Superconducting nanowire single-photon detector

GaAs suitably doped with silicon and boron is a luminous cryogenic scintillator that has no apparent afterglow and is available commercially in the form of large, high-quality crystals.

The length is typically hundreds of micrometers, and the nanowire is patterned in a compact meander geometry to create a square or circular pixel with high detection efficiency.

This produces a measurable voltage pulse that is approximately equal to the bias current multiplied by 50 ohms.

With most of the bias current flowing through the amplifier, the non-superconducting region cools and returns to the superconducting state.

A degree of photon-number resolution can be achieved in SNSPD arrays,[20] through time-binning[21] or advanced readout schemes.

They vary widely, however, due to highly localized regions of the nanowires where the effective cross-sectional area for superconducting current is reduced.

Furthermore, SNSPDs have extremely low rates of dark counts, i.e. the occurrence of voltage pulses in the absence of a detected photon.

Single photon sensitivity up to 10 micrometer wavelength has recently been demonstrated in a tungsten silicide SNSPD.

[82] A number of companies worldwide are successfully commercializing complete single-photon detection systems based on superconducting nanowires, including Single Quantum, Photon Spot, Scontel, Quantum Opus, ID Quantique, PhoTec and Pixel Photonics.

Wider adoption of SNSPD technology is closely linked to advances in cryocoolers for 4 K and below, and SNSPDs have recently been demonstrated in miniaturized systems.