Monras Alex, Paris Matteo G A
Grup de Fisica Teòrica & IFAE, Universitat Autònoma de Barcelona, Bellaterra E-08193, Spain.
Phys Rev Lett. 2007 Apr 20;98(16):160401. doi: 10.1103/PhysRevLett.98.160401. Epub 2007 Apr 17.
We address the estimation of the loss parameter of a bosonic channel probed by Gaussian signals. We derive the ultimate quantum bound with precision and show that no improvement may be obtained by having access to the environmental degrees of freedom. We find that, for small losses, the variance of the optimal estimator is proportional to the loss parameter itself, a result that represents a qualitative improvement over the shot-noise limit. An observable based on the symmetric logarithmic derivative is obtained, which attains the ultimate bound and may be implemented using Gaussian operations and photon counting.
我们研究了由高斯信号探测的玻色子信道的损耗参数估计问题。我们精确地推导了最终的量子界限，并表明通过获取环境自由度无法得到改进。我们发现，对于小损耗，最优估计器的方差与损耗参数本身成正比，这一结果相对于散粒噪声极限有了定性的改进。我们得到了一个基于对称对数导数的可观测量，它达到了最终界限，并且可以通过高斯操作和光子计数来实现。
