Unusual quantum magnetic-resistive oscillations in a superconducting structure of two circular asymmetric loops in series

TL;DR

This study observed unexpected quantum magnetic-resistive oscillations in two asymmetric superconducting loops separated by a large distance, revealing interaction between their quantum states despite expectations of no coupling.

Contribution

It demonstrates the existence of interaction between quantum states of superconducting loops separated beyond the coherence length, using voltage oscillations under different biasing conditions.

Findings

Detected quantum oscillations in both V_{rec}(B) and V_{dc}(B)

Found interaction between loops separated by a large distance

V_{dc}(B) can describe quantum states of the loops

Abstract

We measured both quantum oscillations of a rectified time-averaged direct voltage V_{rec}(B) and a dc voltage V_{dc}(B) as a function of normal magnetic field B, in a thin-film aluminum structure of two asymmetric circular loops in series at temperatures below the superconducting critical temperature T_{c}. The V_{rec}(B) and V_{dc}(B) voltages were observed in the structure biased only with an alternating current (without a dc component) and only with a direct current (without an ac component), respectively. The aim of the measurements was to find whether interaction (nonlinear coupling) exists between quantum magnetic-resistive states of two loops at a large distance from each other. The distance between the loop centers was by an order of magnitude longer than the Ginzburg-Landau coherence length \xi(T). At such distance, one would not expect to detect any interaction between the quantum states of the loops. But we did find such an interaction. Moreover, we found that V_{dc}(B) functions (like V_{rec}(B) ones) can be used to describe the quantum states of the loops.