Abstract
In cavity optomechanics, radiation pressure and photothermal forces are widely utilized to cool and control micromechanical motion, with applications ranging from precision sensing and quantum information to fundamental science. Here, we realize an alternative approach to optical forcing based on superfluid flow and evaporation in response to optical heating. We demonstrate optical forcing of the motion of a cryogenic microtoroidal resonator at a level of 1.46 nN, roughly 1 order of magnitude larger than the radiation pressure force. We use this force to feedback cool the motion of a microtoroid mechanical mode to 137 mK. The photoconvective forces we demonstrate here provide a new tool for high bandwidth control of mechanical motion in cryogenic conditions, while the ability to apply forces remotely, combined with the persistence of flow in superfluids, offers the prospect for new applications.
- Received 23 December 2015
DOI:https://doi.org/10.1103/PhysRevX.6.021012
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Published by the American Physical Society
Physics Subject Headings (PhySH)
Focus
Superfluid Increases Force of Laser Light
Published 29 April 2016
Shining a laser onto a microscopic object coated with a superfluid film induces flows that can generate a controlled force.
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Popular Summary
When helium is cooled to very low temperatures, it becomes a superfluid and one of few naturally occurring forms of quantum matter. Much like the flow of an electrical current in a superconductor, the flow of atoms in a superfluid occurs without dissipation and can therefore, in principle, continue indefinitely. One dramatic consequence of this phenomenon is the well-known superfluid fountain effect in which superfluids flow toward localized heat sources and, since they experience no viscous drag, overshoot to form a fountain. Here, we apply the superfluid fountain effect, for the first time, to actuate a microphotonic system, providing a new tool for the control of photonic circuitry.
We use the momentum from a convective superfluid flow to actuate the motion of an on-chip optical microresonator. We condense a nanometer-thick film of superfluid upon the resonator by placing it inside a helium gas environment, which is cooled to temperatures below 1 K. Heating due to localized optical absorption from a laser within the microresonator then generates superfluid flow and allows forces to be exerted on the resonator that are 1 order of magnitude larger than those achievable with radiation pressure. We employ these forces to cool a vibrational mode of the resonator to a final temperature of 137 mK.
In future experiments, our technique may enable both ground-state cooling and the preparation of nonclassical states of mechanical motion. In addition, while the radiation pressure force exerted by a photon lasts for only the duration that the photon stays within the microphotonic element—typically less than a microsecond—the superflow forces this photon can generate can persist billions of times longer. This phenomenon opens up unique, new capabilities that may be used, for instance, to enable nonvolatile microphotonic memories and routers.