The Experimental Research On Continuous Variable Quantum Simulation And Fight Against Quantum Decoherence In Quantum Communication

Quantum information science is a new subject recently developed on the base of quantum mechanics and classical information technology.Quantum information encode,transmition and computation are implemented based on utilizing fundamental principles of quantum mechanics and novel characteristics of quantum systems,such as quantum parallelism,quantum entanglement and quantum no-cloning.Quantum information is able to break through the limit of classical information systems,to achieve higher capacity of information,information security,computing speed and detection accuracy.There are rich contents to be studied in the developing great field for information science and technology.It is necessary to build a quantum information network consisting of quantum nodes and quantum channels for practical applications.In quantum nodes,processing of quantum information including storage,computing,simulation and error correction and so on is implemented by means of quantum resources.Quantum channels are used for transmission of quantum states and transfer of quantum messages.In quantum simulators,dynamic behaviors of comples quantum systems are simulated by controllable quantum systems,which have the potential to tackle some intractable problems for classical computers.Quantum simulators are expected to open feasible paths for exploring new physics,chemistry,biology phenomena.Since continuous quatum systems are convenient to be applied to effectively simulate continuous evolution of quantum systems,following the rapid development of qubit simulation,quantum simulators with continous quantum variables have been also considered.Our group achieved an experiment of continuous variable quantum simulation,which provides a new possibility to implement quantum simulation.In processes of quantum information transmission and processing,decoherences unavoidably reduce fidelities of quantum states and quantum information.The losses and noises in the quantum channels are main causes to result in decoherence.With the non-Markovian environment,we accomplished an experiment against the deconherence in quantum channels.Quantum steering is another important quantum recourse besides quantum discord and quantum entanglement,a distinguishing feature of which is the directional characteristics.The study on quantum steering is of great significance not only for fundamental physics,but also for the applications in quantum information processing.During my Ph.D study,our group achieved the experimental investigations on continuous variable quantum simulation,against quantum decoherence and multipartite Guassian quantum steering.The main completed works are as following:1.We design and realize a quantum simulator consists of quantum optical field and logic operations,based on which we complete dynamic simulation of time evolution of quantized harmonic oscillators in closed and open systems,respectively.According to the relationship between physical variables of an atomic essemble and quantized harmonic oscillators,we analytically simulated time evolution of physical variables of an atomic essemble in the process of spontaneous emission.For the first time the quantum simulation is implemented with quantization optical field and quantum logic operations.2.We accomplished the experimental researches on the transmission and revival of quantum states.Since quantum states transmitting in the quantum channels must be changed by losses and noises,we analysed the affects on the transmitted squeezing states and tripartite Greenberger-Horne-Zeilinger entangled states induced by losses and noises in the channels,and firstly demonstrated that excess noises may destroy squeezing and entanglement totally.We simulated the non-Markovian environment with a correlated noisy channel,and realized the revival of squeezing and entanglement for transmitted quantum states by means of a correlated channel.3.We studied the Guassian quantum steering in continuous variable four-mode square cluster entangled states.Quantum steering is another important quantum correlation besides quantum entanglement and Bell-nonlocality.It has the directional property and satisfies the monogamy relation.We quantify the steerability of a four-mode optical state with the reconstructed covariance matrix.For the first time the distribution of quantum steering in a continuous variable four-mode square cluster entangled state and the monogamy relation of quantum steering are theoretically and experimentally studied.The physical features of cluster states are deeply understood through the experiments also.The creative works are as follows:1.We implemented the quantum simulation with quantum optical field and logic operations firstly.2.We simulated the non-Markovian environment with a correlated noisy channel,and realized the revival of squeezing and entanglement of transmitted quantum states.3.We studied the distribution of quantum steering in continuous variable four-mode square cluster entangled state and demonstrated the monogamy relation of quantum steering for the first time.