Quantum current spikes in the I-V characteristic of a mesojunction coupledto non-classical em fields

The effect of exposing an ultrasmall Josephson junction to a single-mode no n-classical far-infrared field is investigated. We prove that on irradiatin g such a mesodevice with a quantum superposition of two phi -out-of-phase c oherent states, its I-V characteristic exhibits current spikes which may be directly related to quantum interference effects. Moreover, we show that t he structure of these current spikes is strongly influenced both by the pha se difference phi between the two coherent states and by their relative qua ntum phase. The possibility of exploiting such peculiar aspects of the syst em dynamics to obtain information on the initial state of the field is brou ght to light.