Parity switching in a semiconductor-based transmon qubit*

Unpaired quasiparticles can adversely affect the performance of superconducting devices, including qubits based on Majorana zero modes. We study charge parity switching in a superconductor-semiconductor nanowire-based transmon device that shows Little-Parks oscillations of its frequency as a function of magnetic field. In the recovery regime, where a single flux quantum threads the cross-section of the wire transport measurements recently revealed signatures compatible with Majorana zero modes [1].
We read out the charge parity by dispersive monitoring of a readout resonator to which the transmon qubit is coupled. At zero magnetic field, we measure parity switching times in the range of 10-100 ms. As the magnetic field is increased toward the first closing of the superconducting gap, the switching time is decreased and is consistent with the superconducting gap reduction. In the recovery regime where the gap is re-opened, the switching time is reduced below the sensitivity of our measurement, putting a bound on the minimum observable Majorana hybridization energy in a full-shell nanowire system.

[1] S. Vaitiekenas et al., Flux-induced Majorana modes in full-shell nanowires, arXiv:1809.05513 (2018)