Experimental Demonstration Of Quantum Information Protocol In An Atomic Ensemble Four-wave Mixing Process

Quantum information science is a new field full of vitality.It combines information technology with the basic theory of quantum mechanics and processes quantum information by using the unique properties of quantum systems,such as quantum parallelism,quantum non-cloning,quantum entanglement,et al.Since the birth of this subject,many quantum information protocols have been proposed,such as: quantum key distribution,quantum teleportation,quantum dense coding,et al.These quantum information protocols use quantum states to transfer and exchange information,and show the potential to surpass classical information systems in terms of computing speed,information security,channel capacity,and detection accuracy.In recent years,many quantum information protocols have been experimentally confirmed,and they have begun to develop towards the practical goals of long-distance,large-capacity,and highsecurity.Quantum systems that implement quantum information protocols can be divided into two categories: discrete variables and continuous variables.The eigenstates of discrete variables have separated spectral structures,and the eigenstates of continuous variables have continuous spectral structures.The quantum communication with longdistance,large capacity,and high security in the discrete variable quantum information system has been preliminarily verified in experiments.The development of continuous variable quantum information system in this direction is relatively lagging behind,however,continuous variable systems have the advantages of deterministic preparation and transformation of quantum states,which have aroused extensive research interest in recent years.In this thesis,by using the parametric amplifier based on the four-wave mixing process of the atomic ensemble as a continuous variable quantum resource,we achieve the following four quantum information protocols around the above practical quantum communication goals:1.In experiments,we use the orbital angular momentum multiplexed continuous variable entangled states,combined with an all optical quantum teleportation protocol,to achieve the deterministic multi-mode quantum teleportation in parallel 9 channels.First,we use the spatial multimodality of four-wave mixing to generate 11 sets of entanglements in a series of orthogonal orbital angular momentum modes.Then we use the orbital angular momentum mode matched parametric amplifier to realize the multimode quantum state conversion.Finally,we completed the experimental verification of multimode quantum teleportation.Our scheme provides an example for high-capacity continuous variable quantum information processing,and realizes multi-mode quantum teleportation in the field of continuous variable quantum information for the first time.2.In experiments,we construct a multifunctional all-optical quantum state transfer machine by using a gain-tunable parametric amplifier,a beam splitter and an entanglement source.Through this all-optical quantum state transfer machine,we experimentally demonstrated a partially disembodied quantum state transfer protocol,which can connect the all-optical quantum teleportation protocol and the optimal 1?N coherent state quantum cloning protocol.Therefore,these three protocols with different physical nature and functions can all be implemented in the same all-optical system.In particular,we proved that under the same entanglement strength,compared with alloptical quantum teleportation,the partially disembodied quantum state transfer protocol can improve the fidelity of state transfer.This all-optical quantum state transfer machine paved the way for the realization of a multi-functional quantum information system.3.In experiments,we construct a continuous variable coherent state cloning machine by using a parametric amplifier based on the four-wave mixing process and optical beam splitters.Through this cloning machine,we experimentally realized the continuous variable optimal N?M coherent state quantum cloning and proved that the increase in the number of initial states and the decrease in the number of clone copies can improve the fidelity of cloning.This work is the first time to realize all-optical N?M quantum cloning in the continuous variable field and has the potential to build a highfidelity quantum network4.In experiments,we construct a low noise phase-sensitive amplifier based on the four-wave mixing process of the atomic ensemble.With this phase-sensitive amplifier,we experimentally realize the low noise entanglement amplification.Compared with the conventional phase-insensitive amplifier,our results show that the phase-sensitive amplifier can amplify entanglement better under the same noise.This scheme can be used to recover the intensity information of the entangled state in the loss channel and has potential applications for the long-distance transmission of continuous variable quantum states.