Effect of Thermal Noise on Relaxation Oscillations in Superconducting Quantum Interference Devices

Voiceover

Presenter(s)

Thomas Baker

Abstract or Description

The superconducting quantum interference device (SQUID) is a magnetometer capable of quantum-limited measurements of magnetic flux. When fabricated on the tip of a nanopipette, the resulting SQUID-on-tip sensor can measure spatially distributed fields with a resolution on the order of nanometers. Electrical circuits containing hysteretic SQUIDs such as these are subject to relaxation oscillations under certain operating conditions. These relaxation oscillations degrade the performance of the SQUID. The performance issues caused by relaxation oscillations can be mitigated using shunt resistors, but some circuit designs make it difficult to include effective shunt resistors. An understanding of relaxation oscillations is therefore necessary in order to properly design and operate these SQUID circuits. Many models exist for relaxation oscillations in SQUID circuits, but limited research has been published on the effect of intrinsic thermal noise on relaxation oscillations. For this project, I modified a published model for relaxation oscillations to include noise and wrote a computer program to numerically simulate this model. I then simulated relaxation oscillations both with and without thermal noise in order to determine the effect of this noise on the frequency and dc average of the relaxation oscillations. I found that thermal noise causes a spread in the frequency of the relaxation oscillations and, in some cases, an increase in the average frequency. I also observed a rounding at the corners of the graph of the dc average of the oscillations. This computer program will later be used to simulate relaxation oscillations in SQUIDs that are fabricated and tested in our laboratory.