Optical dilution and feedback cooling of a gram-scale oscillator to 6.9 mK (0705.1018v2)

Abstract: We report on use of a radiation pressure induced restoring force, the optical spring effect, to optically dilute the mechanical damping of a 1 gram suspended mirror, which is then cooled by active feedback (cold damping). Optical dilution relaxes the limit on cooling imposed by mechanical losses, allowing the oscillator mode to reach a minimum temperature of 6.9 mK, a factor of ~40000 below the environmental temperature. A further advantage of the optical spring effect is that it can increase the number of oscillations before decoherence by several orders of magnitude. In the present experiment we infer an increase in the dynamical lifetime of the state by a factor of ~200.

Optical Dilution and Feedback Cooling of a Gram-Scale Oscillator to 6.9 mK

In this paper, Corbitt et al. explore the innovative application of optical mechanics in controlling and reducing thermal fluctuations in macroscopic oscillators. The research primarily focuses on leveraging the optical spring effect for cooling a 1-gram suspended mirror oscillator significantly below environmental temperatures, achieving a minimum temperature of 6.9 mK.

The authors demonstrate that the optical spring effect, a radiation pressure-induced restoring force, can effectively dilute mechanical damping. This optical dilution mitigates the typical limitations imposed by mechanical losses, thereby facilitating more efficient cooling. In their experimental setup, the team utilized active feedback mechanisms for cooling, often referred to as cold damping, which enabled a reduction of the effective temperature of the oscillator mode by a factor of approximately 40,000 from ambient conditions.

Experimentally, this work was executed using a suspended cavity setup with two mirrors, where the end mirror of the cavity was subjected to optical dilution via feedback by means of a laser beam. The experiment achieved a dynamic regime that increased the dynamical lifetime of an oscillator’s quantum state by a factor of roughly 200. This is a substantial enhancement in decoherence timing, which is critical for observing quantum behaviors in macroscopic objects. The mode exhibited an effective quality factor upsurge due to the optical spring, reaching $1.6 \times 10^6$ from an initial 19,950, showcasing the success of the experiment.

The research has significant implications, especially in quantum mechanics and the paper of macroscopic quantum superpositions. The approach of using optical dilution aids in surpassing intrinsic mechanical thermal noise, thereby making the exploration of quantum effects in larger mass systems feasible. Practically, this could open pathways for advanced gravitational wave detectors, where control over thermomechanical noise is crucial.

Future developments in this domain may revolve around integrating enhanced laser stabilization techniques to mitigate frequency noise—a current limitation observed in the paper. Additionally, extending this method's applicability across diverse materials and different oscillator dimensions could enrich our understanding and control of macroscopic quantum states.

In summary, the authors have provided a comprehensive experimental validation of utilizing optical fields for mechanical cooling and show potential for significant advancements in both theoretical and applied physics, particularly within the scope of quantum observability in macroscopic systems.