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Quantum Information Group, Single Photon Detection

We have also pioneered the detection of single photons using quantum dots. The quantum dot single photon detector proposed and demonstrated by Toshiba, shown in the illustration, is based upon a transistor structure in which the conducting channel is closely spaced from a layer of quantum dots. If the separation of the quantum dots and the channel is just several nanometers, the resistance of the transistor is sensitive to a change in the occupancy of a single quantum dot by just a single electron. This attribute allows the device to act as a detector of single photons, since absorption of a photon creates carriers in the semiconductor, which after capture by a dot, produce a detectable change in the resistance of the channel of the transistor.

Schematic of Toshiba’s single photon detector based on a field effect transistor containing a layer of quantum dots

The quantum dot single photon detector is expected to have several advantages over conventional types of single photon detector based on avalanche processes, such as the photomultiplier tube or the avalanche photodiode. Photomultiplier tubes are vacuum tube devices that, while excellent for many applications, are expensive, fragile, bulky and relatively inefficient. On the other hand, avalanche photodiodes are very prone to dark count noise, especially when operated at the high frequencies used in optical communications. This issue is especially important for quantum communication, since the noise levels of avalanche photodiodes are recognized as limiting the transmission distance and bit rate. Several other features of conventional detectors, including the requirement for high bias voltages, cryogenic cooling and extreme sensitivity to temperature changes and excess bias also make them inconvenient to use.

The quantum dot single photon detector works on an entirely different principle to conventional avalanche devices and can therefore, overcome many of their problems. In particular, by avoiding the avalanche process and its associated problems, it is less prone to noise. As it is based upon a transistor, the building block of today's high-speed electronic circuitry, it is predicted to have a fast time response. Another advantage is that the quantum dot detector works at low operating voltages (<5V) and is more robust.

Quantum cryptography is a very attractive emerging application for single photon devices. However, single photon detectors find many other uses in science and technology. In medical imaging, for instance, single photons are detected in PET and CT scanners and, more recently, for laser optical imaging. Lifetime fluorescence measurements using single photon counting is also used in the diagnosis of some medical conditions. It is also widely used in analytical chemistry for determining the chemical recipe of samples. Another application is in laser ranging, tracking and imaging and for industrial scanning and process control. Finally, single photon detection is also widely used in scientific research in the fields of particle physics, astrophysics and materials science

Further Reading

  Type Title and author(s) Source
1 Technical Low-noise photon counting with a radio-frequency quantum-dot field-effect transistor
by B. E. Kardynał et al
Applied Physics Letters 84, 419 (2004)
2 Technical Single photon detection with a quantum dot transistor
by A J Shields et al
Japanese Journal of Applied Physics, 40, p2058-64 (2001)
3 Technical Detection of single photons using a field effect transistor gated by a layer of quantum dots
by A J Shields et al
Applied Physics Letters, 76, 3673, 2000
4 Intermediate

Quantum dots detect single photons
by A.J. Shields and M. Pepper

Photonik, February 2001
5 Intermediate Quantum dots spot single photons
by David Mowbray
Physics World (July 2000)
6 Intermediate To catch one photon
by Gilbert Chin
Science (7 July 2000)
7 Easy Unhackable cryptography using light quanta (in Japanese) Nikkei (3 June 2000)
 
 
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