Disorder in parity–time symmetric quantum walks

We experimentally investigate the impact of static disorder and dynamic disorder on the non-unitary dynamics of parity–time (PT)-symmetric quantum walks. Via temporally alternating photon losses in an interferometric network, we realize the passive PT-symmetric quantum dynamics for single photons. Controllable coin operations allow us to simulate different environmental influences, which result in three different behaviors of quantum walkers: a standard ballistic spread, a diffusive behavior, and a localization, respectively, in a PT-symmetric quantum walk architecture.