Abstract
Coherent feedback stabilizes a system toward a target state without the need of a measurement, thus avoiding the quantum backaction inherent to measurements. Here, we employ optical coherent feedback to remotely cool a nanomechanical membrane using atomic spins as a controller. Direct manipulation of the atoms allows us to tune from strong coupling to an overdamped regime. Making use of the full coherent control offered by our system, we perform spin-membrane state swaps combined with stroboscopic spin pumping to cool the membrane in a room-temperature environment to () in . We furthermore observe and study the effects of delayed feedback on the cooling performance. Starting from a cryogenically precooled membrane, this method would enable cooling of the mechanical oscillator close to its quantum mechanical ground state and the preparation of nonclassical states.
- Received 18 June 2021
- Accepted 16 November 2021
- Corrected 19 April 2022
DOI:https://doi.org/10.1103/PhysRevX.12.011020
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Corrections
19 April 2022
Correction: Equations (A8) and (A10) and text preceding (A8) contained errors and have been fixed.
Viewpoint
ViewpointCoherent Feedback Goes for a Spin
Published 31 January 2022
A cloud of cold atoms can coherently control the vibrations of a millimeter-scale membrane.
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Popular Summary
Feedback is a powerful technique for driving a physical system toward a target state, with applications ranging from electronics to stabilizing the temperature of a room. In the classical world, measurement gives information about the system under control, whose result is then used to act back on the system. In the quantum world, however, measurement changes the system in an irreversible way. An alternative to measurement-based feedback is coherent feedback, where instead of performing a measurement, the system under control interacts with another system, the controller, without destroying its quantum coherence. Here, we use coherent feedback to cool a nanomechanical oscillator by making it interact with the spin of an atomic ensemble, acting as the quantum controller.
In our experiment, the spin responds to the vibrations of the membrane and acts back on them in a coherent way while we periodically apply laser pulses to reinitialize the spin to its quantum-mechanical ground state. In this way, the spin cools the mechanical oscillator from room temperature to about 200 mK in a fraction of a millisecond. We further investigate the effect of delay in the feedback loop and show that, as in classical feedback circuits, it can render the system unstable.
Coherent feedback cooling could be beneficial for applications where nanomechanical oscillators are used to probe fundamental quantum physics and sense small forces very sensitively.
