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Number 560, October 9, 2001 by Phil Schewe, James Riordon, and Ben Stein

The 2001 Nobel Prize in Physics

The 2001 Nobel Prize in Physics goes to Eric Cornell of NIST/JILA, Wolfgang Ketterle of MIT, and Carl Wieman of Colorado/JILA (JILA is an institute run jointly by NIST and the University of Colorado). Cornell and Wieman are recognized for their being the first to achieve a Bose-Einstein condensate (BEC) in neutral atoms (Science, 14 July 1995; see Physics News Update 233). Ketterle soon thereafter produced a larger BEC (Davis et al., Physical Review Letters, 27 November 1995) and has made extensive study of BEC properties.

The BEC phenomenon, foreseen by Satyendra Bose and Albert Einstein in the 1920s, can come about when atoms are chilled to very low temperatures. Quantum theory holds that the wavelike nature of atoms allows them to spread out and even overlap. Indeed at a high enough density and a low enough temperature (billionths of degrees above absolute zero) the atoms can, like the photons in a laser, enter into a common quantum state with a common energy. In other words, the atoms are all coordinated (coherent) with each other and constitute a single "super atom."

BEC was possible experimentally when in a magneto-optic trap (MOT), a combination of laser cooling (a web of laser beams hitting the atoms from many directions) and evaporative cooling (a web of magnetic fields encourage the warmer atoms to depart, leaving the cooler atoms to coalesce in the trap) brought about unprecedentedly low temperatures. BEC is still largely restricted to fundamental research in physics labs, but numerous potential applications beckon, such as the use of BEC beams ("atom lasers") for doing high-resolution lithography for microchips, interferometry (navigation, gravity wave detectors, etc.), high-precision clocks, and "atomtronics" (atoms sent around a microchip or down hollow fibers).

Physics News Update has covered BEC research extensively. Examples include BEC as a superfluid (Update 449), rudimentary atom laser (305), amplifying atom waves (465), all-optical BECs (545), switching BEC interactions from negative to positive (producing miniature "supernovas," Update 530), BEC on a microchip (559), BEC as an immiscible liquid (402), hydrogen BEC (382), lithium BEC (237), helium BEC (532), tunable chemistry (362), sound waves in BEC (319), slowed light in a BEC (472), quantum evaporation (356), and continuous atom laser beam (422). (Background: Wieman and Cornell, Scientific American, March 1998; see also Royal Swedish Academy press release.)

Quantum Fingerprinting

Imagine two offices, located halfway around the world, and their headquarters wants to make sure that they each have the identical copy of a database. Imagine further that the databases are huge--10²⁰ bits each. They could transmit the database to the headquarters, and the headquarters could compare them. But transmitting 10²⁰ bits--equal to about 11 billion gigabytes-would take an enormous amount of time.

There is a method in which they only need to send 10¹⁰ bits--a little over a gigabyte--and the headquarters still gets enough information to determine that they have the exact same database. This method is called "classical fingerprinting." The idea is that each office independently, without communicating to each other, generates a distinctive number, called a fingerprint, by performing a calculation involving the entire database and locally generated random numbers, called keys. The result of the calculation-a fingerprint of 10¹⁰ bits--is then sent to the headquarters.

Now, a Dutch-Canadian team (Harry Buhrman, CWI/University of Amsterdam, 011-31-20-5924076, buhrman@cwi.nl) has suggested a "quantum fingerprinting" scheme which would involve an exponentially smaller transmission of information to do the same job. For the 10²⁰ bit database, each office would only have to transmit a fingerprint of about 70 "quantum bits" (qubits), which could be, for example, specially prepared photons. Such photons could contain the result of a computation between the database and many different random keys simultaneously, rather than a single random key.

The researchers say that one could demonstrate this new fingerprinting technique with quantum computers not much more complex than the ones that exist today. Buhrman estimates that quantum fingerprinting becomes more efficient than classical fingerprinting in a quantum computer with 5 to 10 qubits. (H. Buhrman; R. Cleve; J. Watrous; R. de Wolf, Physical Review Letters, 15 Oct. 2001.)