In this paper, we investigate the dynamics of quantum correlations for the continuous-variable bipartite optomechanical system in the presence of homodyne mediated quantum feedback. The system is constructed using the Fabry–Perot cavity and a mechanical oscillator. In detail, we have studied the quantum entanglement via logarithmic negativity, quantum discord, and quantum steering between the optical and mechanical modes. The results show that the maximum entanglement between the optical and mechanical modes occurred out of the resonance frequency at the steady-state region due to the presence of the optical feedback. We also employ quantum steering to see the steerability between the modes. It is observed that the quantum entanglement increases when the effective detuning frequency increases, however, the quantum discord and steering decrease when the effective detuning frequency increases for a given quantum feedback strength with other parameters of the system are to be fixed. Moreover, the presence of quantum feedback has an enhancement effect on the quantum correlations.
In this paper, we investigate the dynamics of quantum correlations for the continuous-variable bipartite optomechanical system in the presence of homodyne mediated quantum feedback. The system is constructed using the Fabry–Perot cavity and a mechanical oscillator. In detail, we have studied the quantum entanglement via logarithmic negativity, quantum discord, and quantum steering between the optical and mechanical modes. The results show that the maximum entanglement between the optical and mechanical modes occurred out of the resonance frequency at the steady-state region due to the presence of the optical feedback. We also employ quantum steering to see the steerability between the modes. It is observed that the quantum entanglement increases when the effective detuning frequency increases, however, the quantum discord and steering decrease when the effective detuning frequency increases for a given quantum feedback strength with other parameters of the system are to be fixed. Moreover, the presence of quantum feedback has an enhancement effect on the quantum correlations.
In this paper, we investigated the quantum correlation of nano-electro-optomechanical system enhanced by an optical parametric amplifier (OPA) and Coulomb-type interaction. In particular, we consider a hybrid system consisting of a cavity and two charged mechanical oscillators with an OPA, where the optical cavity mode is coupled with a charged mechanical oscillator via radiation pressure, and the two charged mechanical oscillators are coupled through a Coulomb interaction. We use logarithmic negativity to quantify quantum entanglement, and quantum discord to measure the quantumness correlation between the two mechanical oscillators. We characterize quantum steering using the steerability between the two mechanical oscillators. Our results show that the presence of OPA and strong Coulomb coupling enhances the quantum correlations between the two mechanical oscillators. In addition, Coulomb interactions are more prominent in quantum correlations. Besides, in the presence of OPA, the maximum amount of quantum entanglement, quantum steering, and quantum discord were achieved between the two mechanical oscillators is greater than in the absence of OPA. Moreover, a proper phase choice of the optical field driving the OPA enhances quantum correlations under suitable conditions. We obtain quantum entanglement confines quantum steering and quantum discord beyond entanglement. Furthermore, quantum entanglement, quantum steering, and quantum discord decrease rapidly with increasing temperature as a result of decoherence. In addition, quantum discord persists at higher temperature values, although the quantum entanglement between the systems also vanishes completely. Our proposed scheme enhances quantum correlation and proves robust against fluctuations in the bath environment. We believe that the present scheme of quantum correlation provides a promising platform for the realization of continuous variable quantum information processing.
We investigate the correlation of mechanical systems of nondegenerate three-level laser with parametric oscillator in optomechanical cavity coupled to a two-mode squeezed vacuum reservoir. The quantum properties of the mechanical systems as a result of the correlation have been analyzed using the expectation values of mechanical mode variables at steady state and the eigenvalues of the reduced covariance matrix of the two sub-mechanical systems. The logarithmic negativity, steerability, and quantum discord criterion for entanglement, steerability, and quantum discord, respectively confirm that bipartite sub-mechanical systems are correlated. The results show that the bipartite sub-mechanical systems exhibit entanglement two-way steering and non-classical correlation or quantum discord. Moreover, the sub-mechanical system exhibits squeezing in the minus quadrature or momentum. The correlation properties of sub-mechanical systems are depend on the reservoir but the cavity laser has no effect on the quantum correlation of the sub-mechanical systems.
The aim of this paper is to quantify the quantum correlations between mechanical and optical modes in an optomechanical system with two spatially separated Fabry–Pérot cavities. We use logarithmic negativity [Formula: see text] and entanglement of formation (EoF), respectively, to quantify entanglement between optical and mechanical modes, while Gaussian geometric discord (GGD) is used to capture all nonclassical correlations, including entanglement. These quantifiers are evaluated as functions of the physical parameters characterizing the environment and the system (the thermal bath temperature [Formula: see text], the photons number [Formula: see text], the optomechanical cooperativity [Formula: see text], the squeeze parameter [Formula: see text] and the drive pump power [Formula: see text]). By considering recent experimental parameters, we show that GGD is more robust than entanglement for high thermal bath temperature and low optomechanical cooperativity. We also find that these quantifiers improve with increasing optomechanical cooperativity. The effects of the other parameters are also discussed in detail.
In an optomechanical system consisting of two Fabry–Pérot cavities fed by squeezed light and coupled via Coulomb interaction, we respectively use the logarithmic negativity, Gaussian discord and Gaussian coherence to analyze the behavior of three different indicators of nonclassicality, namely the entanglement, quantum discord and quantum coherence. We perform the rotating wave approximation and work in the resolved sideband regime. In two bi-mode states (optical and mechanical), the coherence is generally found to be greater than entanglement and discord. More interestingly, we show that the Coulomb interaction can be used either to degrade or enhance the nonclassical properties of the optical subsystem. In addition, compared with the discord and coherence, the mechanical entanglement is found strongly sensitive to both thermal and Coulomb effects, and it requires a minimum value of cooperativity to be generated. Remarkably, this minimum increases when increasing the Coulomb coupling strength. Finally, we notice that an optimal transfer of quantum correlations between the optical and mechanical subsystems is achieved in the absence of the Coulomb interaction.
Abstract In this paper, we propose a continuous measurement and feedback scheme to achieve strong Einstein–Podolsky–Rosen (EPR) steering and Bell nonlocality of two macroscopic mechanical oscillators in cavity optomechanics. Our system consists of two optomechanical cavities in which two cavity fields are coupled to each other via nondegenerate parametric downconversion. The two cavity output fields are subject to continuous Bell-like homodyne detection and the detection currents are fed back to drive the cavity fields. It is found that when the feedback is absent, the two mechanical oscillators can only be prepared in steady weakly entangled states which however do not display EPR steering and Bell nonlocality, due to the so-called 3 dB limit. But when the feedback is present, it is found that the mechanical entanglement is considerably enhanced such that strong mechanical steering and Bell nonlocality can be obtained in the steady-state regime. We analytically reveal that this is because the feedback drives the mechanical oscillators into a steady approximate two-mode squeezed vacuum state, with arbitrary squeezing in principle. It is shown that the feedback can also obviously improve the purity of the nonclassical mechanical states. The dependences of the mechanical quantum nonlocality on the feedback strength and thermal fluctuations are studied, and it is found that Bell nonlocality is much more vulnerable to thermal noise than EPR steerable nonlocality.
We propose a scheme to enhance entanglement and asymmetric steering between two mechanical oscillators in an optomechanical system with coherent feedback control. In the system, an optical cavity interacts with two mechanical oscillators and an auxiliary cavity whose output field is fed back into the input port of the optical cavity via a feedback loop. Due to the coherence between the auxiliary cavity and feedback, we derive the effective decay rate and a nonzero frequency shift of the optical cavity. Consequently, the induced beam-splitter-type and parametric-type interactions between the two mechanical oscillators are modulated, which leads to the enhancement of entanglement and the generation of asymmetric steering even if the two mechanical oscillators possess identical decoherence properties. And the direction of asymmetric steering can be controlled by tuning the jumping phase between two cavities and optimizing the ratio of drive asymmetry. In contrast to the method of adding losses or noises to one subsystem at the cost of reducing steerability, this scheme provides an active way to achieve enhanced asymmetric steering. Furthermore, the steady-state and dynamical entanglement and asymmetric steering can be generated in the unresolved-sideband regime, which is friendly for experimental implementation.