Continuous-variable Spatial Multimode Entanglement

Continuous-variable entanglement is one of the most intriguing features of quantum information science.It holds unique quantum correlation,ensuring the efficiency and security of information communication.It has been widely applied in quantum cryptography,quantum key distribution,quantum teleportation,and quantum metrology.Recently,considerable attention has been also given to spatial multimode entanglement due to their potential applications in spatial quantum information procession.Based on the spatial modes of optical light,spatial multimode entanglement expands spatial freedom of degree of entanglement,and provides quantum correlation of spatial quantities,such as position-momentum entanglement,orbital angular momentum entanglement.On one hand,the orthogonality of spatial modes allows us to address the parallel channels individually,greatly improving channel capacity and quantum computation efficiency,and is applicable to quantum ultra-dense coding and multi-channel quantum computation,and parallel quantum information communication.On the other hand,due to the more complex spatial distribution than fundamental mode,the entanglement therefore offers the better sensitivity to spatial information,and can be applied to precision measurements of displacement,tilt,and rotation,and super-resolution quantum imaging,quantum state transfer between optical light and atom.In this thesis,we theoretically and experimentally study continuous variables spatial multimode entanglement.The main contents are as follows:1.We theoretically analyze the relation between the pump profile and the entanglement of high-order mode.By optimizing the spatial profile of the pump,we experimentally achieve the maximum entanglement of high-order spatial modes with lower pump power.We also theoretically analyze the relationship between quadrature entanglement and orbital angular momentum entanglement,and then experimentally realize orbital angular momentum entanglement by transforming HG₀₁-mode quadrature entanglement.The entanglement is measured in the Stokes-operator basis using a self-designed detection scheme.2.We analyze the transformation from the hyper-entanglement of spin angular momentum and orbital angular momentum to spatial Cluster state.We also explore simultaneous resonance of multiple spatial modes in an optical parametric amplifier cavity.We then experimentally perform the generation of spatial Cluster state in a single multimode optical parametric amplifier,and further improve the quality of entanglement by optimizing the pump profile.3.We introduce a method to enhance the measurement of a rotating-angle based on orbital angular momentum?or orbital angular position?squeezed state.The commutation relationship between the orbital angular position and the orbital angular momentum is porposed.With the orbital angular momentum squeezed state,we experimentally perfrom the rotating-angle measurement beyond the quantum limit,that beats the Cramer-Rao bound.4.We theoretically analyze that entanglement produced from type II optical parametric amplifier is very sensitive to the phase matching condition,and introduce a novel technique of a long-term entanglement generation via phase matching condition locking in type II optical parametric amplifier.An optical readout of phase matching condition?or temperature?is obtained via polarization technology.A phase matching temperature locking is experimental performed with optical temperature controller-photothermal effect,resulting in an ultrastable entanglement that lasts up to 30 minutes.The creative works in the thesis are as follows:1.We report the first direct experimental demonstration the Stokes-operator entanglement of continuous-variable orbital angular momentum entanglement.2.We report the generation of a continuous-variable quadripartite square cluster state of multiplexing orthogonal spatial modes in a single optical parametric amplifier.3.We introduce a method to enhance the measurement of a rotating angle with continuous-variable orbital-angular-position squeezed state.4.We introduce a novel technique of a long-term entanglement generation via phase matching temperature locking in type II optical parametric amplifier.