Quantum Control of an Oscillator with a Kerr-cat Qubit

TL;DR

This paper demonstrates the experimental realization of a driven parametric coupling between a Kerr-cat qubit and a microwave cavity, enabling universal control and advancing the potential for fault-tolerant quantum error correction with bosonic codes.

Contribution

It introduces a method to couple a Kerr-cat qubit to a cavity and achieves high-fidelity control, addressing decoherence issues and paving the way for fault-tolerant syndrome measurements.

Findings

Successfully coupled Kerr-cat qubit to a microwave cavity.

Engineered dissipation to eliminate excess dephasing.

Demonstrated high on-off ratio of control signals.

Abstract

Bosonic codes offer a hardware-efficient strategy for quantum error correction by redundantly encoding quantum information in the large Hilbert space of a harmonic oscillator. However, experimental realizations of these codes are often limited by ancilla errors propagating to the encoded logical qubit during syndrome measurements. The Kerr-cat qubit has been proposed as an ancilla for these codes due to its theoretically-exponential noise bias, which would enable fault-tolerant error syndrome measurements, but the coupling required to perform these syndrome measurements has not yet been demonstrated. In this work, we experimentally realize driven parametric coupling of a Kerr-cat qubit to a high-quality-factor microwave cavity and demonstrate a gate set enabling universal quantum control of the cavity. We measure the decoherence of the cavity in the presence of the Kerr-cat and discover excess dephasing due to heating of the Kerr-cat to excited states. By engineering frequency-selective dissipation to counteract this heating, we are able to eliminate this dephasing, thereby demonstrating a high on-off ratio of control. Our results pave the way toward using the Kerr-cat to fault-tolerantly measure error syndromes of bosonic codes.