Photon Blockade Effect In Cavity Optomechanical System

Cavity optomechanical system is a powerful platform for studying the interaction between light field and mechanical motion.It is of great significance for quantum memories,weak force detection,ultra-sensitive sensors,macroscopic quantum manipulation,gravitational wave detection,etc.With the progress of process technology,the research in various cavity optomechanical systems has made rapid development in recent decades.Recently,the researchers have found that the nonlinear optomechanical coupling can be used to study different nonlinear phenomena for photon,such as the photon blocking effect,which opens up a completely new route towards nonlinear quantum optics.However,in order to achieve a strong photon blockade effect,the required single-photon optomechanical coupling strength is usually extremely large in the standard cavity optomechanical system.The required single-photon optomechanical coupling strength needs to reach the order of the mechanical frequency,which is very difficult to achieve in current experiments.In order to study how to reduce the dependence of photon blockade on the single-photon optomechanical coupling strength,this dissertation studies photon blockade effect in different cavity optomechanical systems.The main research content is as follows:In the cavity optomechanical system with a trapped optical parametric amplification,we study the single-photon and two-photon blockade phenomena.The result indicates photon blockade effects are significantly enhanced in the nonlinear hybrid cavity optomechanical system.The strong photon blockade phenomena do not rely on a large single-photon optomechanical coupling strength and can eliminate the disadvantages of suppressing multi-photon excitation incompletely.Through analyzing the single-photon blockade mechanism and optimizing the system parameters,we obtain a perfect single-photon blockade with a high occupancy probability of single-photon excitation,which means that a high-quality and efficient single-photon source can be generated.In addition,by studying the two-photon blockade effect,we find that not only the two-photon blockade effect is significantly enhanced,but also the region where two-photon blockade occurs is widened when the optical parametric amplification exists.Different from the traditional cognition,where the optical parametric amplifier enhances the photon blockade effect via enhancing the single-photon optomechanical coupling,we analyze the reason of enhanced photon blockade from the unconventional photon blockade mechanism.Here,the optical parametric amplification is regarded as a two-photon excitation process in the optical cavity,which is used to cause destructive quantum interference with the laser driving.We find that the required gain rate of optical parametric amplification for perfect photon blockade is much smaller than it in the traditional scheme.In the hybrid cavity optomechanical system with a trapped ?-type three-level atom,we investigate in detail the influence of trapped atom on the single-photon blockade effect.We find that the non-resonant coupled ?-type atom can effectively enhance the photon blockade phenomenon even with a weak single-photon optomechanical coupling.Through analyzing the conventional and unconventional blockade mechanisms,we find that the enhanced photon blockade effect can be attributed to two aspects:(i)the nonresonant coupled A-type atom reconstructs the anharmonic eigenenergy spectrum of system;(ii)the microwave driving field promotes the destructive quantum interference for two-photon excitation.By means of the joint enhancement effect,the perfect photon blockade,i.e.,the second-order correlation function g(2)(0)(?)0,can be achieved without the strong single-photon optomechanical coupling as reported in the standard optomechanical system.Moreover,to ensure the efficiency of single-photon emission,we also discuss how to maximize the intracavity photon number when the strong photon blockade occurs.Finally,we test the necessity of microwave driving field in the system by recalculating the correlation function analytically in the absence of the microwave field,and find the perfect photon blockade can not be generated when the microwave driving field is non-existent.For the nonreciprocal coupling double-cavity optomechanical system,we study the influence of nonreciprocal coupling on the photon blockade effect.For the unconventional photon blockade mechanism,the realization of blockade phenomenon mainly relies on the destructive quantum interference between two different excitation paths of two-photon excitation.Here,we talk about the influence of two asymmetric excitation paths caused by nonreciprocal coupling on nonclassical light statistic effect.Then we explore the photon blockade in the weak and strong coupling regions,respectively.To achieve the strong photon blockade,we respectively give the optimal parameter relations under different blockade mechanisms.Moreover,we find that the photon blockades under their respective mechanisms exhibit completely different behaviors with the change of nonreciprocal coupling.Finally,in the weak single-photon optomechanical coupling region,the variation of photon blockade with the optomechanical coupling strength is discussed in detail.Different from the traditional cognition,we find that the optomechanical coupling is not as large as possible.And there is a threshold to make the required nonreciprocal coupling weakest.In a parity-time(PT)symmetric non-Hermitian system,we study the effects of(PT symmetry on the photon blockade and distinguish the different blockade mechanisms.In order to discuss the influence of PT phase transition on the photon blockade effect,we first analytically derive the critical parameter occurring the PT phase transition.Hereafter,the photon blockade phenomena are respectively studied in different phases,i.e.,the PT symmetry broken phase and the PT symmetry unbroken phase.According to the conventional and unconventional photon blockade mechanisms,we distinguish different blockade phenomena in detail.We find that the conventional photon blockade effect only occurs in the unbroken PT symmetry region,while the unconventional photon blockade effect can appear in both PT symmetry regions.In order to further study the influence of PT symmetry on the photon blockade,we also consider the non-PT-symmetric situations which reveals the physical essence of the photon blockade occurring by comparing those results.We find that the balance gain-loss ratio is the main reason for the perfect photon blockade and the different detunings just change the location of the perfect photon blockade occurring.