Study of the limits of single-photon detection in lumped element kinetic inductance detectors

Kinetic inductance detectors (KIDs) have shown promising single-photon detection capabilities. However, there has also been a consistent deviation from the limit in energy resolution predicted by Poisson statistics. The consistent underperformance suggests some additional mechanism has not been taken into account. The work in this thesis has taken the novel approach of using aluminium (Al) lumped element (LE) KIDs to model single-photon detection based on Mattis-Bardeen and Kaplan theory. This work has demonstrated generation-recombination (GR) noise limited performance predicted by theory, when taking into account the quasiparticle density and lifetime saturation at low temperatures. The model requires a single fitting parameter that accounts for the quasiparticle generation efficiency . This work shows = 0:4 is more appropriate for 30 nm Al lm. It has also been recognised, through simulation and measurement, that there is a position dependence in the response to photon absorption, which is dependent upon LEKID architecture. An attempt was made to mitigate this effect by using a hybrid device: an additional niobium (Nb) absorbing layer is used to cover the assumed non-responsive regions of the LEKID structure. However, large amounts of scatter in resonator position across the test array – thought to be due to processing effects – have made it difficult to identify between Al and hybrid devices. Experimental procedures were developed to assist device identification with some degree of success but further development work is required. Nonetheless, the same test array has shown single-photon detection in Al LEKIDs at visible and near-infrared wavelengths