Resonance inversion in a superconducting cavity coupled to artificial atoms and a microwave background

TL;DR

This paper demonstrates how heating-induced interference in a superconducting cavity with artificial atoms can invert the resonance line shape, revealing insights into system fluctuations and dissipation.

Contribution

It introduces a tunable Fano resonance inversion mechanism in superconducting cavities influenced by background interference and heating effects, modeled via modified Jaynes-Cummings boundary conditions.

Findings

Resonance shape can be tuned from peak to dip by bias current.

Background transmission affects cavity line shape and is modeled effectively.

Heating induces interference leading to resonance inversion.

Abstract

We demonstrate how heating of an environment can invert the line shape of a driven cavity. We consider a superconducting coplanar cavity coupled to multiple artificial atoms. The measured cavity transmission is characterized by Fano-type resonances with a shape that is continuously tunable by bias current through nearby (magnetic flux) control lines. In particular, the same dispersive shift of the microwave cavity can be observed as a peak or a dip. We find that this Fano-peak inversion is possible due to a tunable interference between a microwave transmission through a background, with reactive and dissipative properties, and through the cavity, affected by bias-current induced heating. The background transmission occurs due to crosstalk between the control and transmission lines. We show how such background can be accounted for by Jaynes-Cummings type models via modified boundary conditions between the cavity and transmission lines. We find generally that whereas resonance positions determine system energy levels, resonance shapes give information on system fluctuations and dissipation.