Shot-noise-dominant regime for ellipsoidal nanoparticles in a linearly polarized beam

Abstract

Results on the heating and the parametric feedback cooling of an optically trapped anisotropic nanoparticle in the laser shot noise dominant regime are presented. The related dynamical parameters, such as the oscillating frequency and shot noise heating rate, depend on the shape of the trapped particle. For an ellipsoidal particle, the ratio of the axis lengths and the overall size controls the shot noise heating rate relative to the frequency. For a particle with smaller ellipticity or bigger size, the relative heating rate for rotation tends to be smaller than that for translation indicating a better rotational cooling. For one feedback scheme, we also present results on the lowest occupation number that can be achieved as a function of the heating rate and the amount of classical uncertainty in the position measurement.

Probing macroscopic quantum superpositions with nanorotors

“…The orientation of the nanoparticle can be cavity or feedback cooled [30,31] leading to a tight alignment of the rotor with the field polarization direction, so that its trapped dynamics are librational rather than rotational. The quantum state of the rotor is then characterized by its librational temperature T and takes the form…”

“…For CNTs, where excitonic excitations play no role for wavelengths well above 2.5μm [40], the exact position and width of the vibrational excitations depends on the structural details of the particle [41] and the optimal trapping wavelength can be determined experimentally. Cavity or feedback cooling the rotation of the trapped particles to subkelvin temperatures is feasible [30,31], but may require low mode volume cavities to enhance the nanoparticle-light interaction and detection efficiency. The deeply trapped particle librates harmonically, so that well established techniques of center-ofmass optical cooling can be adapted [42][43][44][45].…”

“…We argue that macroscopic orientational quantum revivals can be observed using existing technology for optically manipulating the motion and alignment of levitated particles [26][27][28][29]. The proposed scheme requires cavity-or feedback-cooling of the nanoparticle rotation [30,31] to below a Kelvin, while it is independent of its center-of-mass temperature. An observation of orientational quantum revivals with nanorotors would substantially advance macroscopic superposition tests, provide the first experimental test of the angular momentum quantization of massive objects, and enable quantum coherent gyroscopic torque sensing with the potential of improving state-of-the-art devices [29,32] by many orders of magnitude.…”

Parametric feedback cooling of rigid body nanodumbbells in levitated optomechanics

“…An alternative path to the ground state and a tool for torque sensing [8,32] is accessing control over the rotational DOF [32][33][34][35][36][37][38]. Whereas translational mode frequencies are typically in the kHz range, librational mode frequencies can be in the MHz range, possibly offering a more accessible ground state [3].…”

Quantum angular momentum diffusion of rigid bodies

“…The theory of angular momentum diffusion will be useful to understand optomechanical setups featuring non-spherical particles. Its quantum aspects will become relevant once ro-translational groundstate cooling [11,12,19] has been achieved, opening the door for quantum experiments that involve the orientation [20][21][22][23][24]. Moreover, understanding angular momentum diffusion can be regarded as the first step toward a Markovian quantum theory of rotational friction and thermalization.…”