Decoherence in rf SQUID Qubits

TL;DR

This paper measures coherence times of an rf SQUID qubit with tunable potential parameters, identifying decay mechanisms and comparing experimental results with analytical models for finite decay and flux noise effects.

Contribution

It introduces a modified rf SQUID with independent in situ controls for tilt and barrier height, providing detailed insights into decoherence mechanisms.

Findings

Coherence decay dominated by excited state lifetime and flux noise

Measured coherence times consistent with spectroscopy and tunneling data

Waveform analysis matches analytical models with decay and noise considerations

Abstract

We report measurements of coherence times of an rf SQUID qubit using pulsed microwaves and rapid flux pulses. The modified rf SQUID, described by an double-well potential, has independent, in situ, controls for the tilt and barrier height of the potential. The decay of coherent oscillations is dominated by the lifetime of the excited state and low frequency flux noise and is consistent with independent measurement of these quantities obtained by microwave spectroscopy, resonant tunneling between fluxoid wells and decay of the excited state. The oscillation's waveform is compared to analytical results obtained for finite decay rates and detuning and averaged over low frequency flux noise.