Monte Carlo Spin Simulations of Magnetic Noise – The Search for Pivoting
Physical Review B(2024)
摘要
Superconducting quantum interference devices (SQUIDs) show great promise as
quantum bits (qubits) but continue to be hindered by flux noise. The flux noise
power spectra of SQUIDs go as 1/f^α, where α is the
temperature-dependent noise exponent. Experiments find 0.5 ≲α≲ 1. Furthermore, experiments find that the noise power spectra versus
frequency at different temperatures pivot about or cross at a common point for
each SQUID. To try to better understand the results and motivated by
experimental evidence that magnetic moments on the surface of SQUIDS produce
flux noise, we present the results of our Monte Carlo simulations of various
spin systems on 2D lattices. We find that only spin glasses produce α∼ 1 at low temperature. We find that aliasing of the noise power spectra at
high frequencies can lead to spectral pivoting if it is in proximity to a knee
at a slightly lower frequency. We show that the pivot frequency depends on the
method of site selection and how often the magnetization is recorded. The
spectral pivoting that occurs in our simulations is due to aliasing and does
not explain the spectral pivoting of experiments.
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