Spectral response of an infrared superconducting quantum detector

Abstract

We analyze the spectral performance of recently developed single-photon quantum detector that consists of a narrow, nanometer sized meander-line made from ultra-thin superconducting film. The detector exploits a combined detection mechanism, in which avalanche multiplication of quasiparticles after absorption of a single photon and the bias current jointly produce a normal domain that results in a voltage pulse developing between the meander ends. With either the wavelength increase or the bias current decrease, the single-photon detection regime exhibits a cut-off. The wavelength, at which the cut-off occurs, varies from infrared waves to visible light depending on the superconducting material and operation conditions. Structural and geometrical non-uniformities of the meander line smooth out the otherwise expected sharp drop of the detection efficiency beyond the cut-off. We refine the early detector model and propose a tentative explanation of how superconducting fluctuations may additionally extend the detection efficiency beyond the cut-off wavelength.