New Quantum Dot Transistor Counts Individual Photons

A transistor containing quantum dots that can count individual photons (the smallest particles of light) has been designed and demonstrated at the National Institute of Standards and Technology.

The semiconductor device could be integrated easily into electronics and may be able to operate at higher temperatures than other single-photon detectors—practical advantages for applications such as quantum key distribution (QKD) for “unbreakable” encryption using single photons.

The NIST device, described in a new paper, can accurately count 1, 2 or 3 photons at least 83 percent of the time. It is the first transistor-based detector to count numbers of photons; most other types of single-photon detectors simply “click” in response to any small number of photons.

Counting requires a linear, stepwise response and low-noise operation. This capability is essential for advanced forms of precision optical metrology—a focus at NIST—and could be used both to detect photons and to evaluate single-photon sources for QKD. The new device also has the potential to be cooled electronically, at much higher temperatures than typical cryogenic photon detectors.

Dubbed QDOGFET, the new detector contains about 1,000 quantum dots, nanoscale clusters of semiconductors with unusual electronic properties. The NIST dots are custom-made to have the lowest energy of any component in the detector, like the bottom of a drain. A voltage applied to the transistor produces an internal current, or channel. Photons enter the device and their energy is transferred to electrons in a semiconductor “absorbing layer,” separating the electrons from the “holes” they formerly occupied.

As each photon is absorbed, a positively charged hole is trapped by the quantum dot drain, while the corresponding electron is swept into the channel. The amount of current flowing in the channel depends on the number of holes trapped by quantum dots. By measuring the channel response, scientists can count the detected photons. NIST measurements show that, on average, each trapped hole boosts the channel current by about one-fifth of a nanoampere. The detector has an internal quantum efficiency (percentage of absorbed photons that result in trapped holes) of 68 ± 18 percent, a record high for this type of photon detector.

The QDOGFET currently detects single photons at wavelengths of about 800 nanometers. By using different semiconductor materials, NIST researchers hope to make detectors that respond to the longer near-infrared wavelengths used in telecommunications. In addition, researchers hope to boost the external quantum efficiency (percentage of photons hitting the detector that are actually detected), now below 10 percent, and operate the device at faster speeds.

The research is supported in part by the Disruptive Technology Office. The authors include one from Los Alamos National Laboratory and one from Heriot-Watt University, Edinburgh, UK.

Citation: E.J. Gansen, M.A. Rowe, M.B. Greene, D. Rosenberg, T.E. Harvey, M.Y. Su, R.H. Hadfield, S.W. Nam and R.P. Mirin. Photon-number-discriminating detection using a quantum dot, optically gated, field-effect transistor. Nature Photonics. 1, 585 - 588 (2007). Published on-line Oct. 1, 2007.

Source: NIST

Related stories:

Long-Lasting Quantum Memory Leads to Long-Distance Quantum Communication
(PhysOrg.com) -- Physicists have taken a step closer to realizing long-distance quantum communication, in which a quantum state is transferred from one location to another by becoming entangled with a traveling photon.
A broadband single-photon source
As science makes progress toward practical quantum computing, improved quantum cryptography and scalable quantum communications systems, single photon sources will become more important. Until now, though, efficient solid-state single photon sources are hard to come by. “The standard procedure,” Peter Lodahl tells PhysOrg.com, “has been to put a quantum dot in a photonic crystal cavity.”
Light touch: Controlling the behavior of quantum dots
Researchers from the National Institute of Standards and Technology and the Joint Quantum Institute (JQI), a collaborative center of the University of Maryland and NIST, have reported a new way to fine-tune the light coming from quantum dots by manipulating them with pairs of lasers. Their technique, published in Physical Review Letters, could significantly improve quantum dots as a source of pairs of “entangled” photons, a property with important applications in quantum information technologies.
Researchers make milestone discovery in quantum mechanics
Researchers at UC Santa Barbara have recently reached what they are calling a milestone in experimental quantum mechanics.
Could better spin injection lead to a quantum information device?
One of the more promising types of materials for use in spintronics today is the class of metal alloys known as Heusler alloys. These alloys are named after a German engineer, and might be useful in technology in which electron quantum spin states are used to enhance electronic devices. Additionally, Heusler alloys may have an effect in quantum memory processing and telecommunications.
Physicists Store Images in Vapor
Books are written on solid pieces of paper for an obvious reason: the atoms in a solid don’t move around much, keeping the words and pictures in place for centuries. Trying to store letters and images in a gas medium, on the other hand, seems a little far-fetched. Atoms in a gas are constantly moving around, which would move the images around with them.
Scientists find new 'quasiparticles'
Weizmann Institute physicists have demonstrated, for the first time, the existence of 'quasiparticles' with one quarter the charge of an electron. This finding could be a first step toward creating exotic types of quantum computers that might be powerful, yet highly stable.
New superlattice structure enables high performance infrared imaging
Scientists at the Center for Quantum Devices (CQD) in the McCormick School of Engineering at Northwestern University have demonstrated for the first time a high-performance infrared imager, based on a Type II superlattice, which looks at wavelengths 20 times longer than visible light.

News discussion:

Physics news