[论文解读] Erasure conversion in a high-fidelity Rydberg quantum simulator

Pascal Scholl, Adam L. Shaw+4 more|arXiv (Cornell University)|May 5, 2023

Quantum Information and Cryptography参考文献 52被引用 7

一句话总结

该论文通过碱土金属原子的单点位分辨成像，在Rydberg量子模拟器中实现了高保真度Bell态制备与消去转换。通过快速24 μs成像检测漏态错误并剔除含消去错误的数据，作者在SPAM校正后实现了≥0.9985的Bell态保真度，接近0.999的保真度区间，从而提升了量子相变实验中的模拟保真度。

ABSTRACT

Minimizing and understanding errors is critical for quantum science, both in noisy intermediate scale quantum (NISQ) devices and for the quest towards fault-tolerant quantum computation. Rydberg arrays have emerged as a prominent platform in this context with impressive system sizes and proposals suggesting how error-correction thresholds could be significantly improved by detecting leakage errors with single-atom resolution, a form of erasure error conversion. However, two-qubit entanglement fidelities in Rydberg atom arrays have lagged behind competitors and this type of erasure conversion is yet to be realized for matter-based qubits in general. Here we demonstrate both erasure conversion and high-fidelity Bell state generation using a Rydberg quantum simulator. We implement erasure conversion via fast imaging of alkaline-earth atoms, which leaves atoms in a metastable state unperturbed and yields additional information independent of the final qubit readout. When excising data with observed erasure errors, we achieve a lower-bound for the Bell state generation fidelity of ${\geq} 0.9971^{+10}_{-13}$, which improves to ${\geq}0.9985^{+7}_{-12}$ when correcting for remaining state preparation errors. We further demonstrate erasure conversion in a quantum simulation experiment for quasi-adiabatic preparation of long-range order across a quantum phase transition, where we explicitly differentiate erasure conversion of preparation and Rydberg decay errors. We unveil the otherwise hidden impact of these errors on the simulation outcome by evaluating correlations between erasures and the final readout as well as between erasures themselves. Our work demonstrates the capability for Rydberg-based entanglement to reach fidelities in the ${\sim} 0.999$ regime, with higher fidelities a question of technical improvements, and shows how erasure conversion can be utilized in NISQ devices.

研究动机与目标

• 通过单原子分辨技术在物质基量子模拟器中实现消去转换。
• 在Rydberg阵列平台中实现高保真度两量子比特纠缠。
• 通过快速成像检测并剔除漏态错误，减轻漏态错误影响，提升模拟与态制备保真度。
• 证明消去转换可提升涉及长程序与量子相变的量子模拟保真度。
• 通过在捕获原子系统中实现错误检测与校正，建立通往容错量子计算的可扩展路径。

提出的方法

• 基于光学镊子捕获锶原子的Rydberg量子模拟器，利用一个量子比特子空间和一个独立的测量子空间用于错误检测。
• 通过Rydberg阻塞效应，利用拉比频率为Ω、相互作用移位为V的受控拉比振荡生成Bell态，满足Ω/V ≪ 1的条件。
• 通过在${}^{1}S_{0}$基态中实现0.980保真度的24 μs单次成像，检测漏态错误并将其转换为消去错误。
• 通过剔除在消去图像中检测到原子的实验运行，实现消去-剔除，从而移除已知错误位置的数据。
• 基于Beta分布的联合拟合程序，用于建模实验不确定性，并提取在π和2π时间点的$P_{\text{rr}}$、$P_{\text{gg}}$以及$P_{\text{gr}}+P_{\text{rg}}$的概率分布。
• 通过实验测得的误差模型应用SPAM（态制备与测量）校正，以提升保真度估计。

实验结果

研究问题

• RQ1 能否在捕获原子量子模拟器中，通过单点位分辨探测实现消去转换？
• RQ2 当结合Rydberg阻塞纠缠与快速成像的消去-剔除技术时，可实现的Bell态保真度是多少？
• RQ3 消去-剔除对涉及长程序与量子相变的量子模拟保真度有何影响？
• RQ4 通过检测阈值设置，消去-剔除的控制程度如何？其在保真度增益与数据损失之间如何权衡？
• RQ5 所展示的技术能否扩展至基于长寿命量子比特的容错量子误差校正？

主要发现

• 原始数据的Bell态保真度达到≥0.9971⁺¹⁰₋₁₃，经SPAM校正后提升至≥0.9985⁺⁷₋₁₂，表明实现了近乎理想的纠缠。
• 消去-剔除有效降低了漏态错误的影响，保真度增益随系统尺寸增大而增强，如在量子相变的准绝热扫掠过程中所示。
• 通过检测阈值可调控消去-剔除带来的保真度增益：最佳阈值约为5个光子，超过该值后误报增加将导致保真度下降。
• 通过SPAM校正显著缓解了态制备中的系统性误差，实现了高保真度态制备。
• 该方法能够检测原本隐藏的错误对模拟结果的影响，例如在长程序制备中的影响。
• 结果表明，基于Rydberg的纠缠可达到~0.999的保真度区间，通过技术优化可进一步提升。