Motional Quantum Ground State of a Levitated Nanoparticle from Room Temperature (1911.04406v2)

Abstract: We report quantum ground state cooling of a levitated nanoparticle in a room temperature environment. Using coherent scattering into an optical cavity we cool the center of mass motion of a $143$ nm diameter silica particle by more than $7$ orders of magnitude to $n_x=0.43\pm0.03$ phonons along the cavity axis, corresponding to a temperature of $12~\mu$K. We infer a heating rate of $\Gamma_x/2\pi = 21\pm 3$ kHz, which results in a coherence time of $7.6~\mu$s -- or $15$ coherent oscillations -- while the particle is optically trapped at a pressure of $10^{-6}$ mbar. The inferred optomechanical coupling rate of $g_x/2\pi = 71$ kHz places the system well into the regime of strong cooperativity ($C \approx 5$). We expect that a combination of ultra-high vacuum with free-fall dynamics will allow to further expand the spatio-temporal coherence of such nanoparticles by several orders of magnitude, thereby opening up new opportunities for macrosopic quantum experiments.

• The paper demonstrates ground-state cooling of a 143 nm silica nanoparticle using cavity-enhanced coherent scattering to reach a phonon occupancy of 0.43.
• It employs an optical tweezer and vacuum system to create a harmonic potential, reducing thermal fluctuations by over seven orders of magnitude.
• The findings pave the way for macroscopic quantum experiments and advanced quantum sensing by extending coherence in room temperature environments.

Motional Quantum Ground State of a Levitated Nanoparticle from Room Temperature

The paper by Uroš Delić et al. presents a significant advancement in the field of optomechanics by demonstrating the cooling of a levitated nanoparticle to its motional quantum ground state from a room temperature environment. The centerpiece of this work is the adoption of coherent scattering into an optical cavity to achieve this unprecedented cooling efficiency. The research marks a noteworthy progression in controlling quantum states in macroscopic solid-state systems, previously burdened by environmental noise and thermal fluctuations.

Overview of Experimental Methodology and Findings

The authors detail the implementation of an optical levitation system that suspends a 143 nm diameter silica nanoparticle inside a vacuum chamber. The approach utilizes an optical tweezer setup with a focused laser beam to create a harmonic potential, facilitating the stable levitation of the particle. The particle is strategically placed within an optical cavity to leverage cavity-enhanced coherent scattering, which shifts the particle's center of mass motion.

A distinguishing feature of this methodology is the significantly reduced phonon occupation number achieved, reaching $n_x = 0.43 \pm 0.03$ phonons. This corresponds to a nominal temperature of 12 $\mathrm{\mu K}$, demonstrating a cooling efficiency that surpasses 7 orders of magnitude from initial conditions. This outcome places the nanoparticle in a near-pure quantum ground state, an achievement confirmed by observing the asymmetry between Stokes and anti-Stokes sidebands in the cavity. The paper also infers a heating rate of $\Gamma_x / 2\pi = 21 \pm 3$ kHz, compatible with coherence over $\sim 15$ oscillations within the optical trap at $10^{-6}$ mbar pressure.

Implications and Future Directions in Quantum Optomechanics

Strong implications arise from this research for the broader fields of quantum optomechanics and quantum sensing. Firstly, achieving the ground state cooling of a macroscopic solid in a room temperature environment highlights the potential of levitated nanoparticles for sensing applications that require extreme sensitivity and isolation from thermal noise. Secondly, the demonstrated capability lays groundwork for future explorations of macroscopic quantum phenomena such as superposition states and non-Gaussian quantum states of motion.

Notably, the authors project that further improvements in nanoparticle coherence time and scale of quantum phenomena can be attained by extending the vacuum levels and embracing free-fall dynamics. Such developments could conceivably lead to large-scale interference experiments or even novel examinations of gravitational effects in quantum systems—a discussion conventionally reserved for theoretical exploration.

In conclusion, the work of Delić et al. not only sets a benchmark in the field of quantum optomechanics but also paves the theoretical path for experimental designs aiming to interface macroscale objects with quantum mechanical laws. By refining techniques in coherent scattering, the researchers offer a robust platform for advancing our understanding and application of quantum phenomena in substantial physical systems.