Direct Measurement of Photon Recoil from a Levitated Nanoparticle (1603.03420v2)

Abstract: The momentum transfer between a photon and an object defines a fundamental limit for the precision with which the object can be measured. If the object oscillates at a frequency $\Omega_0$, this measurement back-action adds quanta $\hbar\Omega_0$ to the oscillator's energy at a rate $\Gamma_{\rm recoil}$, a process called photon recoil heating, and sets bounds to quantum coherence times in cavity optomechanical systems. Here, we use an optically levitated nanoparticle in ultrahigh vacuum to directly measure $\Gamma_{\rm recoil}$. By means of a phase-sensitive feedback scheme, we cool the harmonic motion of the nanoparticle from ambient to micro-Kelvin temperatures and measure its reheating rate under the influence of the radiation field. The recoil heating rate is measured for different particle sizes and for different excitation powers, without the need for cavity optics or cryogenic environments. The measurements are in quantitative agreement with theoretical predictions and provide valuable guidance for the realization of quantum ground-state cooling protocols and the measurement of ultrasmall forces

• The paper directly measures photon recoil heating in levitated nanoparticles, achieving an observed rate near 10 kHz that validates theoretical predictions.
• It utilizes a phase-sensitive parametric feedback cooling mechanism to reduce nanoparticle motion to temperatures as low as 450 µK, demonstrating precise thermal control.
• The study reveals how variations in particle size and laser power modulate photon recoil effects, offering actionable insights for advancing quantum optomechanical systems.

Direct Measurement of Photon Recoil from a Levitated Nanoparticle

The paper conducted by Vijay Jain, Jan Gieseler, and colleagues offers a direct measurement of photon recoil effects on optically levitated nanoparticles in ultrahigh vacuum. Utilizing a phase-sensitive feedback scheme, the research demonstrates that photon recoil heating can be quantitatively observed at micro-Kelvin temperatures, providing insight into the challenges of capturing quantum mechanical behavior in cavity optomechanical systems.

Overview

The experimental setup involves trapping silica nanoparticles with radii approximately 50 nm using a tightly focused laser beam, achieving cooling of these particles' motion to micro-Kelvin temperatures, where photon recoil becomes measurable. The primary objective is to measure the recoil heating rate, denoted as $\Gamma_{\rm recoil}$, in various particle sizes and excitation powers. Unlike previous works, this experiment circumvents the need for cavity optics or cryogenic environments, emphasizing the feasibility of using optically levitated nanoparticles to paper light-matter interactions and quantum effects without external mechanical influences.

Key Findings

1. Recoil Heating Rate: The researchers successfully measured $\Gamma_{\rm recoil}$ across different conditions, demonstrating a strong agreement with theoretical predictions. For instance, a $\Gamma_{\rm recoil}$ of approximately 10 kHz was observed for nanoparticles in the nanoscale range.
2. Temperature and Feedback Control: By employing a parametric feedback cooling mechanism, the thermal motion of nanoparticles was reduced to temperatures as low as (450.5 ± 33.1) µK, reaching mean occupation numbers n=63, significantly below the ambient thermal state.
3. Particle Size and Laser Power Effects: Increasing particle size was shown to increase the heating rate, consistent with predictions of photon recoil effects. Similarly, varying laser power modulated the reheating effect owing to photon shot noise.
4. Practical Implications: The results underscore the possibility of refining force sensitivity and cooling protocols aimed at ground state cooling of mechanical oscillators. The measured recoil rates set a limit to further advancement in achieving lower temperatures and higher quality factors in optomechanical systems.

Implications and Future Work

The experimental verification of photon recoil from a mesoscopic object advances our understanding of the boundaries imposed by quantum back-action in mechanical systems. The successful isolation of these effects in a controlled open system simplifies the modeling of quantum behavior in cavity optomechanics, paving the way for potential applications in quantum computing and ultrasensitive force detection. Future research could focus on minimizing residual gas interactions further to enhance the fidelity of photon cooling and the precision of force measurements. Additionally, applying these insights in more complex systems, such as those incorporating spin degrees of freedom or quantum entanglement, could yield further breakthroughs in quantum manipulation and measurement.

This research broadens the experimental capabilities in assessing light-matter interactions and provides comprehensive data needed for both theoretical advancements and practical innovations. As such, these findings mark a significant step towards establishing optically levitated systems as a staple for studying quantum mechanical phenomena in a deterministic and non-invasive manner, facilitating the drive towards next-generation quantum technologies.