Chip-based magnetic levitation of superconducting microparticles

Magnetically levitated superconductors are extremely isolated from the environment, their mechanical properties can be tuned magnetically, and can be coupled to quantum systems such as superconducting quantum circuits. As such, they are a promising experimental platform for the creation of massive spatial quantum states that would test quantum mechanics in a hitherto unexplored parameter regime. Furthermore, they could be used to build ultrasensitive detectors of accelerations and forces, which could find applications in seismology, navigation, geodesy, or dark matter detection.This thesis is about the development and demonstration of a chip-based magnetic levitation platform for um-sized superconducting particles. To this end, we have modeled, designed, and fabricated micrometer-scale superconducting particles as well as chip-based magnetic traps based on planar superconducting coils. We have detected the center-of-mass motion of the levitated particles magnetically, with integrated superconducting coils that transport the signal of the particle motion to a SQUID magnetometer. We demonstrated stable levitation of 50um diameter particles over several days at millikelvin temperatures. This high stability allowed us to thoroughly characterize the particle motion and show that our model of the magnetic trap and the detection scheme captures the nonlinear behavior of the center-of-mass motion. These nonlinearities are observed due to large motional amplitudes caused by the coupling between the particle motion and cryostat vibrations. We have devised a cryogenic vibration isolation system based on an elastic pendulum that mitigates this effect and has enabled ring-down measurements of the center-of-mass motion that give quality factors up to 10^5. Furthermore, we have shown that the mechanical properties of the levitated particle can be controlled. We have tuned the trap frequencies from 30Hz to 180Hz by changing the current in the trap coils, and we have also demonstrated control over the motional amplitude of the particle motion via feedback using feedback coils in the chip to exert an additional magnetic force on the particle. This thesis demonstrates magnetic levitation of superconducting microparticles on a chip as a novel platform for chip-based quantum experiments with um-sized particles and ultrasensitive force and acceleration sensors