Research On Quantum Entanglement In The Laguerre-Gaussian Rotating Cavity Optomechanical System

Quantum entanglement is a natural result when the superposition principle of quantum mechanics is applied to multiple subsystems,which reflects the quantum properties of microscopic systems.It plays a fundamental role in the understanding of quantum mechanics and in the applications in quantum communication and quantum computing etc.Recent years,much attention has been paid to the quantum entanglement in cavity optomechanical systems.For a traditional cavity optomechanics system with the cavity mirror oscillating harmonically,the entanglement between the cavity mode and the mechanical oscillator can be established by exchanging momentum between them.While for a rotating cavity optomechanical system,the quantum entanglement between the cavity mode and the rotating mirror is generated by exchanging angular momentum between them.This dissertation studies the quantum entanglement in two rotating cavity optomechanical systems with the cavity mode being Laguerre-Gauss(L-G)mode.In the dissertation the two-mode and three-mode quantum entanglement are examined and the various physical factors that affect the degree of entanglement are discussed.The dissertation includes the following two parts:Firstly,we have studied a hybrid rotating-cavity optomechanical system containing yttrium iron garnet crystal sphere(YIG sphere)inside the cavity.In such a system the cavity mode interacts with both the rotating cavity mirror by exchanging orbital angular momentum and the excited magnetic mode inside the YIG sphere by a magnetic dipole coupling.Thus,the magnetic mode and the rotating cavity mirror which do not interact with each other are correlated through the cavity mode as a medium.Based on this,we propose a scheme to generate the entanglement for the cavity mode and the magnetic mode and the phonon mode,including three kinds of two-mode entanglements and a kind of three-mode entanglement.We have intensively examined how the various physical factors affect the entanglements mentioned.The results show that the orbital angular momentum of the cavity mode deeply affects the entanglements and the proportion of three kinds of two-mode entanglements will be redistributed via the change of the orbital angular momentum of the cavity mode,thus affecting the generation of the three-mode quantum entanglement and its quantity.Secondly,we have studied an optomechanical system with two mechanically-coupled rotating cavities sharing a common cavity mirror.In such a system,both optical cavity modes a and b inside the cavities A and B respectively are supposed to be L-G modes which do not couple each other directly,while they are are able to exchange orbital angular momenta with the common rotating cavity mirror Thus,the cavity modes a and b can establish an indirect interaction through the macro-mechanical element of the rotating cavity mirror.Based on this,we propose a scheme to generate two-mode entanglements and three-mode entanglements for both cavity modes a,b and rotating cavity mirror.And we have mainly examined the influence of the various physical factors,such as the power of driving field,the orbital angular momenta of the cavity modes and the effective detuning between the cavity modes a and b,on the entanglements.Our research results show that under certain conditions all of the three kinds of two-mode entanglements and the three-mode entanglement can exist stably simultaneously.