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Magnetism in SQUIDs at millikelvin temperatures
S Sendelbach1, D Hover, A Kittel
1Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Physical Review Letters
|July 23, 2008
Summary
We studied how temperature affects magnetic flux in superconducting quantum interference devices (SQUIDs) at millikelvin temperatures. Lowering temperature increased flux, linked to trapped vortices and spin behavior, explaining 1/f noise in SQUIDs and qubits.
Area of Science:
- Superconducting quantum devices
- Low-temperature physics
- Quantum information science
Background:
- Superconducting quantum interference devices (SQUIDs) are sensitive magnetic flux detectors.
- Understanding flux noise is critical for quantum computing and sensitive measurements.
- Previous studies have observed 1/f flux noise in SQUIDs and superconducting qubits.
Purpose of the Study:
- To characterize the temperature dependence of magnetic flux in dc SQUIDs at millikelvin temperatures.
- To investigate the relationship between flux, trapped vortices, and spin polarization.
- To provide an explanation for the universal 1/f flux noise phenomenon.
Main Methods:
- Cooling dc SQUIDs to millikelvin temperatures.
- Measuring magnetic flux threading the SQUIDs as a function of temperature.
- Analyzing the correlation between flux changes and the density of trapped vortices.
- Observing magnetic behavior in the absence of trapped flux.
Main Results:
- Magnetic flux increases as 1/T with decreasing temperature.
- Flux change is directly proportional to the density of trapped vortices.
- Data supports thermal polarization of surface spins within vortex trapped fields.
- Evidence of spin-glass freezing observed at low temperatures in the absence of trapped flux.
Conclusions:
- The temperature dependence of flux in SQUIDs is explained by trapped vortices and surface spin polarization.
- These findings offer a mechanism for the ubiquitous 1/f flux noise in SQUIDs and superconducting qubits.
- Understanding these phenomena is crucial for improving the coherence and performance of superconducting quantum technologies.
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