Quantum detection by current carrying superconducting film

We describe a novel quantum detection mechanism in the superconducting film carrying supercurrent. The mechanism incorporates growing normal domain an d breaking of superconductivity by the bias current. A single photon absorb ed in the film creates transient normal spot that causes redistribution of the current and, consequently, increase of the current density in supercond ucting areas. When the current density exceeds the critical value, the film switches into resistive state and generates the voltage pulse. Analysis sh ows that a submicron-wide film of conventional low temperature superconduct or operated in liquid helium may detect single far-infrared photon. The amp litude and duration of the voltage pulse are in the millivolt and picosecon d range, respectively. The quantitative model is presented that allows simu lation of the detector utilizing this detection mechanism. (C) 2001 Elsevie r Science B.V. All rights reserved.