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Abstract: In this paper, we study the quantum properties of the three-mode squeezed operator. This operator is constructed from the optical parametric oscillator based on the three concurrent χ (2) nonlinearities. We give a complete treatment for this operator including the symmetric and asymmetric nonlinearity cases. The action of the operator on the number and coherent states is studied in the framework of squeezing, second-order correlation function, Cauchy–Schwartz inequality and single-mode quasiprobability function. The nonclassical effects are remarkable in all these quantities. We show that the nonclassical effects generated by the asymmetric case–for certain values of the system parameters–are greater than those of the symmetric one. This reflects the important role for the asymmetry in the system. Moreover, the system can generate particular types of the superposition states. [Copyright &y& Elsevier]

Abstract: In [J.S. Shaari, M. Lucamarini, M.R.B. Wahiddin, Phys. Lett. A 358 (2006) 85] the deterministic six states protocol (6DP) for quantum communication has been developed. This protocol is based on three mutually unbiased bases and four encoding operators. Information is transmitted between the users via two qubits from different bases. Three attacks have been studied; namely intercept-resend attack (IRA), double-CNOT attack (2CNOTA) and quantum man-in-the-middle attack. In this Letter, we show that the IRA and 2CNOTA are not properly addressed. For instance, we show that the probability of detecting Eve in the control mode of the IRA is instead of in the previous study. Moreover, in the 2CNOTA, Eve can only obtain of the data not all of it as argued earlier. [Copyright &y& Elsevier]

For the interaction between a two-level atom and the radiation field in the dipole and the rotating wave approximations, namely, the Jaynes-Cummings model, we obtain a closed form for the atomic Wehrl entropy in terms of the Bloch sphere radius. This explains analytically why the atomic Wehrl entropy has an identical behavior to that of the von Neumann entropy. [ABSTRACT FROM AUTHOR]

In this paper, we study the interaction between two two-level atoms and two nondegenerate cavity modes when the atoms and the field are initially in the atomic superposition states and the pair-coherent state (PCS), respectively. We investigate the atomic inversions, tangles and joint probability distribution. We show that the system can generate long-living entanglement by controlling the values of the interaction parameters. Also we show generally that for obtaining a large amount of entanglement from two qubits interacting with a maximally entangled two-mode state one has to prepare the qubits initially in the decoupled states. Moreover, the system - at certain values of interaction parameters - can generate different types of nonclassical states, such as the mth-photon PCS, statistical mixtures of PCSs and superposition of PCS. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we consider a system of two two-level atoms interacting with a single-mode quantized electromagnetic field in a lossless resonant cavity via l-photon-transition mechanism. The field and the atoms are initially prepared in the coherent state and the excited atomic states, respectively. For this system we investigate the entropy squeezing, the atomic variances, the von Neumann entropy and the atomic inversions for the single-atom case. Also we comment on the relationship between spin squeezing and linear entropy. We show that the amounts of the nonclassical effects exhibited in the entropy squeezing for the present system are less than those produced by the standard Jaynes–Cummings model. The entropy squeezing can give information on the corresponding von Neumann entropy. Also the nonclassical effects obtained from the asymmetric atoms are greater than those obtained from the symmetric ones. Finally, the entropy squeezing gives better information than the atomic variances only for the asymmetric atoms. [Copyright &y& Elsevier]

In this paper, we study the interaction between the two-level atom and a bimodal cavity field, namely, two-mode Jaynes–Cummings model when the atom and the modes are initially in the atomic superposition state and two-mode squeezed vacuum state, respectively. For this system we investigate the atomic inversion, linear entropy and atomic Wehrl entropy. We show that there is a connection between all these quantities. Also we prove that the atomic Wehrl entropy exhibits behaviors similar to those of the linear entropy and the von Neumann entropy. Moreover, we show that the bipartite exhibits periodical disentanglement and derive the explicit forms of the states of the atom and the modes at these values of the interaction times. [ABSTRACT FROM AUTHOR]

For the multiphoton intensity-dependent Jaynes–Cummings model (JCM) described by a two-level atom interacting with a radiation field, we prove that there is a relationship between the atomic inversion and the quadrature squeezing. We give the required condition to obtain best information from this relation. Also we show that this relation is only sensitive to large values of the detuning parameter. Furthermore, we discuss briefly such relation for the off-resonance standard JCM. [ABSTRACT FROM AUTHOR]

Abstract: We prove that the revival-collapse phenomenon occurring in the atomic inversion of the two-photon Jaynes–Cummings model, when the mode is initially prepared in the coherent state and the atom is in the excited state, can be obtained from the evolution of the quadrature squeezing of the four-photon Jaynes–Cummings model. [Copyright &y& Elsevier]

Abstract: We study the evolution of the nth-order single-mode squeezing, sum- and difference-squeezing for a codirectional Kerr nonlinear coupler. We show that squeezing factors can exhibit a series of revival-collapse phenomena and sum-squeezing is stronger than the nth-order () squeezing, whereas difference-squeezing is not a relevant measure. [Copyright &y& Elsevier]

In this paper, we investigate the quantum phase properties for the coherent superposition states (Schrödinger-cat states) for two-mode multiphoton Jaynes–Cummings model in the framework of the Pegg–Barnett formalism. We also demonstrate the behavior of the Wigner (W) function at the phase space origin. We obtain many interesting results such as the existence of a clear relationship between the revival-collapse phenomenon occurring in the atomic inversion (as well as in the evolution of the W function) and the behavior of the phase distribution of both the single-mode and two-mode cases. Furthermore, we find that the phase variances of the single-mode case can exhibit revival-collapse phenomenon about the long-time behavior. We show that such behavior occurs for interaction time several times smaller than that of the single-mode Jaynes–Cummings model. [Copyright &y& Elsevier]

The evolution of the Schrödinger-cat states in a dissipative parametric amplifier is examined. The main tool in the analysis is the normally ordered characteristic function. Squeezing, photon-number distribution and reduced factorial moments are discussed for the single- and compound-mode cases. Also the single-mode Wigner function is demonstrated. In addition to the decoherence resulting from the interaction with the environment (damped case) there are two sources which can cause such decoherence in the system even if it is completely isolated: these are the decay of the pump and the relative phases of the initial cat states. Furthermore, for the damped case there are two regimes, which are underdamped and overdamped. In the first (second) regime the signal mode or the idler mode "collapses" to a statistical mixture (thermal field). [ABSTRACT FROM AUTHOR]

In this communication we investigate the quantum statistics of three harmonic oscillators mutually interacting with each other considering the modes are initially in Fock states. After solving the equations of motion, the squeezing phenomenon, sub-Poissonian statistics and quasiprobability functions are discussed. We demonstrate that the interaction is able to produce squeezing of different types. We show also that certain types of Fock states can evolve in this interaction into thermal state and squeezed thermal state governed by the interaction parameters. [ABSTRACT FROM AUTHOR]

In this communication we investigate the action of a single-mode squeeze operator on the statistical behaviour of different binomial states. For the resulting states (squeezed generalized binomial states) normalized second-order correlation function, quasiprobability distribution functions and the distribution function P(x) associated with the quadrature x are studied both analytically and numerically. Furthermore, the quadrature phase distribution as well as the phase distribution in the framework of Pegg-Barnett formalism are discussed. [ABSTRACT FROM AUTHOR]

In this paper we derive the quantum statistical and dynamical properties of nonlinear optical couplers composed of two nonlinear waveguides operating by second subharmonic generation, which are coupled linearly through evanescent waves and nonlinearly through non-degenerate optical parametric interaction. Main attention is paid to generation and transmission of non-classical light, based on a discussion of the squeezing phenomenon, the normalized second-order correlation function and quasiprobability distribution functions. Initially coherent, number and thermal states of optical beams are considered. In particular, results are discussed with dependence on the strength of the nonlinear coupling relatively to the linear coupling. We show that if the Fock state |1> enters the first waveguide and the vacuume state |0> enters the second waveguide, the coupler can serve as a generator of squeezed vacuum state governed by the coupler parameters. Further, if thermal fields enter initially the waveguides the coupler plays a similar role as a microwave Josephson-junction parametric amplifier to generate squeezed thermal light. [ABSTRACT FROM AUTHOR]

In this article we introduce general class of quantum states, as a single mode vibration of electromagnetic field, sudden squeezed-plus-displaced by a collection of two displacements 180° out of phase. For such class the quantum statistical quantities, such as the second-order correlation function, quasiprobability distribution functions and the photon-number distribution function are examined analytically and numerically. Generation schemes are proposed. Regimes of strongly nonclassical behaviour of such states are demonstrated. [ABSTRACT FROM AUTHOR]

The effect of thermal noise is studied on the statistical behaviour of the superposition of squeezed and displaced number states. In our analysis we have employed the s-parametrized characteristic function. For such superposition states exact expressions for quasiprobability distribution functions, normalized second-order correlation function, photon-number distribution and phase space distribution are obtained and discussed in detail. [ABSTRACT FROM AUTHOR]