Quantum bath engineering of a high impedance microwave mode through quasiparticle tunneling

TL;DR

This paper introduces a novel dissipation engineering method in microwave quantum optics, enabling control over photon loss numbers and state-dependent energy shifts via quasiparticle tunneling, enhancing quantum state manipulation capabilities.

Contribution

It presents a new approach to dissipation engineering that tunes photon loss to two or more, differing from traditional single-photon loss methods, without relying on Josephson effects.

Findings

Photon loss can be tuned to two or more photons per jump.

Measured Lamb shifts agree with Kramers-Kronig predictions.

Different quantum states experience distinct dissipation and energy shifts.

Abstract

We demonstrate a new approach to dissipation engineering in microwave quantum optics. For a single mode, dissipation usually corresponds to quantum jumps, where photons are lost one by one. Here, we are able to tune the minimal number of lost photons per jump to be two (or more) with a simple dc voltage. As a consequence, different quantum states experience different dissipation. Causality implies that the states must also experience different energy shifts. Our measurements of these Lamb shifts are in good agreement with the predictions of the Kramers-Kronig relations for single quantum states in a regime of highly non-linear bath coupling. This work opens new possibilities for quantum state manipulation in circuit QED, without relying on the Josephson effect.