Dressed-atom Approach Research Articles

Coherent beam splitter for atoms based on a bichromatic standing light wave

We propose a new coherent atomic beam splitter that is based on the induced redistribution of photons in the intense field of two collinear standing waves with different frequencies. In the dressed-atom approach, we show that this scheme can provide a clear large-angle splitting into two components without being restricted to the Raman-Nath regime.

Jaynes-Cummings model with stochastic fluctuations

The dynamical evolution of the Jaynes-Cummings model in the presence of stochastic phase fluctuations in the atom-field coupling is studied. A solution for the phase-averaged density operator is obtained in the secular approximation using the dressed atom approach.

Laser-noise suppression in the dressed-atom approach. I. Fluctuations in a regularly pumped laser.

The dressed-atom approach to the fluctuation problem in lasers is described. Such an approach allows one to analyze the fluctuations in various kinds of laser models. The intensity fluctuations in a regularly pumped laser are considered in the framework of the dressed-atom approach. The Fokker-Plank equation for the field density matrix is derived from first principles without heuristic assumptions. An alternative interpretation of the noise suppression in the regularly pumped laser is given. It is based upon the nonstationary picture for atomic variables. In such a regime the statistics of the output laser field may be controlled by the input statistics of the atomic initial conditions. It is the regular pump that provides the best input statistics. In the latter case the atoms are essentially nonstationary and coherently oscillate at the Rabi frequency. They are treated in a framework of the time-dependent picture in spite of the short atomic lifetime as compared with the cavity mode lifetime. The nonstationary version of the dressed-atom approach is employed to treat the regular pump case. It is demonstrated that a coherent coupling of the Rabi oscillations in the quadratic dressed-atom terms gives rise to a survival of a linear inverse proportional dependence of the atomic correlation functions upon field intensity. This survival in turn accounts for the anomalously large dressed-atom contribution to the fluctuations. Our results are in quantitative agreement with those of other approaches.

Laser-noise suppression in the dressed-atom approach. II. Minimization principle for conventionally pumped lasers.

The intrinsic property of laser systems with many internal degrees of freedom to generate a squeezed light is studied. The dressed-atom approach to fluctuations, described in the preceding paper [Khazanov, Koganov, and Shuker, Phys. Rev. A 48, 1661 (1993)], is employed. A minimization principle which governs noise quenching in laser systems is described comprehensively. This principle allows one to avoid complicated quantum-mechanical calculations to assess the squeezing capacity of the system. It is shown that noise in a laser system can be decomposed into noise states. These states interact coherently. For instance, each nonactive level in a multilevel lasing scheme may represent separate noise states under certain conditions while both lasing levels make only one noise state. The squeezing capacity of the system is determined by a quantity called the noise dimension. The theory is extended to laser schemes with many photons (two-photon generation, more than one lasing transition, etc.). The validity of the minimization principle is established for this type of system. Some consequences from the theory, which are relevant to the experiment, are discussed.

Atom–Photon Interactions: Basic Processes and Applications

Transition Amplitudes in Electrodynamics. A Survey of Some Interaction Processes Between Photons and Atoms. Nonperturbative Calculation of Transition Amplitudes. Radiation Considered as a Reservoir: Master Equation for the Particles. Optical Bloch Equations. The Dressed Atom Approach. Exercises. Appendix. References. Index.

Dressed atoms character of quantum fluctuations in the regularly pumped laser

The amplitude fluctuations in a single-mode laser for the case of regular pumping when the atoms are injected in the cavity at fixed, unfluctuating rate are discussed. The dressed atom approach is employed. A comparison is made of such pumping scheme with the conventional one, when the number of active atoms is fixed. The results of the present work agree well with other approaches.

The force on atoms in intense standing wave laser fields: dipole force with doppleron structure

The dressed atom approach is used to investigate the evolution of atoms moving in an intense standing wave laser field. When coherences between the dressed states can be neglected, a simple expression is obtained for the radiative force acting on the atoms. The Landau-Zener model, well-known in the theory of slow atomic collisions, is here used to include coherences in an analytic treatment. At high velocities, where the simplest approach breaks down, the results are in good agreement with exact numerical calculations. Applications outside the field of laser cooling are discussed.

Effect of dipole interaction and phase-interrupting collisions on the collapse-and-revival phenomenon in the Jaynes-Cummings model.

A study of multiatom effects, i.e., dipole-dipole interactions and phase-interrupting collisions between atoms in the Jaynes-Cummings model, is presented here. For this purpose we consider two identical two-level atoms interacting with a single-mode field in a lossless cavity and study the effect of the dipole-dipole interaction between these two atoms on the collapse-and-revival phenomenon of Rabi oscillations by calculating the analytical expression of the excitation probability in the coherent field. We also consider another situation in which a single atom interacting with a single-mode field in a damped cavity undergoes phase-interrupting collisions. The effect of phase-interrupting collisions along with the usual cavity damping on the collapse-and-revival phenomenon has been explicitly calculated using the dressed-atom approach under the secular approximation.

Quantized-field approach to pressure-induced resonances.

Using a fully quantized dressed-atom approach, we present a theory and interpretation of the pressure-induced resonances in four-wave mixing (PIER4) that may arise when three incident fields interact with an ensemble of two-level atoms. The PIER4 resonances are seen to arise from a collisionally created modulation of a dressed-state population when an operator approach is used to solve the problem and from a level crossing between collisionally populated dressed states when an occupation-number formalism is used.

Standing-wave and intensity effects in intracavity laser RF double resonance spectroscopy

The laser and RF absorption spectra in a laser-RF double resonance configuration with the gas sample placed inside the laser cavity are exactly calculated by means of a semiclassical three-level model and interpreted through the dressed atom approach. Laser standing-wave effects and intensity effects are studied. Several kinds of nonlinear coherent phenomena are evidence. High-resolution spectroscopic applications are considered.

Optically pumped far-infrared laser theory based on the dressed-atom (molecule) approach

The small-signal gain and ac Stark effect of optically pumped tunable far-infrared lasers are studied by means of the dressed- atom (molecule) approach and some useful results are presented.

Dressed-atom approach to strong-field double-resonance fluorescence with laser phase fluctuations.

We discuss analytically the resonance fluorescence of a three-level ladder system whose two transitions are simultaneously saturated by the fields from two lasers. The laser fields have fluctuating phases, which may be correlated to some extent. We generalize the dressed-atom approach of Cohen-Tannoudji and Reynaud [J. Phys. B 10, 345 (1977)] to deal with phase fluctuations under conditions of overall two-photon resonance, but not single-photon resonance on the individual transitions. In this respect we also generalize the master-equation approach of Lawande, Puri, and D'Souza [Phys. Rev. A 33, 2504 (1986)]. The effect of spontaneous emission and laser fluctuations on the resonance fluorescence quintet is discussed in detail, and shown to marked effects. We also investigate the effect of these quantities on the steady-state dressed-atom occupation probabilities, and point out that the double-resonance experiment can be used to prepare the atom in a given dressed state with high probability.

Dressed-atom approach to embedding and physisorption in metals.

A number of solid-state situations exhibit mainly atomic characteristics. Accordingly, for phenomena involving metals, we have developed a ``dressed-atom'' approach which is implemented computationally via a coupled Hartree-Fock procedure, and which incorporates the surrounding metallic character self-consistently into the dressed-ground-state or excited-atomic-state wave function. The systems which are studied here are He/Na(001), He/Al(001), and Ar/Na(001). The correlation-energy contribution to the self-consistent metal-adatom interaction is considered in the image-potential approximation. It is found that (i) argon binds on Na(001) with an energy of about 60 meV, and (ii) it is more likely for Ar/Na(001) to exhibit its ionic rather than its neutral configuration during excitation from the ground $^{1}\mathrm{S}$ state.

Backward saturation in four-wave mixing in neon: Case of parallel pump polarizations.

We present in this paper a theoretical and experimental study of the effect of an intense pump beam on four-wave-mixing emission in the geometry of phase conjugation. The theoretical model is developed for \ensuremath{\Gamma} (natural width) ${\ensuremath{\Omega}}_{1}$ (Rabi frequency of the intense pump) ku (Doppler width) and uses the dressed-atom approach. We have analyzed degenerate and nearly degenerate four-wave mixing. In this latter case, we have studied three situations according to which beam (intense pump, weak pump, or probe) has a different frequency. The experimental study has been done in a neon cell using cw lasers. Our experimental results are in excellent agreement with theory. This study shows the need to take into account the atomic motion in the theory. However a quantitative analysis cannot be done assuming an infinite Doppler width and we show the importance of the Boltzmann factor. In the case of nearly degenerate four-wave mixing, narrow resonances corresponding to transitions between energy levels of the dressed atom are observed.

Fluorescent spectra in a four-level atom interacting with strong electromagnetic fields

The fluorescent spectrum of a four-level atomic system is studied when one, two or three nearly resonant waves of arbitrary intensities irradiate the system. Calculations are performed with the dressed-atom approach. The spectrum, according the particular case considered, consists of 3, 9, or 13 lines. Simple analytical expressions are given for the frequencies and the probabilities of different transitions.

Dressed-atom approach to atomic motion in laser light: the dipole force revisited

We show that the dressed-atom approach provides a quantitative understanding of the main features of radiative dipole forces (mean value, fluctuations, velocity dependence) in the high-intensity limit where perturbative treatments are no longer valid. In an inhomogeneous laser beam, the energies of the dressed states vary in space, and this gives rise to dressed-state-dependent forces. Spontaneous transitions between dressed states lead to a multivalued instantaneous force fluctuating around a mean value. The velocity dependence of the mean force is related to the modification, induced by the atomic motion, of the population balance between the different dressed states. The corresponding modification of the atomic energy is associated with a change of the fluorescence spectrum emitted by the atom. The particular case of atomic motion in a standing wave is investigated, and two regimes are identified in which the mean dipole force averaged over a wavelength exhibits a simple velocity dependence. The large values of this force achievable with reasonable laser powers are pointed out with view to slowing down atoms with dipole

Probe spectroscopy of three-level systems with a standing-wave saturator: Influence of the saturator detuning

The absorption of a weak laser beam probing a Doppler-broadened three-level system saturated by a standing-wave pump is studied theoretically for the case of small saturator detunings. The features of the obtained absorption spectra are analysed by means of the dressed-atom approach. A strong influence of radiative and high-order multi-photon processes is showed. The influence of saturator tuning fluctuations on the narrow Doppler-free peak which appears in the resonant case is analysed and its consequences for high-resolution applications are considered.

Resonance fluorescence spectra of a strong bichromatic field interacting with a three-level atom in the ‘‘V’’ configuration

We have considered the fluorescence spectra arising from the interaction of a three-level atom in the ‘‘V’’ configuration with two strong electromagnetic fields whose initially populated modes ωa and ωb are equal to the two atomic transition frequencies, respectively. The excitation spectra are calculated by making use of the Green function formalism where the hierarchy of the Green functions is truncated by a decoupling scheme which takes into account photon–photon correlations from each laser field in the limit of high photon densities. The excitation spectra consist of the central peak of the excitation frequency ωa and four pairs of sidebands, which are peaked at the frequencies ωa±η1(2)1/2, ωa±η2/(2)1/2, ωa±(η21+η22)1/2/(2)1/2, and ωa±2(η21+η22)1/2/(2)1/2, where η1 and η2 are the Rabi frequencies of the two laser fields, respectively. Similar spectra are exhibited near the excitation frequency ωb. Numerical calculations for selected values of the Rabi frequencies are graphically presented and compared with those known in the literature. In the Appendix expressions for the excitation spectra are derived first when the two laser fields are treated classically, and second, when the fields are quantized but photon–photon correlations are neglected. It is shown that when the two laser fields are treated classically, the derived results are identical to those obtained when the fields are quantized only when photon–photon correlations arising from each laser field are discarded. The derived results when the fields are quantized but without photon–photon correlations taken into account are also identical to those obtained by the use of the dressed-atom approach. The appearance of the new sidebands reveals the boson character of the photon fields in question. The merit of the method is that it yields results describing both the classical as well as the quantum nature of the photon fields involved.

Saturation in degenerate four wave mixing: The dressed-atom approach

A dressed atom approach of saturation in degenerate four-wave mixing is presented. Because of the Doppler-shift of the pump and probes waves frequencies, a resonance between levels of the dressed atom occurs for two velocity groups. When the Rabi frequency Ω 1 is smaller than the Doppler width ku, these resonant terms give the essential contribution to the signal which is analytically calculated. When Ω 1 å ku, the signal is expected to be much smaller.

The 'physical spectrum' of the light scattered by a strontium-like atom driven by a pulsed laser

The numerically computed 'physical spectrum' of light scattered near the collisionally perturbed S0-P1 resonance is presented. The authors assume that the strong laser pulse is rectangular, and apply the dressed-atom approach generalized to time-dependent processes. The influence of the interferometer of bandwidth Gamma on the obtained spectra is discussed. The authors show that Gamma either small or large affects the spectra strongly, thus distorting the information about the atomic system.