Study On Quantum Entanglement And Mechanical Squeezing Based On Optical Cavity System

Quantum entanglement and squeezing state play very important role in quantum communication field.At the same time,as a very important resource in quantum mechanics and quantum information,they are widely used in quantum computing,quantum communication and precision measurement.In recent years,the perfect combination of solid-state systems and optical cavities has derived many promising systems,such as the system of quantum dots coupled to optical cavities and the nitrogen-vacancy centers defect in diamond coupled to microtoroidal resonators.The system of nitrogen-vacancy centers defect in diamond coupled to microtoroidal resonators is widely used in quantum information processing and solid-state quantum computing since its long coherence time at room temperature.The fusion scheme is an effective way to prepare large-scale entangled states.How to realize the fusion scheme of large scale W states without using the complex multibit controlled gates in specific experimental devices has attracted many attentions.The cavity optomechanical system is a very typical system in the optical cavity system to deal with the fundamental problems of quantum mechanics on the macroscopic scale.It can effectively connect the macroscopic objects with the microscopic phenomena in quantum mechanics.The mechanical squeezing of mechanical oscillators in cavity optomechanical systems has also attracted the interests of researchers in recent years.This dissertation mainly studies and discusses the fusion of large scale W states in the system of nitrogen-vacancy centers defect in diamond coupled to microtoroidal resonators without using complex multibit controlled gates and the mechanical squeezing of mechanical oscillators in cavity optomechanical systems under the unresolved sideband regime.We propose an effective W-state fusion schemes for the nonlocal electron-spin states and polarization photon states by using the nitrogen-vacancy centers defect in diamond coupled to microtoroidal resonators.A(m + n-1)-qubit W state can be obtained by fusing a n-qubit and a m-qubit W states(m,n ? 2)through these schemes.The construction of these schemes are very compact and simple compared with the previous logical-gatebased fusion schemes.We analyze the feasibility and evaluate the optimal resource cost of the schemes,which shows that the present schemes can be realized with high fidelities and less resource cost than the previous schemes.The present schemes may be meaningful forthe large-scale solid-state-based entanglement generation and the quantum information processing tasks.We propose a scheme for the counterfactual W state fusion of spin electrons in the system of the nitrogen-vacancy centers defect in diamond coupled to microtoroidal resonators.Compared with the existing W state fusion schemes,the main difference of this scheme is that the(n + m-1)W state fusion can be realized without transmitting any particles in participants.Moreover,the complex controlled quantum logical gate is unnecessary for the counterfactual fusion schemes.We numerically evaluate the influence of the fidelity and the number of the cycles,which shows the proposed scheme can be implemented with high fidelity and provides the possibility for quantum information processing based on solid-state quantum systems and counterfactual quantum information processing.We study how to achieve mechanical squeezing via the intrinsic of the mechanical oscillator in a standard cavity optomechanical system with frequency modulation.It is usually difficult to generate mechanical squeezing in standard optomechanical systems when the decay rate of the cavity or the effective coupling strength of the system is too large.We investigate the mechanical squeezing beyond resolved sideband regime and weak coupling regions in a standard optomechanical system via frequency modulation acting on both the cavity field and the mechanical oscillator.It is shown that,in the presence of frequency modulation,the beyond 3 d B strong mechanical squeezing can be achieved better than the standard optomechanical system without frequency modulation.Furthermore,the proposed scheme is feasible even in the unstable region of the standard optomechanical system,and a detailed numerical analysis is carried out from the physical essence to illuminate the reason for achieving better mechanical squeezing with frequency modulation.The scheme may open up promising perspectives for studying the quantum effect in strong coupling regions without the limitations of system stability and the unresolved sideband regime.In a cavity optomechanical system contained degenerate parameter amplifier with frequency modulation,we propose a scheme to generate mechanical squeezing of mechanical oscillator under unresolved sideband regime.We numerically simulate the effect of modulation parameters on the system,which shows that the Stokes heating processes can be modulated separately by modulation parameters in the presence of frequency modulation.In addition,the introduction of frequency modulation makes the mechanicalsqueezing of mechanical oscillator not limited by the resolved sideband regime,that is,mechanical squeezing can be realized effectively even if the decay rate of cavity field is large than the mechanical oscillator frequency.