标题： 基于单个磁通子传输的快速量子比特读出仿真 显示英文标题

标题： Simulation of a rapid qubit readout dependent on the transmission of a single fluxon

摘要： 量子信息科学中，比特的读出速度是纠错的主要限制。 我们展示了对一种建议装置的模拟，该装置通过弹道磁通子来读取fluxonium比特的值，估计的读出时间为不到1纳秒，并且不需要微波输入信号。 这与基于电路量子电动力学的常见读出方式形成对比，但与之前的研究相关，在单个长约瑟夫森结（LJJ）中移动的磁通子可以根据耦合比特的状态表现出时间延迟。 我们的读出电路包含两个LJJ和一个在它们界面处耦合的比特。 我们发现该设备可以实现单次读出一个比特——其中一个比特状态会在界面产生单一的动力学反弹和磁通子反射，而另一个比特状态则会在界面产生几次反弹和磁通子传输。 动态最初是通过对电路的所有约瑟夫森结分别计算自由度得出的。 然而，集体坐标模型将动力学减少到三个自由度：一个用于fluxonium约瑟夫森结，每个LJJ各一个。 该模型中的大质量不平衡使我们可以模拟混合量子-经典动力学，作为全量子动力学的近似。 计算在$\leq 0.1\%$给出对量子比特的反作用。 显示英文摘要

摘要： The readout speed of qubits is a major limitation for error correction in quantum information science. We show simulations of a proposed device that gives readout of a fluxonium qubit using a ballistic fluxon with an estimated readout time of less than 1 nanosecond, without the need for an input microwave tone. This contrasts the prevalent readout based on circuit quantum electrodynamics, but is related to previous studies where a fluxon moving in a single long Josephson junction (LJJ) can exhibit a time delay depending on the state of a coupled qubit. Our readout circuit contains two LJJs and a qubit coupled at their interface. We find that the device can exhibit single-shot readout of a qubit -- one qubit state leads to a single dynamical bounce at the interface and fluxon reflection, and the other qubit state leads to a couple of bounces at the interface and fluxon transmission. Dynamics are initially computed with a separate degree of freedom for all Josephson junctions of the circuit. However, a collective coordinate model reduces the dynamics to three degrees of freedom: one for the fluxonium Josephson junction and one for each LJJ. The large mass imbalance in this model allows us to simulate the mixed quantum-classical dynamics, as an approximation for the full quantum dynamics. Calculations give backaction on the qubit at $\leq 0.1\%$.