Time Evolution for a Three-level Atom in Interaction with Two Modes

Abstract

The problem of a three-level atom and two modes is treated quantum mechanically and constants of motion are obtained. The evolution operator is calculated for the case of exact two-photon resonance. The probability distribution functions are calculated for the atom in one of its states. Some statistical quantities of the fields and the atomic systems are given. The interaction with squeezed light is investigated.     

Cavity field spectrum for multiphoton Jaynes-Cummings model

Abstract

The field spectra in an ideal cavity for the multiphoton Jaynes-Cummings model are studied. The analytical expression for the spectrum is obtained from the finite double-Fourier transform of the two-time field correlation function. The spectral differences between the initial coherent and initial thermal states are discussed, and the comparisons between the field spectra and atomic emission spectra for k = 2, 3 and 4 are presented. It is shown that the kth power of the photon annihilation operator and atomic lowering operator are subjected to identical forms of a second-order differential equation, in which the coefficients consist of the constants of motion. The field spectrum in the cavity and the emission spectrum of the atom for the initial vacuum state are compared.     

N-level Atom Interacting with Single-mode Radiation Field: An Exactly Solvable Model with Multiphoton Transitions and Intensity-dependent Coupling

Abstract

We study the dynamics of an N-level atom coupled in a lossless cavity to a single-mode near-resonant quantized field. The atomic levels are coupled by the multiphoton transitions and the coupling constants between the field and the atomic levels are supposed to be intensity dependent. We find the exact solution for the state vector describing the dynamics of the atom-plus-field system. As an illustration we use the model for studying (i) the time evolution of the atomic occupation probability with the initially coherent field and (ii) the light squeezing, when the cavity field is initially in the vacuum state and the atom is prepared in the atomic ‘coherent state’ (a superposition of atomic states).     

Quantum effects in the transient dynamics of a many mode Jaynes-Cummings model

Abstract

Phenomenology and mechanisms of energy exchange, due to induced atomic processes of absorption and emission, are investigated in the evolution of a two-mode Jaynes-Cummings model. One field mode is initially in a highly coherent populated state and the other one is initially empty. The field mode exchanges energy with the atom by two mechanisms, related to very different atomic dynamics, which operate in complementary phases of the system evolution. One mechanism determines the energy exchanges which involve only the populated mode and the atom. The other is responsible for mode-mode photon exchanges and becomes relevant when the first mechanism is quenched. Thus there is no competition between the atomic emission in the empty mode and processes involving the atom and the highly populated mode. Quantum features related to entanglement of atom and field states are discussed. Cooperative effects between the two field modes and their incompatibility with the predictions of neo-classical theory are evidenced.     

Influence of inhomogeneous broadening on group velocity in coherently pumped atomic vapour

Abstract

We studied experimentally the influence of thermal atomic motion on light propagation in a vacuum atomic vapour cell above room temperature. We found that atomic motion introduces sizable changes in the spectral properties of the medium, such as dispersion and absorption, if the conditions for coherent population trapping are fulfilled. In particular, studying the group delay of light in the atomic vapour, we confirm the theoretical predictions of Kocharovskaya et al. (2001, Phys. Rev. Lett., 86, 628) and demonstrate that a coherent atomic medium has light dragging abilities large enough to make feasible the realization of frozen light based on atomic motion. We also demonstrate that dragging can be observed in measurements of the electromagnetically induced transparency resonance width, as well as in group delay measurements.     

Effective Dipole Squeezing in the Non-degenerate Two-photon Jaynes-Cummings Model with Superposition State Preparation

Abstract

Effective dipole squeezing in the non-degenerate two-photon Jaynes-Cummings model for atom and fields initially prepared in superposition of states is investigated. It is shown that the squeezing can be exhibited in certain periods of time but it cannot be achieved for atomic spontaneous radiation processes.     

Two-level atom and multichromatic waves in a lossless cavity

Abstract

In this paper, we shall examine a generalized version of the Jaynes-Cummings model in which a two-level atom moves in a lossless cavity and is coupled to multichromatic waves with general frequencies and coupling constants. We shall show that both the motion of the atom and the photon conversion between multichromatic waves are dynamically correlated. Using the semiclassical approximations introduced in a previous paper, we obtain the equations which describe the dynamics of this quantum system and discuss the solutions in several special cases. In particular, we point out that the motion of the atom may be controlled by the electromagnetic modes, and vice versa, that is the amplitudes and phases of the electromagnetic fields in the cavity may also be determined by the position of the atom.     

State Evolution in the Two-photon Jaynes-Cummings Model with Initial Squeezed Vacuum and Chaotic Fields

Abstract

An approximate treatment is given for the state evolution in the two-photon Jaynes-Cummings model with initial squeezed vacuum and chaotic state fields. Both initially pure and mixed atomic states are examined. Interesting features such as the evolution of the atom into unique pure states and the recurrence of the initial atomic states at certain times are found. Effects of the dynamic Stark shifts on the system state evolution are also studied.     

Atom probe characterisation of high temperature materials

Abstract

An atom probe is capable of quantitatively analysing materials at the atomic level. Modern atom probes are derived from the field ion microscope, and are coupled with time-of-flight mass spectrometers, permitting identification of individual atoms. The introduction of position-sensitive detectors enables the reconstruction of a small volume of the sample owing to simultaneous determination of the x, y, and zcoordinates and the mass to charge ratios of individual atoms. This paper focuses on the application of atom probe techniques to the microstructural analysis of high temperature materials. Illustrations include carbide precipitation in creep resistant power plant steels and analyses of model and commercial multicomponent nickel based superalloys. It is demonstrated that atom probe field ion microscopy and atom probe tomography are valuable techniques in the development and understanding of technologically important alloys for high temperature service.     

Permanently disentangled states of atom–field system via spontaneously generated coherence

Abstract

The effect of spontaneously generated coherence on evolution of the entanglement between a driven four-level Y-type atom and its spontaneous emission field is studied. We have shown that the atom will be entangled to its spontaneous emission field due to spontaneously generated coherence and coherent population trapping at the steady state. It is found that the degree of entanglement strongly depends on the initial atomic state. So, it can be controlled by the pumping laser pulses used for preparing an initial atomic system. More interestingly, the atom–field system can be found in a permanently disentangled state for a properly prepared atom.     

Population trapping with quantized fields in two-channel models of atomic excitation

Abstract

In this paper, we study several models of two-channel atomic excitation involving quantized fields and search for field states that result in the trapping of the atomic population in a single bare state. This trapping is a result of quantum interference between the two channels. We study the following models: a two-level atom resonantly interacting with two quantized field modes, a two-level atom with competing one and three photon transitions, and a Raman coupled model containing both Stokes and anti-Stokes fields. We find a great variety of trapping states of the field, some of the states being highly non-classical. The effects of dissipation on the stability of the trapping states are discussed and a method for generating some of the states is presented.     

Deflection of Atoms by Circularly Polarized Light Beams in Triple Laue Configuration

Abstract

A new type of atomic interferometer is discussed, in which atoms with two ground-state Zeeman sub-levels m = ± 1, and an excited state with m = 0, pass through three laser interaction zones—each comprising two counter-propagating waves of opposite circular polarization with a large detuning from resonance. By means of Raman-type transitions between the two ground-state levels, which convey a recoil of two photon momenta, the atomic wave function is split up into two coherent spatially separated branches, and subsequently recombined. In this system, conservation of energy and momentum leads to a strong correlation between the external centre of mass motion and internal magnetic degrees of freedom. As a consequence, the paths within the interferometer are tagged by the internal quantum number m. As an example, we calculate the position and momentum distribution function of a helium atom on its way through the interferometer.     

Atomic Dipole Dynamics in the Thermal Quantized Cavity Field

Abstract

We consider the resonant interaction of a two-level atom with a thermal state of the quantized field in a lossless cavity. Non-trivial dynamics of the atomic dipole moment and the field quadrature components arise if the atom is initially prepared in a coherent superposition of its upper and lower states. In particular, the initial thermal field state acquires a well defined phase that corresponds to the initial phase of the superposition atomic state. Population trapping occurs when the intensity grows.     

Preparation of two-mode anticorrelated photon-number state via atom de Broglie wave deflection

Abstract

It is shown that the deflection of an atom de Broglie wave at two adjacent cavities containing non-resonant weak fields can yield a highly entangled quantum state of the atom–field system in which discernible atomic beams are entangled to internal states of the atom and to two-mode photon-number states of the fields. Two-mode anticorrelated entangled photon-number states characterized by the total photon number can be prepared by the detection of the atom in given directions of the propagation.     

Collapse-revival Phenomenon in the Jaynes-Cummings Model Interacting with the Multiphoton Holstein-Primakoff SU(2) Coherent State

Abstract

We have analysed the behaviour of the atomic population inversion of the two-level atom interacting with a single-mode field initially prepared in the multiphoton Holstein-Primakoff SU(2) coherent state. It is shown that the behaviour of the atomic inversion depends on the parameters characterizing the initial state of the field. In particular, the atomic inversion can exhibit periodical oscillations as well as the collapse-revival phenomenon.     

Field oscillations in a micromaser with injected atomic coherence

Abstract

The electric field in a lossless, regularly-pumped micromaser with injected atomic coherence can undergo a period-two oscillation in the steady state. The field changes its value after a single atom passes through the micromaser cavity, but returns to its original value after a second atom travels through. We give a simple explanation for this phenomenon in terms of tangent and cotangent states. We also examine the effect of cavity damping on this steady state.     

Monte Carlo investigation of an atom laser with a modulated quasi-one-dimensional cavity

Abstract

The dynamics of a recently proposed atom laser scheme based on a modulated quasi-one-dimensional atom cavity are investigated. A three-mode model is developed which includes the effects of dipole–dipole collisions as well as pump and loss mechanisms. It is shown that the Monte Carlo wavefunction simulation technique is superior to a direct solution of the resulting master equation because of the existence of constants of motion which are present in the Monte Carlo wavefunctions but not in the full density operator. Under suitable parameter choices, the solution to the master equation leads to Poissonian atom statistics in the occupation of a single-atomic-cavity mode, analogous to the photon statistics of the optical laser. A threshold behaviour is predicted as the losses are varied relative to the gain for the laser mode.     

Controlling decoherence of a two-level atom in a lossy cavity

Abstract

By use of external periodic driving sources, we demonstrate the possibility of controlling the coherent as well as the decoherent dynamics of a two-level atom placed in a lossy cavity. The control of the coherent dynamics is elucidated for the phenomenon of coherent destruction of tunnelling (CDT), i.e. the coherent dynamics of a driven two-level atom in a quantum superposition state can be brought practically to a complete standstill. We study this phenomenon for different initial preparations of the two-level atom. We then proceed to investigate the decoherence originating from the interaction of the two-level atom with a lossy cavity mode. The loss mechanism is described in terms of a microscopic model that couples the cavity mode to a bath of harmonic field modes. A suitably tuned external cw-laser field applied to the two-level atom slows down considerably the decoherence of the atom. We demonstrate the suppression of decoherence for two opposite initial preparations of the atomic state: a quantum superposition state as well as the ground state. These findings can be used to decrease the influence of decoherence in qubit manipulation processes.     

Control of population and atomic coherence by adiabatic rapid passage and optimization of coherent anti-Stokes Raman scattering signal by maximal coherence

Abstract

Robust control of atomic coherence and population transfer among Zeeman sublevels in the ground states of rubidium atom is investigated using adiabatic rapid passage in a nanosecond time scale, which is smaller than the lifetime of first excited Rb. It is shown that a slight change in the pump pulse time delay relative to the Stokes pulse leads to a significant modification of atomic coherence and population transfer, consequently having remarkable impacts on the generation of coherent anti-Stokes Raman scattering (CARS) signal and probe pulse absorption. This coherent control of quantum state and population is presented by numerical simulations based on self-consistent set of density matrix equations and Maxwell equations as well as experimental demonstration in rubidium atom with different atomic densities. Experimental observations are in good agreement with numerical calculations.     

The Interaction of Displaced Number State and Squeezed Number State Fields with Two-level Atoms

Abstract

The time-evolution of a single two-level atom in a single-mode high-Q cavity is sensitive to the quantum fluctuations of the cavity radiation field and to its photon statistics: this sensitivity is realizable experimentally in the Rydberg atom micromaser. We study the effects of the interaction of a two-level atom with two new non-classical radiation fields: the squeezed number state and the displaced number state realizable by nonlinear and linear transformations of field number states which have an initially precise occupation number. The time-varying field fluctuations caused by the atomic interaction are described using the Q-function quasi-probability.