Quasiparticle dynamics in a hybrid Cooper-pair box

LEANDRO TOSI; SIMON SCHMIDLIN; DENIS VION; HELENE LE SUEUR

Aussois

Conferencia; GDR PHysique Mesoscopique; 2016

CNRS

In the context of a collaboration with the Edelweiss project for the direct detection of dark matter we have been working on the development of an electrometer based on the Cooper-pair box. As conceived, a dispersive read-out of this mesoscopic device though a rf-setup would allow an accurate measurement of the charge created by an incident particle in a semi-conductor crystal used as bolometer, with a sensitivity more than one order of magnitude below existing semiconductor electronics. However, as also happens in superconducting qubits, the performance of our device is limited by the presence of non-equilibrium quasiparticles in the superconductors which induce parity jumps in the box. Conventional strategies to handle quasiparticle ?poisoning? are gap engineering of both, the box and the ground, and also the building of quasiparticle traps. We have chosen to fabricate a hybrid Nb/Al island connected to an Al ground through a tunnel junction. I will show that poisoning is still present, but with parity switching rates strongly reduced (of the order of the millisecond) compared to Al based devices, and with no observable difference between even and odd states. We believe that this study on the quasiparticle dynamics is a key step towards the realization of a robust detector.