Guevara Ivonne, Wiseman Howard
Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia.
Phys Rev Lett. 2015 Oct 30;115(18):180407. doi: 10.1103/PhysRevLett.115.180407.
Smoothing is an estimation method whereby a classical state (probability distribution for classical variables) at a given time is conditioned on all-time (both earlier and later) observations. Here we define a smoothed quantum state for a partially monitored open quantum system, conditioned on an all-time monitoring-derived record. We calculate the smoothed distribution for a hypothetical unobserved record which, when added to the real record, would complete the monitoring, yielding a pure-state "quantum trajectory." Averaging the pure state over this smoothed distribution yields the (mixed) smoothed quantum state. We study how the choice of actual unraveling affects the purity increase over that of the conventional (filtered) state conditioned only on the past record.
平滑是一种估计方法，通过该方法，给定时间的经典状态（经典变量的概率分布）以所有时间（包括早期和晚期）的观测为条件。在这里，我们为部分监测的开放量子系统定义一个平滑量子态，该量子态以基于所有时间监测得出的记录为条件。我们计算一个假设的未观测记录的平滑分布，当将该记录添加到真实记录中时，将完成监测，从而产生一个纯态“量子轨迹”。对该平滑分布上的纯态进行平均，得到（混合的）平滑量子态。我们研究实际展开方式的选择如何影响相对于仅以过去记录为条件的传统（滤波）态的纯度增加。
