Orateur
Description
Increasing disorder in a superconductor increases the kinetic inductance. This enables high impedance quantum circuits and sensitive single photon detectors with a high absorption efficiency. These applications are susceptible to quasiparticle excitations. The single photon response in microwave kinetic inductance detectors (MKIDs) is dictated by quasiparticle recombination, and quasiparticles induces loss and decoherence in quantum circuits. Experimentally, the increase of disorder has been shown to increase the microwave loss and enhance quasiparticle recombination, which decreases the sensitivity of MKIDs. Additionally, recombination time of disordered superconductors observed to change after photon absorption, which is in stark contrast to conventional superconductors.
In this poster, we probe the quasiparticle recombination in a disordered β-Ta superconductor by using it as the sensitive element in an MKID. We vary the photon energy, bath temperature and absorption volume, and compare the results with a model based on conventional, pair-wise recombination. We include quasiparticle diffusion and an additional relaxation channel due to quasiparticle localization in the model, which we both expect to be relevant for disordered superconductors. We find that the observed response cannot be explained by these conventional dynamics and hypothesize that quasiparticle localization may play a more intricate role in the non-exponential decay.