Quantum Many-Body Dynamics In Rydberg Atomic Ensembles

This thesis investigates quantum many-body physics of atoms and photons in Rydberg atomic ensembles,mainly focusing on the dynamics and exotic phenomena of the system,as well as some potential applications in quantum information processing.First,we study Rydberg dressing induced interaction and its related many-body dynamics in ordered atomic arrays.In the first scheme,we find that the laser dressing gives rise to asymmetric perturbative coupling paths,which induces an effective spinexchange between ground state and Rydberg atoms.Its long-range feature as well as the dynamical tunability facilitates quantum simulation of transport physics unattainable in conventional spin systems,e.g.,topological transport and strongly correlated transport of Rydberg excitons in the presence of decoherence.In the second scheme,we find that Rydberg dressing in systems containing different species of atoms facilitates the construction of a multi-qubit phase gate,with which one can produce a macroscopic quantum superposition state in a single step,and simulate some interesting models in topological quantum computation,such as Kitaev Toric Code model.Coupling photons to Rydberg atomic ensembles can transfer strong atomic interactions to that between photons,supporting the exploration of quantum nonlinear optics.To suppress the loss induced by dissipative photonic interactions in conventional Rydberg EIT(Electromagnetically Induced Transparency)systems,we propose a multi-mode quantum nonlinear optics paradigm.In the presence of multiple photonic modes,a novel coupling-blockade mechanism exists,which could transform the dissipative interaction to a coherent one.Taking Rydberg atomic ensemble as an example,we illustrate several intriguing protocols for manipulating photonic quantum states based on this mechanism,including single-photon based quantum optical switching,deterministic generation of EPR(Einstein-Podolsky-Rosen)entangled photon pairs,and the implementation of an all-optical quantum logic gate.Finally,by combining Rydberg dressing and Rydberg EIT together,we establish a new type of atom-photon interaction: spin-exchange interaction between a single photon and a single atom.Such a spin-exchange collision exhibits both dissipative and coherent features,depending on the interaction strength.For strong interaction,the collision dissipatively drives the system into an entangled dark state of the photon and an atom.In the weak interaction regime,the scattering coherently flips the spin of a single photon in the multi-photon input pulse,demonstrating a generic single-photon subtracting process.An analytic analysis of this process reveals a universal trade-off between efficiency and purity of the extracted photon.We show that for a large input photon number,a perfect single-photon subtractor can be realized by adjusting the scattering rate under a novel phase-matching condition.