Dissipative stabilization of a squeezed cat qubit

Bosonic codes offer an hardware-efficient approach to quantum error correction by exploiting the infinite-dimensional Hilbert space of the quantum harmonic oscillator to implement a first layer of error correction. In particular, dissipative cat qubits autonomously stabilize two coherent states of opposite phases of the oscillator by engineering an interaction exchanging photons in pairs with the oscillator’s environment. Since the overlap of the wavefunctions of the coherent states decreases exponentially with mean photon number, bit-flip errors of the cat qubit are also suppressed exponentially, at the cost of a linear increase of phase-flip errors.

It was predicted recently (Xu et al., npj Quantum Information 9, 78 (2023)) that squeezing the cat qubit should allow to enhance the exponential scaling factor of the bit-flip time, owing to the smaller overlap in between squeezed coherent states. Importantly, this improvement is expected to incur no additional cost regarding the phase-flip time.

In this work, we experimentally demonstrate dissipative stabilization of a squeezed cat qubit by engineering an additional interaction term in between the oscillator and its environment, on top of the two-photon exchange.