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Japanese Journal of Applied Physics

Experimental Method for Evaluating Circulating Current Noise and Intrinsic Voltage Noise of a DC Superconducting Quantum Interference Device

Masakazu Nakanishi

Published Apr 1, 1997• 0 citations
Publisher

Abstract

We demonstrated an experimental method for individually evaluating the circulating current noise and intrinsic voltage noise of a current-biased dc superconducting quantum interference device (dc-SQUID), which was previously considered impossible.
DOI
10.1143/jjap.36.2428

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There are two bias schemes, namely current-bias and voltage-bias, for the directly coupled readout circuit of direct current superconducting quantum interference device (dc SQUID). In order to find out the difference between two bias schemes, we present the theoretical analyses on their equivalent circuits, working point locations, and noise performances. The theoretical analysis and experimental validation prove that the voltage-bias scheme achieves a larger transfer coefficient and exhibits a better noise performance than the current-bias scheme in the reading of conventional dc SQUID.
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Critical current fluctuations with a 1∕f spectral density (f is frequency) are potentially a limiting source of intrinsic decoherence in superconducting quantum bits (qubits) based on Josephson tunnel junctions. Prior measurements of this noise were made at nonzero voltages whereas qubits are operated in the zero voltage state. We report measurements of 1∕f noise in a dc superconducting quantum interference device first, coupled to a resonant tank circuit and operated in a dispersive mode at zero voltage, and, second, operated conventionally with a current bias in the voltage regime. Both measurements yield essentially the same magnitude of critical current 1∕f noise.