Characterizing decoherence rates of a superconducting qubit by direct microwave scattering

Yong Lu,Anita Fadavi Roudsari,Philip Krantz,Per Delsing,Baladitya Suri,Simone Gasparinetti,Anton Frisk Kockum,Jonathan J Burnett,Andreas Bengtsson,Emely Wiegand,Göran Johansson

doi:10.1038/s41534-021-00367-5

Abstract

We experimentally investigate a superconducting qubit coupled to the end of an open transmission line, in a regime where the qubit decay rates to the transmission line and to its own environment are comparable. We perform measurements of coherent and incoherent scattering, on- and off-resonant fluorescence, and time-resolved dynamics to determine the decay and decoherence rates of the qubit. In particular, these measurements let us discriminate between non-radiative decay and pure dephasing. We combine and contrast results across all methods and find consistent values for the extracted rates. The results show that the pure dephasing rate is one order of magnitude smaller than the non-radiative decay rate for our qubit. Our results indicate a pathway to benchmark decoherence rates of superconducting qubits in a resonator-free setting.

Highlights

Superconducting circuits are promising building blocks for implementing quantum computers[1,2,3]
Such artificial atoms are used in the field of superconducting waveguide quantum electrodynamics[4,5], where they interact with a continuum of light modes in a 1D waveguide
Many quantum effects from atomic physics and quantum optics have been demonstrated in waveguide QED, e.g., the Mollow triplet[6], giant cross-Kerr effect[7], and cooperative effects[5,8,9]

Summary

INTRODUCTION

Superconducting circuits are promising building blocks for implementing quantum computers[1,2,3]. We investigate a qubit whose radiative decay rate into the transmission line is larger than, yet comparable to, other decoherence mechanisms This allows us to explore the pure dephasing rate Γφ, the radiative decay rate Γr from the capacitive coupling to the waveguide, and the nonradiative decay rate Γn. Similar to the results in circuit QED36–40, our methods can enable the evaluation of the decoherence of qubits over a broad range of frequencies They provide a pathway to investigate Josephson junctions or superconducting quantum interference devices (SQUIDs) without any resonator. We have investigated waveguide QED with a qubit weakly coupled to a transmission line which is an unexplored regime In this regime, it becomes possible to quantify the nonradiative decay rate of the qubit. We show that time-domain analysis of decay rates can be done in waveguide QED

RESULTS

51. The corresponding fitting equation is r

DISCUSSION