Superconducting single-photon detectors

Single-photon sources in the optical and the near-infrared wavelength ranges are essential components for procedures of optical quantum communication. A promising method of manufacturing sources for single photons or for few photons is based on quantum dot micro-resonator structures. The better the emission statistics of these sources are known, the more precisely is it possible to understand their behavior.

Within the scope of an ongoing European research project, PTB is collaborating with the Technische Universität Berlin where single-photon emitters and microlasers are being developed on the basis of self-assembled InAs/GaAs quantum dots. At PTB, a measuring system has been set up to characterize sources that emit single photons or few photons with wavelengths in the range from 800 nm to 1000 nm. Superconducting microcalorimeters (“Transition Edge Sensors”, TESs, developed by the National Institute of Standards and Technology (NIST) are employed as detectors. But it is only through the combination with PTB's highly sensitive SQUID current sensors for readout that the number of single photons absorbed can be determined exactly.

The new system is the enhanced form of a setup which has already been used successfully at the Austrian Academy of Sciences for a loophole-free Bell test experiment with entangled optical photons. Due to the use of TES/SQUID detectors, it is possible to directly determine the photon number distribution of the InAs/ GaAs quantum dot sources in a range of up to approx. 20 photons. This enables the characterization of quantum dot microlasers under varying operating conditions. With this measuring system, it has recently even been possible to detect one- and two-photon states of a singlequantum dot emitter directly.