Enhancing Kerr-Cat Qubit Coherence with Controlled Dissipation

TL;DR

This paper demonstrates that combining Hamiltonian confinement with engineered dissipation significantly extends the coherence time of Kerr-cat qubits, advancing their potential for scalable quantum error correction.

Contribution

It provides the first experimental evidence that engineered dissipation can mitigate leakage and enhance Kerr-cat qubit coherence times.

Findings

Leakage out of the qubit manifold can be coherently controlled and measured.

Engineered dissipation can cool leakage populations back into the qubit manifold.

Bit-flip times were increased up to 3.6 milliseconds with combined stabilization methods.

Abstract

Quantum computing crucially relies on maintaining quantum coherence for the duration of a calculation. Bosonic quantum error correction protects this coherence by encoding qubits into superpositions of noise-resilient oscillator states. In the case of the Kerr-cat qubit (KCQ), these states derive their stability from being the quasi-degenerate ground states of an engineered Hamiltonian in a driven nonlinear oscillator. KCQs are experimentally compatible with on-chip architectures and high-fidelity operations, making them promising candidates for a scalable bosonic quantum processor. However, their bit-flip time must increase further to fully leverage these advantages. Here, we present direct evidence that the bit-flip time in a KCQ is limited by leakage out of the qubit manifold and experimentally mitigate this process. We coherently control the leakage population and measure it to be > 9%, twelve times higher than in the undriven system. We then cool this population back into the KCQ manifold with engineered dissipation, identify conditions under which this suppresses bit-flips, and demonstrate increased bit-flip times up to 3.6 milliseconds. By employing both Hamiltonian confinement and engineered dissipation, our experiment combines two paradigms for Schr\"odinger-cat qubit stabilization. Our results elucidate the interplay between these stabilization processes and indicate a path towards fully realizing the potential of these qubits for quantum error correction.