We theoretically and experimentally investigate conditional enhancement of overall coherence of quantum states by probabilistic quantum operations that apply to the input state a quantum filter diagonal in the basis of incoherent states. We identify the optimal filters that for a given probability of successful filtering maximize the output coherence. We verify the performance of the studied quantum filters in a proof-of-principle experiment with linear optics, where a pair of two-level quantum systems is represented by polarization states of two photons. We comprehensively characterize the implemented two-qubit linear optical quantum filters by full quantum process tomography and we experimentally observe the optimal quantum coherence enhancement by quantum filtering.

我们在理论上和实验上研究了通过概率量子操作对量子状态整体相干性的条件增强，该操作适用于输入状态的量子滤波器对角线在非相干状态的基础上。我们确定对于给定的成功过滤概率最大化输出相干性的最佳过滤器。我们在线性光学原理验证实验中验证了所研究的量子滤波器的性能，其中一对两能级量子系统由两个光子的偏振态表示。我们通过全量子过程断层扫描全面表征了实现的双量子位线性光学量子滤波器，并通过实验观察了量子滤波的最佳量子相干增强。