Bunching and Antibunching Effects in a System of N Two-level Atoms

Abstract

The problem of exhibiting bunching and antibunching phenomena for a system of N two-level atoms in interaction with light is investigated. The conditions for the change from bunching to antibunching and vice versa are obtained for resonance, and for time-independent and time-dependent coupling constant. The conditions for the case of resonance and time-independent coupling constant are investigated for both generalized coherent states and squeezed coherent states.     

Higher-generation Schrödinger cat states in cavity QED

Abstract

Higher-generation Schrödinger cat states of the quantized electromagnetic field can be produced in a high-Q cavity, starting from a coherent state, through the passage of prepared Rydberg atoms interacting dispersively across it. These states are natural generalizations of the even and odd coherent states, the N ^th-generations corresponding to specific superpositions of 2 ^N states on a circle in phase space with well defined parity, and present very peculiar properties. Their photon statistics interchange between super- and sub-Poissonian behaviours and the nature of the photon bunching oscillates as the field intensity in the cavity is varied. For higher-generation even states, the minimum value of the Mandel factor almost reaches ?1.0 and the state represents the Fock state |2 ^N ). Squeezing properties and the Wigner function of these higher-generation Schrödinger cat states are also considered.     

Quantum phase distribution by projection synthesis

Abstract

We show how the recently-introduced method of projection synthesis can be applied to find the phase probability distribution for a single-mode field. The realization of such a measurement scheme requires the production of reciprocal-binomial states of light or suitable alternative states. We describe how such states might be produced in the laboratory.     

Phase Fluctuations and Squeezing

Abstract

We investigate the relationship between squeezing and reduced phase fluctuations for various states of the single-mode electromagnetic field, including the strongly-squeezed vacuum and phase states. We find that, although squeezing the fluctuations of the electric field that arise from the vacuum guarantees a more well-defined phase, reducing phase fluctuations does not guarantee a squeezed electric field. We also investigate the evolution of the electric field and its fluctuations for a phase state. Our results show that even though the electric field fluctuations never vanish for a phase state, the times when the electric field changes sign are precisely defined. We also discuss why it is not always possible to attribute physical properties to certain states, such as simple superpositions of phase states.     

Phase properties of coherent phase and generalized geometric states

Abstract

We examine some properties of a class of partial phase states of a single field mode. The quasiprobability distribution function and the phase properties of both the generalized geometric and even geometric states are investigated. The relation between the coherent phase states and the SU(1, 1) coherent states is sought.     

Phase Properties of Squeezed Number States

Abstract

We have studied the phase properties of the squeezed number states by evaluating the expression for the phase probability distribution and the phase variance. In addition, the expression for the photon number distribution of the squeezed phase states has been evaluated.     

Phase States and Their Statistical Properties

Abstract

We study the statistical properties of radiation in the single-mode phase states by evaluating the expression for the photon-counting distribution and its factorial moments. A detailed comparison has been made of the properties of phase states with those of coherent and chaotic states.     

Operational phase distributions via displaced squeezed states

Abstract

We introduce an ‘effective’ phase state with which high-sensitivity phase-shift measurements can be performed. These states can be used for high-precision operational measurements of phase distributions of states which in phase space are localized in regions whose angular width is much larger than π. We propose a method by means of which the corresponding operational phase distribution can be measured.     

Partial phase state as a nonlinear coherent state and some of its properties

Abstract

One introduces the phase state as a nonlinear coherent state. Some of its properties, such as the sub-Poissonian statistics, the squeezing effects, the phase properties in the Pegg-Barnett formalism and the quasiprobability function of the nonlinear coherent states, are calculated and discussed in this paper. The results show that the phase states are squeezed.     

Generation of amplitude squeezed states of light from phase squeezed coherent states

Abstract

We propose a scheme to generate a displaced macroscopic superposition of phase squeezed coherent states by incorporating an optical parametric oscillator (OPO) and a nonlinear Kerr medium in a Mach-Zhender interferometer configuration. We show that the phase squeezed coherent state generated by the OPO evolves into a macroscopic superposition of phase squeezed coherent states on spending a specific amount of time inside a Kerr medium. The phase space displacement is achieved by the interference of the intense reference beam with the signal in the final beam splitter of the interferometer. The noise of the reference beam contaminating the signal is prevented by making this beam splitter highly reflective. We have calculated the photon number uncertainty of the outcoming beam and have shown that it is smaller than the usual amplitude squeezed coherent state's value.     

Superposition of displaced number states and interference effects

Abstract

We introduce a new state of light field by superposing two displaced number states having a phase difference between them in the phase space. The influence of this phase upon its various non-classical properties is investigated, including a discussion on the generation of this state, which contains as particular cases important states studied in the literature.     

A computer‐aided design system for NC part program

Abstract

The electron cyclotron maser is a novel electromagnetic radiation mechanism employed in a new class of microwave devices called the gyrotron. In this expository paper, the electron cyclotron maser interaction is analyzed on the basis of a simple physical model. The purpose of the analysis is to quantitatively elucidate the details of the interaction processes, such as the electron bunching in the cyclotron phase space, the time scale of interest to the interation, the matching condition between the wave and cyclotron frequencies, and the parametric dependence of the electron energy loss rate.     

The Two Energy Scales of Tunneling Spectra of Cuprate Superconductors

The atomically resolved energy gap Δ(r) measured by Scanning Tunneling Microscopy has become a major challenge connecting to the nature of electronic states in cuprates superconductors. More recently, a two-energy-gap structure has been observed by many different experiments. We show that it is possible that the charge inhomogeneity gives rise to a potential barrier between the microscopic regions or grains that are the origin of these gaps. A larger Δ(r) is due to the single-particle bound states and the same potential gives rise to a smaller superconducting gap Δ _d (r). These results support the two-gap scenario and give a clear interpretation to the pseudogap phase.     

The Birth of a Phase-cat

Abstract

We present a recipe for constructing a phase-cat, that is a superposition of two coherent states of identical phase but different amplitudes. The method relies on an effective rotation of an amplitude-cat, that is a superposition of two coherent states with identical amplitudes but different phases. We create the amplitude-cat by a dispersive atom-field interaction and achieve its effective rotation via the combination of two beam splitters and a phase shifter. We optimize the amount of phase narrowing by choosing the appropriate initial atomic superposition and by performing the appropriate delayed measurement of the final atomic coherence.     

Effect of losses on phase noise

Abstract

We study the effect of losses on the phase noise of single-mode field states. The losses are described by the standard loss master equation, and it is used to find an upper bound for the increase in the phase noise as a function of time. We compare the time dependence of the phase noise of an initial coherent state to that of a state that initially has very small phase noise. Both states have the same initial mean photon number. While the small-phase noise state is more susceptible to losses, the difference between its behaviour and that of the coherent state is not great.     

Squeezing in Finite Superpositions of Photon-number States without the Vacuum

Abstract

We show that a finite superposition of photon-number states without the vacuum state can lead to squeezed fluctuations. The properties of these states are discussed.     

Phase distribution and superstructures on the phase correlation of copropagating electromagnetic fields

Abstract

The phase distribution and phase correlation of two initially coherent electromagnetic field modes copropagating through a lossless nonlinear medium are investigated. We show that the number of distinguishable components in the phase distribution depends on the set of nonlinear parameters through a simple relation and that it is connected with the number of entangled field states as well as the number of components that a single field state acquires after propagating through the medium. The phase correlation between the two field modes is shown to exhibit a rich pattern of collapses and revivals, similar to those observed in the quantum inversion of several generalizations of the Jaynes-Cummings model and is related to beats of the various eigenstates of the total Hamiltonian.     

Preparation of W,GHZ, and two-qutrit states using bimodal cavities

Abstract

We show how one can prepare three-qubit entangled states like W-states, Greenberger-Horne-Zeilinger states as well as two-qutrit entangled states using the multi-atom two-mode entanglement. We propose a technique of preparing such a multi-particle entanglement using stimulated Raman adiabatic passage. We consider a collection of three-level atoms in Λ configuration simultaneously interacting with a resonant two-mode cavity for this purpose. Our approach permits a variety of multi-particle extensions.     

Optical and evaporative cooling of caesium atoms in the gravito-optical surface trap

Abstract

We report on cooling of an atomic caesium gas closely above an evanescent-wave atom mirror. At high densities, optical cooling based on inelastic reflections is found to be limited by a density-dependent excess temperature and trap loss due to ultracold collisions involving repulsive molecular states. Nevertheless, very good starting conditions for subsequent evaporative cooling are obtained. Our first evaporation experiments show a temperature reduction from 10 μK down to 300 nK along with a gain in phase-space density of almost two orders of magnitude.