Observing the dynamics of quantum states generated inside nonlinear optical cavities

TL;DR

This paper introduces a novel method for reconstructing and observing the dynamics of quantum states generated inside nonlinear optical cavities, overcoming measurement challenges by analyzing steady-state statistics.

Contribution

It presents a new framework for intracavity quantum state tomography that directly links cavity field distributions to steady-state measurement statistics.

Findings

Successfully reconstructed the Husimi Q function of a cavity squeezed vacuum state.

Demonstrated real-time observation of quantum vacuum state evolution during phase-sensitive amplification.

Validated the method in a degenerate optical parametric oscillator setup.

Abstract

Quantum states at optical frequencies are often generated inside cavities to facilitate strong nonlinear interactions. However, measuring these quantum states with traditional homodyne techniques poses a challenge, as outcoupling from the cavity disturbs the state's quantum properties. Here, we propose a framework for reconstructing quantum states generated inside nonlinear optical cavities and observing their dynamics. Our approach directly imprints the field distribution of the cavity quantum state onto the statistics of bistable cavity steady-states. We propose a protocol to fully reconstruct the cavity quantum state, visualized in 2D phase-space, by measuring the changes in the steady-state statistics induced by a probe signal injected into the cavity under different condition. We experimentally demonstrate our approach in a degenerate optical parametric oscillator, generating and reconstructing the quasi-probability distribution of different quantum states. As a validation, we reconstruct the Husimi Q function of the cavity squeezed vacuum state. In addition, we observe the evolution of the quantum vacuum state inside the cavity as it undergoes phase-sensitive amplification. By enabling generation and measurement of quantum states in a single nonlinear optical cavity, our method realizes an "end-to-end" approach to intracavity quantum tomography, facilitating studies of quantum optical phenomena in nonlinear driven-dissipative systems.