A levitated nanomechanical oscillator under ultra-high vacuum (UHV) is highly isolated from its environment. It has been predicted that this isolation leads to very low mechanical dissipation rates. However, a gap persists between predictions and experimental data. Here, we levitate a silica nanoparticle in a linear Paul trap at room temperature, at pressures as low as 7e-11 mbar. We measure a dissipation rate of 2*pi*80(20) nHz, corresponding to a quality factor exceeding 1e10, more than two orders of magnitude higher than previously shown. A study of the pressure dependence of the particle's damping and heating rates provides insight into the relative dissipation mechanisms.
The field of levitated optomechanics studies the interaction between light and the mechanical motion of mesoscopic objects that are suspended by means of magnetic, optical, or electrodynamic traps. The lack of a clamping structure drastically reduces mechanical and thermal coupling with the environment, making these physical systems particularly suitable as ultrasensitive force detectors and as a test bench for quantum mechanics in new regimes. In our experiment, we use a Paul trap to levitate a charged glass sphere that is 300 nm in diameter. We use an ultra-high-vacuum compatible technique to load a nanosphere into the trap. Furthermore, we have developed a method to control the electric charge of the trapped particle, which allows us to tune its oscillation frequency as well as to measure its mass precisely. Here we also report on the observation of cooling of the particle’s secular motion by means of feedback cooling, reaching a few tens of mK starting from room temperature. In future work, in order to reach quantum regimes, we plan to couple the center-of-mass motion of the nanoparticle and a single Ca+ ion to an optical cavity. Such a system offers new opportunities for levitated optomechanics, including new cooling schemes in the unresolved sideband regime and protocols for nonclassical motional state preparation.
Levitated particles are unique among optomechanical systems in that they benefit from the absence of physical contact with the external environment. Recently, a new research direction known as levitated optomechanics has attracted interest in numerous research groups, with a major focus on optically suspended particles. In contrast to optical trapping experiments, we levitate charged silica nanospheres in high vacuum by means of a Paul trap. This method provides a deeper confining potential than that of optical traps and enables trapping of optically opaque objects. A detection system based on back-focal-plane interferometry allows us to observe center-of-mass (CoM) motion of the particle. We introduce an additional laser beam that is focused on the particle and provides optical forces with projections on all three principal axes of the Paul trap. This additional beam is intensity-modulated by an acousto-optic modulator controlled by feedback electronics. In this way, we are able to cool the secular motion of the CoM below 1 K, the effective temperature in all three directions being currently limited only by the detection efficiency. This is the first time, to the best of our knowledge, that laser cooling of mechanical motion of a nanoparticle in a Paul trap potential has been demonstrated. Such cooling acts locally on a single particle, in contrast to feedback provided by auxiliary electric fields, and opens up possibilities for sympathetic cooling of particles levitated in Paul traps when other methods are not suitable, for example, in the case of highly absorptive particles.
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