Controlling the spontaneous emission of a superconducting transmon qubit

TL;DR

This paper characterizes coherence in superconducting transmon qubits, revealing how off-resonant cavity modes influence spontaneous emission and demonstrating long coherence times of over a microsecond.

Contribution

It provides a detailed semiclassical model predicting qubit lifetimes based on cavity mode interactions, enhancing understanding of decoherence mechanisms in circuit QED.

Findings

Spontaneous emission rates are affected by off-resonant cavity modes.

The model accurately predicts qubit lifetimes over a wide frequency range.

Coherence times exceeding one microsecond are reproducibly achieved.

Abstract

We present a detailed characterization of coherence in seven transmon qubits in a circuit QED architecture. We find that spontaneous emission rates are strongly influenced by far off-resonant modes of the cavity and can be understood within a semiclassical circuit model. A careful analysis of the spontaneous qubit decay into a microwave transmission-line cavity can accurately predict the qubit lifetimes over two orders of magnitude in time and more than an octave in frequency. Coherence times $T_1$ and $T_2^*$ of more than a microsecond are reproducibly demonstrated.