Past Quantum States of a Monitored System
Past Quantum States of a Monitored System
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DOI：
10.1103/physrevlett.111.160401
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发表时间：
2013-10-15
影响因子：
8.6
通讯作者：
Molmer, Klaus
中科院分区：
文献类型：
--
作者：
Gammelmark, Soren;Julsgaard, Brian;Molmer, Klaus
密度矩阵rho(t)产生关于量子系统测量结果的概率信息。我们在这里引入过去的量子态，它在时间T时解释了量子系统在更早时间T < T时的状态。过去的量子态Xi(T)由两个对象组成，rho(T)和E(T)，分别取决于系统的动力学和探测，直到T和在时间区间[T， T]内。过去的量子态的特点是它能够比当时的传统量子态更好地预测任何测量的未知结果。一方面，我们的形式说明了如何平滑过程估计过去经典信号的量子探针[M]。Rev. Lett. 102, 250403(2009)]也适用于描述量子系统本身过去的状态。另一方面，它推广了前选择和后选择量子态的理论[Y]。Aharonov和L. Vaidman， J.物理学。[A] 24,2315(1991)]对任何量子测量场景、任何相干演化和任何马尔可夫耗散过程的系统。
A density matrix rho(t) yields probabilistic information about the outcome of measurements on a quantum system. We introduce here the past quantum state, which, at time T, accounts for the state of a quantum system at earlier times t < T. The past quantum state Xi(t) is composed of two objects, rho(t) and E(t), conditioned on the dynamics and the probing of the system until t and in the time interval [t, T], respectively. The past quantum state is characterized by its ability to make better predictions for the unknown outcome of any measurement at t than the conventional quantum state at that time. On the one hand, our formalism shows how smoothing procedures for estimation of past classical signals by a quantum probe [M. Tsang, Phys. Rev. Lett. 102, 250403 (2009)] apply also to describe the past state of the quantum system itself. On the other hand, it generalizes theories of pre- and postselected quantum states [Y. Aharonov and L. Vaidman, J. Phys. A 24, 2315 (1991)] to systems subject to any quantum measurement scenario, any coherent evolution, and any Markovian dissipation processes.