# Photon-assisted charge-parity jumps in a superconducting qubit

## TL;DR

This paper investigates how stray photons with sufficient energy cause charge-parity jumps in superconducting qubits, leading to energy and phase relaxation, and distinguishes this mechanism from other relaxation processes.

## Contribution

It introduces a new mechanism for qubit relaxation involving photon-assisted charge-parity jumps, with a method to separate it from other relaxation channels.

## Key findings

- Photon-assisted charge-parity jumps cause comparable energy gain and loss rates.
- The relaxation mechanism is linked to stray photons exceeding the Cooper pair breaking energy.
- Charge parity changes serve as signatures for this relaxation process.

## Abstract

We evaluate the rates of energy and phase relaxation of a superconducting qubit caused by stray photons with energy exceeding the threshold for breaking a Cooper pair. All channels of relaxation within this mechanism are associated with the change in the charge parity of the qubit, enabling the separation of the photon-assisted processes from other contributions to the relaxation rates. Among the signatures of the new mechanism is the same order of rates of the transitions in which a qubit looses or gains energy.