May 18, 2010
Prototype senses individual terahertz photons
Individual photons in a very obscure terahertz region of electromagnetic radiation have been detected using a specially designed system consisting of a quantum dot and a superconducting single electron transistor (SET) both cooled to a very low temperature.
A joint team of scientists from Royal Holloway University of London, UK, Tokyo University, Japan, and the Institute for Solid State Physics, Russia, has fabricated a single-photon detector for terahertz radiation, which could help to bring about prolific new applications in chemistry, physics and biology.
An incoming terahertz photon incident at the patterned semiconductor heterostructure (for more details, click on the image) is absorbed by the electron gas so that the photon energy is transferred to a plasma wave localized inside the quantum dot (QD). The plasma wave may decay to an electron-hole pair in such a way so that one of the electrons leaves the QD. Because of this, the QD undergoes a transition to a meta-stable charge excited state and the electrostatic potential in close proximity to the QD changes stepwise. The SET probes this change in potential and indicates absorption of the photon. Thus, counting of terahertz photons can be performed.
In fact, only one of 1000 photons is counted in this way, but even with such low quantum efficiency, the sensor has an unprecedented high sensitivity that exceeds existing terahertz sensors by a few orders of magnitude.
More details are available in the journal Nanotechnology.
About the author
The collaborative study was conducted at the Royal Holloway University of London (RHUL), England. The PhD student Hideomi Hashiba and his supervisor Dr Vladimir Antonov from RHUL designed the fabrication technique for making the terahertz sensors. In collaboration with Prof. Susumu Komiyama, a group leader in Tokyo University, Japan; Prof. Alexander Tzalenchuk, chief researcher from National Physics Laboratory, United Kingdom; and Prof. Leonid Kulik, a leading scientist at the Institute for Solid State Physics, Russia, they performed extensive studies of the optical and transport properties of QDs coupled capacitively to SETs, and finally came up with a working prototype of a single-photon counter of terahertz photons.