Giant Cross Kerr Effect for Propagating Microwaves Induced by an Artificial Atom

TL;DR

This paper demonstrates a significant cross Kerr effect in propagating microwaves coupled to a superconducting qubit, achieving large phase shifts at the single-photon level, advancing quantum gate development in microwave quantum optics.

Contribution

It reports the first observation of large cross Kerr phase shifts induced by an artificial atom on propagating microwave fields, reaching up to 30 degrees.

Findings

Average phase shift of 11 degrees per photon at the single-photon level

Phase shifts up to 30 degrees at high control power

Progress towards microwave quantum gates

Abstract

We have investigated the cross Kerr phase shift of propagating microwave fields strongly coupled to an artificial atom. The artificial atom is a superconducting transmon qubit in an open transmission line. We demonstrate average phase shifts of 11 degrees per photon between two coherent microwave fields both at the single-photon level. At high control power, we observe phase shifts up to 30 degrees. Our results provide an important step towards quantum gates with propagating photons in the microwave regime.