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

The effect of exposing an ultrasmall Josephson junction to a single-mode non-classical far-infrared field is investigated. We prove that on irradiating such a mesodevice with a quantum superposition of two phi -out-of-phase coherent states, its I-V characteristic exhibits current spikes which may be directly related to quantum interference effects. Moreover, we show that the structure of these current spikes is strongly influenced both by the phase difference phi between the two coherent states and by their relative quantum phase. The possibility of exploiting such peculiar aspects of the system dynamics to obtain information on the initial state of the field is brought to light.