Ultralow mechanical damping with Meissner-levitated ferromagnetic microparticles

Levitated nanoparticles and microparticles are excellent candidates for the realization of extremely isolated mechanical systems, with a huge potential impact in sensing applications and in quantum physics. Magnetic levitation based on static fields is a particularly interesting approach, owing to the unique property of being completely passive and compatible with low temperatures. Here, we show experimentally that micromagnets levitated above type-I superconductors feature very low damping at low frequency and low temperature. In our experiment, we detect five out of six rigid body mechanical modes of a levitated ferromagnetic microsphere, using a dc superconducting quantum interference device with a single pick-up coil. The measured frequencies are in agreement with a finite-element simulation based on an ideal Meissner effect. For two specific modes, we find further substantial agreement with analytical predictions based on the image method. We measure damping times τ exceeding 104s and quality factors Q beyond 107, an improvement of 2-3 orders of magnitude over previous experiments based on the same principle. We investigate the possible residual loss mechanisms besides gas collisions, and argue that a much longer damping time can be achieved with further effort and optimization. Our results open the way towards the development of ultrasensitive magnetomechanical sensors with potential applications to magnetometry and gravimetry, as well as to fundamental and quantum physics.