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IEEE Transactions on Applied Superconductivity

Noise-Induced Hopping in an RF SQUID

Ji-Quan Zhai, Zhican Du, Yu Zhou, Jianxin Shi, Weiwei Xu, Guozhu Sun, Lin Kang, Jian Chen, Peiheng Wu

Published Sep 23, 2014• 1 citation
Publisher

Abstract

An RF superconducting quantum interference device (RF SQUID), which is an important bistable system, has attracted much attention for its important applications in nonlinear fields. With different potential shapes at 20 mK, we perform detailed research on the relationship between the probability of the phase particle in the left potential well (PL) of an RF SQUID and the external noise intensity (D), which provides a method to identify the symmetry of any tunable bistable systems. A qualitative model is proposed to understand the physical process, and the numerical results are well consistent with the experimental results.

DOI
10.1109/tasc.2014.2359766

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At an extremely low temperature of 20 mK, we measured the loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop (Φ f ) and the small dc-SQUID (Φ cjj f ), respectively, the potential shape of the system can be fully controlled in situ. Variation in the transition step and overlap size in the switching current with a barrier flux bias are analyzed, from which we can obtain some relevant device parameters and build a model to explain the experimental phenomenon.
At an extremely low temperature of 20 mK, we measured the loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop ( Φ f ) and the small dc-SQUID ( Φ f cjj ), respectively, the potential shape of the system can be fully controlled in situ . Variation in the transition step and overlap size in the switching current with a barrier flux bias are analyzed, from which we can obtain some relevant device parameters and build a model to explain the experimental phenomenon.
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The harmonic oscillator is one of the most widely used model systems in physics: an indispensable theoretical tool in a variety of fields. It is well known that an otherwise linear oscillator can attain novel and nonlinear features through interaction with another dynamical system. We investigate such an interacting system: a superconducting LC-circuit dispersively coupled to a superconducting quantum interference device (SQUID). We find that the SQUID phase behaves as a classical two-level system, whose two states correspond to one linear and one nonlinear regime for the LC-resonator. As a result, the circuit's response to forcing can become multistable. The strength of the nonlinearity is tuned by the level of noise in the system, and increases with decreasing noise. This tunable nonlinearity could potentially find application in the field of sensitive detection, whereas increased understanding of the classical harmonic oscillator is relevant for studies of the quantum-to-classical crossover of Jaynes-Cummings systems.