Achintya Paradkar

PhD student at the Department of Microtechnology and Nanoscience, Quantum Technology Laboratory

Project Description

Magnetically levitated particles promise to reach ultra-low mechanical dissipation [1] due to the
absence of clamping and internal material losses, which are otherwise limiting factors in clamped
nanomechanical resonators, and the absence of photon recoil heating, a limiting factor in optical
levitation experiments. Furthermore, the magnetically levitated particle can be coupled via flux to
superconducting circuits, which allows for quantum manipulation of its centre-of-mass (COM) motion.
Thus, magnetically levitated particles are a promising novel platform for developing ultra-sensitive
force and acceleration sensors, both in the classical [2] and in the quantum regime [3]. In our project,
we demonstrate levitation of micrometer-sized superconducting particles by using a chip-based
magnetic trap architecture [4]. The chip-trap generates a quadrupole-like magnetic field of tunable
strength. It is fabricated from multi-winding superconducting Niobium coils on two separate chips,
which are stacked vertically. We have achieved levitation of sub-100 mm lead spheres at a temperature
of 7K in a low-vibration, dry cryostat, when using a current larger than 0.3A in the trap. Crucially,
this current generates a strong magnetic lift force, which overcomes the Van der Waals force of the
particle resting on the chip surface. Currently, we observe levitation by optical means. Experiments are
underway to read out the COM motion using a SQUID, which will facilitate feedback cooling in order
to reduce the phonon occupation of the COM motion. The latter is a requirement for future quantum
control of particle motion. In parallel, we construct an experimental platform that enables levitation
of the superconducting particle at mK temperature, which will facilitate coupling to superconducting
circuits. Ultimately, this coupling allows generation of quantum states of the COM motion, such as
superposition or squeezed states, which are a crucial resource for quantum sensing experiments
aiming at measuring minute forces, e.g., gravity.

[1] Romero-Isart, O., et al., Phys. Rev. Lett. 109, 147205 (2012); Cirio, M. et al., Phys. Rev. Lett.
109, 147206 (2012)
[2] Prat-Camps, J., et al., Physical Review Applied 8, 034002 (2017)
[3] Johnsson, Mattias T., et al., Scientific Reports 6, 37495 (2016)
[4] Gutierrez Latorre, M. et al., Supercond. Sci. Technol. 33, 105002 (2020)

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