发表机构
California Institute of Technology; AWS Center for Quantum Computing（加州理工学院; 亚马逊量子计算中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究提出Bang-bang非色散量子比特读出协议，以耦合常数突然淬灭替代参数扫描，可实现高保真QND单次投射测量，误差随光子数倒数减小，无需预加载腔即可通过经典通量驱动实现。
AI 中文摘要
超导量子比特的快速、精确且量子非破坏（QND）读出是高保真量子传感与计算的核心组成部分。传统方法通常工作在色散区域，此时量子比特-腔耦合强度$g$远小于失谐量$\triangle$，虽具备良好的QND特性，但读出速率被限制为$\backsim g^2\backslash sqrt(N)/\triangle\backslash ll g$，其中$N$为腔中的光子数。非色散区域的QND读出可使读出速率达到$\backsim g$的全部潜力，但该方案依赖参数扫描，可能遭遇共振并引发测量诱导态跃迁（MIST）。本研究提出一种非色散读出协议，用耦合常数的突然淬灭替代此类扫描，采用预加载光子的腔，将该协议命名为Bang-bang读出，证明其可实现单次投射测量，测量后量子比特的保真度与QND特性极高，误差随$1/N$减小。为得出上述结果，本研究针对Jaynes-Cummings（JC）模型的动力学与测量建立解析理论，包括以$1/\backslash sqrt(N)$为幂次的修正项系统展开，还证明该协议也可通过强驱动量子比特（如经典通量驱动）在不预加载腔的情况下实现。
英文摘要
Fast, precise, and quantum-non-demolition (QND) readout of superconducting qubits is a fundamental component of high-fidelity quantum sensing and computation. Conventional approaches typically operate in the dispersive regime, where the qubit-resonator coupling $g$ is weak compared to the detuning $Δ$. While exhibiting good QND properties, the readout rate is limited to $\sim g^2\sqrt{N}/Δ\ll g$, where $N$ is the number of photons in the resonator. QND readout in the nondispersive regime, where the readout rate reaches its full potential $\sim g$, relies on parameter sweeps that may encounter resonances, leading to measurement-induced state transitions (MIST). In this work, we study a nondispersive readout protocol that replaces these sweeps by sudden quenches of the coupling constant, using a resonator that is preloaded with photons. We call this protocol bang-bang readout, and show that it realizes single-shot projective measurements. The fidelity and QNDness of the qubit post-measurement are remarkably high, with an error that decreases like $1/N$. We show that the protocol can also be implemented without preloading the resonator by instead strongly driving the qubit, e.g., with a classical flux drive.
Comments22 pages, 15 figures. Supplementary: 29 pages, 1 figure. v2: references added, Fig. 11&12 merged into one figure. Link to metadata stored in Zenodo and anc folder with animations added
