While coherently driven Kerr microcavities have rapidly matured as a platform for frequency-comb formation, such microresonators generally possess weak Kerr coefficients; consequently, triggering comb generation requires millions of photons to be circulating inside the cavity. This suppresses the role of quantum fluctuations in the dynamics of the comb. In this paper, we realize a minimal version of coherently driven Kerr-mediated microwave-frequency combs in the circuit quantum electrodynamics (cQED) architecture, where the fluctuations of the quantum vacuum are the primary limitation on comb coherence. We achieve a comb phase coherence of up to 35 $\mu \mathrm{s}$, approaching the theoretical device quantum limit of 55 $\mu \mathrm{s}$ and vastly longer than the inherent lifetimes of the modes, of 13 ns. The ability within cQED to engineer stronger nonlinearities than optical microresonators, together with operation at cryogenic temperatures, and the excellent agreement of comb dynamics with quantum theory indicates a promising platform for the study of complex dynamics of quantum nonlinear systems.

中文翻译：

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近似量子限制的约瑟夫逊结频率梳状合成器

尽管相干驱动的Kerr微腔已迅速成熟，成为形成频率梳的平台，但此类微谐振器通常具有较弱的Kerr系数；因此，触发梳子的产生需要数百万个光子在腔体内循环。这抑制了量子涨落在梳子动力学中的作用。在本文中，我们实现了电路量子电动力学（cQED）架构中相干驱动的Kerr介导的微波频率梳的最小版本，其中量子真空的波动是梳齿相干性的主要限制。我们实现了高达35的梳状相位相干性$\mu \mathrm{s}$，接近理论装置的量子极限55 $\mu \mathrm{s}$并且比这些模式的固有寿命（13 ns）长得多。cQED具有比光学微谐振器更强的工程非线性能力，以及在低温下运行的能力，以及梳状动力学与量子理论的出色一致性，为研究量子非线性系统的复杂动力学提供了一个有前途的平台。