DiMario M T, Becerra F E
Center for Quantum Information and Control, Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131, USA.
Phys Rev Lett. 2020 Sep 18;125(12):120505. doi: 10.1103/PhysRevLett.125.120505.
Estimation of the properties of a physical system with minimal uncertainty is a central task in quantum metrology. Optical phase estimation is at the center of many metrological tasks where the value of a physical parameter is mapped to the phase of an electromagnetic field and single-shot measurements of this phase are necessary. While there are measurements able to estimate the phase of light in a single shot with small uncertainties, demonstrations of near-optimal single-shot measurements for an unknown phase of a coherent state remain elusive. Here, we propose and demonstrate strategies for single-shot measurements for ab initio phase estimation of coherent states that surpass the sensitivity limit of heterodyne measurement and approach the Cramer-Rao lower bound for coherent states. These single-shot estimation strategies are based on real-time optimization of coherent displacement operations, single photon counting with photon number resolution, and fast feedback. We show that our demonstration of these optimized estimation strategies surpasses the heterodyne limit for a wide range of optical powers without correcting for detection efficiency with a moderate number of adaptive measurement steps. This is, to our knowledge, the most sensitive single-shot measurement of an unknown phase encoded in optical coherent states.
以最小不确定性估计物理系统的特性是量子计量学的核心任务。光学相位估计处于许多计量任务的核心，在这些任务中，物理参数的值被映射到电磁场的相位，并且需要对该相位进行单次测量。虽然存在能够以小不确定性单次估计光相位的测量方法，但对于相干态未知相位的近最优单次测量的演示仍然难以实现。在这里，我们提出并演示了用于相干态从头开始相位估计的单次测量策略，该策略超越了外差测量的灵敏度极限，并接近相干态的克拉美-罗下限。这些单次估计策略基于相干位移操作的实时优化、具有光子数分辨率的单光子计数以及快速反馈。我们表明，在不通过适度数量的自适应测量步骤校正检测效率的情况下，我们对这些优化估计策略的演示在很宽的光功率范围内超过了外差极限。据我们所知，这是对光学相干态中编码的未知相位最灵敏的单次测量。
