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arXiv:2209.05858

Suppressing Recoil Heating in Levitated Optomechanics Using Squeezed Light

Carlos Gonzalez-Ballestero, Joanna A. Zielińska, Massimiliano Rossi, Andrei Militaru, Martin Frimmer, Lukáš Novotný, P. Maurer, Oriol Romero‐Isart

Published Sep 13, 2022• 1 citation
arXivHTMLPDF

Abstract

We theoretically show that laser recoil heating in free-space levitated optomechanics can be arbitrarily suppressed by shining squeezed light onto an optically trapped nanoparticle. The presence of squeezing modifies the quantum electrodynamical light-matter interaction in a way that enables us to control the amount of information that the scattered light carries about a given mechanical degree of freedom. Moreover, we analyze the trade-off between measurement imprecision and back-action noise and show that optical detection beyond the standard quantum limit can be achieved. We predict that, with state-of-the-art squeezed light sources, laser recoil heating can be reduced by at least 60% by squeezing a single Gaussian mode with an appropriate incidence direction, and by 98% by squeezing a properly mode-matched mode. Our results, which are valid both for motional and librational degrees of freedom, will lead to improved feedback cooling schemes as well as boost the coherence time of optically levitated nanoparticles in the quantum regime.

DOI
10.3929/ethz-b-000635366

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We theoretically show that laser recoil heating in free-space levitated optomechanics can be arbitrarily suppressed by shining squeezed light onto an optically trapped nanoparticle. The presence of squeezing modifies the quantum electrodynamical light-matter interaction in a way that enables us to control the amount of information that the scattered light carries about a given mechanical degree of freedom. Moreover, we analyze the trade-off between measurement imprecision and back-action noise and show that optical detection beyond the standard quantum limit can be achieved. We predict that, with state-of-the-art squeezed light sources, laser recoil heating can be reduced by at least 60% by squeezing a single Gaussian mode with an appropriate incidence direction, and by 98% by squeezing a properly mode-matched mode. Our results, which are valid both for motional and librational degrees of freedom, will lead to improved feedback cooling schemes as well as boost the coherence time of optically levitated nanoparticles in the quantum regime.
Recoil heating from photon scattering is a fundamental source of decoherence in optical trapping, severely limiting the preparation of nonclassical motional states. In cavity setups in the coherent scattering configuration, a predictive theory of recoil heating rate is missing, as usual perturbative approaches fail in the presence of sharp optical resonances. Hence, current works assume that the recoil heating rate is approximately equal to its free-space value. Here we show that this is not the case, as the electromagnetic environment can strongly modify recoil heating rate by the Purcell effect. Specifically, we predict that this rate can be significantly suppressed in state-of-the-art microcavities, for both center-of-mass and librational motion. To establish these results, we develop a general theoretical framework based on macroscopic quantum electrodynamics and on the few-mode quantization approach developed in nanophotonics. Our method applies to particles trapped in the presence of arbitrary electromagnetic structures, thus providing a route to engineering motional decoherence in levitated optomechanics by photonic structure design.
Optically levitated and cooled nanoparticles are a new quantum system whose application to the creation of non-classical states of motion and quantum limited sensing is fundamentally limited by recoil and bulk heating. We study the creation of stable 3D optical traps using optical cylindrically polarized vortex beams with radial and azimuthal polarization and show that a significant reduction in recoil heating by up to an order of magnitude can be achieved when compared with conventional single Gaussian beam tweezers. Additionally these beams allow trapping of larger particles outside the Rayleigh regime using both bright and dark tweezer trapping with reduced recoil heating. By changing the wavelength of the trapping laser, or the size of the particles, non-linear and repulsive potentials of interest for the creation of non-classical states of motion can also be created.
We demonstrate optical levitation and feedback cooling of a silica nanoparticle (radius = 78~nm) trapped within a radial vector beam (RVB) in high vacuum. Radial vector beams, when focused by a high-NA lens, produce a smaller focal spot than conventional Gaussian beams, yielding tighter optical potentials and potentially reduced photon-recoil heating rates. A vortex wave plate was used to generate the RVB using an aspheric lens (NA = 0.77) to form the trap. Cold-damping feedback was used to cool the center of mass motion in the radial and axial trap directions to temperatures in the mK range. At higher temperatures and pressures, additional trap frequencies arising from the nonlinear RVB optical potential are observed. This demonstration is a step toward exploiting structured light for levitated quantum optomechanics where these traps can be used to suppress bulk and motional heating.
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