Josephson mesojunctions as detectors of low-intensity quantized coherent far-infrared fields

We show that the quantum nature of a mesoscopic Josephson junction may be e xploited for detecting low-intensity electromagnetic quantized fields. In p articular we prove that intensity and phase of single-mode quantized cohere nt field may be reconstructed measuring amplitude and quantum noise of the first quantum Shapiro step occurring in the I-V characteristic of the ultra small Josephson junction.