Single-photon Resolved Cross-Kerr Interaction for Autonomous Stabilization of Photon-number States

TL;DR

This paper demonstrates a reservoir engineering protocol using a cross-Kerr effect in circuit QED to stabilize specific photon-number states in a microwave cavity, advancing quantum state control.

Contribution

It introduces a novel reservoir engineering method leveraging a single-photon resolved cross-Kerr interaction for stabilizing Fock states.

Findings

Successful stabilization of Fock states in a microwave cavity.

Implementation of a nonlinear coupling via Josephson junctions.

Analysis of steady states using Wigner function measurements.

Abstract

Quantum states can be stabilized in the presence of intrinsic and environmental losses by either applying active feedback conditioned on an ancillary system or through reservoir engineering. Reservoir engineering maintains a desired quantum state through a combination of drives and designed entropy evacuation. We propose and implement a quantum reservoir engineering protocol that stabilizes Fock states in a microwave cavity. This protocol is realized with a circuit quantum electrodynamics platform where a Josephson junction provides direct, nonlinear coupling between two superconducting waveguide cavities. The nonlinear coupling results in a single photon resolved cross-Kerr effect between the two cavities enabling a photon number dependent coupling to a lossy environment. The quantum state of the microwave cavity is discussed in terms of a net polarization and is analyzed by a measurement of its steady state Wigner function.