The Kerr-cat qubit is a bosonic qubit in which multiphoton Schrödinger cat states are stabilized by applying a two-photon drive to an oscillator with a Kerr nonlinearity. The suppressed bit-flip rate with increasing cat size makes this qubit a promising candidate to implement quantum error correction codes tailored for noise-biased qubits. However, achieving strong light-matter interactions necessary for stabilizing and controlling this qubit has traditionally required strong microwave drives that heat the qubit and degrade its performance. In contrast, increasing the coupling to the drive port removes the need for strong drives at the expense of large Purcell decay. By integrating an effective band-block filter on chip, we overcome this trade-off and realize a Kerr-cat qubit in a scalable 2D superconducting circuit with high coherence. This filter provides 30 dB of isolation at the qubit frequency with negligible attenuation at the frequencies required for stabilization and readout. We experimentally demonstrate quantum nondemolition readout fidelity of 99.6% for a cat with eight photons. Also, to have high-fidelity universal control over this qubit, we combine fast Rabi oscillations with a new demonstration of the X(π/2) gate through phase modulation of the stabilization drive. Finally, the lifetime in this architecture is examined as a function of the cat size of up to ten photons in the oscillator, achieving a bit-flip time higher than 1 ms and only a linear increase in the phase-flip rate, in good agreement with the theoretical analysis of the circuit. Our qubit shows promise as a building block for fault-tolerant quantum processors with a small footprint. Published by the American Physical Society 2024

中文翻译：

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2D 架构中的高相干 Kerr-Cat 量子比特


Kerr-cat 量子比特是一种玻色子量子比特，其中通过对具有 Kerr 非线性的振荡器施加双光子驱动来稳定多光子薛定谔猫态。随着 cat 大小的增加，抑制的位翻转率使该量子比特成为实现为噪声偏倚量子比特量身定制的量子纠错码的有前途的候选者。然而，实现稳定和控制该量子比特所需的强光-物质相互作用传统上需要强大的微波驱动器来加热量子比特并降低其性能。相比之下，增加与驱动端口的耦合消除了对强大驱动器的需求，但代价是 Purcell 衰减较大。通过在片上集成有效的带区滤波器，我们克服了这种权衡，并在具有高相干性的可扩展 2D 超导电路中实现了 Kerr-cat 量子比特。该滤波器在量子比特频率下提供 30 dB 的隔离，在稳定和读出所需的频率下衰减可以忽略不计。我们实验证明，对于具有 8 个光子的猫，量子非爆破读出保真度为 99.6%。此外，为了实现对这个量子比特的高保真通用控制，我们将快速 Rabi 振荡与通过稳定驱动器的相位调制的 X（π/2） 门的新演示相结合。最后，将这种架构中的寿命作为振荡器中最多 10 个光子的 cat 大小的函数进行检查，实现高于 1 ms 的位翻转时间，并且相位翻转率仅线性增加，这与电路的理论分析非常一致。我们的量子比特有望成为占用空间小的容错量子处理器的构建块。 美国物理学会 2024 年出版