Recently, after a decade of experimental and theoretical efforts, coherent scattering has enabled the motional ground state of levitated nanoparticles at room temperature. While this represents an important milestone towards the creation of mesoscopic quantum objects, coherent quantum control of levitated nanoparticles still remains elusive.
A valuable but less stringent condition is the so-called strong coupling regime (SCR), where the optomechanical coupling strength between the mechanical motion of a particle and an external optical cavity exceeds the particle’s mechanical damping and the cavity linewidth, as has been demonstrated in opto- and electromechanical systems.
Here, we demonstrate the SCR at room temperature between a levitated silica particle and a
high finesse optical cavity. Normal mode splitting is achieved by employing coherent scattering. Our table top experiment offers numerous ways to tune the optomechanical coupling strength at room temperature.
In the context of cavity optomechanics alternative techniques without the need of atomic resonances have widened the possibilities towards the cooling of macroscopic objects. Recently the radiation pressure cooling of mechanical oscillators, optomechanically induced transparency and ground state cooling have been demonstrated. Current progress in optomechanics has brought forward multiple experimental platforms of which many platforms necessitate complex cryogenic environments and suffer from clamping losses as major decoherence sources. An alternative approach is the cooling of levitated nanoparticles from room temperature, which have been suggested for probing quantum mechanics on the mesoscopic scale. In levitated systems collisions with residual gas molecules and photon recoil heating are now the remaining decoherence sources paving the way towards low phonon occupations. In the context of cavity optomechanics, resolved sideband cooling of a levitated nanoparticle has recently been realised. Here we demonstrate the resolved sideband cooling of a levitated nanoparticle within a high nesse cavity at high vacuum. Trapping the nanoparticle in an external optical tweezer allows on one hand the free positioning of the particle within the cavity fi eld and on the other hand the additional cooling via parametric feedback cooling. The combination with well-established resolved sideband cooling techniques creates a powerful platform for controlling the centre of mass motion (COM) of a mesoscopic object. By exploiting cavity enhanced Anti-Stokes scattering we all optically cool the COM to minimum temperatures of T ~ 100mK for a silica particle of 235nm diameter. Power dependent laser noise heating is observed, being the main current limitation in reaching lower temperatures. In the future laser noise suppression for resolved side band cooling brings low phonon occupation numbers of mesoscopic systems via passive cooling schemes within the reach of table top experiments at room temperatures.
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