Realisation of a Protected Cat-Qutrit Manifold via Engineered Quantum Tunnelling

TL;DR

This work demonstrates a three-photon Kerr parametric oscillator as a protected bosonic qutrit, showing quantum coherence, phase space dynamics, and potential for quantum information protection.

Contribution

First experimental realization and analysis of a three-photon KPO as a protected qutrit platform with observed quantum coherence and dynamic phase space behavior.

Findings

Confirmed three-photon Rabi oscillations in the KPO.

Measured Wigner functions showing cat-like states.

Identified a parasitic pump term limiting photon number.

Abstract

Engineering quantum tunnelling in phase space has emerged as a viable method for creating a protected logical qubit manifold with biased-noise properties. A promising approach is to combine a Kerr nonlinearity with a multi-photon drive, resulting in a system known as a Kerr parametric oscillator (KPO). In this work, we implement a three-photon KPO and explore its potential as a protected bosonic qutrit. We confirm quantum coherence by demonstrating three-photon Rabi oscillations and performing direct Wigner function measurements that reveal the formation of three-component cat-like states. Crucially, we observe a breathing-like dynamic in phase space, a characteristic feature of driven quantum systems. This dynamic arises from macroscopic temporal interference between the cat-qutrit manifold and the excited states. The frequency of resulting oscillations in the mean photon number provides a direct, time-domain measurement of the energy gap separating the qutrit from the excited states, thereby establishing an experimental hallmark of qutrit manifold protection. Furthermore, we identify a parasitic higher-order pump term as the primary mechanism constraining the mean photon number, highlighting its mitigation as a requisite for maximising protection. Our findings elucidate the basic quantum properties of the three-photon KPO and establish the first step towards its use as an alternative qutrit platform.