APS Physics Tip Sheet – Jul 22, 2014
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Single-Photon Transistors
Two research groups have built optical transistors that turn on in the presence of just one photon.
Optical transistors, which handle photons instead of electrical currents, could be much faster than their electrical counterparts. However, a fundamental obstacle hinders their development: photons cannot easily be used to control other photons because, unlike electrons, they do not interact strongly. Two independent research groups in Germany have now demonstrated all-optical transistor devices in which a “gate” light pulse (consisting of a single photon) acts as a switch that either blocks or transmits another light pulse. Both schemes are based on the strong interaction between photons that can occur in atomic gases prepared by lasers in highly excited states. The transistors might be used to realize more complex logic gates for ultrafast all-optical signal processing.
* Hannes Gorniaczyk (contact author) et al., “Single-photon transistor mediated by interstate Rydberg interactions,”Physical Review Letters (expected publication date: Jul 28)
** D. Tiarks, Stephan Duerr (contact author) et al., “Single-photon transistor using a Förster resonance,” Physical Review Letters (expected publication date: Jul 28)
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Direct Test of Cosmic Acceleration
Future radio surveys of intergalactic hydrogen clouds could offer the first direct measurement of the Universe's acceleration
Measurements of distant supernovae have revealed that the universe is accelerating—a finding most often explained by a yet-to-be-deciphered form of dark energy. But this conclusion is based on assumptions on the Universe’s uniformity and expansion history. A team of researchers in China has now suggested that upcoming radio-telescope surveys could offer a more direct proof of the universe’s acceleration by tracking intergalactic hydrogen clouds. The velocity of these clouds could be determined by observing redshifts of the hydrogen absorption line, which occurs at a wavelength of 21 centimeters. The authors’ calculations suggest a few additional modifications that planned radio surveys should implement to measure—over the course of a decade—cosmically relevant accelerations of around 1 millimeter/second/year
* Hao-Ran Yu, Tong-Jie Zhang (contact author), Ue-Li Pen: Oleg Brandt), “Method for direct measurement of cosmic acceleration by 21-cm absorption systems,” Physical Review Letters (expected publication date: Jul 24)
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A Cooper-Pair Laser
A superconducting transistor embedded in a microcavity acts like a laser that could be used to generate nonclassical light.
By placing a single emitter (like an atom or a quantum dot) inside a microcavity, researchers can realize lasers whose properties are remarkably different from conventional ones: they can be extremely compact, require little power to operate, and generate quantum states of light, such as single photons. A team of physicists from the US and the UK has built and tested a new single-emitter laser consisting of a superconducting circuit embedded in a microwave cavity. The authors argue the device is particularly suitable to generate “amplitude-squeezed” light, a quantum state of light that has reduced intensity fluctuations compared to conventional lasers—a property useful for high-precision measurements and quantum communication protocols.
* F. Chen, Alex Rimberg (contact author) et al., “Realization of a Single-Cooper-Pair Josephson Laser,” Physical Review B(expected publication date: Jul 22)
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Antineutrinos As Nuclear Watchdogs
Researchers in the US and Austria have proposed a system for monitoring a nuclear reactor using an antineutrino detector placed right outside the reactor walls. The authors’ calculations suggest that the method could determine the level of fuel enrichment inside the reactor, which could be used to infer whether spent nuclear fuel has been removed for possible weapons development.
* E. Christensen, Patrick Huber (contact author), P. Jaffke, T.E. Shea, “Antineutrino monitoring for heavy water reactors,”Physical Review Letters (expected publication date: Jul 25)
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Journal articles and preprints are available to journalists on request.
Matteo Rini, PhD
Deputy Editor, Physics
