Quantum States Of Spatially Multimode Light From The Four-wave Mixing Process In Hot Atomic Ensembles

Optical quantum states are indispensable carriers of optical quantum information and important non-classical resources for quantum information processing.For generating optical quantum states,there are two main kinds of quantum systems,i.e.,discrete-variable quantum systems and continuous-variable(CV)quantum systems.Due to the limitation of optical cavities in the traditional schemes for generating CV quantum states,the degree of freedom(DOF)of spatial mode is often ignored in the CV quantum systems.The generation of quantum states of spatially multimode light is crucial to increase the scale of quantum states and meet the diverse needs of quantum information processing.The four-wave mixing(FWM)process in hot atomic ensembles is a promising method for generating optical quantum states.This FWM process can realize strong third-order nonlinearity without the use of an optical cavity,avoiding the limitation of an optical cavity on the spatial modes of optical quantum states.This thesis introduces the generation of quantum states of spatially multimode light from the FWM process in hot atomic ensembles and the application of quantum states of spatially multimode light in the distribution of quantum entanglement and quantum steering.This thesis mainly includes the following four parts:1.Based on the FWM process in hot atomic ensembles,we realize the generation of CV entanglement of large-scale Hermite-Gaussian(HG)modes.The FWM process simultaneously generates 56 pairs of entangled HG modes,which greatly increases the number of entangled spatial mode pairs in the CV quantum systems.Meanwhile,we experimentally verify the existence of CV entanglement between the evolution process from HG mode to Laguerre-Gaussian(LG)mode.These results provide an effective method for constructing high-capacity and deterministic quantum information protocols.2.Based on the FWM process in hot atomic ensembles,we realize the generation of large-scale CV hyperentanglement in three DOFs.The FWM process deterministically generates 216 pairs of hyperentangled modes which are simultaneously entangled in the three DOFs of azimuthal and radial indices of LG modes and frequency.In addition,we also experimentally verify that the system can generate entanglement between superposed LG modes represented by azimuthal and radial quantum numbers.Such large-scale CV hyperentanglement in three DOFs provides an effective scheme to significantly increase the information capacity of CV quantum systems and opens the way for constructing high-capacity parallel and multiple-DOF CV quantum information protocols.3.We realize the self-healing of quantum steering after an obstruction.Due to the self-healing property of the Bessel-Gaussian(BG)beam which is used to distribute quantum steering,the quantum steering destroyed by the obstruction-introduced noise can self-heal after free-space propagation of a certain distance.As a comparison,we experimentally show that quantum steering cannot self-heal after an obstruction under similar experimental conditions when the Gaussian beam is used to distribute quantum steering.These results shed new light on constructing quantum-steering-based quantum information tasks in practical environments and provide a promising platform to study quantum steering.4.We realize the self-healing of multipartite CV entanglement after an obstruction.Due to the self-healing property of the BG beam which is used to distribute tripartite entanglement,the tripartite entanglement destroyed by the obstruction-introduced noise can self-heal after free-space propagation of a certain distance.In addition,we also realize the self-healing of five sets of tripartite entanglement and 10 sets of bipartite entanglement in orbital-angular-momentum-multiplexed optical quantum networks.These results pave the way for constructing obstruction-tolerant high-capacity CV optical quantum networks.