Quantum currents in mesoscopic Josephson junctions in the presence of non-classical microwaves

Abstract

Superconducting rings with mesoscopic Josephson junctions are considered in the presence of a do voltage bias Vo and of non-classical electromagnetic fields (coherent states, squeezed states, number eigenstates etc.). Due to the quantum nature of these devices the current I is a quantum mechanical operator and therefore «I2» is in general different from «I»2. Using «I2» we define the rms current Irms, and using the various harmonics of «I» as if they belong to a classical current we define the “classical rms current” Irms, class. In the case of classical currents these two quantities are identical, but for quantum currents they are different. We study their difference for various non-classical fields, and find that in some cases this difference is large. These predictions could be observed experimentally through the electromagnetic power that these currents radiate. An experiment that confirms the Irms and refutes the Irms, class would prove the quantum nature of these currents.