Pressure-dependent damping of a particle levitated in vacuum

Abstract

A novel method of levitation, using an actively controlled electric field, launches, captures, and stably suspends a microscopic (∼15 μm) particle in high vacuum. While held to within one diameter in the vertical direction, the particle is allowed to oscillate nearly freely in the horizontal plane under the influence of a central restoring force. The damping of horizontal oscillations was measured over the pressure range from 10−2 to 10−8 Torr. The damping was observed to be proportional to pressure down to less than 10−6 Torr, where residual (pressure independent) damping became significant. An absolute high vacuum gauge based on the pressure-dependent damping observed with this apparatus could operate linearly throughout at least a six decade range. A prototype gauge design is suggested.

Short-Range Force Detection Using Optically Cooled Levitated Microspheres

“…Such large Q factors enable cavity cooling, for which the lowest possible phonon occupation of the mechanical oscillator is n T /Q, where n T is the number of room-temperature thermal phonons. Although such Q factors have yet to be observed in experiment, optically levitated microspheres have been trapped in vacuum for lifetimes exceeding 1000 s [1] and electrically levitated microspheres have exhibited pressurelimited damping that is consistent with theoretical predictions down to ∼ 10 −6 Torr [7].In addition to being beneficial for ground-state cooling and studies of quantum coherence in mesoscopic systems, mechanical oscillators with high quality factors also enable sensitive resonant force detection [8,9]. Optically levitated microspheres in vacuum have been studied theoretically in the context of reaching and exceeding the standard quantum limit of position measurement [10].…”

“…Such large Q factors enable cavity cooling, for which the lowest possible phonon occupation of the mechanical oscillator is n T /Q, where n T is the number of room-temperature thermal phonons. Although such Q factors have yet to be observed in experiment, optically levitated microspheres have been trapped in vacuum for lifetimes exceeding 1000 s [1] and electrically levitated microspheres have exhibited pressurelimited damping that is consistent with theoretical predictions down to ∼ 10 −6 Torr [7].…”

“…Extrapolating the results of Ref. [7] at 10 −6 Torr for the system we consider would yield a pressure-limited Q ∼ 10 9 . In the absence of additional damping mechanisms, we expect that Q ≈ 10 12 could be achieved at lower pressure.…”

Toward quantum-limited position measurements using optically levitated microspheres

“…The noise from gas damping is below the radiation pressure noise if gasdamp τ is longer than the damping time that derives from radiation pressure acting on the sphere [12], which in our case is , and such a measurement would be the first of its kind to observe this form of radiation damping. We also note that launching and trapping dielectric spheres in ultra-high-vacuum has been demonstrated using ultrasonic launching coupled with optical position detection and feedback damping of charged spheres [13]. Similar techniques with somewhat smaller spheres would be the first step in the experiments we are proposing.…”