Pirandola Stefano, Lupo Cosmo
Computer Science and York Centre for Quantum Technologies, University of York, York YO10 5GH, United Kingdom.
Phys Rev Lett. 2017 Mar 10;118(10):100502. doi: 10.1103/PhysRevLett.118.100502. Epub 2017 Mar 7.
We consider the estimation of noise parameters in a quantum channel, assuming the most general strategy allowed by quantum mechanics. This is based on the exploitation of unlimited entanglement and arbitrary quantum operations, so that the channel inputs may be interactively updated. In this general scenario, we draw a novel connection between quantum metrology and teleportation. In fact, for any teleportation-covariant channel (e.g., Pauli, erasure, or Gaussian channel), we find that adaptive noise estimation cannot beat the standard quantum limit, with the quantum Fisher information being determined by the channel's Choi matrix. As an example, we establish the ultimate precision for estimating excess noise in a thermal-loss channel, which is crucial for quantum cryptography. Because our general methodology applies to any functional that is monotonic under trace-preserving maps, it can be applied to simplify other adaptive protocols, including those for quantum channel discrimination. Setting the ultimate limits for noise estimation and discrimination paves the way for exploring the boundaries of quantum sensing, imaging, and tomography.
我们考虑在量子信道中估计噪声参数，假设采用量子力学允许的最一般策略。这基于对无限纠缠和任意量子操作的利用，使得信道输入可以交互式更新。在这种一般情况下，我们在量子计量学和量子隐形传态之间建立了一种新颖的联系。事实上，对于任何隐形传态协变信道（例如，泡利信道、擦除信道或高斯信道），我们发现自适应噪声估计无法超越标准量子极限，量子费希尔信息由信道的蔡矩阵确定。例如，我们确定了热损耗信道中估计过量噪声的最终精度，这对量子密码学至关重要。由于我们的一般方法适用于在保迹映射下单调的任何泛函，它可用于简化其他自适应协议，包括那些用于量子信道区分的协议。设定噪声估计和区分的最终极限为探索量子传感、成像和层析成像的边界铺平了道路。
