Squeezing in multi-mode nonlinear optical state truncation

In this paper, we show that multi-mode qubit states produced via nonlinear optical state truncation driven by classical external pumpings exhibit squeezing condition. We restrict our discussions to the two and three-mode cases.Comment: 7 pages, 5 eps figures. Revised manuscript. Accepted for publication in Phys. Lett.

Quantum properties of the three-mode squeezed operator: triply concurrent parametric amplifiers

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 $\chi^{(2)}$ nonlinearities. We give a complete treatment for this operator including the symmetric and asymmetric nonlinearities cases. The action of the operator on the number and coherent states are 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 different types of the Schr\"odinger-cat states.Comment: 21 pages, 14 figures; comments are most welcom

Quantum phase properties of two-mode Jaynes-Cummings model for Schr\"odinger-cat states: interference and entanglement

In this paper we investigate the quantum phase properties for the coherent superposition states (Schr\"odinger-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 there is 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.Comment: 23, 8 figure

Single-atom entropy squeezing for two two-level atoms interacting with a single-mode radiation field

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. We show that the more the number of the parties in the system the less the amounts of the nonclassical effects exhibited in the entropy squeezing. The entropy squeezing can give information on the corresponding von Neumann entropy. Also the nonclassical effects obtained form the asymmetric atoms are greater than those obtained form the symmetric atoms. Finally, the entropy squeezing gives better information than the atomic variances only for the asymmetric atoms.Comment: 15 pages, 4 figures, comments are most welcom

Population inversion and stationary lineshapes in a driven two-atom system in a squeezed vacuum

We study the effect of a broadband squeezed vacuum on the dynamics of a two-atom system driven by a near resonant laser field. We show that only in the absence of the driving field are the collective atomic levels selectively populated. Otherwise all collective atomic levels are populated independently of the initial conditions and time. Moreover, we show that the mode correlations, characteristics for the squeezed vacuum, induce a population inversion which, in contrast to the selective population of the collective levels, is not destroyed by the driving field. The stationary lineshapes for the two atomic transitions are also studied. We show that in the squeezed vacuum the population in the upper collective level can exhibit three distinct peaks centred at the frequencies omega and omega +or- Omega , where omega is the atomic transition frequency and Omega is the dipole-dipole interaction potential. The central peak is induced by the mode correlations, whereas the sidebands are induced by the driving field and show a strong dependence on the relative phase between the squeezed vacuum and the driving field. The population in the intermediate level shows a distinct peak at the frequency omega + Omega , and holes at omega and omega - Omega

The effect of finite bandwidth squeezed light on entanglement creation in the Dicke model

We analyse the relation between local two-atom and total multi-atom entanglements in the Dicke system composed of a large number of atoms. We use concurrence as a measure of entanglement between two atoms in the multi-atom system, and the spin squeezing parameter as a measure of entanglement in the whole n-atom system. In addition, the influence of the squeezing phase and bandwidth on entanglement in the steady-state Dicke system is discussed. It is shown that the introduction of a squeezed field leads to a significant enhancement of entanglement between two atoms, and the entanglement increases with increasing degree of squeezing and bandwidth of the incident squeezed field. In the presence of a coherent field the entanglement exhibits a strong dependence on the relative phase between the squeezed and coherent fields, that can jump quite rapidly from unentangled to strongly entangled values when the phase changes from zero to pi. We find that the jump of the degree of entanglement is due to a flip of the spin squeezing from one quadrature component of the atomic spin to the other component when the phase changes from zero to pi. We also analyse the dependence of the entanglement on the number of atoms and find that, despite the reduction in the degree of entanglement between two atoms, a large entanglement is present in the whole n-atom system and the degree of entanglement increases as the number of atoms increases