Cavity optomechanics using an optically levitated nanosphere (0909.1548v2)

Abstract: Recently, remarkable advances have been made in coupling a number of high-Q modes of nano-mechanical systems to high-finesse optical cavities, with the goal of reaching regimes where quantum behavior can be observed and leveraged toward new applications. To reach this regime, the coupling between these systems and their thermal environments must be minimized. Here we propose a novel approach to this problem, in which optically levitating a nano-mechanical system can greatly reduce its thermal contact, while simultaneously eliminating dissipation arising from clamping. Through the long coherence times allowed, this approach potentially opens the door to ground-state cooling and coherent manipulation of a single mesoscopic mechanical system or entanglement generation between spatially separate systems, even in room temperature environments. As an example, we show that these goals should be achievable when the mechanical mode consists of the center-of-mass motion of a levitated nanosphere.

• The paper demonstrates that optical levitation eliminates material clamping, significantly reducing thermal contact and approaching quantum ground-state cooling.
• The study uses a Fabry-Perot cavity to trap a sub-wavelength dielectric sphere, precisely controlling its center-of-mass motion through optomechanical interactions.
• These findings pave the way for room-temperature quantum state control, enabling squeezed state generation and entanglement for advanced sensing and communication applications.

An Overview of Cavity Optomechanics with Optically Levitated Nanospheres

This paper explores an advanced and novel approach in the field of cavity optomechanics by investigating the use of an optically levitated nanosphere to achieve high-quality mechanical systems coupled to optical cavities. The primary motivation behind this research is the desire to isolate mechanical systems from environmental thermal contact, facilitating the cooling of these systems to their quantum ground state. The authors propose that by eliminating material clamping and using optical levitation, thermal contact can be significantly reduced, thereby minimizing dissipation and enhancing coherence times—one of the key technical challenges in the field.

The paper presents a systematic exploration into the dynamics of a sub-wavelength dielectric sphere inside a Fabry-Perot cavity. The nanosphere's center-of-mass (CM) motion, which is optically trapped, can effectively be cooled via optomechanical interactions with a second cavity mode. This configuration allows the emergence of quantum behavior even in room-temperature environments, a significant advancement over traditional methods that typically rely on cryogenic settings.

Thermal Isolation and Cooling

The paper emphasizes the importance of thermal isolation, presenting the concept that optically levitating the mechanical element negates the need for clamping, thus reducing mechanical dissipation to near fundamental limits. The authors carefully derive the expected reduction in environmental coupling predominantly due to background gas collisions and discount significant contributions from optical shot noise and blackbody radiation, among others. A potentially transformative aspect is that the approach theoretically allows for ground-state cooling of the CM motion, even from a room-temperature start point, given optimal conditions for sideband resolution and coupling.

Quantum State Manipulation and Entanglement

The implications of achieving quantum ground-state cooling extend to facilitating novel applications, such as squeezed state preparation and the generation of Einstein-Podolsky-Rosen (EPR) correlations between separated systems. This can be achieved by mapping non-classical light properties onto the mechanical system, offering new avenues for high-fidelity quantum state transfer. The authors delve into entanglement transfer and squeezed light generation as concrete examples, showing that optical forces can be used not merely for cooling but also for coherent state manipulations, yielding significant mechanical squeezing.

Future Directions

The theoretical and practical implications of this research are substantial, suggesting pathways to explore nanoscale material property investigation under near-isolation conditions. Moreover, by integrating optomechanical systems with atomic trapping and manipulation techniques, or even extending to systems with internal electronic transitions, there could be advances in quantum information processing and hybrid quantum systems.

As scientific inquiry continues to transcend classical boundaries, this work on cavity optomechanics with levitated nanospheres posits a realistic model rich with experimental and theoretical potential. It lays groundwork for exploring rich quantum phenomena in mesoscopic systems, offering a promising framework for future applications in precision sensing and quantum communications. Through developments like these, there is potential to build on existing technologies and push the boundaries of what's achievable with quantum optomechanics in practical and scalable systems.