A superconducting qubit with Purcell protection and tunable coupling

TL;DR

This paper introduces a superconducting qubit with tunable coupling that can be adjusted from zero to strong coupling, providing Purcell protection and maintaining measurability even in decoherence-free states.

Contribution

The authors demonstrate a superconducting qubit with tunable coupling and Purcell protection, enabling decoherence-free operation while preserving measurement capabilities.

Findings

Coupling strength can be tuned from zero to strong values.

At zero coupling, the qubit is protected from Purcell-induced decoherence.

Measurement is possible even in the decoherence-free subspace.

Abstract

We present a superconducting qubit for the circuit quantum electrodynamics architecture that has a tunable coupling strength g. We show that this coupling strength can be tuned from zero to values that are comparable with other superconducting qubits. At g = 0 the qubit is in a decoherence free subspace with respect to spontaneous emission induced by the Purcell effect. Furthermore we show that in the decoherence free subspace the state of the qubit can still be measured by either a dispersive shift on the resonance frequency of the resonator or by a cycling-type measurement.