Radiation pressure cooling of a micromechanical oscillator using dynamical backaction

Optoacoustic Cooling of Traveling Hypersound Waves

We experimentally demonstrate optoacoustic cooling via stimulated Brillouin-Mandelstam scattering in a 50 cm long tapered photonic crystal fiber. For a 7.38 GHz acoustic mode, a cooling rate of 219 K from room temperature has been achieved. As anti-Stokes and Stokes Brillouin processes naturally break the symmetry of phonon cooling and heating, resolved sideband schemes are not necessary. The experiments pave the way to explore the classical to quantum transition for macroscopic objects and could enable new quantum technologies in terms of storage and repeater schemes.

From cavity optomechanics to cavity-less exciton optomechanics: a review

Cavity optomechanical coupling based on radiation pressure, photothermal forces and the photoelastic effect has been investigated widely over the past few decades, including optical measurements of mechanical vibration, dynamic backaction damping and amplification, nonlinear dynamics, quantum state transfer and so on. However, the delicate cavity operation, including cavity stabilization, fine detuning, tapered fibre access etc., limits the integration of cavity optomechanical devices. Dynamic backaction damping and amplification based on cavity-less exciton optomechanical coupling in III-V semiconductor nanomechanical systems, semiconductor nanoribbons and monolayer transition metal dichalcogenides have been demonstrated in recent years. The cavity-less exciton optomechanical systems interconnect photons, phonons and excitons in a highly integrable platform, opening up the development of integrable optomechanics. Furthermore, the highly tunable exciton resonance enables the exciton optomechanical coupling strength to be tuned. In this review, the mechanisms of cavity optomechanical coupling, the principles of exciton optomechanical coupling and the recent progress of cavity-less exciton optomechanics are reviewed. Moreover, the perspectives for exciton optomechanical devices are described.

Photothermal effect in macroscopic optomechanical systems with an intracavity nonlinear optical crystal

Intracavity squeezing is a promising technique that may improve the sensitivity of gravitational wave detectors and cool optomechanical oscillators to the ground state. However, the photothermal effect may modify the occurrence of optomechanical coupling due to the presence of a nonlinear optical crystal in an optical cavity. We propose a novel method to predict the influence of the photothermal effect by measuring the susceptibility of the optomechanical oscillator and identifying the net optical spring constant and photothermal absorption rate. Using this method, we succeeded in precisely estimating parameters related to even minor photothermal effects, which could not be measured using a previously developed method.

Cooling of mechanical resonator in a hybrid intracavity squeezing optomechanical system

A hybrid intracavity squeezing optomechanical cooling system, in which an auxiliary cavity couples to an optomechanical cavity with a nonlinear medium inside it, is proposed to realize the ground state cooling of the mechanical resonator in the highly unresolved sideband regime. We demonstrate that the quantum backaction heating can be suppressed perfectly by the intracavity squeezing, and the cooling process can be further promoted by adjusting the tunnel coupling between the coupled cavities. The scheme has good performance in resisting the environmental thermal noise and better tolerance for the auxiliary cavity quality factor and provides the possibility for the quantum manipulation of the mechanical resonator with large mass and low frequency.

Electromagnetic forces in the time domain

We look beyond the standard time-average approach and investigate optical forces in the time domain. The formalism is developed for both the Abraham and Minkowski momenta, which appear to converge in the time domain. We unveil an extremely rich - and by far unexplored - physics associated with the dynamics of the optical forces, which can even attain negative values over short time intervals or produce low frequency dynamics that can excite mechanical oscillations in macroscopic objects under polychromatic illumination. The magnitude of this beating force is tightly linked to the average one. Implications of this work for transient optomechanics are discussed.

An electro-mechano-optical NMR probe for 1H–13C double resonance in a superconducting magnet

A compact nanomembrane radiofrequency-to-light transducer brings the emerging Electro-Mechano-Optical (EMO) NMR technique into the realm of practical NMR in chemistry using a superconducting magnet.

On-chip optical pulse train generation through the optomechanical oscillation

This paper proposes a novel on-chip optical pulse train generator (OPTG) based on optomechanical oscillation (OMO). The OPTG consists of an optical cavity and mechanical resonator, in which OMO periodically modulates the optical cavity field and consequently generates optical pulse trains. The dimensionless method are introduced to simulate the OMO-based OPTG with reduced analysis complexity. We investigate the optomechanical coupling and the dynamic back-action processes, by which we found a dead zone that forbids the OMO, and derived the optimal laser detuning and the minimum threshold power. We analysed the OMO-based OPTG in terms of the pulse shape distortion, extinction ratio (ER) and duty-cycle (DC). Increasing input power, mechanical and optical Q-factors will increase ER, reduce DC and produce sharper and shorter optical pulses. We also discuss the design guidance of OMO-based OPTG and explore its application in distributed fibre optical sensor (DFOS).

Cooling photon-pressure circuits into the quantum regime

Quantum control of electromagnetic fields was initially established in the optical domain and has been advanced to lower frequencies in the gigahertz range during the past decades extending quantum photonics to broader frequency regimes. In standard cryogenic systems, however, thermal decoherence prevents access to the quantum regime for photon frequencies below the gigahertz domain. Here, we engineer two superconducting LC circuits coupled by a photon-pressure interaction and demonstrate sideband cooling of a hot radio frequency (RF) circuit using a microwave cavity. Because of a substantially increased coupling strength, we obtain a large single-photon quantum cooperativity 𝒞_q0 ∼ 1 and reduce the thermal RF occupancy by 75% with less than one pump photon. For larger pump powers, the coupling rate exceeds the RF thermal decoherence rate by a factor of 3, and the RF circuit is cooled into the quantum ground state. Our results lay the foundation for RF quantum photonics.

Polariton multistability in a nonlinear optomechanical cavity

We theoretically study the polariton multistability in a solid state based optomechanical resonator embedded with a quantum well and aχ⁽²⁾second order nonlinear medium. The excitonic transition inside the quantum well is strongly coupled to the optical cavity mode. The polariton formed due to the mixing of cavity photons and exciton states are coupled to the mechanical mode which gives rise to the bistable behavior. A transition from bistability to tristability occurs in the presence of a strongχ⁽²⁾nonlinearity. Switching between bistability and tristability can also be controlled using exciton-cavity and optomechanical coupling making the system highly tunable. Tristability appears at low input power making it a suitable candidate for polaritonic devices which requires low input power.

Radiation pressure measurement using a macroscopic oscillator in an ambient environment

In contrast to current efforts to quantify the radiation pressure of light using nano-micromechanical resonators in cryogenic conditions, we proposed and experimentally demonstrated the radiation pressure measurement in ambient conditions by utilizing a macroscopic mechanical longitudinal oscillator with an effective mass of the order of 20 g. The light pressure on a mirror attached to the oscillator was recorded in a Michelson interferometer and results showed, within the experimental accuracy of 3.9%, a good agreement with the harmonic oscillator model without free parameters.

Tunable polarization beam splitter and broadband optical power sensor using hybrid microsphere resonators

Based on silica microsphere resonators embedded with iron oxide nanoparticles, we proposed and fabricated an all-optical and continuously tunable polarization beam splitter (PBS), and a broadband optical power sensor (OPS) with high sensitivity. The PBS is realized since the effective refractive indexes of the transverse-electric and transverse-magnetic polarization modes in the microsphere resonator are different. Due to the excellent photothermal effect of iron oxide nanoparticles, we realized the all-optical and continuously tunable PBS based on the hybrid microsphere resonator. A maximum polarization splitting ratio of 20 dB and a tuning range of 5 nm are achieved. Based on this mechanism, the hybrid microsphere resonator can also be used as a broadband OPS. The sensitivity of the OPS is 0.487 nm/mW, 0.477 nm/mW, and 0.398 nm/mW when the probe wavelength is 690 nm, 980 nm, and 1550 nm, respectively. With such good performances, the tunable PBS and the broadband OPS have great potential in applications such as optical routers, switches and filters.

Laser Cooling of a Nanomechanical Oscillator to Its Zero-Point Energy

Optomechanical systems in the well-resolved-sideband regime are ideal for studying a myriad of quantum phenomena with mechanical systems, including backaction-evading measurements, mechanical squeezing, and nonclassical states generation. For these experiments, the mechanical oscillator should be prepared in its ground state, i.e., exhibit negligible residual excess motion compared to its zero-point motion. This can be achieved using the radiation pressure of laser light in the cavity by selectively driving the lower motional sideband, leading to sideband cooling. To date, the preparation of sideband-resolved optical systems to their zero-point energy has eluded laser cooling because of strong optical absorption heating. The alternative method of passive cooling suffers from the same problem, as the requisite milliKelvin environment is incompatible with the strong optical driving needed by many quantum protocols. Here, we employ a highly sideband-resolved silicon optomechanical crystal in a ^{3}He buffer-gas environment at ∼2  K to demonstrate laser sideband cooling to a mean thermal phonon occupancy of 0.09_{-0.01}^{+0.02} quantum (self-calibrated using motional sideband asymmetry), which is -7.4  dB of the oscillator's zero-point energy and corresponds to 92% ground state probability. Achieving such low occupancy by laser cooling opens the door to a wide range of quantum-optomechanical experiments in the optical domain.

Entanglement of two rotating mirrors coupled to a single Laguerre-Gaussian cavity mode

We theoretically investigate the entanglement between two macroscopic rotating mirrors in a Laguerre-Gaussian (L-G) cavity, in which they exchange orbital angular momentum with a same L-G cavity mode, and we examine the influence of various factors such as angular frequencies of two mirrors, effective detuning, temperature and orbital angular momentum of L-G cavity mode on the entanglement. The results show that in some range of mirrors' angular frequencies the entanglement will appear and has strong robustness. And we also study the range of effective detuning and the minimum orbital angular momentum of the L-G cavity mode required to generate entanglement.

Optomechanics in anisotropic liquid crystal -filled micro-bubble resonators

In this paper, we report on the realization of optomechanics and its broad tuning in liquid crystal-filled micro-bubble resonators (LC-MBR). Acoustic anisotropy of LC has enriched optomechanical resonant modes in such whispering-gallery modes (WGM) cavities. Meanwhile anisotropic dependence of sound speed of LC on temperature strongly enhances the tuning ability of the resonances. By applying magnetic field to control re-orientation of LC in MBR, optomechanical resonant frequency changes significantly after magnetic field goes beyond Fréedericksz transition threshold. By designing such an optomachanical system, optomechanical oscillator with broad tuning range can be realized.

High-frequency cavity optomechanics using bulk acoustic phonons

To date, microscale and nanoscale optomechanical systems have enabled many proof-of-principle quantum operations through access to high-frequency (gigahertz) phonon modes that are readily cooled to their thermal ground state. However, minuscule amounts of absorbed light produce excessive heating that can jeopardize robust ground-state operation within these microstructures. In contrast, we demonstrate an alternative strategy for accessing high-frequency (13 GHz) phonons within macroscopic systems (centimeter scale) using phase-matched Brillouin interactions between two distinct optical cavity modes. Counterintuitively, we show that these macroscopic systems, with motional masses that are 1 million to 100 million times larger than those of microscale counterparts, offer a complementary path toward robust ground-state operation. We perform both optomechanically induced amplification/transparency measurements and demonstrate parametric instability of bulk phonon modes. This is an important step toward using these beam splitter and two-mode squeezing interactions within bulk acoustic systems for applications ranging from quantum memories and microwave-to-optical conversion to high-power laser oscillators.

Cavity Cooling of a Levitated Nanosphere by Coherent Scattering

We report three-dimensional (3D) cooling of a levitated nanoparticle inside an optical cavity. The cooling mechanism is provided by cavity-enhanced coherent scattering off an optical tweezer. The observed 3D dynamics and cooling rates are as theoretically expected from the presence of both linear and quadratic terms in the interaction between the particle motion and the cavity field. By achieving nanometer-level control over the particle location we optimize the position-dependent coupling and demonstrate axial cooling by two orders of magnitude at background pressures of 6×10^{-2}  mbar. We also estimate a significant (>40  dB) suppression of laser phase noise heating, which is a specific feature of the coherent scattering scheme. The observed performance implies that quantum ground state cavity cooling of levitated nanoparticles can be achieved for background pressures below 1×10^{-7}  mbar.

Demonstration of Enhanced Optical Pressure on a Structured Surface

The interaction of electromagnetic waves with condensed matter and the resultant force is fundamental in the physical sciences. The maximum pressure on a planar surface is understood to be twice the incident wave power density normalized by the background velocity. We demonstrate for the first time that this pressure can be exceeded by a substantial factor by structuring a surface. Experimental results for direct optomechanical deflection of a nanostructured gold film on a silicon nitride membrane illuminated by a laser beam are shown to significantly exceed those for the planar surface. This enhanced pressure can be understood as being associated with an asymmetric optical cavity array realized in the membrane film. The possible enhancement depends on the material properties and the geometrical parameters of the structured material. Such control and increase of optical pressure with nanostructured material should impact applications across the physical sciences.

Measurement of wavelength-dependent radiation pressure from photon reflection and absorption due to thin film interference

Opto-mechanical forces result from the momentum transfer that occurs during light-matter interactions. One of the most common examples of this phenomenon is the radiation pressure that is exerted on a reflective surface upon photon reflection. For an ideal mirror, the radiation pressure is independent of the wavelength of light and depends only on the incident power. Here we consider a different regime where, for a constant input optical power, wavelength-dependent radiation pressure is observed due to coherent thin film Fabry-Perot interference effects. We perform measurements using a Si microcantilever and utilize an in-situ optical transmission technique to determine the local thickness of the cantilever and the light beam’s angle of incidence. Although Si is absorptive in the visible part of the spectrum, by exploiting the Fabry-Perot modes of the cantilever, we can determine whether momentum is transferred via reflection or absorption by tuning the incident wavelength by only ~20 nm. Finally, we demonstrate that the tunable wavelength excitation measurement can be used to separate photothermal effects and radiation pressure.

Phase-dependent Fano-shape optomechanically induced transparency

We present a detailed study of a three-mode-coupling cavity optomechanical system where one mechanical mode and two optical whispering-gallery modes are coupled together. We extend the earlier investigation of regular optomechanically induced transparency (OMIT) [Science330, 1520 (2010)SCIEAS0036-807510.1126/science.1195596] in a more general case. A complete analytical description of the present system is obtained, and quantitative analyses of the Fano-shape OMIT spectrum are provided. It is clearly shown that a sharp and asymmetric Fano-shape OMIT lineshape, which is decided by the phase difference between the probe field and the mechanical driving, can be observed from the probe output.

Quantum nondemolition measurement of mechanical motion quanta

The fields of optomechanics and electromechanics have facilitated numerous advances in the areas of precision measurement and sensing, ultimately driving the studies of mechanical systems into the quantum regime. To date, however, the quantization of the mechanical motion and the associated quantum jumps between phonon states remains elusive. For optomechanical systems, the coupling to the environment was shown to make the detection of the mechanical mode occupation difficult, typically requiring the single-photon strong-coupling regime. Here, we propose and analyse an electromechanical setup, which allows us to overcome this limitation and resolve the energy levels of a mechanical oscillator. We found that the heating of the membrane, caused by the interaction with the environment and unwanted couplings, can be suppressed for carefully designed electromechanical systems. The results suggest that phonon number measurement is within reach for modern electromechanical setups.

Although electro-and optomechanics has recently moved towards the quantum regime, the quantized energy spectrum of a mechanical oscillator has not been directly observed. Here Dellantonio et al. propose an electromechanical setup with a membrane resonator that could enable phonon number measurements.

Negative-Mass Instability of the Spin and Motion of an Atomic Gas Driven by Optical Cavity Backaction

We realize a spin-orbit interaction between the collective spin precession and center-of-mass motion of a trapped ultracold atomic gas, mediated by spin- and position-dependent dispersive coupling to a driven optical cavity. The collective spin, precessing near its highest-energy state in an applied magnetic field, can be approximated as a negative-mass harmonic oscillator. When the Larmor precession and mechanical motion are nearly resonant, cavity mediated coupling leads to a negative-mass instability, driving exponential growth of a correlated mode of the hybrid system. We observe this growth imprinted on modulations of the cavity field and estimate the full covariance of the resulting two-mode state by observing its transient decay during subsequent free evolution.

Integrated nano-opto-electro-mechanical sensor for spectrometry and nanometrology

Spectrometry is widely used for the characterization of materials, tissues, and gases, and the need for size and cost scaling is driving the development of mini and microspectrometers. While nanophotonic devices provide narrowband filtering that can be used for spectrometry, their practical application has been hampered by the difficulty of integrating tuning and read-out structures. Here, a nano-opto-electro-mechanical system is presented where the three functionalities of transduction, actuation, and detection are integrated, resulting in a high-resolution spectrometer with a micrometer-scale footprint. The system consists of an electromechanically tunable double-membrane photonic crystal cavity with an integrated quantum dot photodiode. Using this structure, we demonstrate a resonance modulation spectroscopy technique that provides subpicometer wavelength resolution. We show its application in the measurement of narrow gas absorption lines and in the interrogation of fiber Bragg gratings. We also explore its operation as displacement-to-photocurrent transducer, demonstrating optomechanical displacement sensing with integrated photocurrent read-out.

Micromechanical Resonator Driven by Radiation Pressure Force

Radiation pressure exerted by light on any surface is the pressure generated by the momentum of impinging photons. The associated force - fundamentally, a quantum mechanical aspect of light - is usually too small to be useful, except in large-scale problems in astronomy and astrodynamics. In atomic and molecular optics, radiation pressure can be used to trap or cool atoms and ions. Use of radiation pressure on larger objects such as micromechanical resonators has been so far limited to its coupling to an acoustic mode, sideband cooling, or levitation of microscopic objects. In this Letter, we demonstrate direct actuation of a radio-frequency micromechanical plate-type resonator by the radiation pressure force generated by a standard laser diode at room temperature. Using two independent methods, the magnitude of the resonator's response to forcing by radiation pressure is found to be proportional to the intensity of the incident light.

Optical Spring Effect in Micro-Bubble Resonators and Its Application for the Effective Mass Measurement of Optomechanical Resonant Mode

In this work, we present a novel approach for obtaining the effective mass of mechanical vibration mode in micro-bubble resonators (MBRs). To be specific, the effective mass is deduced from the measurement of optical spring effect (OSE) in MBRs. This approach is demonstrated and applied to analyze the effective mass of hollow MBRs and liquid-filled MBRs, respectively. It is found that the liquid-filled MBRs has significantly stronger OSE and a less effective mass than hollow MBRs, both of the extraordinary behaviors can be beneficial for applications such as mass sensing. Larger OSE from higher order harmonics of the mechanical modes is also observed. Our work paves a way towards the developing of OSE-based high sensitive mass sensor in MBRs.

High-order exceptional points in optomechanics

We study mechanical cooling in systems of coupled passive (lossy) and active (with gain) optical resonators. We find that for a driving laser which is red-detuned with respect to the cavity frequency, the supermode structure of the system is radically changed, featuring the emergence of genuine high-order exceptional points. This in turn leads to giant enhancement of both the mechanical damping and the spring stiffness, facilitating low-power mechanical cooling in the vicinity of gain-loss balance. This opens up new avenues of steering micromechanical devices with exceptional points beyond the lowest-order two.

Cavity Cooling of Many Atoms

We demonstrate cavity cooling of all motional degrees of freedom of an atomic ensemble using light that is far detuned from the atomic transitions by several gigahertz. The cooling is achieved by cavity-induced frequency-dependent asymmetric enhancement of the atomic emission spectrum, thereby extracting thermal kinetic energy from the atomic system. Within 100 ms, the atomic temperature is reduced from 200 to 10  μK, where the final temperature is mainly limited by the linewidth of the cavity. In principle, the technique can be applied to molecules and atoms with complex internal energy structure.

Cavity-Assisted Measurement and Coherent Control of Collective Atomic Spin Oscillators

We demonstrate continuous measurement and coherent control of the collective spin of an atomic ensemble undergoing Larmor precession in a high-finesse optical cavity. The coupling of the precessing spin to the cavity field yields phenomena similar to those observed in cavity optomechanics, including cavity amplification, damping, and optical spring shifts. These effects arise from autonomous optical feedback onto the atomic spin dynamics, conditioned by the cavity spectrum. We use this feedback to stabilize the spin in either its high- or low-energy state, where, in equilibrium with measurement backaction heating, it achieves a steady-state temperature, indicated by an asymmetry between the Stokes and the anti-Stokes scattering rates. For sufficiently large Larmor frequency, such feedback stabilizes the spin ensemble in a nearly pure quantum state, in spite of continuous measurement by the cavity field.

Cooling a mechanical resonator with nitrogen-vacancy centres using a room temperature excited state spin-strain interaction

Cooling a mechanical resonator mode to a sub-thermal state has been a long-standing challenge in physics. This pursuit has recently found traction in the field of optomechanics in which a mechanical mode is coupled to an optical cavity. An alternate method is to couple the resonator to a well-controlled two-level system. Here we propose a protocol to dissipatively cool a room temperature mechanical resonator using a nitrogen-vacancy centre ensemble. The spin ensemble is coupled to the resonator through its orbitally-averaged excited state, which has a spin–strain interaction that has not been previously studied. We experimentally demonstrate that the spin–strain coupling in the excited state is 13.5±0.5 times stronger than the ground state spin–strain coupling. We then theoretically show that this interaction, combined with a high-density spin ensemble, enables the cooling of a mechanical resonator from room temperature to a fraction of its thermal phonon occupancy.

An efficient cooling mechanism for nanoscale mechanical resonators would help improve their properties for use in sensing applications. Here, the authors demonstrate a strong interaction between NV centres and a resonator and show how it could be harnessed to achieve a large cooling rate.

Role of optical density of states in Brillouin optomechanical cooling

Dynamical back-action cooling of phonons in optomechanical systems having one optical mode is well studied. Systems with two optical modes have the potential to reach significantly higher cooling rate through resonant enhancement of both pump and scattered light. Here we experimentally investigate the role of dual optical densities of states on Brillouin optomechanical cooling, and the deviation from theory caused by thermal locking to the pump laser. Using this, we demonstrate a room temperature system operating very close to the strong coupling regime, where saturation of cooling is anticipated.

Multimode optomechanical system in the quantum regime

We realize a simple and robust optomechanical system with a multitude of long-lived (Q > 107) mechanical modes in a phononic-bandgap shielded membrane resonator. An optical mode of a compact Fabry-Perot resonator detects these modes' motion with a measurement rate (96 kHz) that exceeds the mechanical decoherence rates already at moderate cryogenic temperatures (10 K). Reaching this quantum regime entails, inter alia, quantum measurement backaction exceeding thermal forces and thus strong optomechanical quantum correlations. In particular, we observe ponderomotive squeezing of the output light mediated by a multitude of mechanical resonator modes, with quantum noise suppression up to -2.4 dB (-3.6 dB if corrected for detection losses) and bandwidths ≲90 kHz. The multimode nature of the membrane and Fabry-Perot resonators will allow multimode entanglement involving electromagnetic, mechanical, and spin degrees of freedom.

Measuring and imaging nanomechanical motion with laser light

We discuss several techniques based on laser-driven interferometers and cavities to measure nanomechanical motion. With increasing complexity, they achieve sensitivities reaching from thermal displacement amplitudes, typically at the picometer scale, all the way to the quantum regime, in which radiation pressure induces motion correlated with the quantum fluctuations of the probing light. We show that an imaging modality is readily provided by scanning laser interferometry, reaching a sensitivity on the order of 10 fm / Hz 1 / 2 , and a transverse resolution down to 2 μ m . We compare this approach with a less versatile, but faster (single-shot) dark-field imaging technique.

Stable Optical Trap from a Single Optical Field Utilizing Birefringence

We report a stable double optical spring effect in an optical cavity pumped with a single optical field that arises as a result of birefringence. One end of the cavity is formed by a multilayer Al_{0.92}Ga_{0.08}As/GaAs stack supported by a microfabricated cantilever with a natural mode frequency of 274 Hz. The optical spring shifts the resonance to 21 kHz, corresponding to a suppression of low frequency vibrations by a factor of about 5 000. The stable nature of the optical trap allows the cavity to be operated without any external feedback and with only a single optical field incident.

Long-distance synchronization of unidirectionally cascaded optomechanical systems

Synchronization is of great scientific interest due to the abundant applications in a wide range of systems. We propose an all-optical scheme to achieve the controllable long-distance synchronization of two dissimilar optomechanical systems, which are unidirectionally coupled through a fiber with light. Synchronization, unsynchronization, and the dependence of the synchronization on driving laser strength and intrinsic frequency mismatch are studied based on the numerical simulation. Taking the fiber attenuation into account, we show that two optomechanical resonators can be unidirectionally synchronized over a distance of tens of kilometers. We also analyze the unidirectional synchronization of three optomechanical systems, demonstrating the scalability of our scheme.

Mechanical Resonators for Quantum Optomechanics Experiments at Room Temperature

All quantum optomechanics experiments to date operate at cryogenic temperatures, imposing severe technical challenges and fundamental constraints. Here, we present a novel design of on-chip mechanical resonators which exhibit fundamental modes with frequencies f and mechanical quality factors Q_{m} sufficient to enter the optomechanical quantum regime at room temperature. We overcome previous limitations by designing ultrathin, high-stress silicon nitride (Si_{3}N_{4}) membranes, with tensile stress in the resonators' clamps close to the ultimate yield strength of the material. By patterning a photonic crystal on the SiN membranes, we observe reflectivities greater than 99%. These on-chip resonators have remarkably low mechanical dissipation, with Q_{m}∼10^{8}, while at the same time exhibiting large reflectivities. This makes them a unique platform for experiments towards the observation of massive quantum behavior at room temperature.

Cavity magnomechanics

A dielectric body couples with electromagnetic fields through radiation pressure and electrostrictive forces, which mediate phonon-photon coupling in cavity optomechanics. In a magnetic medium, according to the Korteweg-Helmholtz formula, which describes the electromagnetic force density acting on a medium, magneostrictive forces should arise and lead to phonon-magnon interaction. We report such a coupled phonon-magnon system based on ferrimagnetic spheres, which we term as cavity magnomechanics, by analogy to cavity optomechanics. Coherent phonon-magnon interactions, including electromagnetically induced transparency and absorption, are demonstrated. Because of the strong hybridization of magnon and microwave photon modes and their high tunability, our platform exhibits new features including parametric amplification of magnons and phonons, triple-resonant photon-magnon-phonon coupling, and phonon lasing. Our work demonstrates the fundamental principle of cavity magnomechanics and its application as a new information transduction platform based on coherent coupling between photons, phonons, and magnons.

Molecular cavity optomechanics as a theory of plasmon-enhanced Raman scattering

The exceptional enhancement of Raman scattering by localized plasmonic resonances in the near field of metallic nanoparticles, surfaces or tips (SERS, TERS) has enabled spectroscopic fingerprinting down to the single molecule level. The conventional explanation attributes the enhancement to the subwavelength confinement of the electromagnetic field near nanoantennas. Here, we introduce a new model that also accounts for the dynamical nature of the plasmon-molecule interaction. We thereby reveal an enhancement mechanism not considered before: dynamical backaction amplification of molecular vibrations. We first map the system onto the canonical Hamiltonian of cavity optomechanics, in which the molecular vibration and the plasmon are parametrically coupled. We express the vacuum optomechanical coupling rate for individual molecules in plasmonic 'hot-spots' in terms of the vibrational mode's Raman activity and find it to be orders of magnitude larger than for microfabricated optomechanical systems. Remarkably, the frequency of commonly studied molecular vibrations can be comparable to or larger than the plasmon's decay rate. Together, these considerations predict that an excitation laser blue-detuned from the plasmon resonance can parametrically amplify the molecular vibration, leading to a nonlinear enhancement of Raman emission that is not predicted by the conventional theory. Our optomechanical approach recovers known results, provides a quantitative framework for the calculation of cross-sections, and enables the design of novel systems that leverage dynamical backaction to achieve additional, mode-selective enhancements. It also provides a quantum mechanical framework to analyse plasmon-vibrational interactions in terms of molecular quantum optomechanics.

Squeezing of Quantum Noise of Motion in a Micromechanical Resonator

A pair of conjugate observables, such as the quadrature amplitudes of harmonic motion, have fundamental fluctuations that are bound by the Heisenberg uncertainty relation. However, in a squeezed quantum state, fluctuations of a quantity can be reduced below the standard quantum limit, at the cost of increased fluctuations of the conjugate variable. Here we prepare a nearly macroscopic moving body, realized as a micromechanical resonator, in a squeezed quantum state. We obtain squeezing of one quadrature amplitude 1.1±0.4  dB below the standard quantum limit, thus achieving a long-standing goal of obtaining motional squeezing in a macroscopic object.

Design of a femtogram scale double-slot photonic crystal optomechanical cavity

We present the design of a double-slot photonic crystal cavity as an optomechanical device which contains a nanomechanical resonator with an effective mass as small as 6.91 fg. The optical Q-factor is optimized to 2 × 10(5). Using phononic crystals, the mechanical vibration is confined in a small volume to form a mechanical mode of 4 GHz with a high mechanical Q-factor and a femtogram effective mass. The localized mechanical mode overlaps with the optical field and strengthens the optomechanical coupling with a vacuum optomechanical coupling rate g0/2π exceeding 600 kHz. Considering fabrication imperfections, structures with deviation from ideal design are studied. The symmetry breakage of the structures and the displacement fields makes the mechanical effective masses reduced and close to 4 fg. The devices can be used in ultrasensitive sensing of mass, force and displacement.

Laser optomechanics

Cavity optomechanics explores the interaction between optical field and mechanical motion. So far, this interaction has relied on the detuning between a passive optical resonator and an external pump laser. Here, we report a new scheme with mutual coupling between a mechanical oscillator supporting the mirror of a laser and the optical field generated by the laser itself. The optically active cavity greatly enhances the light-matter energy transfer. In this work, we use an electrically-pumped vertical-cavity surface-emitting laser (VCSEL) with an ultra-light-weight (130 pg) high-contrast-grating (HCG) mirror, whose reflectivity spectrum is designed to facilitate strong optomechanical coupling, to demonstrate optomechanically-induced regenerative oscillation of the laser optomechanical cavity. We observe >550 nm self-oscillation amplitude of the micromechanical oscillator, two to three orders of magnitude larger than typical, and correspondingly a 23 nm laser wavelength sweep. In addition to its immediate applications as a high-speed wavelength-swept source, this scheme also offers a new approach for integrated on-chip sensors.

2-D optical/opto-mechanical microfluidic sensing with micro-bubble resonators

In this paper a new sensing scheme by simultaneously measuring optical refractive index change and sound speed change in an optofluidic thin wall micro-bubble resonator is reported. Sensitivity of sound speed is 4.2-6.8 MHz/ (km/s) for 3 types of mechanical modes. A 2-D optical/opto-mechanical sensing map is plotted by detecting both the whispering gallery mode resonance shift and the optomechanical resonance shift. This novel scheme provides a supplementary support to optical sensing when analytes do not respond to refractive index (RI) change.

Cavity ring-up spectroscopy for ultrafast sensing with optical microresonators

Spectroscopy of whispering-gallery mode microresonators has become a powerful scientific tool, enabling the detection of single viruses, nanoparticles and even single molecules. Yet the demonstrated timescale of these schemes has been limited so far to milliseconds or more. Here we introduce a scheme that is orders of magnitude faster, capable of capturing complete spectral snapshots at nanosecond timescales—cavity ring-up spectroscopy. Based on sharply rising detuned probe pulses, cavity ring-up spectroscopy combines the sensitivity of heterodyne measurements with the highest-possible, transform-limited acquisition rate. As a demonstration, we capture spectra of microtoroid resonators at time intervals as short as 16 ns, directly monitoring submicrosecond dynamics of their optomechanical vibrations, thermorefractive response and Kerr nonlinearity. Cavity ring-up spectroscopy holds promise for the study of fast biological processes such as enzyme kinetics, protein folding and light harvesting, with applications in other fields such as cavity quantum electrodynamics and pulsed optomechanics.

Whispering-gallery mode microresonators are powerful sensing tools, but spectrum acquisition has taken milliseconds or longer. Here, Rosenblum et al. introduce cavity ring-up spectroscopy, in which sharply rising detuned probe pulses capture spectra of microresonators on nanosecond timescales.

From laser ultrasonics to optical manipulation

During the interaction of a laser pulse with the surface of a solid object, the object always gains momentum. The delivered force impulse is manifested as propulsion. Initially, the motion of the object is composed of elastic waves that carry and redistribute the acquired momentum as they propagate and reflect within the solid. Even though only ablation- and light-pressure-induced mechanical waves are involved in propulsion, they are always accompanied by the ubiquitous thermoelastic waves. This paper describes 1D elastodynamics of pulsed optical manipulation and presents two diametrical experimental observations of elastic waves generated in the confined ablation and in the radiation pressure regime.

Optomechanical photon shuttling between photonic cavities

Mechanical motion of photonic devices driven by optical forces provides a profound means of coupling between optical fields. The current focus of these optomechanical effects has been on cavity optomechanics systems in which co-localized optical and mechanical modes interact strongly to enable wave mixing between photons and phonons, and backaction cooling of mechanical modes. Alternatively, extended mechanical modes can also induce strong non-local effects on propagating optical fields or multiple localized optical modes at distances. Here, we demonstrate a multicavity optomechanical device in which torsional optomechanical motion can shuttle photons between two photonic crystal nanocavities. The resonance frequencies of the two cavities, one on each side of this 'photon see-saw', are modulated antisymmetrically by the device's rotation. Pumping photons into one cavity excites optomechanical self-oscillation, which strongly modulates the inter-cavity coupling and shuttles photons to the other empty cavity during every oscillation cycle in a well-regulated fashion.

Control of integrated micro-resonator wavelength via balanced homodyne locking

We describe and experimentally demonstrate a method for active control of resonant modulators and filters in an integrated photonics platform. Variations in resonance frequency due to manufacturing processes and thermal fluctuations are corrected by way of balanced homodyne locking. The method is compact, insensitive to intensity fluctuations, minimally disturbs the micro-resonator, and does not require an arbitrary reference to lock. We demonstrate long-term stable locking of an integrated filter to a laser swept over 1.25 THz. In addition, we show locking of a modulator with low bit error rate while the chip temperature is varied from 5 to 60° C.

Quantum optomechanical heat engine

We investigate theoretically a quantum optomechanical realization of a heat engine. In a generic optomechanical arrangement the optomechanical coupling between the cavity field and the oscillating end mirror results in polariton normal mode excitations whose character depends on the pump detuning and the coupling strength. By varying that detuning it is possible to transform their character from phononlike to photonlike, so that they are predominantly coupled to the thermal reservoir of phonons or photons, respectively. We exploit the fact that the effective temperatures of these two reservoirs are different to produce an Otto cycle along one of the polariton branches. We discuss the basic properties of the system in two different regimes: in the optical domain it is possible to extract work from the thermal energy of a mechanical resonator at finite temperature, while in the microwave range one can in principle exploit the cycle to extract work from the blackbody radiation background coupled to an ultracold atomic ensemble.

Heralded single-phonon preparation, storage, and readout in cavity optomechanics

We show how to use the radiation pressure optomechanical coupling between a mechanical oscillator and an optical cavity field to generate in a heralded way a single quantum of mechanical motion (a Fock state). Starting with the oscillator close to its ground state, a laser pumping the upper motional sideband produces correlated photon-phonon pairs via optomechanical parametric down-conversion. Subsequent detection of a single scattered Stokes photon projects the macroscopic oscillator into a single-phonon Fock state. The nonclassical nature of this mechanical state can be demonstrated by applying a readout laser on the lower sideband to map the phononic state to a photonic mode and performing an autocorrelation measurement. Our approach proves the relevance of cavity optomechanics as an enabling quantum technology.

Optomechanics with cavity polaritons: dissipative coupling and unconventional bistability

We study a hybrid system formed from an optomechanical resonator and a cavity mode strongly coupled to an excitonic transition inside a quantum well. We show that due to the mixing of cavity photon and exciton states, the emergent quasiparticles-polaritons-possess coupling to the mechanical mode of both a dispersive and dissipative nature. We calculate the occupancies of polariton modes and reveal bistable behavior, which deviates from conventional Kerr nonlinearity or dispersive coupling cases due to the dissipative coupling. The described system serves as a good candidate for future polaritonic devices.

Near-self-imaging cavity for three-mode optoacoustic parametric amplifiers using silicon microresonators

Three-mode optoacoustic parametric amplifiers (OAPAs), in which a pair of photon modes are strongly coupled to an acoustic mode, provide a general platform for investigating self-cooling, parametric instability and very sensitive transducers. Their realization requires an optical cavity with tunable transverse modes and a high quality-factor mirror resonator. This paper presents the design of a table-top OAPA based on a near-self-imaging cavity design, using a silicon torsional microresonator. The design achieves a tuning coefficient for the optical mode spacing of 2.46  MHz/mm. This allows tuning of the mode spacing between amplification and self-cooling regimes of the OAPA device. Based on demonstrated resonator parameters (frequencies ∼400  kHz and quality-factors ∼7.5×10(5) we predict that the OAPA can achieve parametric instability with 1.6 μW of input power and mode cooling by a factor of 1.9×10(4) with 30 mW of input power.