Chip-based magnetic levitation of superconducting microparticles
Doctoral thesis, 2022

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.

Kollektorn, lecture room, MC2-huset, Campus Johanneberg
Opponent: Prof. Dr. Tjerk Oosterkamp, Leiden Instituut Onderzoek Natuurkunde, Netherlands


Martí Gutierrez Latorre

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Technology

Chip-based superconducting traps for levitation of micrometer-sized particles in the Meissner state

Superconductor Science and Technology,; Vol. 33(2020)

Journal article

A chip-based superconducting magnetic trap for levitating superconducting microparticles

IEEE Transactions on Applied Superconductivity,; Vol. 32(2022)

Journal article

Levitation is a fascinating phenomenon. Magnetically levitated objects in vacuum become extremely isolated from the environment because they only interact with gravity, blackbody radiation, the eventual collision with gas molecules, and the magnetic field. Thus, they are very sensitive to vibrations and magnetic fields, which makes them very well suited for detecting minute forces and accelerations. Furthermore, they could be used to perform quantum experiments with massive objects due to their capability to interact magnetically with quantum systems such as superconducting qubits.

In this thesis, we have laid the groundwork required to perform such experiments. We started by building a model to accurately simulate levitated superconductors in magnetic traps of complex geometries. We used this model to design magnetic traps based on coils made of superconducting material, fabricated on silicon chips. Then, we developed microfabrication processes to manufacture such chip traps and microparticles of superconducting materials such as niobium and lead in the shape of disks, rings, and spheres of tens of micrometers in size.
We used the magnetic chip traps to levitate these spheres, in vacuum, at temperatures near absolute zero using a dilution refrigerator. To study the particle motion, we tracked the levitated spheres with a camera using a cryogenic-compatible custom-made microscope, which demonstrated the levitation of a microparticle on a chip for a few seconds when under illumination. Using a magnetic field sensor instead of light to measure the particle motion allowed the particles to levitate over days. Thanks to this long stability, we could thoroughly characterize the system and show that our model properly describes the particle motion in the magnetic trap and its detection. We observed that the amplitude of the particle motion is increased by mechanical vibrations, caused by the dilution refrigerator. To decrease the amplitude of motion, we devised a vibration isolation system that isolates the levitated particle from the mechanical vibrations in the refrigerator by hanging the experiment from a pendulum inside the refrigerator. To further reduce the amplitude of motion, we have implemented a means of particle motion control, based on the application of a magnetic feedback force on the particle. We have shown the proof-of-principle of this approach and studied the possibility of using it to bring the particle motion into the quantum regime.

The results in this thesis provide a stepping stone towards quantum experiments, as well as force and acceleration sensing using magnetically levitated superconducting microparticles.

Continuously Monitored Quantum Sensors: Smart Tools and Applications

Swedish Research Council (VR) (2019-00390), 2020-01-01 -- 2022-12-31.

Levitated superconducting mechanical resonators: a novel platform for quantum experiments and sensing

Knut and Alice Wallenberg Foundation (2019.0231), 2020-07-01 -- 2025-06-30.

Exploring nonclassical states of center-of-mass mechanical motion with superconducting magneto- and levitomechanics

European Commission (EC) (EC/HE/101080143), 2022-10-01 -- 2026-09-30.

Areas of Advance

Nanoscience and Nanotechnology

Subject Categories

Physical Sciences

Nano Technology


Basic sciences


Nanofabrication Laboratory



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5253



Kollektorn, lecture room, MC2-huset, Campus Johanneberg


Opponent: Prof. Dr. Tjerk Oosterkamp, Leiden Instituut Onderzoek Natuurkunde, Netherlands

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