| Based on fundamental theory of quantum physics, the main research of the atom-photon system is investigating the nonclassical properties of light field, re-vealing novel quantum effects in the interaction between light and matter, and us-ing the singular characteristics to design versatile quantum devices. As a frontier field of quantum optics and quantum information technology, many novel quan-tum effects are found in atom-photon field. For example, as the ideal platform for coherent interaction between atoms and photons-cavity quantum electrodynamics (cavity QED), scientists have found the Rabi oscillations, vacuum Rabi splitting in cavity QED. In addition, the researchers have also observed atomic material waves light velocity slowing and superluminal phenomena, electromagnetically in-duced transparency, the single atom laser trapping, quantum phase transition from superfluid to Mott insulation, photon blockade effect, the atom Bose-Einstein con-densation and so on. Especially, Feshbach resonance is used to control scattering length in the cold atomic physics, by adjusting the parameter of scattering centers to control quantum state, and it has become a skillful experimental technology. Therefore, quantum physics has undergone a stage from passive observation to active control, and human will enter the era of quantum control.Recently, researchers have paid much attention to the quantum cooperative effect-one of novel quantum effects in quantum physics. Generally speaking, many practical systems are composed of a large number of similar subsystems, and there is interaction between subsystems, so the system of macroscopic properties is not the simple addition of each subsystem of the microscopic properties. In fact, all the subsystems will correlate with each other in a certain way, making the whole system macroscopic ordered. This is the so-called "cooperative effect" [1]. In atom-photon system, there are many effects of quantum interference can be considered as cooperative effects, such as superradiance and subradiance, collective Lamb shift, electromagnetically induced transparency, etc.The quantum cooperative effects provide a useful way to observe the quan-tum interference effect. Under certain conditions, we can make many particles coordinate collaboratively, and prepare in a single quantum state. When numer-ous particles’phase satisfy the matching conditions, they will form a macroscopic quantum state [2]. By using this method, we can eliminate the environmental effects caused by the random phase, and make them exhibit abundant quantum effects. When plenty of particles cooperative coherent aggregate in a single quan-tum state shall amplify its quantum effects, and fancy quantum properties will be rich brilliant and wonderful.From the perspective of quantum information, how quantum correlations and quantum entanglement affect the cooperative effect is a very interesting issue for researchers. In this thesis, we focus on the collective effect of few body system, and study cooperative effect and coherent control in atom-photon system. To be specific, we discuss superradiance and subradiance radiant properties of two separated atoms, two photon localization in a coupled-cavity-array and so on.In Chapter 1, we introduce background materials about present subject under our consideration as well as the significance of atom-photon system.In Chapter 2, we give a brief introduction about the basic theory of quantum optics and quantum information in atom-photon system, emphasising on intro-ducing quantum entanglement and quantum correlation. Then we introduce three common methods of measuring the nonclassical properties of light field:second-order correlation functions, squeezed property and the negative of the Wigner function.In Chapter 3, We investigate collective radiant properties of two separated atoms in X-type quantum states. We show that quantum correlations measured by quantum discord (QD) can induce and enhance superradiance and subradiance in the two-atom system even in the absence of interatomic quantum entanglement. We also explore quantum statistical properties of photons in the superradiance and subradiance by addressing the second-order correlation function. In partic-ular, when the initial state of the two separated atoms is the Werner state with non-zero QD, we find that radiation photons in the superradiant region exhibit the nonclassical sub-Poissonian statistics and the degree of the sub-Poissonian statistics increases with the QD amount increasing, while radiation photons in the subradiant region have either the sub-Poissonian or super-Poissonian statistics de-pending on the amount of QD and the directional angle. In the subradiant regime we predict the QD-induced photon statistics transition from the super-Poissonian to sub-Poissonian statistics. In addition, we also study the squeezing feature of photons in superradiance and subradiance region, and found that they could not exhibit any squeezed properties, such as first and second order or higher order squeezed property. When one of the atoms accelerates, while the other is mo-tionless, the superradiance characteristics will be weakened, and the subradiance properties are enhanced. These results shed a new light on applications of QD as a quantum resource, which play an important role in quantum computation and quantum information.In Chapter 4, based on one-dimensional coupled-cavity-array without impu-rity atom, we have studied photonic transport properties and TPD dynamics in the two-photon CCA when two entangled photons are initially injected into two nearest-neighbor coupling cavities in the form of two-photon NOON-type states which are superposition states of two-photon states |2,0) and |0,2). We have investigated the TPD dynamics by introducing the concept of the TPD degree for the initial two-photon entangled states |ψ>=cos θ|2,0)+sin θ|0,2). It has been found that photonic transport dynamics in the two-photon CCA exhibits the entanglement-enhanced TPD phenomenon. It has demonstrated that the CCA can realize the localization-to-delocalization transition for two entangled photons. Based on the foundations, we give a further discussion on the relevant dynam- ics properties of increasing capacities and the products of increasing capacities, when considering that the initial state (|2,0) and |0,2)) for a NOONtype entangle-ment has the relative phase. Due to the concept of two-photon-localization degree, analysis, it is found that photonic transport dynamics in the two-photon CCA ex-hibits the quantum ratchet phenomenon of two-photon delocalization effect, i.e., entanglement-enhanced (-suppressed) two-photon delocalization (TPD). The TPD degree reaches the maximum (minimum) value when the entanglement amount be-comes 1 and initial relative phase two-photon states|2,0) and|0,2) is 0 (π). It is shown that the two-photon CCA can realize a transition from entanglement-enhanced mode to entanglement-suppressed mode when relative phase of two nearest-neighbor coupling cavities changes from 0 to π. It is worthwhile to point out that the entanglement-enhanced TPD phenomenon is a two-photon coopera-tive effect induced by quantum interference of two entangled photons due to the initial quantum entanglement. The entanglement-enhanced TPD vanishes in the absence of entanglement between two photons.In Chapter 5, we propose an XKNL-based scheme for performing a two-photon polarization-parity QND measurement with near unity efficiency. It has been shown that two-photon parity check has widespread applications in optical quantum information processing. In recent years much effort has been made to im-plement nondestructive two-photon parity detection using cross-Kerr nonlinearity (XKNL) effect. We here put forward an XKNL-based scheme for nearly deter-ministic two-photon parity detection without destroying the photons, in which the required cross-Kerr phase shift could be much (even several orders of magnitude) smaller than that required for previous schemes. The scheme utilizes a ring cavity fed by a coherent state beam as a quantum information bus which interacts with one of the two path modes of two polarized photons through a cross-Kerr medium. The measurement outcome of the bus mode reveals the polarization-parity of the two photons.In Chapter 6, we present a summary and outlook. |
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