Quasi-particle transitions in charge-phase qubits probed by rf oscillations

TL;DR

This paper explores how charge-phase qubits in superconducting circuits undergo quasi-particle transitions, using rf oscillations to probe their states and uncovering stochastic tunneling effects and a selection rule for these transitions.

Contribution

It introduces a method to read out qubit states via inductance measurements and discusses a model for quasi-particle-induced transitions with a specific selection rule.

Findings

Detection of stochastic quasi-particle tunneling events.

Identification of a selection rule for quasi-particle transitions.

Observation of state changes depending on flux, charge bias, and rf amplitude.

Abstract

We investigated transitions in Al charge-phase qubits of SQUID-configuration inductively coupled to an rf tank circuit that made it possible to read out the state by measuring the inductance of the qubit. Depending on the flux and charge bias and the amplitude of the rf oscillations we probed either the ground state or a dynamic change of the qubit states which we attributed to stochastic single quasi-particle tunneling onto and off the qubit island and exchange of energy with the qubit. Within this model, a selection rule for quasi-particle-induced transitions in the qubit is discussed.