where the quantum statistics of the system is preserved. So, it’s kind of a setup for quantum information processing. Quantum computing. And also, the fact of course, just the fact that we can hold onto light pulses says we have a memory for information. Optical information or quantum information. So, it’s a setup for quantum information processing, quantum computing. And then of course, it’s a fundamentally different system from any other system.

Zierler:

Lene, what were the circumstances leading you to decide to join Harvard full time?

Hau:

I think at that point, it’s generally good sometimes to try something new. As I said, I am a curious person and I don’t like things to be too predictable. It was partly trying something new, but also that I really had an interest in teaching.

Zierler:

And you wanted to be able to do that in an academic setting at this point.

Hau:

Yes.

Zierler:

Were you able to seamlessly transfer your research over to Harvard? Or was this an opportunity to take on new projects?

Hau:

Yeah. We kind of did both. We transferred our setup to Harvard. At the same time, we also started building new projects. So, it was really an opportunity to do both.

Zierler:

What was exciting or different, on a day to day level, when you joined Harvard versus Rowland?

Hau:

Yeah. So, when I was at Rowland, I could really be in the lab all the time. And twig all the knobs. That, of course, became different when I came to Harvard because you have so many other obligations in terms of teaching and committee work. Then you also end up with a bigger group. And have to go for outside funding. But definitely teaching, a big part of it. So, it meant that I would have much less time to be in the lab. But I have always wanted to sort of interact with people in my group in a very detailed way. Because I feel that’s how I- it’s how I can best help the students. And also, how I can be the most creative. By really thinking in detail about the experiments. So, we end up having very many meetings talking in great detail about what’s going on in the lab. And also, during critical runs, I would be in the lab.

Zierler:

Now in 2001, when you stopped light completely. Did you see this more as a theoretical achievement or an experimental achievement?

Hau:

Uh. I mean, both really. The field I’m in is so, sort of, theory and experiment entangled. So, I would say in some sense both. It’s an example of how counterintuitive quantum mechanics is. So, I mean in many ways I would say both. But ultimately, it’s really if I should state that- I think it’s both, but I think it’s an experimental achievement.

Zierler:

And when you did achieve this, what opportunities did that afford you in terms of the science? Where could you take the science from there?

Hau:

Yes. Because then, given that we could do this experimentally, we could then start to create what we named quantum shockwaves in Bose-Einstein condensates. Because we could use these stopped light pulses to probe these condensates. Part of what we had in mind was the later experiment that I mentioned. Sort of stop a light pulse in one part of space and regenerate it in a different location. That was one thing we had in mind.

Another thing we had in mind was that we could let this- when we create this matter copy in the atom cloud from this light pulse that has really slowed down, what happens is that part of the atoms in that holographic imprint will be in a different internal state and we can make it such that that different internal state gets kicked out of the condensate. So now we can use these ultra-compressed light pulses to create very small holes in Bose-Einstein condensate. So now all of a sudden you have a condensate. Instead of having a very uniform distribution, you can poke a hole in it in the middle. And a condensate doesn’t like that. So, it reacts. The way it reacts is it creates the quantum analog of shockwaves. And they come in the form of what is called solitons and quantized vortices. And in many ways, the presence of quantized vortices is a very defining characteristic of Bose-Einstein condensates. That you basically have whirling patterns of atoms with quantized circulation. By creating these very slowed and compressed light pulses in the Bose-Einstein condensates, we could poke small holes in the condensates and then have a condensate break down into quantum shockwaves that we could directly observe and later make the shockwaves collide also. To create new nonlinear structures. So, it sort of gave us a whole realm of possibilities both in terms of quantum storage of light, quantum information processing of light, and also manipulation, not just of light, but also of the atoms themselves. The Bose-Einstein condensates themselves. And make them do really crazy things. So, we really got a whole new set of eyes on the behavior of these atomic Bose-Einstein condensates as superfluids. Because we can directly photograph the condensates, we can see what happens in real time by taking photographs.

Zierler:

In what ways was this research so important for other researchers who had already been working in the quantum world? What did this allow them to do? Or in what new ways did this allow them to understand the work that they were doing?

Hau:

Yeah. So, for sure one big spinoff. I mean it’s like after our experiments, which was exciting, a ton of groups, all over the world, started to want to slow light. And they ended up trying to slow light in all kinds of different media. Then also, it led to quantum memory. That we can use this system to store quantum information of light. And that allows for quantum computing. It’s very important for quantum computing. And remote quantum entanglement that is used, for example, for secure cryptography.

Zierler:

So, the practical applications of this became apparent immediately?

Hau:

Yes, both in terms of- I would say it spurred both interesting theory. Interesting fundamental experiments. And also, applications. Immediately.

Zierler:

When we’re talking about transferring light into matter and then back into light, does this tell us fundamentally new things about exactly what light is that goes back to Einstein or even before?

Hau:

Yes. Because this system, there’s a complete analog between light and matter. We start with light. And then turn light into matter. And then back to light. But at the same time, so we can sort of say it’s a way to manipulate light. But we can just as well say it’s a way to manipulate matter.

Zierler:

Right.

Hau:

Because what happens is that when a light pulse comes in and we stop and extinguish it, as I said, we can actually take a little piece of that condensate to create the matter copy. And then we can take that matter copy- when we then turn the coupling laser back on, we revive the light pulse. But then now this matter copy is in a different position. And the atoms in the matter copy are in a different internal state. Once we turn the matter copy back to light, the atoms in this matter copy will end up in the same internal state as the atoms in the condensate. So now, these atoms in the matter copy will join the condensate. So, we will actually add a little bump on the condensate, so we can manipulate and sculpt the condensate wave function. And we can dump it in the same condensate, or we can dump it in a different condensate. And of course, we have full control over where we dump this little piece of atomic matter.

So, we can use this system to manipulate light. But we can also use it to sculpt the atomic wave function of the condensate by the control that we have. And I should say that laser light and a condensate, they have very similar properties. And it’s really the fact that we can revive a light pulse in a different condensate…partly in a different location. But in particular, in a different condensate, this is only possible because we are dealing with a Bose-Einstein condensate. Imagine the matter copy starts to overlap with the second condensate and then you shine the coupling laser on. If the condensate had not been present, you’ll just a have a bunch of atoms that you illuminate with light. They will absorb light and then reemit completely spontaneously. And it’ll be radiating in all different directions. And there’s no information content in that light. But, if you shine the light on the matter copy when the matter copy is embedded in the condensate, the story is different.

Because the fact that the atoms in the condensate are in lockstep will force the light from these different atoms in the matter copy to be in lockstep. It’ll phase lock the light, so you can recreate the light pulse and get the information back out into the light field for precisely that reason. So, it’s extremely important that you have this lockstep nature of the condensate to be able to recreate the light pulse. We are talking about that it’s the coherent properties of the condensate that allows that. So, it’s interesting because when we stop the light pulse initially, it’s the coherence properties of the coupling laser that allows us to stop it. And preserve the matter copy. Or create the matter copy. But when we regenerate the light pulse, it’s the coherence properties of the Bose-Einstein condensate of the atoms that allows us to recreate that light pulse in the different condensate. So light and matter are on exactly equal footing.

Zierler:

When you moved into nanoscale systems, did you see this as a natural progression from this earlier research? Or was this a new field entirely as far as you were concerned?

Hau:

I mean in some sense, both. Because it was driven partly by trying to see if we can start to get cold atoms to interact with nanostructures. And of course, you could ultimately use that to build, if you want to think about applications of these systems, you would probably want to build them in a nanoscale structure. So, you can integrate it on a chip. So instead of having a roomful of optics, if you can sort of bring things down to a nanoscale, you could start to think in terms of applications of these results. You would probably want to do that in a nanoscale system. So, it was also driven by possible applications of what we were doing. But also, from purely basic research interests, to see what will happen if these cold atoms, if these Bose-Einstein condensates start to interact with nanoscale structures. So, it was also driven by basic research.

Zierler:

And what were some of the motivations in terms of nanoscale systems? Where, besides the basic science or the basic research, did you see potential applications for this technology?

Hau:

Yeah. So, definitely in terms of, what I mentioned before, in terms of quantum information processing. We actually have a theoretical paper out where we predict or show how you can…basically, I should rephrase and say there are different systems that we have been studying in terms of nanoscale structures. One of them in particular deals with that you can use nanoscale structures to focus light enormously. Because you really only need light basically where the atom is. And the atom cloud is pretty small. You don’t need to have these big laser beams illuminating big volumes. If you can get the nanoscale system to focus light down and get very strong electric fields in a small region, so you can just focus down on the atoms with the light, then you can use that focused light to cool atoms. And use extremely low powered systems. And that’s the kind of thing, if you want to scale it down to a chip, that’s important. Because you really don’t need laser light everywhere. You just need to hit the atom. And that’s sort of a perfect match with a nanoscale system. Because a nanoscale system will take- can focus light to a very small volume. So, you just have the light where you need it to hit the atoms.

Zierler:

Lene, in talking to you and listening to you explain the science, it’s so obvious that you’re in it for the discovery. You’re in it for the basic research for just understanding how these things work. And yet, given your fundamental contributions to being able to manipulate light, I can’t help but think that there have been times when you have considered the commercial viability of these discoveries. And so, I want to ask specifically, have you ever been approached by private industry about partnering with them? About applying for patents? About thinking of the ways that this technology really could be scaled broadly for all kinds of new technologies?

Hau:

I mean we have to take out patents on some of this work. It’s certainly something that I am very interested in. Certainly, my skillset would be different than somebody taking this and turning it into a practical product. But it is definitely something I have in mind, and I’m very interested in. But it kind of- it takes a while. Because the system we have created is so new that even scientists, I don’t think, have discovered its full potential. And of course, it takes a while to sort of- you have something new, to people realizing its full potential. And then also in terms of applications. But it is something that, as I said, we have taken patents on some of the work. I am definitely very interested in applications. I have been talking a couple of times about potential applications with commercial people. But it is kind of…there is this delay in time from when it’s discovered. Particularly, it’s such a new system- to it becomes a practical system. But, you know, maybe in the future we will see a little chip of some of this.

Zierler:

(Laughter) So, I would have to ask you only to use your imagination given that the science is still unfolding up to this very day. What do you see ten or twenty years from now where the applications could be viable? They could be feasible? And what technological developments might need to occur, in order to make the manipulation of light have a practical or a commercial or a technological viability?

Hau:

Yeah. I mean, thinking about it as a nanoscale system. Really combining cold atom physics with nanoscale structures. That I think is where it will happen. That interface.

Zierler:

What about in the world of deep learning and artificial intelligence? Do you see applications in those realms as well?

Hau:

There could be. But it’s hard for me to say. It’s really hard for me to say. As I say, there could be, but it’s hard for me to say.

Zierler:

Lene, I know you have an interest in energy technologies and you’ve taught courses at Harvard in those areas. Is that sort of like a quote-unquote extracurricular activity or interest of yours? Or do you tend to integrate your interest in energy systems with your broader research agenda?

Hau:

Yeah. No, it’s definitely something I’ve been interested in, research wise. Again, in terms of combining, taking, learning from nature. And in particular, in photosynthesis. Photosynthesis in nature is very inefficient.

Zierler:

Inefficient relative to what? It’s nature. Doesn’t nature decide what efficiency is?

Hau:

Relative to solar cells, for example.

Zierler:

A-ha.

Hau:

In terms of harvesting light and turn it into energy. Or I should say, turn it into stored energy. So solar cells can convert light to electricity with say, fifteen to twenty percent efficiency. And then of course, you can store it for example, by using that electricity to split water into oxygen and hydrogen. So, you can do that whole process with probably fifteen percent, maybe even getting close to twenty percent efficiency. But, plants, they convert solar energy to stored energy with something like 0.1 percent efficiency. And it’s good enough for nature. So, there hasn’t been a push to optimize the efficiency.

But if you- because with solar cells, solar cells work great. But the problem is when the sun is shining you can pull a current; when the sun is not shining, you need to have a way of storing that energy. And as I mentioned using the electricity to split water into hydrogen and oxygen is one way of doing it. But that sort of requires a combination of the solar cell and an electrolysis apparatus with very expensive catalytic electrodes. Typically made of platinum. So, then it’s worthwhile turning to plants and say, “How do they do it? How do they turn light into stored energy?” And then you look at photosynthesis and you discover that actually photosynthesis is a very modular system. Some of the modules work really efficiently. Others much less efficiently. And then if you could now take the modules that work efficiently and then throw the bad parts away and then take the modules that work efficiently and combine them with some man-made systems like nanofabricated systems. Then you could potentially have applications for solar driven water splitting. Or solar driven direct current. So, it’s definitely a real interest in saying could we make hybrid structures where we take maybe enzymes, proteins from the natural system, and combine them with nanoscale systems to harvest light and turn it into stored energy?

Zierler:

Now of course, you’re in it for the research and the discovery. But I wonder if you have motivations beyond the science such as concerns over climate change and an interest in—

Hau:

Absolutely. Yes. Yes.

Zierler:

Yes. Do you think that these alternative energy systems really do show promise in terms of global energy demand?

Hau:

I think they do. And I think it’s extremely important that we push on different fronts to figure out what works the best, it might not be a single technology. Most likely the optimal technology depends on the application. But it’s extremely important that we push on different systems to- partly we could learn from each other and one system might be pushed to a certain level and then we can maybe take the technology from that and use in another one and push that further. So, I think it’s really important that we push in many directions in terms of optimizing these systems.

Zierler:

And are you optimistic that the systems can be optimized to create meaningful solutions to climate change?

Hau:

Yeah. Optimizing or even creating new systems. Because sometimes people get very locked in in their thinking about a system. And they might try to squeeze a little bit extra out of this system, where maybe the right thing is to take a big jump and think about something totally new. And start pushing in that direction. I think it’s very important. It’s very important that we keep the big jump in mind, so we don’t get locked in in some sort of a local minimum. But really, try to think out of the box in new ways of doing things.

Zierler:

And Lene, just to bring the narrative up to the present day, what are some of the projects you’ve been working on in recent years.

Hau:

It has very much been, in terms of this combining photosynthesis with nanoscale structures. And thinking about that and pursuing that.

Zierler:

Lene, one aspect of your career we haven’t talked about so much is your role as a mentor to graduate students. So, I’m very curious to learn a little bit about some of your successful graduate students and the kinds of projects that they have worked on.

Hau:

Yes. Okay. And maybe I can just add also that I’m very interested in optics with nanoscale structures. That I have been involved in recently.

Zierler:

Okay.

Hau:

Yes, so what I’m really very happy about is that my graduate students have picked quite diverse careers, I would say. A third of them in academia, and a third of them in sort of- depends on how you split it, but you could sort of say maybe half- a third in academia, a third in organizations where they still- it’s not academia but they still are allowed to do really fundamental research. And then a third in sort of real business so to speak, right? So, I’m very pleased to see that it’s really both academia and industry. Both, industry, business, and also doing research in industry. So, it’s really a combination of that. And two of them, Naomi Ginsberg and Anne Goodsell, they are professors. Naomi at Berkeley and Anne at Middlebury College. And then I can mention Trygve Ristroph. He left my lab and ended up as master engineer at Agilent Technologies. Then I can mention Chris Slowe, who was one of the few who started Reddit.

Zierler:

Oh. Wow.

Hau:

So, it’s really a mix. A real mix.

Zierler:

And it sounds like you encourage your students to pursue their interests wherever it takes them.

Hau:

Absolutely. And I’m very, very glad that it’s a mixture.

Zierler:

Right.

Hau:

That’s sort of coming back to one of the concerns I have. Because quite a few of my colleagues at Harvard have come from Bell Labs. But that’s sort of the generation that’s a little bit older than me. And Bell Labs was a particularly American thing.

Zierler:

Right.

Hau:

That they chose to have the telephone company have a real research lab. A real basic research lab where many, many discoveries were made. And many great scientists came from there or worked there. And for me, Rowland was Bell Labs for me. Because it was actually- Land modeled it after Bell Labs. It was smaller of course, in size. But the idea was the same. To take in researchers and have them in small groups. And they work in the lab and really go for big breakthroughs.

Zierler:

And your concern now is that that model is becoming less available to students?

Hau:

Yes. Yes. Because Bell Labs no longer exists. And those kinds of research labs no longer exist. And Rowland is also no longer an independent lab. But it’s part of Harvard. Of course, Harvard is great. But it’s a university. So, the Rowland Institute I saw was more like Bell Labs. An independent place. So, it’s extremely important for young people to have options. Because some fit really well into the model of going out and becoming an assistant professor if they want to do research. For some others, that’s not a great model. They would rather do what I did. And then I remember once-

Zierler:

So, Lene, for example, Google has a lab. You don’t see that as the next generation? You don’t see it in the same category, for example?

Hau:

It could potentially be, but I don’t see it yet. Because it means sort of- it definitely means a hands off approach for the researchers, time to develop something that might at first look like this is not very- this can’t be used in applications.

Zierler:

Right.

Hau:

But the thing with Bell Labs is that many of the applications are still coming to light fifty years after.

Zierler:

Well, they could afford not to care about applicability because they were a monopoly and the money wasn’t a concern.

Hau:

Yes. Yes. But sort of having places like that. That’s really important for the young generation. The kind of people who want to be tinkerers.

Zierler:

I wonder, Lene, with the European perspective, I wonder if that model- you said, of course, with Bell Labs that it was a distinctly American model. But I wonder with the more state centric approach in Europe, if European countries are able to support basic science, not from the corporate perspective, but from a government perspective. If those kinds of opportunities might be more viable in Europe nowadays than they are in the United States.

Hau:

Yes. I mean- but I haven’t seen anything like Bell Labs emerge anywhere.

Zierler:

It’s truly unique.

Hau:

It’s truly unique (laughter).

Zierler:

Well, Lene, at this point we’ve taken the conversation right up to the present day. I think for the last part of our talk, I’d like to ask a few broadly retrospective questions about your overall career. And then ask you something sort of forward facing into the prospects for the future. So, the first thing I’d like to ask is to get back to this idea that quantum mechanics, when you were first exposed to quantum mechanics, how it really captured you and fully brought you in to your devotion to physics, right? Can you talk a little bit about on a daily basis, the ongoing influence of those first early things that you learned about quantum mechanics, and how those concepts or theories have informed all of the research you’ve done in the intervening years?

Hau:

Yes. It certainly has affected my teaching in the sense that I try to use the methods of teaching that I felt really appealed to me and really helped me think deeply about physics. I’m trying to keep in mind what made that special and sort of guide me in terms of my teaching. Very much. So, that definitely. But that’s maybe an interesting perspective because, sort of both in terms of teaching but also mentoring a group. Having a research group. The role models that I have seen- my mentors were males. And I’m obviously a female. There are examples from my own learning process when a mentor would teach me something in a specific way and I thought, “This worked great!” And I saw how the mentors operated and learned from that. But then, by actually working with people, I realized that what works for males does not necessarily work for females.

It can be perceived incorrectly. If you sort of work in the same way as what you saw your male mentors do, some students can feel threatened and you can be perceived as a very pushy, very aggressive woman. And that’s something I have really had to learn by working with people. And if I give advice to young women, it is to interact with women role models because I think it would have been helpful for me to have access to women mentors. Not any woman mentor, because again, women are different as well as men are different. And I think that’s sometimes forgotten. But there are certain female mentors that I would have loved to have learned from because things for a woman can be more difficult.

Being a woman in physics is difficult. But there are tricks you can play, so to speak. In lack of a better word. There are ways you can learn to somehow get around some of the problems. Not all of them necessarily. But get around some of the problems. And maybe having more female role models and some ways of learning leadership, I think is particularly important for women. Because there’s also the fact that often women don’t get second chances, you know? I can see males who make a mistake; they get an infinite number of second chances. Second and third, etc. But women tend to not get second chances. So, this combined with the problem that what works for men don’t necessarily work for women. And successful women will often be perceived as aggressive and cold and uncaring. I think that is important to realize. And also, often you can have different strikes against you. And if you have multiple strikes against you, the problems amplify. Maybe a woman can be accepted if she behaves in a very narrowly defined way. But like men, all women are different. And it takes different kinds to succeed. And as we know, very creative people are often quirky people. And it’s hard for people to accept the quirky woman. So now you have two strikes against you. And if we think about Bell Labs again, there were quite a few quirky people at Bell Labs, as I’ve been told. So, we have to learn to take women for what they are and allow them more phase space, to be quirky, for example.

Zierler:

Have these problems, the additional challenges that women face in science, over the course of your career, have you seen significant progress been made? Or do you see it’s essentially the same issues that you first encountered at the beginning of your career?

Hau:

Well, I would say in many ways, I didn’t see it so much at the beginning of my career. I think I have actually seen it more in recent years.

Zierler:

Huh. That’s very discouraging to hear, of course.

Hau:

Yeah, but it could also have to do with- I think the higher the women get in the system-

Zierler:

A-ha.

Hau:

-and this was actually very well described in the 1999 report by the women at MIT who really got together and started investigating what the conditions were for women at MIT.

Zierler:

The more prominent you are, the higher up you go, the more scrutiny you face, and the more difficult it is. Is that the idea?

Hau:

That’s the idea. They described it as a phase transition. When a woman goes from being untenured to tenured, that’s a phase transition. So, where men perhaps were able to accept you when you were still maybe a student or an assistant professor because you still- they’re still at a higher level. They’re still sort of, okay, I can help this person. Or whatever. There’s still a level difference. But then if you become tenured, you’re suddenly at the same level. And you have to be accepted as a peer. And that creates very particular problems. I think they really described that quite well. And that’s- I think is exactly right. And we should also keep in mind that sometimes women are actually their own worst enemies. Because women can discriminate as much as men can. Sometimes one forgets that. And of course, there’s a lot of unconscious bias. It’s very easy to convince people via unconscious bias that a woman is, as I said before, unlikeable. Aggressive, uncaring, cold. You can easily convince a whole community of that without most in the community having ever interacted with a woman. Then they go into a meeting with a woman with those expectations that they have picked up from elsewhere. And of course, that will affect the interactions and perhaps create a negative outcome.

Zierler:

What kinds of advice have you given your female graduate students in order for them to best navigate these challenges ahead?

Hau:

In some sense, I’ve been hoping that the best I could do was being a role model. Because I also didn’t want to sit them down and sort of create problems at a time when they didn’t have them. But being a role model and of course during conversations, issues would come up that we would then discuss, and I would give my input. And just recently I had a chance to chat with a group of undergraduate and graduate students over dinner. And some of the women would ask me about advice around being a woman in physics. Part of what I just told you, I told them also. I think it is important being open about what the problems are. And I think also, I’m discovering these problems myself over time and trying to think about what is actually going on. Of course, then you can be more vocal about it because you know what some of these problems are. You don’t know it initially. That it’s actually, often subconscious gender bias. You don’t know that. But then you realize it sort of after the fact. Like, gee, if you look back, what was that actually about? And then you realize there was a lot of perhaps, gender bias going on and causing problems.

Zierler:

Well, the field is certainly going through a reckoning right now in terms of greater diversity and inclusivity. So, it’s quite discouraging to hear that these are things that you’ve had to deal with yourself. And that they happen at your level. But I do want to ask a happier question. Given how seamlessly you have combined, or even blurred the lines between applied physics and theoretical physics and experimental physics, I want to ask you generally over the course of your career, have your theoretical ideas, have they outpaced the technological capacity? In other words, did you have ideas about what you wanted to accomplish, but the technology wasn’t yet there to do those experiments? Or were you inspired by new advances in technologies that allowed you to explore new areas of physics that, in turn, uncovered new theoretical perspectives?

Hau:

Yeah. I would say combining- trying to create combined structures of cold atoms and nanostructures. That’s one example of that. Because when we wanted to capture atoms and have them spiral around a very thin wire, there were theoretical aspects of that problem that were really, really interesting. Because it was basically, if you have a very thin charged wire and you send an atom in towards that wire, the system creates what is called a singular potential. It can act as effectively, the analog of a black hole, in that there’s a particular radius of death, we can call it. So, that if the atom gets within that radius, comes closer to the wire than that distance, it will for sure be captured in a gigantic, spiraling orbit. And spiral faster and faster around this wire until it finally hits the wire. And with no possibility of escape. This was a system we were very interested in studying because there were theoretical issues that were just really odd and could affect the description of higher-spin particles, that is, particles with high internal angular momentum.

And perhaps the theory might need a revision in terms of the basic dynamical equations of motion for such systems. It might require rewriting of those equations to understand this problem. This was a problem we really wanted to pursue. But the technology for making very thin wires wasn’t there. So, to create a black hole for cold atoms, we actually had to wait for nanowires, nanotubes to be discovered. And then we really succeeded in creating freestanding nanotubes. Very long, freestanding nanotubes that we could then charge to very high voltages. And then we sent cold atoms in and we indeed saw the effects of this spiraling behavior. You know, the kind of black-hole-like behavior for these cold atoms around nanotubes. So that’s an example of a case where we didn’t understand the theory and wanted to explore the system in the lab. But we couldn’t create thin enough wires to start looking at these spiraling atoms. And we had to wait for the technology for growing nanotubes to be discovered before we could start studying these systems.

Zierler:

Now Lene, when outside people would look at what you were doing in its conceptual stage and say, “This is impossible. This is crazy.” Right? How would you know that you shouldn’t give up? How did you know? What are some of the feedback mechanisms early in on a research endeavor where you don’t look at yourself in the mirror and go, “I don’t have anything here”? When do you know that you really are onto something and that it’s worth continuing to push forward?

Hau:

Yeah, that actually happened as early as with my thesis work. My thesis work was about channeling in single crystals. You know, in a crystal the atoms are arranged in a three-dimensional periodic pattern - it can be a silicon crystal, for example. Where the silicon atoms are organized in a nice, periodic pattern. And then we shoot a relativistic electron beam into this crystal. And if we align the crystal such that the electron beam is parallel or almost parallel to strings of atoms in the crystal then the electrons can be captured in spiraling orbits around the atomic strings of silicon atoms. And then there’ll be discreet quantum mechanical energy levels for these spiraling electrons. And when an electron jumps between one spiraling orbit to another one, it emits light primarily in the forward direction, and with a characteristic frequency determined by the energy level difference between the spiraling orbits. And the emitted light is actually in the x-ray part of the spectrum because the spiraling electron is relativistic. I believed very strongly that the light matter interactions that caused the emitted light to be boosted into the x-ray region could be brought directly into the model from first principles by quantizing the electromagnetic radiation field and incorporating the interaction of that quantized radiation field with the electron which in turn interacts with the atomic string. But my adviser said he didn’t believe that. He didn’t think that would be possible. And he said, “I don’t think it’s possible. You’re on your own here.”

And then it ended up being that it was possible to describe. And actually, with a model that I’m quite proud of. But when it then worked, this was a really good feeling - this was something that I just knew could be done. And I had to believe in my myself in going forward with it. But I think that experience, being able to do that at that stage as a graduate student, very much taught me not to get discouraged later you know when I wanted to build a setup for Bose-Einstein condensates, when five referees said that was impossible. That’s a situation where you really have to believe in yourself. And I think maybe that early experience, I think that really helped me maintain my conviction in going for it.

Zierler:

Lene, it’s amazing how many areas of physics your research has touched. I’m curious, one thing we have not talked about- I’m curious if you see your research being relevant in the world of cosmology or astrophysics?

Hau:

Uh. I would say only in, perhaps in terms of making sensitive detectors. I shouldn’t say only. That’s a big thing, actually. But I would say there are different ways in that sometimes our system can act as a model system for astrophysics and cosmology. It can act as a model system where maybe the mathematical equations are the same and we can use a kind of tabletop experiment to study astrophysical systems. But in another way, the systems we have are very sensitive to their surroundings. Like I described it earlier with a condensate. It’s very sensitive to light. Even a single photon can act as a bull in a china shop in a Bose-Einstein condensate. So, the systems are very sensitive. So, in terms of sensitive detectors, yes, there is potential, and it’s also being pursued in terms of sensitive detection of small astrophysical effects.

Zierler:

You are so widely admired among your colleagues. And you have been appropriately recognized by so many institutions and societies. I wonder if there are any awards or recognitions or honors that stand out in your mind as being most professionally or personally significant to you?

Hau:

I would say that that would be the MacArthur Fellowship.

Zierler:

Why so?

Hau:

Because I think it’s given to daring, bold, creative people. With a belief in the future of these people. And it creates a community of fellows. I’ve sometimes been to retreats with these fellows. And it’s such an astonishing experience to talk to fellows from so many different fields because the Fellowship can be given in any field. And I would say that one thing that characterizes the MacArthur Fellows that I have discovered is their curiosity. And I would never have guessed that, but I discovered at my first retreat with the MacArthur Fellows, that I had a special affinity for the poets. We seemed to be communicating really well. And that was a big surprise to me.

Zierler:

(Laughter) That’s great. It’s all those humanities courses that you never were able to take during school.

Hau:

That’s right.

Zierler:

Well, Lene, I think that’s a great segue. This concept of the MacArthur Fellows being bold and daring as they look to the future. And so, on that note, I think for my last question I want to ask: There are so many different ways that you can take your interests and your curiosities into the future. And of course, the future is limited in time and in resources and in energy, right? So, what are the areas of inquiry that are most precious to you going forward? The things that you personally want to focus on, both because you are interested in them from a basic science perspective and both because you see opportunities to make a lasting mark on humanity?

Hau:

Yeah. I think research being what it is and given my own curiosity and going from theoretical solid-state physics to experimental cold atom physics. I think I would hate to predict - just in the nature of who I am - I would hate to predict the research. But what I would love to do would be to be able to help younger people. And certainly, like the teachers and mentors that I have been talking about that were very instrumental for me. But also, I know how important it was for me to have opportunities like the Rowland Institute as a place that really appealed to me as somebody who wanted to build. Coming back to the engineering perspective: I was allowed to build. So, I was allowed to explore my engineering interests by being in the lab and building. And the Rowland Institute allowed me to do that. It allowed me to be a tinkerer and an experimentalist and an engineer and a physicist all at the same time. And I’m really hoping that I can help pave the way such that the current generation of young people will have the variety of opportunities, the diversity of opportunities, the way I had it.

And also, I didn’t come from an academic environment at all. I think often there are so many roadblocks for young people coming from nonacademic backgrounds. And getting a more diverse population into the field I’m working in is really important. I hope I can help open their eyes to it and if they’re interested, giving them a chance. So, this can be people from non-academic homes. It can be females. It can be people of color. You know, the people we don’t see many of in physics. If we could approach more people who are first generation students, make sure we have real opportunities that we give these young people. But it has to be done right. It’s not a question of just getting them in the door. We have to be sure that they actually get into the living room. And that is constant work that has to be done. And then at the same time, so it can be done in a way, so they don’t lose connection with where they came from. Because of course, one thing is, they can maybe learn the culture in an Ivy League school. But that could mean that they lose the cultural connection with their background and their family.

So, to have a more balanced approach, I think we have to open up. For example, in the Ivy League schools. That we don’t get stuck in traditions that seemingly only people who come from academic homes, or come from the upper class, feel are natural environments. For people who don’t come from such a background, they first have to figure out what is going on here. I mean, they might not understand a lot of the traditions or that possibilities even exist because how would they know? And then we have to make sure that they have a way of maintaining the connection to their culture in this environment, so they don’t lose the connection to their background and their family.

Zierler:

Well, for the sake of science and in extension, civilization, I wish you a tremendous amount of luck in being a positive force of change in all of these areas.

Hau:

Thank you.

Zierler:

Lene, it’s been an absolute delight speaking with you today. I had so much fun learning and hearing from all of your perspectives and insights on all areas in your career. And this is a truly unique and remarkable set of events that you’ve been involved in. And it’s just really special that we were able to spend this time together and that we can capture this for the historical record. I’m greatly honored by the time you’ve spent with me and I want to thank you so much.

Hau:

Well, thank you, David.