Enhanced Photon Blockade And Nonreciprocal Photon Blockade In Nonlinear Opticl Systems

As an important branch of physics,quantum optics has attracted extensive attention of researchers.Quantum properties of quantum optics have unique functions in the field of information.It is expected to break through the limits of classical information systems in terms of ensuring information security,improving the computing speed,increasing information capacity and improving detection accuracy by using the properties of squeezed state and entangled state.There are three core technologies in quantum communication,namely single photon source,quantum coding and transmission,and single photon detection.A large number of studies have proved that quantum communication using single photon source is absolutely safe and has high efficiency.Thus,the ideal single photon source is the foundation of quantum communication,and the study of its characteristics is of great value.The generation of a single photon source is very important for the application of photon in quantum information and quantum communication.Photon blockade is an essential mechanism for the generation of single photon source.Photon blockade is usually classified into two categories: conventional photon blockade and unconventional photon blockade.Conventional photon blockade is based on the anharmonicity of energy levels.Conventional photon blockade requires high coupling intensity and low cavity decay rate to achieve the separability of energy level splitting in dressed space.The main advantage is that the unconventional photon blockade effect can be achieved in the case of weak coupling,which based on the quantum destructive interference between different paths.In this thesis,we propose two schemes to explore the photon blockade effect.How to improve the effect of photon blockade in the case of weak coupling is the major challenge in research of single photon source.The first scheme proposed in this thesis is to increase the coupling strength by introducing optical parametric amplification(OPA)in the second-order nonlinear system to improve photon blockade.In this system,two cavities are driven by two lasers of the same amplitude.Moreover,even if the original nonlinear coupling is quite weak,we can obtain a significant photon blockade.From an analytical perspective,the optimal condition for steady-state photon blockade are derivated.By numerically solving the master equation under steady state,the photon blockade in the low-frequency cavity can be obtained,which is consistent with the optimal conditions.Different from the traditional weakly coupled systems,the effective coupling strength of the our scheme can be more significantly enhance than the decay rate of the cavity mode by adjusting the squeezing parameters.The second-order correlation function and cross-correlation function of the two cavities can be reduced obviously under the condition of appropriate squeezing parameters.The results show that the initial weak coupling coefficient can be effectively amplified by introducing OPA and adjusting the squeezing parameters.These results have certain guiding significance for further research of photon statistical properties.Nonreciprocal optical devices have an essential role in practical applications.Nonreciprocal optical devices are those with different physical properties when the incident light is transmitted from different directions.The second scheme proposed in this thesis is to achieve non-reciprocal photon blockade by adjusting the Fizeau shift via using the spin angular velocity in a spinning whispering-gallery cavity.In this system,the elastic deformation of the cavity caused by the drive is considered.Theoretically,such a cavity optomechanical system is also a nonlinear system.By analyzing the energy level structure,the conditions are obtained for achieving nonreciprocal photon blockade,and the second-order correlation function is numerically simulated,which proves the nonreciprocity of photon blockade by analyzing.The results show that when the cavity has fixed counterclockwise spinning,the photon blockade effect happens when we drive the system from one side but disappears when we drive the system from the other side,so the nonreciprocal photon blockade is achieved.The research of this scheme makes it possible to adjust the unidirectional single photon source,which will plays an important role in the future quantum information security.