Optomechanical Coupling Research Articles

Acousto-optic modulation in lithium niobate on sapphire

We demonstrate the first acousto-optic modulators in lithium niobate films on sapphire, detailing the dependence of the piezoelectric and optomechanical coupling coefficients on the crystal orientation. This platform supports highly confined, strongly piezoelectric mechanical waves without suspensions, making it a promising candidate for broadband and efficient integrated acousto-optic devices, circuits, and systems.

Proposal for a quantum traveling Brillouin resonator.

Brillouin systems operating in the quantum regime have recently been identified as a valuable tool for quantum information technologies and fundamental science. However, reaching the quantum regime is extraordinarily challenging, owing to the stringent requirements of combining low thermal occupation with low optical and mechanical dissipation, and large coherent phonon-photon interactions. Here, we propose an on-chip liquid based Brillouin system that is predicted to exhibit large phonon-photon coupling with exceptionally low acoustic dissipation. The system is comprised of a silicon-based "slot" waveguide filled with superfluid helium. This type of waveguide supports optical and acoustical traveling waves, strongly confining both fields into a subwavelength-scale mode volume. It serves as the foundation of an on-chip traveling wave Brillouin resonator with an electrostrictive single photon optomechanical coupling rate exceeding 240 kHz. Such devices may enable applications ranging from ultra-sensitive superfluid-based gyroscopes, to non-reciprocal optical circuits. Furthermore, this platform opens up new possibilities to explore quantum fluid dynamics in a strongly interacting condensate.

Fisher-information-based estimation of optomechanical coupling strengths

The formalism of quantum estimation theory, focusing on the quantum and classical Fisher information, is applied to the estimation of the coupling strength in an optomechanical system. In order to estimate the optomechanical coupling, we have considered a cavity optomechanical model with non-Markovian Brownian motion of the mirror and employed input-output formalism to obtain the cavity output field. Our estimation scenario is based on balanced homodyne photodetection of the cavity output field. We have explored the difference between the associated measurement-dependent classical Fisher information and the quantum Fisher information, thus addressing the question of whether it is possible to reach the lower bound of the mean squared error of an unbiased estimator by means of balanced homodyne detection. We have found that the phase of the local oscillator in the homodyne detection is crucial; certain quadrature measurements allow very accurate estimation.

Single-Photon Cooling in Microwave Magnetomechanics.

Cavity optomechanics, where photons are coupled to mechanical motion, provides the tools to control mechanical motion near the fundamental quantum limits. Reaching single-photon strong coupling would allow to prepare the mechanical resonator in non-Gaussian quantum states. Preparing massive mechanical resonators in such states is of particular interest for testing the boundaries of quantum mechanics. This goal remains however challenging due to the small optomechanical couplings usually achieved with massive devices. Here we demonstrate a novel approach where a mechanical resonator is magnetically coupled to a microwave cavity. We measure a single-photon coupling of g_{0}/2π∼3 kHz, an improvement of one order of magnitude over current microwave optomechanical systems. At this coupling we measure a large single-photon cooperativity with C_{0}≳10, an important step to reach single-photon strong coupling. Such a strong interaction allows us to cool the massive mechanical resonator to a third of its steady state phonon population with less than two photons in the microwave cavity. Beyond tests for quantum foundations, our approach is also well suited as a quantum sensor or a microwave to optical transducer.

Cavity piezo-mechanics for superconducting-nanophotonic quantum interface

Hybrid quantum systems are essential for the realization of distributed quantum networks. In particular, piezo-mechanics operating at typical superconducting qubit frequencies features low thermal excitations, and offers an appealing platform to bridge superconducting quantum processors and optical telecommunication channels. However, integrating superconducting and optomechanical elements at cryogenic temperatures with sufficiently strong interactions remains a tremendous challenge. Here, we report an integrated superconducting cavity piezo-optomechanical platform where 10 GHz phonons are resonantly coupled with photons in a superconducting cavity and a nanophotonic cavity at the same time. Taking advantage of the large piezo-mechanical cooperativity (Cem ~7) and the enhanced optomechanical coupling boosted by a pulsed optical pump, we demonstrate coherent interactions at cryogenic temperatures via the observation of efficient microwave-optical photon conversion. This hybrid interface makes a substantial step towards quantum communication at large scale, as well as novel explorations in microwave-optical photon entanglement and quantum sensing mediated by gigahertz phonons.

Controllable bistable optical switch and normal mode splitting in hybrid optomechanical semiconductor microcavity containing single quantum dot driven by amplitude modulated field

We theoretically explore optical bistability for the possible signature of all-optical switching and their performance in a hybrid quantum optomechanical system comprising of two semiconductor microcavities coupled optically. One of the cavity is driven by an external amplitude-modulated pump laser while the second cavity, which contains a quantum dot (QD), is indirectly driven by light transmitted from the first cavity and a transverse optical field. The generated bistable behavior due to optomechanical nonlinearity shows a typical optical switching behavior and it can be controlled by changing the laser power, QD cavity coupling, modulating amplitude/frequency and the optomechanical coupling. A clear signature of energy exchange between the mechanical and optical modes is visible from the mechanical displacement spectrum. These results suggest that the present system can be used in sensitive optical switches and optical sensors.

Four‐Wave Mixing Response via Hybrid Coulomb‐Coupled Cavity Optomechanics

AbstractThe generation and manipulation of the four‐wave mixing (FWM) phenomenon is reported in a hybrid electrostatically Coulomb‐coupled optomechanical system as a result of light–matter interaction. The cavity is driven by a strong coherent pump and a weak probe field simultaneously in the presence of nanomechanical resonators (NMRs), and the output field can produce a new frequency component called the FWM frequency. In a hybrid Coulomb‐coupled cavity scheme, the existence of optomechanical coupling due to radiation pressure gives rise to the FWM phenomenon, which is shown both analytically and numerically. A controllable enhancement of the FWM intensity is found by tuning the pump field strength and its spectrum disappears upon switching the strength off. A significant enhancement in the FWM spectrum with two peaks is also predicted due to the Coulomb coupling strength existing between two electrostatically coupled NMR1 and NMR2. A suppressive behavior of the FWM signal is also observed upon increasing the cavity decay rate and a substantial modulation in the signal by changing the probe‐pump field detuning. Finally, the FWM spectrum is very sensitive to both the effective resonance frequencies and effective masses of the NMRs.

Bound states in the continuum for optomechanical light control with dielectric metasurfaces.

We investigate a reconfigurable dielectric metasurface merging optomechanical interaction and quasi-bound states in the continuum promising for all-optical light control light. The surface consists of a dimerized high-contrast grating with a compliant bilayer structure. The optical forces induced by a control light field lead to structural deformations changing the optical response. We discuss requirements for the geometry and optical force distribution to enable an efficient optomechanical coupling, which can be exploited to tune reflectivity, phase and polarization of a beam impinging on the metasurface. Numerical results explore some tunable devices as mirrors, saturable output couplers, phase modulators and retarder plates.

Kerr-Nonlinearity-Induced Mode-Splitting in Optical Microresonators.

The Kerr effect in optical microresonators plays an important role for integrated photonic devices and enables third harmonic generation, four-wave mixing, and the generation of microresonator-based frequency combs. Here we experimentally demonstrate that the Kerr nonlinearity can split ultra-high-Q microresonator resonances for two continuous-wave lasers. The resonance splitting is induced by self- and cross-phase modulation and counterintuitively enables two lasers at different wavelengths to be simultaneously resonant in the same microresonator mode. We develop a pump-probe spectroscopy scheme that allows us to measure power dependent resonance splittings of up to 35 cavity linewidths (corresponding to 52MHz) at 10mW of pump power. The required power to split the resonance by one cavity linewidth is only 286 μW. In addition, we demonstrate threefold resonance splitting when taking into account four-wave mixing and two counterpropagating probe lasers. These Kerr splittings are of interest for applications that require two resonances at optically controlled offsets, e.g., for optomechanical coupling to phonon modes, optical memories, and precisely adjustable spectral filters.

Generalized ultrastrong optomechanical-like coupling

We propose a reliable scheme to realize a generalized ultrastrong optomechanical coupling in a two-mode cross-Kerr-type coupled system, where one of the bosonic modes is strongly driven. The effective optomechanical interaction takes the form of a product of the photon number operator of one mode and the quadrature operator of the other mode. The coupling strength and quadrature phase are both tunable via the driving field. The coupling strength can be strongly enhanced to reach the ultrastrong-coupling regime, where the few-photon optomechanical effects such as photon blockade and macroscopically distinct quantum superposition become accessible. The presence of tunable quadrature phase also enables the implementation of geometric quantum operations. Numerical simulations show that this method works well in a wide parameter space. We also present an analysis of the experimental implementation of this scheme.

Realizing modular quadrature measurements via a tunable photon-pressure coupling in circuit QED

One of the most direct preparations of a Gottesman-Kitaev-Preskill qubit in an oscillator uses a tunable photon-pressure (also called optomechanical) coupling of the form $g \hat{q} a^{\dagger} a$, enabling to imprint the modular value of the position $\hat{q}$ of one oscillator onto the state of an ancilla oscillator. We analyze the practical feasibility of executing such modular quadrature measurements in a parametric circuit-QED realization of this coupling. We provide estimates for the expected GKP squeezing induced by the protocol and discuss the effect of photon loss and other errors on the resulting squeezing.

Strong mechanical squeezing in a standard optomechanical system by pump modulation

Being beneficial for the amplitude modulation of the pump laser, we propose a simple yet surprisingly effective mechanical squeezing scheme in a standard optomechanical system. By merely introducing a specific kind of periodic modulation into the single-tone driving field to cool down the mechanical Bogoliubov mode, the far beyond 3-dB strong mechanical squeezing can be engineered without requiring any additional techniques. Specifically, we find that the amount of squeezing is not simply dependent on the order of magnitude of the effective optomechanical coupling but strongly on the ratio of sideband strengths for it. To maximize the mechanical squeezing, we numerically and analytically optimize this ratio in the steady-state regime, respectively. The mechanical squeezing engineered in our scheme also has strong robustness and can survive at a high bath temperature. Compared with previous schemes based on the two-tone pump technique, our scheme involves fewer external control laser source and can be extended to other quantum systems to achieve strong squeezing effect.

Topological phase induced by distinguishing parameter regimes in a cavity optomechanical system with multiple mechanical resonators

We propose two kinds of distinguishing parameter regimes to induce a topological Su-Schrieffer-Heeger (SSH) phase in a one-dimensional (1D) multiresonator cavity optomechanical system via modulation of the frequencies of both cavity fields and resonators. The introduction of frequency modulations allows us to eliminate the Stokes heating process for mapping of the tight-binding Hamiltonian without the usual rotating-wave approximation, which is totally different from the traditional mapping of the topological tight-binding model. We find that the tight-binding Hamiltonian can be mapped into a topological SSH phase via modification of the Bessel function originating from the frequency modulations of cavity fields and resonators, and the induced SSH phase is independent of the effective optomechanical coupling strength. On the other hand, the insensitivity of the system to the effective optomechanical coupling provides us another new path to induce the topological SSH phase based on the present 1D cavity optomechanical system. And we show that the system can exhibit a topological SSH phase via variation of the effective optomechanical coupling strength in an alternative way, which is much easier to achieve in experiments. Furthermore, we also construct an analogous bosonic Kitaev model with trivial topology by keeping the Stokes heating processes. Our scheme provides a steerable platform for investigation of the effects of next-nearest-neighbor interactions on the topology of the system.

Optical nonreciprocity in a three-mode optomechanical system within a common reservoir

Optical nonreciprocity in a three-mode optomechanical system within a common optical reservoir is considered. It is found that optomechanically induced nonreciprocity is generated by the interference between the incoherent coupling induced by the common reservoir and the optomechanical coupling mediated by the interactions of two optical modes with a mechanical mode. There exist two symmetric nonreciprocal regimes that respectively correspond to the forward and backward photon transmissions, and the optical nonreciprocity for the relative phase φ between the optomechanical couplings is in opposite direction to that for the phase 2 π − φ . Additionally, it is shown that the optimal nonreciprocity as well as the nonreciprocal amplification can be achieved only by adjusting the optomechanical couplings. To compare nonreciprocity induced by incoherent coupling with that in the case of coherent coupling, we consider the optomechanically induced nonreciprocity created by interference between the optomechanical and direct couplings between the two optical modes. The nonreciprocal behaviors and their differences in these two cases are explained by using analytic findings.

Enhanced photon blockade in an optomechanical system with parametric amplification.

We propose a scheme to enhance the single- and two-photon blockade effects significantly in a nonlinear hybrid optomechanical system with optical parametric amplification (OPA). The scheme does not rely on strong single-photon optomechanical coupling and can eliminate the disadvantages of suppressing multi-photon excitation incompletely. Through analyzing the single-photon blockade (1PB) mechanism and optimizing the system parameters, we obtain a perfect 1PB with a high occupancy probability of single-photon excitation, which means that a high-quality and efficient single-photon source can be generated. Moreover, we find that not only the two-photon blockade (2PB) effect is significantly enhanced, but also the region where 2PB occurs is widened when OPA exists, where we also derive the optimal parameter condition to maximize two-photon emission and higher photon excitations intensely suppressed at the same time.

Hybrid plasmonic–phononic cavity design for enhanced optomechanical coupling in lithium niobate

A hybrid plasmonic–phononic cavity design which enables high vacuum coupling rate has been proposed in lithium niobate (LN) phononic crystals (Phncs) that have been perforated by air holes and coated with thin silver film. By tailoring the geometry, optomechanical interaction between the plasmonic modes (produced by the metal/insulator) and the phononic modes (confined by the phononic bandgap effect) is greatly enhanced. Numerical results based on finite-element method (FEM) reveal that in this hybrid plasmonic–phononic design, high vacuum coupling rate that predominantly contributed by moving boundary effect is on the order of 106 Hz, which is about one to two orders higher than that contributed by photoelastic effect shown in conventional phoxonic crystal designs. Results evidence how the vacuum coupling rate depends on geometrical parameters like the radius of the defect air hole, the thickness of silver layer, and LN layer. The simultaneous confinement and strong coupling, combined with other advantages as lack of constraint to the refractive index, and integration of piezoelectric material and metal in a chip, this hybrid design may be suitable for non-invasive biological sensing, optomechanically tunable plasmonic heater for drug release and lab-on-chip devices.

Quantum capacitance mediated carbon nanotube optomechanics

Cavity optomechanics allows the characterization of a vibration mode, its cooling and quantum manipulation using electromagnetic fields. Regarding nanomechanical as well as electronic properties, single wall carbon nanotubes are a prototypical experimental system. At cryogenic temperatures, as high quality factor vibrational resonators, they display strong interaction between motion and single-electron tunneling. Here, we demonstrate large optomechanical coupling of a suspended carbon nanotube quantum dot and a microwave cavity, amplified by several orders of magnitude via the nonlinearity of Coulomb blockade. From an optomechanically induced transparency (OMIT) experiment, we obtain a single photon coupling of up to g0 = 2π ⋅ 95 Hz. This indicates that normal mode splitting and full optomechanical control of the carbon nanotube vibration in the quantum limit is reachable in the near future. Mechanical manipulation and characterization via the microwave field can be complemented by the manifold physics of quantum-confined single electron devices.

Enhancement of photon–phonon entanglement transfer in optomechanics

In this work, we propose a theoretical scheme to enhance stationary entanglement of the mechanical modes of two Fabry–Perot cavities via broadband squeezed light. We employ the rotating wave approximation, and we consider the adiabatic and nonadiabatic regimes in the situation where a parametric amplifier is placed inside each cavity. The logarithmic negativity is employed to quantify the amount of entanglement. Stationary entanglement is optimal for high value of squeezing parameter and for strong optomechanical coupling. We show that the stationary entanglement is fragile under thermal effects. We show that it is possible to enhance the quantum correlations between the two movable mirrors via tuned parametric amplifier. Besides, we show that the enhancement of the stationary entanglement is deeply related to the gain of the parametric amplifier, the bath temperature of the movable mirrors, the optomechanical cooperativity and the squeezing parameter. We find that the stationary entanglement of two movable mirrors is strong in the adiabatic regime in comparison with the nonadiabatic case.

Optimal optomechanical coupling strength in multimembrane systems

We calculate the optomechanical coupling strength for a multi-membrane in a cavity system. The optimal configuration for an array of $N$ membranes placed near the center of a cavity is identified. This results in a coupling strength much greater than previously proposed multi-membrane configurations. We find that the coupling strength scales exponentially with the number of membranes until saturating due to complete localization of the field within the array. Furthermore we explore two sources of loss, those due to light absorption within the membrane(s) and leakage through the cavity's end-mirrors, and evaluate how they affect the possibility of achieving strong coupling.

Ground-State Cooling and High-Fidelity Quantum Transduction via Parametrically Driven Bad-Cavity Optomechanics.

Optomechanical couplings involve both beam splitter and two-mode-squeezing types of interactions. While the former underlies the utility of many applications, the latter creates unwanted excitations and is usually detrimental. In this Letter, we propose a simple but powerful method based on cavity parametric driving to suppress the unwanted excitation that does not require working with a deeply sideband-resolved cavity. Our approach is based on a simple observation: as both the optomechanical two-mode-squeezing interaction and the cavity parametric drive induce squeezing transformations of the relevant photonic bath modes, they can be made to cancel one another. We illustrate how our method can cool a mechanical oscillator below the quantum backaction limit, and significantly suppress the output noise of a sideband-unresolved optomechanical transducer.