Quantum Network Regulation By Using Spatial Multiplexing Four-wave Mixing Processes

In recent years,the field of quantum information develops rapidly.Quantum resource is a crucial physical resource to quantum information.It can be used in remote quantum communication,quantum computation,quantum metrology and so on.There are three aspects to improve the performance of quantum resource,which are quantum correlation,channel capacity and the number of light beams.Quantum correlation directly determines the fidelity of quantum communication,while the number of light beams and channel capacity determine the scale of quantum resource and further determine the complexity and information capacity of quantum communication.Conventionally,complex linear and nonlinear successive beam splitting processes are needed to improve the number of beams,which seriously limits the scalability of the scheme.To circumvent these inherent defects,previous attempts have been focused on integrating multiple nonlinear processes into a single device using the concept of multiplexing.In this paper,we will introduce our work in improving the quantum correlation and the number of beams by using four wave mixing processes.The main contents of this paper are as follows:1.We experimantally demonstrate the generation of quantum correlated twin beams by using the four wave mixing process in a hot rubidium vapor,and the covariance matrix of the output beams is measured by using the balanced homodyne detection.We use two different entanglement criteria,i.e.,Duan criterion and positive partial transposition(PPT)criterion,to witness the entanglement property of the twin beams.In addition,we study the influence of different experimental parameters(single photon detuning,two-photon detuning,and temperature)on the entanglement property and find the best experimental parameters.2.We experimantally demonstrate the robustness of bipartite entanglement with respect to losses.Here,we use two different ways to mimic the losses in a realistic quantum communication channel in which the interaction with environment is unavoidable.It is routinely used to attenuate light beam by the combination of half-wave plate and polarization beam-splitter.We find that entanglement can survive for all partial losses in this scenario.In addition,the condition of utilizing razor blade to cut is also studied.Under this condition,disentanglement which is known as entanglement sudden death appears.3.We experimentally demonstrate a scheme to generate spatially separated hexapartite entangled states by means of spatially multiplexing seven concurrent four-wave mixing processes.In addition,we show that the entanglement structure characterized by subsystem entanglement distribution can be modified by appropriately shaping the pump characteristics.Such reconfigurability of the entanglement structure gives the possibility to target a desired multipartite entangled state for a specific quantum communication protocol.Our results here provide a new platform for generating large scale spatially separated reconfigurable multipartite entangled beams.