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Register a new userDetecting nonclassical correlations in levitated cavity optomechanics
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Nonclassical optomechanical correlations enable optical control of mechanical motion beyond the limitations of classical driving. Here we investigate the feasibility of using pulsed cavity-optomechanics to create and verify nonclassical phase-sensitive correlations between light and the motion of a levitated nanoparticle in a realistic scenario. We show that optomechanical two-mode squeezing can persist even at the elevated temperatures of state-of-the-art experimental setups. We introduce a detection scheme based on optical homodyning that allows revealing nonclassical correlations without full optomechanical state tomography. We provide an analytical treatment using the rotating wave approximation (RWA) in the resolved-sideband regime and prove its validity with a full numerical solution of the Lyapunov equation beyond the RWA. We build on parameters of current experiments for our analysis and conclude that the observation of nonclassical correlations is possible today.
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We describe a proposal for a new type of optomechanical system based on a drop of liquid helium that is magnetically levitated in vacuum. In the proposed device, the drop would serve three roles: its optical whispering gallery modes would provide the optical cavity, its surface vibrations would constitute the mechanical element, and evaporation of He atoms from its surface would provide continuous refrigeration. We analyze the feasibility of such a system in light of previous experimental demonstrations of its essential components: magnetic levitation of mm-scale and cm-scale drops of liquid He, evaporative cooling of He droplets in vacuum, and coupling to high-quality optical whispering gallery modes in a wide range of liquids. We find that the combination of these features could result in a device that approaches the single-photon strong coupling regime, due to the high optical quality factors attainable at low temperatures. Moreover, the system offers a unique opportunity to use optical techniques to study the motion of a superfluid that is freely levitating in vacuum (in the case of $^{4}mathrm {He}$). Alternatively, for a normal fluid drop of $^3 mathrm{He}$, we propose to exploit the coupling between the drops rotations and vibrations to perform quantum non-demolition measurements of angular momentum.
Ultra-high sensitivity detection of quantum-scale displacements in cavity optomechanics optimises the combined errors from measurement back-action and imprecisions from incoming quantum noises. This sets the well-known Standard Quantum Limit (SQL). Normal quantum cavity optomechanics allows cooling and detection of a single degree of freedom, along the cavity axis. However, a recent breakthrough that allows quantum ground-state cooling of levitated nanoparticles [Delic et al, arxiv:1911.04406], is uniquely 3D in character, with coupling along the $x$, $y$ and $z$ axes. We investigate current experiments and show that the underlying behaviour is far from the addition of independent 1D components and that ground-state cooling and sensing analysis must consider- to date neglected- 3D hybridisation effects. We characterise the additional 3D spectral contributions and find direct and indirect hybridising pathways can destructively interfere suppressing of 3D effects at certain parameters in order to approach, and possibly surpass, the SQL. We identify a sympathetic cooling mechanism that can enhance cooling of weaker coupled modes, arising from optomechanically induced correlations.
We report dispersive coupling of an optically trapped silica nanoparticle ($143~$nm diameter) to the field of a driven Fabry-Perot cavity in high vacuum ($4.3times 10^{-6}~$mbar). We demonstrate nanometer-level control in positioning the particle with respect to the intensity distribution of the cavity field, which allows access to linear, quadratic and tertiary optomechanical interactions in the resolved sideband regime. We determine all relevant coupling rates of the system, i.e. mechanical and optical losses as well as optomechanical interaction, and obtain a quantum cooperativity of $C_Q = 0.01$. Based on the presented performance the regime of strong cooperativity ($C_Q > 1$) is clearly within reach by further decreasing the mode volume of the cavity.
Cavity optomechanical systems are approaching a strong-coupling regime where the coherent dynamics of nanomechanical resonators can be manipulated and controlled by optical fields at the single photon level. Here we propose an interferometric scheme able to detect optomechanical coherent interaction at the single-photon level which is experimentally feasible with state-of-the-art devices.
We analyze magnetometry using an optically levitated nanodiamond. We consider a configuration where a magnetic field gradient couples the mechanical oscillation of the diamond with its spin degree of freedom provided by a Nitrogen vacancy center. First, we investigate measurement of the position spectrum of the mechanical oscillator. We find that conditions of ultrahigh vacuum and feedback cooling allow a magnetic field gradient sensitivity of 1 $mu$Tm$^{-1}$/$sqrt{mbox{Hz}}$. At high pressure and room temperature, this sensitivity degrades and can attain a value of the order of 100 $m$Tm$^{-1}$/$sqrt{mbox{Hz}}$. Subsequently, we characterize the magnetic field gradient sensitivity obtainable by maneuvering the spin degrees of freedom using Ramsey interferometry. We find that this technique can offer photon-shot noise and spin-projection noise limited magnetic field gradient sensitivity of 100 $mu$Tm$^{-1}$/$sqrt{mbox{Hz}}$. We conclude that this hybrid levitated nanomechanical magnetometer provides a favorable and versatile platform for sensing applications.
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