Detection of individual metallic nanoparticles via plasmon-mediated optomechanical coupling.

Characterization of individual nanoparticles is a challenge due to the diffraction limit. To overcome this constraint we investigate the transfer of their optical properties to a mechanical degree of freedom of a larger object. From finite-difference time-domain computations, we estimate the mechanical frequency shift caused by metallic nanoparticles traveling through a microfluidic channel. Due to plasmonic effects we find relative shifts on the order of 1% for a 1 mW incident optical power for particles with radius ranging from 25 to 150 nm. The extreme sensitivity of this detection scheme enables real-time and in situ observation of optical dynamics at nanoscale.

Inducing micromechanical motion by optical excitation of a single quantum dot.

Hybrid quantum optomechanical systems1 interface a macroscopic mechanical degree of freedom with a single two-level system such as a single spin2-4, a superconducting qubit5-7 or a single optical emitter8-12. Recently, hybrid systems operating in the microwave domain have witnessed impressive progress13,14. Concurrently, only a few experimental approaches have successfully addressed hybrid systems in the optical domain, demonstrating that macroscopic motion can modulate the two-level system transition energy9,10,15. However, the reciprocal effect, corresponding to the backaction of a single quantum system on a macroscopic mechanical resonator, has remained elusive. In contrast to an optical cavity, a two-level system operates with no more than a single energy quantum. Hence, it requires a much stronger hybrid coupling rate compared to cavity optomechanical systems1,16. Here, we build on the large strain coupling between an oscillating microwire and a single embedded quantum dot9. We resonantly drive the quantum dot's exciton using a laser modulated at the mechanical frequency. State-dependent strain then results in a time-dependent mechanical force that actuates microwire motion. This force is almost three orders of magnitude larger than the radiation pressure produced by the photon flux interacting with the quantum dot. In principle, the state-dependent force could constitute a strategy to coherently encode the quantum dot quantum state onto a mechanical degree of freedom1.

Dynamically-enhanced strain in atomically thin resonators.

Graphene and related two-dimensional (2D) materials associate remarkable mechanical, electronic, optical and phononic properties. As such, 2D materials are promising for hybrid systems that couple their elementary excitations (excitons, phonons) to their macroscopic mechanical modes. These built-in systems may yield enhanced strain-mediated coupling compared to bulkier architectures, e.g., comprising a single quantum emitter coupled to a nano-mechanical resonator. Here, using micro-Raman spectroscopy on pristine monolayer graphene drums, we demonstrate that the macroscopic flexural vibrations of graphene induce dynamical optical phonon softening. This softening is an unambiguous fingerprint of dynamically-induced tensile strain that reaches values up to ≈4 × 10-4 under strong non-linear driving. Such non-linearly enhanced strain exceeds the values predicted for harmonic vibrations with the same root mean square (RMS) amplitude by more than one order of magnitude. Our work holds promise for dynamical strain engineering and dynamical strain-mediated control of light-matter interactions in 2D materials and related heterostructures.

Design of Quantum Dot-Nanowire Single-Photon Sources that are Immune to Thermomechanical Decoherence.

Nanowire antennas embedding a single quantum dot (QD) have recently emerged as versatile platforms to realize bright sources of quantum light. In this theoretical work, we show that the thermally driven, low-frequency vibrations of the nanowire have a major impact on the QD light emission spectrum. Even at liquid helium temperatures, these prevent the emission of indistinguishable photons. To overcome this intrinsic limitation, we propose three designs that restore photon indistinguishability thanks to a specific engineering of the mechanical properties of the nanowire. We anticipate that such a mechanical optimization will also play a key role in the development of other high-performance light-matter interfaces based on nanostructures.

Stabilization of a linear nanomechanical oscillator to its thermodynamic limit.

The rapid development of micro- and nanomechanical oscillators in the past decade has led to the emergence of novel devices and sensors that are opening new frontiers in both applied and fundamental science. The potential of these devices is however affected by their increased sensitivity to external perturbations. Here we report a non-perturbative optomechanical stabilization technique and apply the method to stabilize a linear nanomechanical beam at its thermodynamic limit at room temperature. The reported ability to stabilize a nanomechanical oscillator to the thermodynamic limit can be extended to a variety of systems and increases the sensitivity range of nanomechanical sensors in both fundamental and applied studies.