Nonlinear Optomechanical Coupling Research Articles

Ultrasensitive displacement measurement with nonlinear optomechanical coupling and squeezed light injection

We propose an ultrasensitive displacement measurement scheme to overcome the standard quantum limit (SQL) in the unresolved sideband cavity optomechanical system with nonlinear optomechanical coupling and squeezed light injection. By introducing the optimized quantum correlation, which is enabled by suitable choices of the squeezing angle, squeezing level, power of the probe light, and measurement angle of homodyne detection, the off-resonant displacement sensitivity reaches 6 dB below the SQL in linear optomechanical coupling. In contrast, displacement sensitivities with a coherent probe plus variational readout and squeezed probe plus fixed measurement angle (phase quadrature) are 2.6 dB and 4.6 dB below the SQL, respectively. By combining linear and quadratic optomechanical coupling, we show that the displacement sensitivity can be further improved to 9.6 dB below the SQL. Our results have potential applications in gravitational-wave detectors, quantum metrology, and the search for dark matter.

Quantum simulation of a three-mode optomechanical system based on the Fredkin-type interaction

The realization of multimode optomechanical interactions in the single-photon strong-coupling regime is a desired task in cavity optomechanics, but it remains a challenge in realistic physical systems. In this work, we propose a reliable scheme to simulate a three-mode optomechanical system working in the single-photon strong-coupling regime based on the Fredkin-type interaction. This is achieved by utilizing two strong drivings to the two exchangly-coupled modes in the Fredkin-type coupling involving one optical mode and two mechanical-like modes. As an application of this enhanced three-mode nonlinear optomechanical coupling, we show how to generate entangled-cat states of the mechanical-like modes using the conditional displacement mechanism. The quantum coherence effects in the generated states are investigated by calculating two-mode joint Wigner function and quantum entanglement. The influence of the dissipation effect on the state generation is considered in the open-system case.

Nonlinearity enhancement and photon blockade in hybrid optomechanical systems.

The nonlinear optomechanical coupling is an attracting characteristic in the field of optomechanics. However, the strength of single photon optomechanical coupling is still within weak coupling regime. Using the optomechanical coupling to achieve strong nonlinear interaction between photons is still a challenge. In this paper, we propose a scheme by employing optomechanical and spin-mechanical interactions to enhance the nonlinearity of photons. An effective Hamiltonian is derived, which shows that the self-Kerr and cross-Kerr nonlinearity strengths can be enhanced by adjusting the classical pumping or enhancing the spin-mechanical coupling strength. In addition, we investigate the potential usage of the nonlinearity in the photon blockade. We demonstrate that the single and two photon blockades can occur in two super modes.

Comparing nonlinear optomechanical coupling in membrane-in-the-middle and single-cavity systems

In cavity optomechanics, nonlinear interactions between an optical field and a mechanical resonator mode enable a variety of unique effects in classical and quantum measurement and information processing. Here, we describe nonlinear optomechanical coupling in the membrane-in-the-middle (MIM) system in a way that allows direct comparison to the intrinsic optomechanical nonlinearity in a standard, single-cavity optomechanical system. We find that the enhancement of nonlinear optomechanical coupling in the MIM system as predicted by Ludwig et al (2012 Phys. Rev. Lett. 109 063601) is limited to the degree of sideband resolution of the system. Moreover, we show that the selectivity of the MIM system of nonlinear over linear transduction has the same limit as in a single cavity system. These findings put constraints on the experiments in which it is advantageous to use an MIM system. We discuss dynamical backaction effects in this system and find that these effects per cavity photon are exactly as strong as in a single cavity system, while allowing for reduction of the required input power. We propose using the nonlinear enhancement and reduced input power in realistic MIM systems towards parametric squeezing and heralding of phonon pairs, and evaluate the limits to the magnitude of both effects.

Quantum signatures of transitions from stable fixed points to limit cycles in optomechanical systems

Optomechanical systems, due to its inherent nonlinear optomechanical coupling, owns rich nonlinear dynamics of different types of motion. The interesting question is that whether there exist some common quantum features to infer the nonlinear dynamical transitions from one type to another. In this paper, we have studied the quantum signatures of transitions from stable fixed points to limit cycles in an optomechanical phonon laser system. Our calculations show that the entanglement of stable fixed points in the long run does not change with time, however, it will oscillate periodically with time at the mechanical vibration frequency for the limit cycles. Most strikingly, the entanglement quite close to the boundary line keeps as a constant, and it is very robust to the thermal phonon noise, as strong indications of this particular classical transitions.

Molecular Optomechanics in the Anharmonic Cavity-QED Regime Using Hybrid Metal–Dielectric Cavity Modes

Using carefully designed hybrid metal-dielectric resonators, we study molecular optomechanics in the strong coupling regime ($g_{\rm }^2/\omega_m {>} \kappa$), which manifests in anharmonic emission lines in the sideband-resolved region of the cavity-emitted spectrum ($\kappa{<}\omega_m$). This nonlinear optomechanical strong coupling regime is enabled through a metal-dielectric cavity system that yields not only deep sub-wavelength plasmonic confinement, but also dielectric-like confinement times that are more than two orders of magnitude larger than those from typical localized plasmon modes. These hybrid metal-dielectric cavity modes enable one to study new avenues of quantum plasmonics for single molecule Raman scattering.

Optomechanically induced transparency in optomechanics with both linear and quadratic coupling

We explore the optomechanically induced transparency (OMIT) of a compound optomechanical system, which contains two cavities and a membrane. Due to the linear and quadratic coupling between the membrane and the cavity, i.e., ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{a}}_{1}^{\ifmmode\dagger\else\textdagger\fi{}}{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{a}}_{1}\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}$ and ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{a}}_{1}^{\ifmmode\dagger\else\textdagger\fi{}}{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{a}}_{1}{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}}^{2}$, OMIT can be observed near $\ensuremath{\delta}={\ensuremath{\omega}}_{m}$ and $\ensuremath{\delta}=2{\ensuremath{\omega}}_{m}$ simultaneously. The transmission rate of the probe field near $\ensuremath{\delta}=2{\ensuremath{\omega}}_{m}$ has the same order of magnitude with the transmission rate near $\ensuremath{\delta}={\ensuremath{\omega}}_{m}$. This is in contrast to the second-order sideband OMIT effect which is caused by the intrinsic nonlinear optomechanical coupling. We also find that the positions of the two transmission windows depend on the power of the control field. By modulating the equilibrium position of the membrane, the transmission rate near $\ensuremath{\delta}={\ensuremath{\omega}}_{m}$ can be controlled. The group delay of the transmitted light near $\ensuremath{\delta}={\ensuremath{\omega}}_{m}$ is more sensitive to the equilibrium position of the membrane than the transmitted light near $\ensuremath{\delta}=2{\ensuremath{\omega}}_{m}$. So we can separate the two transmitted lights by modulating the equilibrium position of the membrane. Our investigation provides a method to steer the performance of OMIT devices.

Transformation Optics: Large Multiphysics Simulation of Nonlinear Optomechanical Coupling in Microstructured Resonant Cavities

Transformation Optics: Large Multiphysics Simulation of Nonlinear Optomechanical Coupling in Microstructured Resonant Cavities

Transformation Optics: Large Multiphysics Simulation of Nonlinear Optomechanical Coupling in Microstructured Resonant Cavities

The interfacing between optical cavities and mechanical systems has given rise to the rapid development of cavity optomechanics, which aims to confine light into small volumes by means of high-Q resonant recirculation [1], [2]. The purpose of an optomechanical system is to investigate the interaction of light with a mechanical oscillator. Its highly interdisciplinary nature leads to several potential applications in various fields of research, especially in quantum processing.

Optimal estimation of the optomechanical coupling strength

We apply the formalism of quantum estimation theory to obtain information about the value of the nonlinear optomechanical coupling strength. In particular, we discuss the minimum mean-square error estimator and a quantum Cram\'er--Rao-type inequality for the estimation of the coupling strength. Our estimation strategy reveals some cases where quantum statistical inference is inconclusive and merely result in the reinforcement of prior expectations. We show that these situations also involve the highest expected information losses. We demonstrate that interaction times in the order of one time period of mechanical oscillations are the most suitable for our estimation scenario, and compare situations involving different photon and phonon excitations.

Rigorous simulation of nonlinear optomechanical coupling in micro- and nano-structured resonant cavities

A numerical method aimed to predict the optomechanical dynamics in micro- and nano-structured resonant cavities is introduced here. The rigorousness of it is ensured by exploiting the harmonic version of the transformation optics (TO) technique and by considering all the energy-transduction contributions of electrostriction, radiation pressure, photoelasticity and moving boundaries. Since our full-wave approach implements a multi-modal analysis and also considers material losses, from both a mechanical and an optical point of view, a considerable step further has been made in respect to the standard optomechanical perturbative theory. The efficiency and the versatility of the strategy are tested by analysing the optomechanical behaviour of a corrugated Si-based nanobeam and comparing numerical results to experimental ones from the literature.

Nonlinear optomechanical paddle nanocavities

Nonlinear optomechanical coupling is the basis for many potential future experiments in quantum optomechanics (e.g., quantum non-demolition measurements, preparation of non-classical states), which to date have been difficult to realize due to small non-linearity in typical optomechanical devices. Here we introduce an optomechanical system combining strong nonlinear optomechanical coupling, low mass and large optical mode spacing. This nanoscale "paddle nanocavity" supports mechanical resonances with hundreds of fg mass which couple nonlinearly to optical modes with a quadratic optomechanical coupling coefficient $g^{(2)} > 2\pi\times400$ MHz/nm$^2$, and a two phonon to single photon optomechanical coupling rate $\Delta \omega_0 > 2\pi\times 16$ Hz. This coupling relies on strong phonon-photon interactions in a structure whose optical mode spectrum is highly non--degenerate. Nonlinear optomechanical readout of thermally driven motion in these devices should be observable for T $> 50 $ mK, and measurement of phonon shot noise is achievable. This shows that strong nonlinear effects can be realized without relying on coupling between nearly degenerate optical modes, thus avoiding parasitic linear coupling present in two mode systems.

Strong and tunable nonlinear optomechanical coupling in a low-loss system

A major goal in optomechanics is to observe and control quantum behavior in a system consisting of a mechanical resonator coupled to an optical cavity. Work towards this goal has focused on increasing the strength of the coupling between the mechanical and optical degrees of freedom; however, the form of this coupling is crucial in determining which phenomena can be observed in such a system. Here we demonstrate that avoided crossings in the spectrum of an optical cavity containing a flexible dielectric membrane allow us to realize several different forms of the optomechanical coupling. These include cavity detunings that are (to lowest order) linear, quadratic, or quartic in the membrane's displacement, and a cavity finesse that is linear in (or independent of) the membrane's displacement. All these couplings are realized in a single device with extremely low optical loss and can be tuned over a wide range in situ; in particular, we find that the quadratic coupling can be increased three orders of magnitude beyond previous devices. As a result of these advances, the device presented here should be capable of demonstrating the quantization of the membrane's mechanical energy.