Generation Of Multipartite Entangled State From Cascaded Four-wave Mixing Processes

One of the most important and incredible concept in quantum mechanics is quantum entanglement.It is necessary to study the basic properties of quantum entanglement for the better understanding of this concept and realizing various applications exploiting quantum entanglement.This thesis contains the following four aspects based on quantum entanglement:1.We demonstrate the first experimental realization of tripartite entanglement in cascaded four-wave mixing processes.We use high power Gaussian laser as pump beam to pump cascaded rubidium atom ensembles,where four-wave mixing processes take place and tripartite Gaussian state is generated.To experimentally study its entanglement property,we exploit balanced homodyne detection technique to measure the amplitude and phase quadratures of the fields and then construct the CM.The entanglement property of the state is studied using the PPT criterion.2.We use spatial light modulator to transfer Gaussian beam into LG beam.We use such LG beam as probe beam to seed cascaded four-wave mixing processes,where OAM multiplexed tripartite entanglement is generated.It is proven experimentally that there exist 9 sets of tripartite entangled states and 20 sets of bipartite entangled states.3.To further study properties of multipartite entanglement,we exploit symmetric cascaded four-wave mixing processes to generate quadripartite entangled state.Experimentally we measure amplitude and phase quadratures with balanced homodyne detection and then construct the CM,which is used to analyze the quantum entanglement properties of the state.In additon,we study robustness of the present quadripartite entangled state.4.Quantum steering is another incredible phenomenon in quantum mechanics and differs from entanglement due to its asymmetric nature.Most of the studies of quantum steering is confined in bipartite system.Extending steering to multipartite system can help us understand the distribution of such quantum correlation among different subsystems and can bring about new researches.Based on the device before,we generate quadripartite Gaussian state and construct the CM.Then we exploit criterion for quantifying Gaussian EPR steering to demonstrate various present multipartite EPR steering.In addition,we study the robustness of the quadripartite EPR steering.The present experimental results form the basis for realizing asymmetric quantum information protocols exploiting multipartite EPR steering.