Nonclassical Properties Of Superposed Coherent States Under Action Of Beam Splitter Systems

Recently, with the development of quantum mechanics, quantum information theory has become one of the frontest areas in modern physics and information science. Quantum mechanics is composed of theory foundation of modern physics with relativity. Quantum entanglement has been the focus of much work in the foundations of quantum mechanics. Beyond this fundamental aspect, creating and manipulating of entangled states are essential for quantum information applications. Among these applications are quantum computation, quantum teleportation, quantum dense coding, quantum cryptography, and quantum positioning and clock synchronization. Hence, quantum entanglement has been viewed as an essential resource for quantum information processing.In this thesis, we investigate nonclassical properties of superposed coherent states after optical beam-splitter(BS) systems such as the photon antibunching effect, the single-mode squeezing, the sum squeezing, the difference squeezing, and quantum entanglement. In chapter 2, we briefly present the foundational theory of optical BSs. In chapter 3, we introduce basic concepts on nonclassical properties of optical fields, including the photon antibunching effect, the single-mode squeezing, the sum squeezing, the difference squeezing, and the measure of entanglement.In chapter 4, we study nonclassical effects of a single BS. We show that the entanglement is affected by the BS when the input state of the BS is the entangled coherent state (ECS). In general, the output state of the BS is a ECS when the input state of the BS is a ECS. We find that the entanglement amount of the output state is less than or equal to that of the input state. In particular, when the phase difference isπ/2, 3π/2 between reflected and transmission optical field on the BS, the entanglement amount of the output state is same as the input state, the BS does not change the entanglement. When the reflection coefficient of the BS is equal to the transmission coefficient, and the phase difference is 0,π, 2πbetween reflected and transmission optical field, the output state is an unentangled state, i.e., the entanglement vanishes in the output state. We also investigate nonclassical properties of superposed coherent states related to photon statistical properties such as the single-mode squeezing, sum squeezing, and difference squeezing. We find that the BS can affect the single-mode squeezing and the difference squeezing, but it can not affect the photon antibunching and the sum squeezing effect when the the input state of the BS is the ECS.In chapter 5, we have studied entangling and disentangling functions of optical Fourier multiport devices. It has be shown that these Fourier multiport devices can act as entanglement converters which can not only create entanglement from an unentangled state at the input but also destroy entanglement in an entangled state at the input. Creation and destruction of two-mode and three-mode entangled coherent states (ECSs) have be investigated in detail. The creation and destruction of Bell-type two-mode ECS, GHZ-type and W-type three-mode ECSs have be indicated explicitly through using Fourier four-port and six-port devices, respectively. It should be pointed out that the entangling and disentangling ability of these devices is state-dependent. It depends on the state parameters of the input state.