May 18, 2012
Physics News Highlights of the American Institute of Physics (AIP) contains summaries of interesting research from the AIP journals, notices of upcoming meetings, and other information from the AIP Member Societies. Copies of papers are available to journalists upon request.
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TOPICS IN THIS ISSUE
1. Return of the Vacuum Tube: Retro technology makes a comeback in a nanoscale transistor that is light weight, low cost, and long lasting.
2. Quantum Computing: The light at the end of the tunnel may be a single photon: Semiconductors are the foundation of modern computer technology. Now a photon’s literal quantum leap may point the way to a semiconductor-based quantum computer.
3. Engineers Use Droplet Microfluidics to Create Glucose-sensing Microbeads: Tiny beads may act as minimally invasive glucose sensors for a variety of applications in cell culture systems and tissue engineering.
4. Other Content: Upcoming Conferences of Interest
1. Return of the Vacuum Tube
Vacuum tubes have been retro for decades. They almost completely disappeared from the electronics scene when consumers exchanged their old cathode ray tube monitors for flat screen TVs. Their replacement – the semiconductor – is generally the cheaper, lighter, more efficient, and easier to manufacture of the two technologies. But vacuum tubes are more robust in high-radiation environments such as outer space. And since electrons travel faster in a vacuum than through a semiconductor, vacuum tubes are an intrinsically better medium for electricity.
An international team of researchers from NASA’s Ames Research Center in Moffett Field, Calif., and the National Nanofab Center in Korea have combined the best traits of both technologies by making a tiny version of vacuum tubes that could be incorporated into circuits. Their prototype, a vacuum channel transistor, is just 150 nanometers long and was made using conventional semiconductor fabrication methods. Its small size allows it to operate at fewer than 10 volts, much less than a retro vacuum tube requires; with further work, the device could be made to use about 1 volt, which would make it competitive with modern semiconductor technology.
In a paper accepted to the American Institute of Physics’ (AIP) journal Applied Physics Letters, the authors write that such a transistor could be useful for applications in hazardous chemical sensing, noninvasive medical diagnostics, and high-speed telecommunications, as well as in so-called “extreme environment” applications for military and space.
Article: “Vacuum nanoelectronics: back to the future? – gate insulated nanoscale vacuum channel transistor,” is accepted for publication in Applied Physics Letters.
Authors: Jin-Woo Han (1), Jae Sub Oh (2), and M. Meyyappan (1).
(1) Center for Nanotechnology, NASA Ames Research Center, Moffett Field, Calif.
(2) National Nanofab Center, South Korea
2. Quantum Computing: The light at the end of the tunnel may be a single photon
Quantum physics promises faster and more powerful computers, but quantum versions of basic logic functions are still needed to bring this technology to fruition. Researchers from the University of Cambridge and Toshiba Research Europe Ltd. have taken one step toward this goal by creating an all-semiconductor quantum logic gate, a controlled-NOT (CNOT) gate. They achieved this breakthrough by coaxing nanodots to emit single photons of light on demand.
“The ability to produce a photon in a very precise state is of central importance,” said Matthew Pooley of Cambridge University and co-author of a study accepted for publication in the American Institute of Physics’ (AIP) journal Applied Physics Letters. “We used standard semiconductor technology to create single quantum dots that could emit individual photons with very precise characteristics.” These photons could then be paired up to zip through a waveguide, essentially a tiny track on a semiconductor, and perform a basic quantum calculation.
Classical computers perform calculations by manipulating binary bits, the familiar zeros and ones of the digital age. A quantum computer instead uses quantum bits, or qubits. Because of their weird quantum properties, a qubit can represent a zero, one, or both simultaneously, producing a much more powerful computing technology. To function, a quantum computer needs two basic elements: a single qubit gate and a controlled-NOT gate. A gate is simply a component that manipulates the state of a qubit. Any quantum operation can be performed with a combination of these two gates.
To produce the all-important initial photon, the researchers embedded a quantum dot in a microcavity on a pillar of silicon. A laser pulse then excited one of the electrons in the quantum dot, which emitted a single photon when the electron returned to its resting state. The pillar microcavity helped to speed up this process, reducing the time it took to emit a photon. It also made the emitted photons nearly indistinguishable, which is essential because it takes two photons, or qubits, to perform the CNOT function: one qubit is the "control qubit" and the other is the "target qubit." The NOT operation is performed on the target qubit, but the result is conditional on the state of the control qubit. The ability for qubits to interact with each other in this way is crucial to building a quantum computer.
The next step is to integrate the components into a single device, drastically reducing the size of the technology. “Also, we use just one photon source to generate both the photons used for the two-photon input state. An obvious next step would be to use two synchronized photon sources to create the input state,” said Pooley.
Article: “Controlled-NOT gate operating with single photons” is accepted for publication in Applied Physics Letters.
Authors: M.A. Pooley (1,2), D.J.P. Ellis (1), R.B. Patel (1,2), A.J. Bennett (1), K.H.A. Chan (1,2), I. Farrer (2), D.A. Ritchie (2), and A.J. Shields.
(1) Toshiba Research Europe Limited, Cambridge Research Laboratory, Cambridge, U.K.
(2) Cavendish Laboratory, Cambridge University
3. Engineers Use Droplet Microfluidics to Create Glucose-sensing Microbeads
Cell cultures need glucose for energy, but too much sugar can create a diabetic-like environment in which cell proteins undergo unwanted structural changes. Standard methods to monitor glucose levels require invasive and time-consuming handling of the cell culture. A team of engineers at the National University of Singapore and Singapore’s Institute of Microelectronics is developing an alternative approach that takes advantage of new microfluidic techniques. In a continuous and controlled process, the researchers created small droplets of polymer that encapsulated pairs of fluorescing molecules. These microbeads can be added to cell cultures where, in the presence of glucose, they emit a stronger fluorescent signal. The team demonstrated the glucose sensing abilities of the microbeads across the normal physiological range, as reported in the American Institute of Physics’ (AIP) journal Biomicrofluidics.
“The method is simple, inexpensive, and produces glucose-sensing microbeads of different sizes,” says Dieter Trau, assistant professor in the Departments of Bioengineering and Chemical & Biomolecular Engineering at the National University of Singapore. “Our work automates the process of microbead preparation onto a single narrow chip – with minimal use of reagents. Sensing microbeads can act as small, minimally invasive glucose sensors and be optically integrated in cell culture systems to monitor glucose levels. These microbeads have the potential to detect the local glucose concentration in the microenvironment around a cell, as well as gradual changes due to cell metabolism.”
Article: “Utilizing Microfluidics to Synthesize PEG Microbeads for FRET-based Glucose Sensing” is published in Biomicrofluidics.
Authors: Chaitanya Kantak (1,2), Qingdi Zhu (1), Sebastian Beyer (1), Tushar Bansal (2), and Dieter Trau (1,3).
(1) Department of Bioengineering, National University of Singapore, Singapore.
(2) Institute of Microelectronics, A*STAR (Agency for Science, Technology and Research), Singapore.
(3) Department of Chemical & Biomolecular Engineering, National University of Singapore, Singapore.
Upcoming Conferences of Interest
- The American Astronomical Society’s 220th meeting will be held June 10 – 14, 2012, in Anchorage, Alaska.
- The American Crystallographic Association’s annual meeting will be held July 28 – August 1, 2012, in Boston, Mass.
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