Zeno and Anti Zeno effect for a two level system in a squeezed bath

We discuss the appearance of Zeno (QZE) or anti-Zeno (QAE) effect in an exponentially decaying system. We consider the quantum dynamics of a continuously monitored two level system interacting with a squeezed bath. We find that the behavior of the system depends critically on the way in which the squeezed bath is prepared. For specific choices of the squeezing phase the system shows Zeno or anti-Zeno effect in conditions for which it would decay exponentially if no measurements were done. This result allows for a clear interpretation in terms of the equivalent spin system interacting with a fictitious magnetic field.Comment: 18 pages, 7 figures;added references for section 4;changes in the nomenclatur

Wehrl information entropy and phase distributions of Schrodinger cat and cat-like states

The Wehrl information entropy and its phase density, the so-called Wehrl phase distribution, are applied to describe Schr\"odinger cat and cat-like (kitten) states. The advantages of the Wehrl phase distribution over the Wehrl entropy in a description of the superposition principle are presented. The entropic measures are compared with a conventional phase distribution from the Husimi Q-function. Compact-form formulae for the entropic measures are found for superpositions of well-separated states. Examples of Schr\"odinger cats (including even, odd and Yurke-Stoler coherent states), as well as the cat-like states generated in Kerr medium are analyzed in detail. It is shown that, in contrast to the Wehrl entropy, the Wehrl phase distribution properly distinguishes between different superpositions of unequally-weighted states in respect to their number and phase-space configuration.Comment: 10 pages, 4 figure

Phase properties of a new nonlinear coherent state

We study phase properties of a displacement operator type nonlinear coherent state. In particular we evaluate the Pegg-Barnett phase distribution and compare it with phase distributions associated with the Husimi Q function and the Wigner function. We also study number- phase squeezing of this state.Comment: 8 eps figures. to appear in J.Opt

Dissipation and entanglement dynamics for two interacting qubits coupled to independent reservoirs

We derive the master equation of a system of two coupled qubits by taking into account their interaction with two independent bosonic baths. Important features of the dynamics are brought to light, such as the structure of the stationary state at general temperatures and the behaviour of the entanglement at zero temperature, showing the phenomena of sudden death and sudden birth as well as the presence of stationary entanglement for long times. The model here presented is quite versatile and can be of interest in the study of both Josephson junction architectures and cavity-QED.Comment: 14 pages, 3 figures, submitted to Journal of Physics A: Mathematical and Theoretica

Vacuum Squeezing in Atomic Media via Self-Rotation

When linearly polarized light propagates through a medium in which elliptically polarized light would undergo self-rotation, squeezed vacuum can appear in the orthogonal polarization. A simple relationship between self-rotation and the degree of vacuum squeezing is developed. Taking into account absorption, we find the optimum conditions for squeezing in any medium that can produce self-rotation. We then find analytic expressions for the amount of vacuum squeezing produced by an atomic vapor when light is near-resonant with a transition between various low-angular-momentum states. Finally, we consider a gas of multi-level Rb atoms, and analyze squeezing for light tuned near the D-lines under realistic conditions.Comment: 10 pages, 6 figures; Submitted to PR

Quantum statistical properties of the radiation field in a cavity with a movable mirror

A quantum system composed of a cavity radiation field interacting with a movable mirror is considered and quantum statistical properties of the field are studied. Such a system can serve in principle as an idealized meter for detection of a weak classical force coupled to the mirror which is modelled by a quantum harmonic oscillator. It is shown that the standard quantum limit on the measurement of the mirror position arises naturally from the properties of the system during its dynamical evolution. However, the force detection sensitivity of the system falls short of the corresponding standard quantum limit. We also study the effect of the nonlinear interaction between the moving mirror and the radiation pressure on the quadrature fluctuations of the initially coherent cavity field.Comment: REVTeX, 9 pages, 5 figures. More info on http://www.ligo.caltech.edu/~cbrif/science.htm

Wigner function evolution in self-Kerr Medium derived by Entangled state representation

By introducing the thermo entangled state representation, we convert the calculation of Wigner function (WF) of density operator to an overlap between "two pure" states in a two-mode enlarged Fock space. Furthermore, we derive a new WF evolution formula of any initial state in self-Kerr Medium with photon loss and find that the photon number distribution for any initial state is independent of the coupling factor with Kerr Medium, where the number state is not affected by the Kerr nonlinearity and evolves into a density operator of binomial distribution.Comment: 9 pages, 1 figur

Linear canonical transformations and quantum phase:a unified canonical and algebraic approach

The algebra of generalized linear quantum canonical transformations is examined in the prespective of Schwinger's unitary-canonical basis. Formulation of the quantum phase problem within the theory of quantum canonical transformations and in particular with the generalized quantum action-angle phase space formalism is established and it is shown that the conceptual foundation of the quantum phase problem lies within the algebraic properties of the quantum canonical transformations in the quantum phase space. The representations of the Wigner function in the generalized action-angle unitary operator pair for certain Hamiltonian systems with the dynamical symmetry are examined. This generalized canonical formalism is applied to the quantum harmonic oscillator to examine the properties of the unitary quantum phase operator as well as the action-angle Wigner function.Comment: 19 pages, no figure

Using squeezed field to preserve two-atom entanglement against spontaneous emissions

Tunable interaction between two atoms in a cavity is realized by interacting the two atoms with an extra controllable single-mode squeezed field. Such a controllable interaction can be further used to control entanglement between the two atoms against amplitude damping decoherence caused by spontaneous emissions. For the independent amplitude damping decoherence channel, entanglement will be lost completely without controls, while it can be partially preserved by the proposed strategy. For the collective amplitude damping decoherence channel, our strategy can enhance the entanglement compared with the uncontrolled case when the entanglement of the uncontrolled stationary state is not too large.Comment: 5 figure

Bullying and Victimization in Overweight and Obese Outpatient Children and Adolescents: An Italian Multicentric Study

Objective Being overweight or obese is one of the most common reasons that children and adolescents are teased at school. We carried out a study in order to investigate: i) the relation between weight status and school bullying and ii) the relation between weight status categories and types of victimization and bullying in an outpatient sample of Italian children and adolescents with different degrees of overweight from minimal overweight up to severe obesity. Participants/Methods Nine-hundred-forty-seven outpatient children and adolescents (age range 6.0'14.0 years) were recruited in 14 hospitals distributed over the country of Italy. The participants were classified as normal-weight (N = 129), overweight (N = 126), moderately obese (N = 568), and severely obese (N = 124). The nature and extent of verbal, physical and relational bullying and victimization were assessed with an adapted version of the revised Olweus bully-victim questionnaire. Each participant was coded as bully, victim, bully-victim, or not involved. Results Normal-weight and overweight participants were less involved in bullying than obese participants; severely obese males were more involved in the double role of bully and victim. Severely obese children and adolescents suffered not only from verbal victimization but also from physical victimization and exclusion from group activities. Weight status categories were not directly related to bullying behaviour; however severely obese males perpetrated more bullying behaviour compared to severely obese females. Conclusions Obesity and bullying among children and adolescents are of ongoing concern worldwide and may be closely related. Common strategies of intervention are needed to cope with these two social health challenges