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Modern Physics Letters B

INTERACTION OF MESOSCOPIC JOSEPHSON JUNCTION WITH A SUCCESSIVE SQUEEZED COHERENT FIELD

Vasile A. Popescu

Published Jul 10, 2000• 0 citations
Publisher

Abstract

Signal-to-quantum noise ratio for quantum current in mesoscopic Josephson junction of a circular superconducting ring can be improved if the electromagnetic field is in a successive squeezed coherent state. The mesoscopic Josephson junctions can feel the difference between the successive squeezed coherent states and other types of squeezed coherent states because their current–voltage Shapiro steps are different. We compare our method with another procedure for superposition of two squeezed coherent states (a squeezed even coherent state) and consider the effect of different large inductances on the supercurrent.

DOI
10.1142/s021798490000077x

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Signal-to-quantum noise ratio for quantum current in mesoscopic Josephson junction of a circular superconducting ring can be improved if the electromagnetic field is in a successive squeezed coherent state. The mesoscopic Josephson junctions can feel the difference between the successive squeezed coherent states and other types of squeezed coherent states because their current–voltage Shapiro steps are different. We compare our method with another procedure for superposition of two squeezed coherent states (a squeezed even coherent state) and consider the effect of different large inductances on the supercurrent.
Circular superconducting devices with mesoscopic Josephson junctions are considered in the presence of a dc voltage bias V0{\mathit{V}}_{0}V0​ and of nonclassical electromagnetic fields. It is shown that when the voltage V0{\mathit{V}}_{0}V0​ is an integer multiple of a certain value, the current through the junction has a dc component. This is broadly similar to Shapiro steps in macroscopic Josephson junctions, but the details depend on the nature of the nonclassical electromagnetic field. Coherent states, squeezed states, and number eigenstates are considered and the corresponding Shapiro steps are studied in detail. The presence of thermal noise in the nonclassical fields is also considered and its effect on the results is studied.
The interaction of a mesoscopic Josephson junction with superposition of even and odd coherent states is investigated. It is found that the expectation value and the fluctuation of a supercurrent can exhibit dc components. The number of current-voltage steps (CVSs) for the former are less than the latter. For the former the static supercurrent flows in a positive or negative direction, which depends on the phase of the light field. The correlation function and squeezing of the dc components of a supercurrent depend on the value of CVS. For some special value of a CVS, the squeezing disappears.
In this paper, we study the supercurrent in a mesoscopic Josephson junction (MJJ) and its quantum statistical properties in the presence of nonclassical light fields. We investigate in detail the influence of external nonclassical light fields on current-voltage step structures of the MJJ. We also study in detail quantum statistical properties of the supercurrent when the external quantum electromagnetic fields are even and odd coherent-state light fields. It is shown that the supercurrent in the MJJ exhibits both squeezing effect and quantum coherences. It is demonstrated that the MJJ can feel the difference not only between classical light fields and nonclassical light fields but also between different nonclassical light fields.
A mesoscopic Josephson junction in a superconducting ring enclosing a magnetostatic flux with dissipation is considered. The dissipation in this system is described as a consequence of its coupling to a reservoir. By solving the master equation it is shown that the state of the junction can evolve into a quantum superposition of two coherent states even when the dissipation is present. It is also shown that squeezing effects can exist in such a system, and the dynamic behavior of the supercurrent shows collapse and revival phenomena. The quantum decoherence is also discussed.