Combined Dissipative and Hamiltonian Confinement of Cat Qubits

TL;DR

This paper proposes a novel combined dissipative and Hamiltonian confinement method for cat qubits, enhancing gate performance and noise protection, and is feasible with minor experimental modifications.

Contribution

It introduces a new confinement scheme combining two-photon dissipation with a TPE Hamiltonian, improving cat qubit gate performance and robustness.

Findings

Demonstrates faster, bias-preserving gates with improved performance.

Shows the combined scheme can be implemented with minor modifications.

Provides a new approach to confining and protecting cat qubits.

Abstract

Quantum error correction with biased-noise qubits can drastically reduce the hardware overhead for universal and fault-tolerant quantum computation. Cat qubits are a promising realization of biased-noise qubits as they feature an exponential error bias inherited from their non-local encoding in the phase space of a quantum harmonic oscillator. To confine the state of an oscillator to the cat qubit manifold, two main approaches have been considered so far: a Kerr-based Hamiltonian confinement with high gate performances, and a dissipative confinement with robust protection against a broad range of noise mechanisms. We introduce a new combined dissipative and Hamiltonian confinement scheme based on two-photon dissipation together with a Two-Photon Exchange (TPE) Hamiltonian. The TPE Hamiltonian is similar to Kerr nonlinearity, but unlike the Kerr it only induces a bounded distinction between even- and odd-photon eigenstates, a highly beneficial feature for protecting the cat qubits with dissipative mechanisms. Using this combined confinement scheme, we demonstrate fast and bias-preserving gates with drastically improved performance compared to dissipative or Hamiltonian schemes. In addition, this combined scheme can be implemented experimentally with only minor modifications of existing dissipative cat qubit experiments.