Cavity cooling of an optically levitated nanoparticle (1304.6679v2)

Abstract: The ability to trap and to manipulate individual atoms is at the heart of current implementations of quantum simulations, quantum computing, and long-distance quantum communication. Controlling the motion of larger particles opens up yet new avenues for quantum science, both for the study of fundamental quantum phenomena in the context of matter wave interference, and for new sensing and transduction applications in the context of quantum optomechanics. Specifically, it has been suggested that cavity cooling of a single nanoparticle in high vacuum allows for the generation of quantum states of motion in a room-temperature environment as well as for unprecedented force sensitivity. Here, we take the first steps into this regime. We demonstrate cavity cooling of an optically levitated nanoparticle consisting of approximately 10e9 atoms. The particle is trapped at modest vacuum levels of a few millibar in the standing-wave field of an optical cavity and is cooled through coherent scattering into the modes of the same cavity. We estimate that our cooling rates are sufficient for ground-state cooling, provided that optical trapping at a vacuum level of 10e-7 millibar can be realized in the future, e.g., by employing additional active-feedback schemes to stabilize the optical trap in three dimensions. This paves the way for a new light-matter interface enabling room-temperature quantum experiments with mesoscopic mechanical systems.

• The paper demonstrates an innovative cavity cooling technique that dampens the center-of-mass motion of a levitated nanoparticle with cooling rates up to 2π×49 kHz and a temperature drop to 64±5 K.
• The paper employs a high-finesse Fabry-Perot optical cavity with dual beams to manipulate trapping and control fields, enhancing coherent photon scattering for effective cooling.
• The paper's findings indicate that quantum ground state cooling could be attainable with further vacuum improvements and active feedback stabilization.

Cavity Cooling of an Optically Levitated Nanoparticle

The paper presents a novel experimental technique in the field of quantum optomechanics, focusing on the cavity cooling of a dielectric nanoparticle. This experiment demonstrates the cooling of a nanoparticle's center-of-mass (CM) motion through interactions with an optical cavity, marking a significant step in realizing quantum control over larger particles outside cryogenic environments.

In the presented setup, the nanoparticle consists of approximately $10^{9}$ atoms, optically trapped in a Fabry-Perot cavity at modest vacuum levels. By leveraging the cavity's optical field, the particle is both levitated and cooled. The primary cooling mechanism involves coherent scattering of photons, a process intensified by the optical cavity's standing wave structure. This cooling could theoretically reach the CM's ground state, assuming further improvements in vacuum conditions and trapping stability.

Experimental Approach

The experiment utilizes a high-finesse optical cavity with a dual-beam scheme: a strong "trapping" field to secure the nanoparticle and a weaker "control" field for CM motion manipulation. The authors meticulously manage the intracavity power ratio, emphasizing the interplay between the trapping and control beams.

At the heart of the system lies the optical gradient force, which traps the particle by counteracting the momentum transfer of incident photons. Cooling is achieved through an optical spring effect and damping, modulated by detuning the control beam relative to the cavity resonance. The cooling performance showcases rates feasible for ground-state cooling, provided that damping due to gas pressures is further reduced.

Numerical Findings

The paper discusses the achievement of cooling rates up to $\Gamma=2\pi\times49$ kHz and provides an effective optomechanical coupling rate of up to $g_{0}\sqrt{\langle\hat{n}_{c}\rangle}=2\pi\times66$ kHz. The effective CM-mode temperature was reduced significantly, reaching approximately $64 \pm 5$ K — an outstanding result, considering the setup operates at room temperature without cryogenic assistance.

These findings show promising proximity to the theoretical limits required for quantum ground state preparation, contingent on improved mechanical quality through reduced environmental interactions.

Implications and Future Directions

The experimental validation of cavity cooling for nanoparticles offers several implications. First, this technique could expand the scope of quantum optomechanics by facilitating experiments at room temperature that typically require cryogenic conditions. Notably, the ability to cool and manipulate larger mass particles in a non-cryogenic setting expands the potential for high-precision quantum sensing technologies and fundamental tests of macroscopic quantum theories.

Future research could focus on enhancing the vacuum quality and incorporating active feedback mechanisms to stabilize the trap further. Such developments would allow broader applications, including force sensing that explores fundamental physics and potential industrial applications in precision measurement technologies.

Overall, this research elucidates a robust methodology for optically cooling and controlling mesoscopic particles, potentially extending the quantum toolkit available for studying complex mechanical systems and envisioning new quantum technologies operating outside the strictly controlled environments previously deemed necessary.