Non-Hermitian quantum rings

We investigate the spectral and dynamical properties of a quantum particle constrained on a ring threaded by a magnetic flux in the presence of a complex (non-Hermitian) potential. For a static magnetic flux, the quantum states of the particle on the ring can be mapped onto the Bloch states of a complex crystal, and magnetic flux tuning enables us to probe the spectral features of the complex crystal, including the appearance of exceptional points. For a time-varying (linearly ramped) magnetic flux, Zener tunneling among energy states is realized owing to the induced electromotive force. Compared to the Hermitian case, striking effects are observed in the non-Hermitian case, such as a highly asymmetric behavior of particle motion when reversing the direction of the magnetic flux and field-induced delayed transparency.