Generation Of Multipartite Entangled States Based On Optical Frequency Comb

Quantum entangled states is an important resource for quantum computation and quantum communication,the preparation of quantum entangled states that can be maintained for a long period of time is a core element for realizing various quantum information processing,such as quantum teleportation,quantum dense coding,quantum cryptography,and quantum computation,etc.In recent years,various systems and schemes for generating quantum entangled states have been studied widely.Bipartite and multipartite entangled states have been experimentally generated and can be applied in different protocols of quantum communication.With the rapid development of quantum communication technology,constructing quantum information networks with high transmission speed and high channel capacity,which is an important research direction in domestic and foreign.The optical frequency comb refers to a good phase relationship from a series of frequency space equidistant lines to each spectral line,which has the characteristics of multi-channel,multi-frequency points and high channel capacity.It is a perfect tool for constructing quantum communication network and realizing high-precision measurement.In this paper,we mainly studied the generation of continuous variable multipartite entanglement based on optical frequency combs.The Hamiltonian and Langevin equations of light fields are given,we can obtain the steady-state solutions and the quadrature component of the fields through a series of calculation.Under the condition of experimentally feasible parameters,by using the relative criterion to confirm existence of entanglement,in addition,we also discuss the entanglement relying on relevant parameters.Multipartite entanglement based on the optical frequency comb is a scheme for generating entangled states at multiple frequency points.Combining the wavelength division multiplexing(WDM)technology,optical frequency comb can improve the channel capacity and transmission rate.It has unique value in the fields of multi-channel quantum key distribution,multipartite parallel quantum information processing,and is helpful to achieving efficient quantum communication and quantum computation.The main work are as follows:(1)We put forward a theoretical scheme to generate 31 continuous variable tripartite entangled states based on optical frequency combs,and investigate the spectral characteristics of three frequency combs.The center wavelengths of the three combs are designed as 852 nm,780nm and 1550 nm,which corresponding to transition line of Cs and Rb atoms and fiber communication wavelength respectively.The sufficient and necessary criterion(PPT)is used to investigate the entanglement properties of 31 tripartite modes.Based on this scheme,with the technology of WDM,high efficiency and high capacity can be achieved for quantum communications and quantum dense coding.This scheme has practical value for quantum communication and quantum information storage in future.(2)We put forward a theoretical scheme for generating of continuous variable quadripartite entangled states based on optical frequency comb,and investigate the entanglement characteristic of two pairs of two-photon outputs from dual-port OPO cavity.The VLF criterion is used to verify the existence of quadripartite entangled states.The quadripartite entangled states generated by this scheme is stronger,and the method and device are relatively simple.Therefore,this scheme have high experimental feasibility.(3)We put forward a theoretical scheme of improving squeezing level by a cascaded frequency doubling system,and investigate the squeezed characteristic of harmonic fields.The results show that the squeezing of the forth harmonic field is higher than the second harmonic field obviously.We also investigate the relation of harmonic fields relying on the pump parameter.The system not only can enhance the squeezed level of light fields,but also can achieve shorter wavelength squeezed light,which has certain practical value for quantum storage,quantum precision measurement and so on.