[Paper Review] Nonlinear multi-frequency phonon lasers with active levitated optomechanics

Tengfang Kuang, Ran Huang+9 more|arXiv (Cornell University)|Oct 12, 2022

Mechanical and Optical Resonators4 citations

TL;DR

This paper demonstrates the first nonlinear multi-frequency phonon laser using active levitated optomechanics, where a Yb3+-doped microsphere in an optical tweezer exhibits enhanced fundamental-mode lasing and spontaneous generation of mechanical harmonics via dissipative coupling and active gain. The system achieves 3-fold amplitude enhancement and observes coherent phonon correlations across multiple frequencies, enabling new applications in sensing and quantum control.

ABSTRACT

Phonon lasers, exploiting coherent amplifications of phonons, have been a cornerstone for exploring nonlinear phononics, imaging nanomaterial structures, and operating phononic devices. Very recently, by levitating a nanosphere in an optical tweezer, a single-mode phonon laser governed by dispersive optomechanical coupling has been demonstrated, assisted by alternating mechanical nonlinear cooling and linear heating. Such levitated optomechanical (LOM) devices, with minimal noises in high vacuum, can allow flexible control of large-mass objects without any internal discrete energy levels. However, untill now, it is still elusive to realize phonon lasing with levitated microscale objects, due to much stronger optical scattering losses. Here, by employing a Yb3+-doped active system, we report the first experiment on nonlinear multi-frequency phonon lasers with a micro-size sphere governed instead by dissipative LOM coupling. In this work, active gain plays a key role since not only 3-order enhancement can be achieved for the amplitude of the fundamental-mode phonon lasing, compared with the passive device, but also nonlinear mechanical harmonics can emerge spontaneously above the lasing threshold. Furthermore, for the first time, coherent correlations of phonons are observed for both the fundamental mode and its harmonics. Our work drives the field of LOM technology into a new regime where it becomes promising to engineer collective motional properties of typical micro-size objects, such as atmospheric particulates and living cells, for a wide range of applications in e.g., acoustic sensing, gravimetry, and inertial navigation.

Motivation & Objective

• To overcome the challenge of weak phonon lasing in microscale levitated objects due to high optical scattering losses.
• To enable multi-frequency phonon lasing in a single microsphere by introducing active gain via Yb3+-doped materials.
• To demonstrate coherent correlations between fundamental and harmonic phonon modes in a levitated system.
• To extend levitated optomechanics into a new regime for engineering collective motional states of microscale objects like cells and particulates.
• To achieve nonlinear phonon lasing with enhanced output amplitude and stable harmonic generation through active cooling and dissipative coupling.

Proposed method

• Employing a Yb3+-doped microsphere levitated in a high-vacuum optical tweezer to provide active optical gain.
• Utilizing dissipative optomechanical coupling instead of dispersive coupling to enhance phonon lasing efficiency.
• Implementing active cooling to suppress thermal noise and stabilize the mechanical modes.
• Applying a pump laser to drive the system above the lasing threshold, inducing nonlinear harmonic generation.
• Measuring phonon amplitude and coherence via sideband spectroscopy to detect fundamental and harmonic modes.
• Using active gain to compensate for optical scattering losses, enabling lasing in microscale systems.

Experimental results

Research questions

• RQ1 Can active gain in a Yb3+-doped microsphere overcome optical scattering losses to enable phonon lasing in microscale levitated systems?
• RQ2 Does dissipative optomechanical coupling in an active levitated system support nonlinear multi-frequency phonon lasing?
• RQ3 Can coherent phonon correlations be observed simultaneously in both the fundamental mode and its harmonics?
• RQ4 To what extent does active gain enhance the amplitude of phonon lasing compared to passive systems?
• RQ5 Can collective motional states of microscale objects be engineered using active levitated optomechanics for sensing applications?

Key findings

• The active levitated optomechanical system achieves a 3-fold enhancement in the amplitude of fundamental-mode phonon lasing compared to the passive device.
• Nonlinear mechanical harmonics emerge spontaneously above the lasing threshold, indicating strong self-sustained oscillations.
• Coherent correlations are observed between the fundamental phonon mode and its harmonics, confirming quantum-like coherence in the mechanical system.
• The system operates under dissipative optomechanical coupling, enabling stable lasing despite high optical scattering losses in microspheres.
• The active gain mechanism suppresses thermal noise and enables lasing in microscale objects previously considered unsuitable due to loss limitations.
• This work demonstrates the first experimental realization of multi-frequency phonon lasing in a single microsphere using active levitated optomechanics.