Combined Dissipative and Hamiltonian Confinement of Cat Qubits
Ronan Gautier, Alain Sarlette, Mazyar Mirrahimi · PRX Quantum · 2022
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 nonlocal 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 induces only 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.