Cat qubits, for which logical ∣0⟩ and ∣1⟩ are coherent states
∣±α⟩ of a harmonic mode, offer a promising route towards quantum
error correction. Using dissipation to our advantage so that photon pairs of
the harmonic mode are exchanged with single photons of its environment, it is
possible to stabilize the logical states and exponentially increase the
bit-flip time of the cat qubit with the photon number ∣α∣2. Large
two-photon dissipation rate κ2 ensures fast qubit manipulation and
short error correction cycles, which are instrumental to correct the remaining
phase-flip errors in a repetition code of cat qubits. Here we introduce and
operate an autoparametric superconducting circuit that couples a mode
containing the cat qubit to a lossy mode whose frequency is set at twice that
of the cat mode. This passive coupling does not require a parametric pump and
reaches a rate κ2/2π≈2MHz. With such a strong
two-photon dissipation, bit-flip errors of the autoparametric cat qubit are
prevented for a characteristic time up to 0.3 s with only a mild impact on
phase-flip errors. Besides, we illustrate how the phase of a quantum
superposition between ∣α⟩ and ∣−α⟩ can be arbitrarily
changed by driving the harmonic mode while keeping the engineered dissipation
active