Spin current and noise in a mesoscopic ring under a quantum electromagnetic field irradiation

We have investigated the behaviors of spin transport in a mesoscopic ring interacting with a quantum electromagnetic field (QEMF). The mesoscopic ring is described by a non-interacting one-dimensional electron system. The QEMF is considered to be in coherent state (CS) or in squeezed coherent state (SCS) separately. This induces nonclassical AB and AC effects, and the novel dynamic spin current is associated with the U(1)×SU(2) gauge quantum field. The phase oscillations and spin current noise are derived by considering the spin fluctuations in a particular QEMF state. The Zeeman split term takes effect in the spin current formula for a state, while it disappears as ω→0. This means that there is no persistent spin current contributed by static scalar AC effect. The spin current noise exhibits nonclassical behaviors in our system. This indicates the situation that quantum effects are transferred to the spin current. The spin current and spin current noise versus photon energy exhibit stair-like behaviors which are different in different QEMF.