Experimental tests of coherence and entanglement conservation

TL;DR

This paper experimentally investigates how quantum coherence migrates between a composite system and its parts, confirming a conservation law for maximal accessible coherence using photon polarization states in two different optical setups.

Contribution

It provides the first experimental verification of coherence conservation law in quantum systems using polarization-encoded photons.

Findings

Maximal accessible coherence is conserved during global evolutions.

Coherence migration between subsystems and the composite system was observed.

Verification of a theoretical coherence conservation law in practical quantum systems.

Abstract

We experimentally demonstrate the migration of coherence between composite quantum systems and their subsystems. The quantum systems are implemented using polarization states of photons in two experimental setups. The first setup is based on linear optical controlled-phase quantum gate and the second scheme is utilizing effects of nonlinear optics. Our experiment allows to verify the relation between correlations of the subsystems and the coherence of the composite system, which was given in terms of a conservation law for maximal accessible coherence by Svozil\'ik \emph{et al.} [Phys. Rev. Lett. {\bf 115}, 220501 (2015)]. We observe that the maximal accessible coherence is conserved for the implemented class of global evolutions of the composite system.