Optomechanical Entanglement Research Articles

Optomechanical entanglement induced by backward stimulated Brillouin scattering

We propose a scheme to generate robust optomechanical entanglement, i.e., the entanglement between a mechanical and an optical modes. This scheme is based on a Backward Stimulated Brillouin Scattering (BSBS) process, which is hosted within an optomechanical structure. Our benchmark system consists of an acoustic (mechanical) mode coupled to two optical modes through an electrostrictive (radiation pressure) effect. After determining the optimal acoustic parameters allowing the entanglement in our system, we have shown that both the acoustic coupling and the decay rate require a certain threshold from where the optomechanical entanglement is generated. For instance, to generate an optomechanical entanglement in our proposal, the strength of the used acoustic decay rate most exceed both the mechanical and optical decay rates, which is the figure of merit of our proposal. The generated entanglement is robust enough against thermal fluctuation. Our work provides a new scheme for entanglement generation based on BSBS effect, and can be extended to microwaves and hybrid optomechanical structures. Such a generated entangled states can be used for quantum information processing, quantum sensing, and quantum computing.

Optomechanical entanglement manipulation and switching in a squeezed-cavity-assisted optomechanical system

Quantum entanglement is pivotal in modern quantum technologies, spanning applications from quantum networks to quantum metrology. Controllable quantum entanglement in cavity optomechanical systems has been an enduring pursuit. We propose a unique method for flexible manipulation and switching of optomechanical entanglement in a squeezed-cavity-assisted optomechanical system consisting of a χ(2)-nonlinear optical cavity and an optomechanical cavity. Squeezing the nonlinear optical cavity through parametric pumping allows effective control of light-light and light-vibration interactions within the system. This capability of the squeezed system plays a key role in manipulating quantum entanglement. We find that quantum entanglement between the unsqueezed cavity mode and the mechanical mode can be effectively regulated by adjusting the pump laser parameters. Furthermore, by turning the phase of the pump, we can achieve highly flexible quantum switching between entanglement and separability. Additionally, we demonstrate increased entanglement between the squeezed cavity mode and the mechanical mode when completely suppressing the pump-induced optical input noise. Our findings pave the way not only towards the manipulation and protection of fragile quantum entanglement but also to achieve photon-phonon quantum control by exploiting quantum squeezing.

Atom-magnon entanglement in a coupled cavity-magnon atom-optomechanical system

We propose an alternative way to realize macroscopic entanglement between an atomic ensemble and ferrimagnetic magnons in a hybrid cavity-magnon atom-optomechanics, in which a microwave cavity couples to the magnons via magnetic dipole interaction, and simultaneously couples to a standard optomechanical cavity with an ensemble of two-level atoms. We show that in experimental feasible parameters, the optomechanical entanglement can be transferred to the bipartite subsystems, which makes it possible to generate the macroscopic atom-magnon entanglement and genuine tripartite entanglement. We mainly analyze the effects of coupling strengths on the efficiency of the entanglement transfer and the generation of the atom-magnon entanglement. We find that by selecting appropriate coupling strengths, both the degree of the atom-magnon entanglement and its robustness against the environmental temperature are enhanced significantly.

Perturbation theoretical approach to determine optomechanical entanglement in mirror-field systems

An analytical method is developed that can be applied to a large variety of optomechanical systems to study entanglement between two subsystems of interest. The method is based on a system parameter that can be considered as perturbation parameter. It is shown that the method allows researchers to draw both qualitative and quantitative conclusions about the perturbation parameter at hand. First, the conclusion can be drawn whether or not the parameter when scaled up slightly induces entanglement between the subsystems. Second, physical insights into the role of model parameters for the emergence of entanglement can be obtained based on the perturbation theoretical analytical expressions. Third, quantitative predictions of numerical simulations that so far dominate the literature in the field of optomechanical entanglement can be validated at least in the limit of the vanishing perturbation parameter.

Improving the Performance of Cooling and Entanglement in a Double Cavity Optomechanical System Assisted by the Quantum Coherent Feedback

AbstractA theoretical scheme is proposed for improving the performance of cooling and entanglement, where the physical model is based on a double cavity optomechanical system assisted by the field‐mediated coherent feedback. The cooling performance is evaluated by calculating the final mean phonon number. The steady‐state bipartite entanglement between the optical mode and mechanical mode is measured by the logarithmic negativity. The result manifests that with assistance of the quantum coherent feedback, the mechanical resonator (MR) can be cooled close to its quantum ground state and the steady‐state optomechanical entanglement is simultaneously created, all of which are obtained under the condition beyond the resolved sideband. The presented feedback strategy is measurement‐independent, which can effectively preserve the quantum coherence of system. The scheme is conducive to relaxing the current experimental condition and it may provide a new path for the optomechanical manipulation involving the low‐frequency MR.

Nonlinearly induced entanglement in dissipatively coupled optomechanical system

Nonlinearly induced steady-state photon–phonon entanglement of a dissipative coupled system is studied in the bistable regime. Quantum dynamical characteristics are analysed by solving the mean-field and fluctuation equations of the system. It is shown that dissipative coupling can induce bistable behaviour for the effective dissipation of the system. Under suitable parameters, one of the steady states significantly reduces the dissipative effect of the system. Consequently, a larger steady-state entanglement can be achieved compared to linear dynamics. Furthermore, the experimental feasibility of the parameters is analysed. Our results provide a new perspective for the implementation of steady-state optomechanical entanglement.

Optomechanical squeezing and entanglement in cavities optomechanical system

We present the squeezing and entanglement features of the vibrational phonon modes in a double-cavity optomechanical system with input squeezed light. The non-classical features of the vibrational phonon modes arise from the transfer of quantum coherence from the optical to the phonon modes. The phonon modes exhibit squeezing, and the degree of squeezing increases with the increase in the input squeezed light. To quantify the entanglement between the phonon modes, we apply the Hillery and Zubairy criterion. We demonstrate that the entanglement between the phonon modes increases with an increase in optomechanical cooperativity. Moreover, the input squeezed light has a substantial effect on the degree entanglement between the phonon modes.

Multi-field-driven optomechanical entanglement.

Cavity optomechanical (COM) entanglement, playing an essential role in building quantum networks and enhancing quantum sensors, is usually weak and easily destroyed by noises. As feasible and effective ways to overcome this obstacle, optical or mechanical parametric modulations have been used to improve the quality of quantum squeezing or entanglement in various COM systems. However, the possibility of combining these powerful means to enhance COM entanglement has yet to be explored. Here, we fill this gap by studying a COM system containing an intra-cavity optical parametric amplifier (OPA), driven optically and mechanically. By tuning the relative strength and the frequency mismatch of optical and mechanical driving fields, we find that constructive interference can emerge and significantly improve the strength of COM entanglement and its robustness to thermal noises. This work sheds what we believe to be a new light on preparing and protecting quantum states with multi-field driven COM systems for diverse applications.

Quantum squeezing-induced quantum entanglement and EPR steering in a coupled optomechanical system.

We propose a theoretical project in which quantum squeezing induces quantum entanglement and Einstein-Podolsky-Rosen steering in a coupled whispering-gallery-mode optomechanical system. Through pumping the χ(2)-nonlinear resonator with the phase matching condition, the generated squeezed resonator mode and the mechanical mode of the optomechanical resonator can generate strong quantum entanglement and EPR steering, where the squeezing of the nonlinear resonator plays the vital role. The transitions from zero entanglement to strong entanglement and one-way steering to two-way steering can be realized by adjusting the system parameters appropriately. The photon-photon entanglement and steering between the two resonators can also be obtained by deducing the amplitude of the driving laser. Our project does not need an extraordinarily squeezed field, and it is convenient to manipulate and provides a novel and flexible avenue for diverse applications in quantum technology dependent on both optomechanical and photon-photon entanglement and steering.

Enhancing the Steady-State Entanglement between a Laguerre–Gaussian-Cavity Mode and a Rotating Mirror via Cross-Kerr Nonlinearity

Quantum entanglement will play an important role in future quantum technologies. Here, we theoretically study the steady-state entanglement between a cavity field and a macroscopic rotating mirror in a Laguerre–Gaussian-(LG)-cavity optomechanical system with cross-Kerr nonlinearity. Logarithmic negativity is used to quantify the steady-state entanglement between the cavity and mechanical modes. We analyze the impacts of the cross-Kerr coupling strength, the cavity detuning, the input laser power, the topological charge of the LG-cavity mode, and the temperature of the environment on the steady-state optomechanical entanglement. We find that cross-Kerr nonlinearity can significantly enhance steady-state optomechanical entanglement and make steady-state optomechanical entanglement more robust against the temperature of the thermal environment.

Optical response properties of a hybrid optomechanical system with quantum dot molecules assisted by second-order optomechanical coupling

We theoretically investigated the optical response properties of the optical field in three-level quantum dot molecules assisted optomechanical system consisting of the mechanical resonator. We show that various system parameters like second-order optomechanical coupling can control these nonlinear effects. In this work, we study how the system parameters affect the normal mode splitting of the movable mirror and output field. Further, we show that the second-order optomechanical coupling plays an important role in creating optomechanical entanglement as well as producing a strong squeezing spectrum of the optical field.

Normal-mode splitting in an optomechanical system enhanced by an optical parametric amplifier and coherent feedback

Normal-mode splitting (NMS) is an evident signature of strong coupling interactions for observing quantum phenomena, such as optomechanical squeezing and entanglement. In the previous literature, optical parametric amplifier (OPA) and coherent feedback are independently proposed to enhance the NMS. Here, we combine OPA and coherent feedback into a single optomechanical system to enhance the NMS. Controllable parameters, such as input optical power, OPA gain and phase, coherent feedback strength, are varied to observe NMS variations. In particular, we consider positive and negative feedback in terms of the amplitude reflectivity of the beam splitter for coherent feedback. The NMS appears mostly with the positive coherent feedback rather than the negative. Furthermore, the largest mode separation occurs at an OPA phase of approximately rather than zero because the effective cavity detuning changes the effective intracavity round-trip phase, and therefore changes the OPA amplification/deamplification condition. The results indicate that the interplay between OPA and coherent feedback can enhance the NMS with more controllable parameter freedoms. This scheme provides a promising way to increase the optomechanical coupling strength, thereby having potential applications in the ground state cooling of a mechanical oscillator, the preparation of optomechanical quantum states, and the sensitive detection of a weak force.

Optomechanical entanglement affected by exceptional point in a WGM resonator system.

Entanglement of optical mode and mechanical mode plays a significant role for quantum information processing and memory. This type of optomechanical entanglement is always be suppressed by the mechanically dark-mode (DM) effect. However, the reason of the DM generation and how to control the bright-mode (BM) effect flexibly are still not resolved. In this letter, we demonstrate that the DM effect occurs at the exceptional point (EP) and it can be broken by changing the relative phase angle (RPA) between the nano scatters. We find that the optical mode and mechanical mode are separable at EPs but entangled when the RPA is tuned away from the EPs. Remarkably, the DM effect will be broken if the RPA away from EPs, resulting in the ground-state cooling of the mechanical mode. In addition, we prove that the chirality of the system can also influence the optomechanical entanglement. Our scheme can control the entanglement flexible merely depend on the relative phase angle, which is continuously adjustable and experimentally more feasible.

Strong squeezing and robust entanglement in a second-order coupled optomechanical cavity assisted by a Kerr nonlinear medium

We investigate theoretically an optomechanical system composed of an optical mode and a mechanical mode interacting through first-order coupling and second-order coupling in the presence of a Kerr nonlinear medium. We study how the nonlinearities (second-order optomechanical coupling and Kerr nonlinearity) alter the optical output spectrum, optical quadrature squeezing and optomechanical entanglement. It is shown that the intensity of the output optical spectrum decreases drastically with an increase in second-order optomechanical coupling while it increases significantly with an increase in Kerr nonlinear parameter. More interestingly, by choosing suitable second-order optomechanical coupling and detuning of the optical cavity field, one can achieve strong squeezing of the cavity light field. Further, these nonlinearities play an important role in creating robust optomechanical entanglement between optical and mechanical modes. Hence, the presence of various nonlinearities in the system can be a good platform for achieving the squeezing of light and robust optomechanical entanglement which can be used in realizing better quantum optomechanical devices.

Robust mechanical squeezing beyond 3 dB in a quadratically coupled optomechanical system

We demonstrate the dissipation-enabled generation of strong mechanical squeezing in a cavity optomechanical system by periodically modulating the amplitude of a single-tone laser driving the system. The Bogoliubov mode of the quadratically coupled mechanical oscillator cools down to its ground state due to optomechanical sideband cooling, which contributes to strong squeezing exceeding the 3 dB standard quantum limit. This sideband cooling mechanism is further optimized by numerically maximizing the ratio of the coupling sidebands. Then we look at the crucial role of the cavity mode dissipation in inducing enhanced squeezing. We also verify our results with the analytical solution (under adiabatic approximation) and the exact numerical solution. Compared with previous setups, the quadratic coupling between the mechanical oscillator and the optical mode gives rise to robust mechanical squeezing and strong optomechanical entanglement even for a large thermal occupancy of the mechanical mode.

Qubit-assisted enhancement of quantum entanglement in an optomechanical system in the presence of Kerr medium

In this work, we investigate a theoretical study of the stationary entanglement of an optomechanical system by adding a Kerr medium in the cavity where the mechanical resonator is perturbatively connected to an auxiliary qubit. The degree of entanglement between the cavity field and the mechanical system is measured by using the logarithmic negativity. We show that optomechanical entanglement is decreased by Kerr interaction due to photon blockage enhanced by mirror–qubit coupling, we also show that this enhancement is influenced by the temperature. In addition, we find that, in the presence of the mirror–qubit coupling, entanglement can arise with far weaker optomechanical coupling. The proposed scheme shows that the presence of the mirror–qubit coupling and Kerr medium is an effective control for an optomechanical system.

Phase-controlled asymmetric optomechanical entanglement against optical backscattering

Quantum entanglement plays a key role in both understanding the fundamental aspects of quantum physics and realizing various quantum devices for practical applications. Here we propose how to achieve coherent switch of optomechanical entanglement in an optical whispering-gallery-mode resonator, by tuning the phase difference of the driving lasers. We find that the optomechanical entanglement and the associated two-mode quantum squeezing can be well tuned in a highly asymmetric way, providing an efficient way to protect and enhance quantum entanglement against optical backscattering, in comparison with conventional symmetric devices. Our findings shed a new light on improving the performance of various quantum devices in practical noisy environment, which is crucial in such a wide range of applications as noise-tolerant quantum processing and the backscattering-immune quantum metrology.

Thermal-noise-resistant optomechanical entanglement via general dark-mode control

Quantum entanglement not only plays an important role in the study of the fundamentals of quantum theory, but also is considered as a crucial resource in quantum information science. The generation of macroscopic entanglement involving multiple optical and mechanical modes is a desired task in cavity optomechanics. However, the dark-mode effect is a critical obstacle against the generation of quantum entanglement in multimode optomechanical systems consisting of multiple degenerate or near-degenerate mechanical modes coupled to a common cavity mode. Here we propose an auxiliary-cavity-mode method to enhance optomechanical entanglement in a multimode optomechanical system by breaking the dark-mode effect. We find that the introduction of the auxiliary cavity mode not only assists the entanglement creation between the cavity mode and the mechanical modes, but also improves the immunity of the optomechanical entanglement to the thermal excitations by about three orders of magnitude. We also study the optomechanical entanglement in the network-coupled optomechanical system consisting of two mechanical modes and two cavity modes. By analyzing the correspondence between the optomechanical entanglement and the dark-mode effect, we find that optomechanical entanglement can be largely enhanced once the dark mode is broken. In addition, we study the mechanical entanglement and find that it is negligibly small. We also present some discussions on the experimental implementation with a microwave optomechanical setup, on the relationship between the dark-mode-breaking mechanism and the center-of-mass and relative coordinates, and on the explanation of the important role of the dark-mode breaking in the enhancement of optomechanical entanglement. Our results pave the way towards the preparation of entangled optomechanical networks and noise-resistant quantum resources.

Coherent feedback in optomechanical systems in the sideband-unresolved regime

Preparing macroscopic mechanical resonators close to their motional quantum groundstate and generating entanglement with light offers great opportunities in studying fundamental physics and in developing a new generation of quantum applications. Here we propose an experimentally interesting scheme, which is particularly well suited for systems in the sideband-unresolved regime, based on coherent feedback with linear, passive optical components to achieve groundstate cooling and photon-phonon entanglement generation with optomechanical devices. We find that, by introducing an additional passive element – either a narrow linewidth cavity or a mirror with a delay line – an optomechanical system in the deeply sideband-unresolved regime will exhibit dynamics similar to one that is sideband-resolved. With this new approach, the experimental realization of groundstate cooling and optomechanical entanglement is well within reach of current integrated state-of-the-art high-Q mechanical resonators.

Manipulation and enhancement of asymmetric steering via down-converted nondegenerate photons

We investigate the asymmetric Gaussian steering with the nondegenerate parametric amplifier in a three-mode optomechanical system composed of two optical cavities and a mechanical oscillator. In the presence of the nondegenerate parametric amplifier, we find that the Gaussian steering between the auxiliary cavity and the mechanical resonator without direct interaction is significantly enhanced. By cooling the delocalized Bogoliubov modes over the auxiliary cavity and the mechanical oscillator, the optimal optomechanical entanglement and Gaussian steering can be realized and enhanced. Furthermore, we observe a wider range of parameters for the Gaussian steering with the case of cooling double delocalized modes. In addition, the magnitudes of the asymmetric Gaussian steering in two different directions can be adjusted by altering the decay rate of the auxiliary optical mode. Therefore, our proposal provides an effective method to manipulate and enhance the one-way Gaussian steering between the two modes.