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Cat qubits, for which logical $|0\rangle$ and $|1\rangle$ are coherent states$|\pm\alpha\rangle$ of a harmonic mode, offer a promising route towards quantumerror correction. Using dissipation to our advantage so that photon pairs ofthe harmonic mode are exchanged with single photons of its environment, it ispossible to stabilize the logical states and exponentially increase thebit-flip time of the cat qubit with the photon number $|\alpha|^2$. Largetwo-photon dissipation rate $\kappa_2$ ensures fast qubit manipulation andshort error correction cycles, which are instrumental to correct the remainingphase-flip errors in a repetition code of cat qubits. Here we introduce andoperate an autoparametric superconducting circuit that couples a modecontaining the cat qubit to a lossy mode whose frequency is set at twice thatof the cat mode. This passive coupling does not require a parametric pump andreaches a rate $\kappa_2/2\pi\approx 2~\mathrm{MHz}$. With such a strongtwo-photon dissipation, bit-flip errors of the autoparametric cat qubit areprevented for a characteristic time up to 0.3 s with only a mild impact onphase-flip errors. Besides, we illustrate how the phase of a quantumsuperposition between $|\alpha\rangle$ and $|-\alpha\rangle$ can be arbitrarilychanged by driving the harmonic mode while keeping the engineered dissipationactive.

Autoparametric resonance extending the bit-flip time of a cat qubit up to 0.3 s