Group delay controlled by the decoherence of a single artificial atom

TL;DR

This paper demonstrates two methods to control the group delay of microwave photons using a single artificial atom in waveguide QED, enabling dynamic light velocity manipulation through decay rate tuning.

Contribution

It introduces novel techniques for controlling microwave light delay using decay rate interference and pumping in a single superconducting artificial atom.

Findings

Positive group delay when radiative decay dominates

Negative group delay when non-radiative decay dominates

Advances in signal processing in waveguide QED

Abstract

The ability to slow down light at the single-photon level has applications in quantum information processing and other quantum technologies. We demonstrate two methods, both using just a single artificial atom, enabling dynamic control over microwave light velocities in waveguide quantum electrodynamics (waveguide QED). Our methods are based on two distinct mechanisms harnessing the balance between radiative and non-radiative decay rates of a superconducting artificial atom in front of a mirror. In the first method, we tune the radiative decay of the atom using interference effects due to the mirror; in the second method, we pump the atom to control its non-radiative decay through the Autler--Townes effect. When the half the radiative decay rate exceeds the non-radiative decay rate, we observe positive group delay; conversely, dominance of the non-radiative decay rate results in negative group delay. Our results advance signal-processing capabilities in waveguide QED.