Superconducting microsphere magnetically levitated in an anharmonic potential with integrated magnetic readout

TL;DR

This paper demonstrates the stable magnetic levitation of a superconducting microsphere in an anharmonic trap with integrated readout, characterizing nonlinearities and setting the stage for quantum experiments and sensitive sensors.

Contribution

It introduces a method for levitating and detecting a superconducting microsphere in a tunable, anharmonic magnetic trap with integrated readout, advancing quantum and sensing applications.

Findings

Stable levitation of a 700ng superconducting microsphere over days.

Characterization of trap anharmonicities and nonlinear frequency shifts.

Finite element modeling explains the observed nonlinear behavior.

Abstract

Magnetically levitated superconducting microparticles offer a promising path to quantum experiments with picogram to microgram objects. In this work, we levitate a 700ng $\sim 10^{17}$amu superconducting microsphere in a magnetic chip trap in which detection is integrated. We measure the particle's center-of-mass motion using a DC-SQUID magnetometer. The trap frequencies are continuously tunable between 30 and 160 Hz and the particle remains stably trapped over days in a dilution refrigerator environment. We characterize motional-amplitude-dependent frequency shifts, which arise from trap anharmonicities, namely Duffing nonlinearities and mode couplings. We explain this nonlinear behavior using finite element modelling of the chip-based trap potential. This work constitutes a first step towards quantum experiments and ultrasensitive inertial sensors with magnetically levitated superconducting microparticles.