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.
@article{arxiv.2108.00221,
title = {Experimental demonstration of optimal probabilistic enhancement of quantum coherence},
author = {Robert Stárek and Michal Mičuda and Michal Kolář and Radim Filip and Jaromír Fiurášek},
journal= {arXiv preprint arXiv:2108.00221},
year = {2021}
}