Detector finds single photons in far-infrared

Detection of single photons in the far-infrared, from 10 (m to 1 mm, has not been achieved before, but the region is interesting to spectroscopists because it covers the rotational spectra of molecules and the vibrational spectra of solids, liquids, and gases. Now researchers at the University of Tokyo (Tokyo, Japan) have built a device to perform single-photon detection between 175 and 210 µm.

The researchers fabricated a 700 x 700-nm quantum dot on a gallium arsenide/aluminum gallium arsenide single-heterostructure crystal. They placed the dot in a high magnetic field that affected the state of the dot's electrons, so that when it absorbed a far-infrared photon an electron hole was created, changing the conductance of the quantum dot. Absorbing a single photon created a current of from 10⁶ to 10¹² electrons through the quantum dot. Researchers were able to detect an incident flux of 0.1 photons/s on an effective detector area of 0.1 mm², with a time resolution of 1 ms. This sensitivity is more than 10⁴ greater than previously reported values. Contact Susumu Komiyama at [email protected].