Magnetic Monopole Noise

This thesis presents the first ever measurement of the noise emitted by magnetic monopoles and the development of an exquisitely sensitive magnetic-field-noise spectrometer based on a superconducting quantum interference device (SQUID) that enabled it. Magnetic monopoles are highly elusive elementary particles exhibiting quantized magnetic charge. The prospects for studying them brightened recently with the theoretical discovery that the thermally excited states in certain classes of magnetic insulators exhibit all the characteristics of magnetic monopoles. Furthermore, in 2018, it was predicted that the random motion of magnetic monopoles inside would generate a very specific kind of magnetization noise. In this thesis, the author describes a new experimental technique, so-called spin noise spectroscopy, and the subsequent discovery of virtually all of the predicted features of the magnetic noise expected from a dense fluid of magnetic monopoles in crystals of Dy2Ti2O7. Remarkably, because this magnetic monopole noise occurs in the frequency range below 20kHz, when amplified by the SQUID it is actually audible to humans.


Ritika Dusad received her PhD from Cornell University under the supervision of Prof. Séamus Davis. In her dissertation work, she designed and built a novel spin noise spectrometer that has led to the discovery of 'Magnetic Monopole Noise' in Dysprosium Titanate. The results of that study are presented in this thesis. Remarkably, the motion of magnetic monopoles and frustration of the magnets she studied can actually be heard at temperatures between 1K and 4K.
Ritika Dusad was born and raised in Delhi, India and studied physics at University of California, Los Angeles as an undergraduate student. She is an expert in conceptualizing, designing and building experiments for low temperature physics.
In her spare time she likes to sing Hindustani Classical Music, paint, and read fiction written by Indian authors.