Zeitschrift für Physik B Condensed Matter

ISSN: 0722-3277 (printed version)
ISSN: 1431-584X (electronic version)

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Abstract Volume 100 Issue 3 (1996) pp 455-460

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

A. Vourdas

Department of Electrical Engineering and Electronics, The University of Liverpool, Brownlow Hill, P.O. Box 147, Liverpool L69 3BX, UK

Received: 4 April 1995/Revised version: 22 August 1995

Abstract. Superconducting rings with mesoscopic Josephson junctions are considered in the presence of a dc voltage bias V₀ 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 \langleI²\rangle is in general different from \langleI\rangle². Using \langleI²\rangle we define the rms current I_rms, and using the various harmonics of \langleI\rangle as if they belong to a classical current we define the "classical rms current" I_{rms, 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 I_rms and refutes the I_{rms, class} would prove the quantum nature of these currents.

PACS: 74.50.+r

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