ELECTRONIC NOISE OF SUPERCONDUCTING TUNNEL JUNCTION DETECTORS

The optimal signal to noise ratio for detectors based on superconducti ng tunnel junctions is calculated and compared for the cases of a dete ctor consisting of one single tunnel junction, as well as of series an d of parallel connections of such tunnel junctions. The influence of 1 /f noise and its dependence on the dynamical resistance of tunnel junc tions is discussed quantitatively. A single tunnel junction yields the minimum equivalent noise charge. Such a tunnel junction exhibits the best signal to noise ratio if the signal charge is independent of dete ctor size. In case, signal charge increases with detector size, a para llel or a series connection of tunnel junctions would provide the opti mum signal to noise ratio. The equivalent noise charge and the respect ive signal to noise ratio are deduced as functions of tunnel junction parameters such as tunneling time, quasiparticle lifetime, etc.