Cat qubits, for which logical $|0⟩$ and $|1⟩$ are coherent states $|\pm \alpha ⟩$ 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 $|\alpha {|}^2$. A large two-photon dissipation rate ${\kappa }_2$ 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 it reaches a rate ${\kappa }_2/2\pi \approx 2\mathrm{MHz}$. 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. In addition, we illustrate how the phase of a quantum superposition between $|\alpha ⟩$ and $|-\alpha ⟩$ can be arbitrarily changed by driving the harmonic mode while keeping the engineered dissipation active.

中文翻译：

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自动参数共振将 Cat 量子位的位翻转时间延长至 0.3 秒

Cat 量子位，其逻辑$|0⟩$和$|1⟩$是相干态$|\pm \alpha ⟩$谐波模式的研究为量子纠错提供了一条有前途的途径。利用耗散的优势，使谐波模式的光子对与其环境中的单个光子进行交换，可以稳定逻辑状态，并随光子数以指数方式增加猫量子位的位翻转时间$|\alpha {|}^2$。双光子耗散率大${\kappa }_2$确保快速的量子位操作和短的纠错周期，这有助于纠正猫量子位重复码中剩余的相位翻转错误。在这里，我们介绍并操作一个自动参数超导电路，该电路将包含猫量子位的模式耦合到有损模式，其频率设置为猫模式的两倍。这种被动耦合不需要参数泵，它达到的速率${\kappa }_2/2\pi \approx 2\mathrm{兆赫兹}$。凭借如此强大的双光子耗散，可以在长达 0.3 s 的特征时间内防止自参猫量子位的位翻转错误，并且对相位翻转错误仅产生轻微影响。此外，我们还说明了量子叠加的相位如何$|\alpha ⟩$和$|-\alpha ⟩$可以通过驱动谐波模式任意改变，同时保持工程耗散活跃。