论文标题
在云量子计算机上的量子cramér-rao限制处的多参数传输估计
Multiparameter transmission estimation at the quantum Cramér-Rao limit on a cloud quantum computer
论文作者
论文摘要
估计传输或损失是光谱的核心。为了达到最终的量子分辨率极限，必须使用具有确定光子数量的探针状态，并且能够区分撞击其撞击的光子数量的检测器。在实践中，可以使用两种模式挤压光优于经典的限制，该光线可用于预言确定的光子数探针，但是当先驱臂或其探测器损失的情况下，预一保留剂不保证会产生所需的探针。我们表明，该范式可用于同时测量具有可实现的量子优势的两种模式中的不同损耗参数。我们在Xanadu的X8芯片上演示了此协议，该协议是通过云访问的，构建光子数概率分布从$ 10^6 $拍摄，并在这些分布上执行最大似然估计（MLE）$ 10^3 $独立时间。因为在挤压之前可能会丢失泵的光，所以我们还使用滋扰参数理论同时估算实际输入功率。 MLE converges to estimate the transmission amplitudes in X8's eight modes to be 0.39202(6), 0.30706(8), 0.36937(6), 0.28730(9), 0.38206(6), 0.30441(8), 0.37229(6), and 0.28621(8) and the squeezing parameters, which are proxies for effective input相干状态振幅，损失和非线性相互作用时间为1.3000（2），1.3238（3），1.2666（2）和1.3425（3）;所有这些不确定性都在量子cramér-rao结合的两个因子之内。这项研究为量子多参数估计理论，MLE收敛以及实际量子设备的表征和性能提供了至关重要的见解。
Estimating transmission or loss is at the heart of spectroscopy. To achieve the ultimate quantum resolution limit, one must use probe states with definite photon number and detectors capable of distinguishing the number of photons impinging thereon. In practice, one can outperform classical limits using two-mode squeezed light, which can be used to herald definite-photon-number probes, but the heralding is not guaranteed to produce the desired probes when there is loss in the heralding arm or its detector is imperfect. We show that this paradigm can be used to simultaneously measure distinct loss parameters in both modes of the squeezed light, with attainable quantum advantages. We demonstrate this protocol on Xanadu's X8 chip, accessed via the cloud, building photon-number probability distributions from $10^6$ shots and performing maximum likelihood estimation (MLE) on these distributions $10^3$ independent times. Because pump light may be lost before the squeezing occurs, we also simultaneously estimate the actual input power, using the theory of nuisance parameters. MLE converges to estimate the transmission amplitudes in X8's eight modes to be 0.39202(6), 0.30706(8), 0.36937(6), 0.28730(9), 0.38206(6), 0.30441(8), 0.37229(6), and 0.28621(8) and the squeezing parameters, which are proxies for effective input coherent-state amplitudes, their losses, and their nonlinear interaction times, to be 1.3000(2), 1.3238(3), 1.2666(2), and 1.3425(3); all of these uncertainties are within a factor of two of the quantum Cramér-Rao bound. This study provides crucial insight into the intersection of quantum multiparameter estimation theory, MLE convergence, and the characterization and performance of real quantum devices.
