Institut für Theoretische Physik, Albert-Einstein-Allee 11, Universität Ulm, D-89069 Ulm, Germany.
Phys Rev Lett. 2012 Dec 7;109(23):233601. doi: 10.1103/PhysRevLett.109.233601. Epub 2012 Dec 4.
We analyze precision bounds for a local phase estimation in the presence of general, non-Markovian phase noise. We demonstrate that the metrological equivalence of product and maximally entangled states that holds under strictly Markovian dephasing fails in the non-Markovian case. Using an exactly solvable model of a physically realistic finite bandwidth dephasing environment, we demonstrate that the ensuing non-Markovian dynamics enables quantum correlated states to outperform metrological strategies based on uncorrelated states using otherwise identical resources. We show that this conclusion is a direct result of the coherent dynamics of the global state of the system and environment and therefore the obtained scaling with the number of particles, which surpasses the standard quantum limit but does not achieve Heisenberg resolution, possesses general validity that goes beyond specific models. This is in marked contrast with the situation encountered under general Markovian noise, where an arbitrarily small amount of noise is enough to restore the scaling dictated by the standard quantum limit.
我们分析了在存在一般非马尔可夫相位噪声的情况下局部相位估计的精度界限。我们证明了在非马尔可夫情况下，严格的马尔可夫退相位下保持的乘积和最大纠缠态的计量等价性失效。使用物理上现实的有限带宽退相位环境的精确可解模型，我们证明了随后的非马尔可夫动力学使得量子相关态能够利用相同的资源超越基于非相关态的计量策略。我们表明，这一结论是系统和环境全局状态的相干动力学的直接结果，因此与标准量子极限相比，粒子数量的这种扩展超越了特定模型，具有普遍的有效性。这与一般马尔可夫噪声情况下的情况形成鲜明对比，在一般马尔可夫噪声情况下，任意小量的噪声足以恢复标准量子极限所规定的扩展。
