The interaction of a pair of copropagating pulses with three-level Λ-type atoms is discussed in terms of time-dependent coupled and decoupled superpositions ‖±〉 of the lower levels. Due to the explicit time dependence of these states there is a nonadiabatic coupling between the ‘‘bright’’ state ‖+〉 and the ‘‘dark’’ state ‖-〉 in addition to the strong coupling between ‖+〉 and the upper level ‖a〉 . We show that under quasiadiabatic conditions and in the presence of decay from the upper level this coupling can be treated perturbatively and the Maxwell-Bloch equations can be solved analytically. With the help of such a perturbation approach, coherent population transfer and formstable laser pulse propagation are studied. © 1996 The American Physical Society.

We apply the Jaynes principle of maximum entropy [Phys. Rev. 106, 620 (1957); 108, 171 (1957)] for a reconstruction of Wigner functions of quantum-mechanical states of light on different observation levels. We study how quantum interference between components of superpositions of coherent states, which is responsible for the appearance of nonclassical effects, can be detected on different observation levels. We analyze in detail the reconstruction of Wigner functions of squeezed states on different observation levels in the case of nonunit detection efficiency modeled as a decay of the state under consideration into a zero-temperature reservoir. © 1996 The American Physical Society.

We present a method of the summation of the divergent series. We show that in the case of the divergent perturbation expansion for the quartic anharmonic oscillator, the method allows one to construct the sequence of the analytic approximations to the E(β) exact ground-state energy. The constructed sequence converges for any value of the coupling constant β, allowing one to reconstruct the function E(β) in a whole β plane. © 1996 The American Physical Society.

The theory of continuous measurement of the photon number has been applied to a two-mode light field and it has been assumed that the second mode is being measured. An entanglement of the two-mode state has been supposed. The destructive and nondemolition continuous photon-number measurements have been compared according to their response in the first mode to the parameters of the quantum correlation and the detection time. © 1996 The American Physical Society.

The behavior of short quantum light pulses propagating in dispersive and absorbing linear ground-state dielectrics is studied, with special emphasis on squeezed pulses. The analysis is based on normally ordered correlation functions of the electric-field strength, which are related to quantities at the entrance plane, on using quantum Langevin equations. Using nonmonochromatic-mode expansion and restricting attention to a single-mode pulse in a squeezed state, the influence on squeezing of the pulse propagation in the medium is discussed in both the time and frequency domains, and it is shown that the noise reduction observable in homodyne detection sensitively depends on the phase control used. Effects, such as squeezing enhancement associated with pulse compression and the destructive influence of the spectral shift caused by absorption, are demonstrated. The numerical results are supplemented by analytical estimations derived for narrow-bandwidth Gaussian pulses. © 1996 The American Physical Society.

We show that the quantum state of an N-mode light field can be reconstructed from the difference statistics recorded in multiport homodyning with N unused input ports. The theory is applied to balanced homodyne six-port detection, which is shown to be suited for measuring the Q function of a single-mode radiation field. © 1996 The American Physical Society.

The frequency detuning curves of the spatial subharmonic intensity of photorefractive moving gratings are calculated using a simple theory based on coupled-mode analysis of wave equations combined with Kukhtarev’s materials equations. The optimum detuning frequency and the intensity distribution of K/2 spatial subharmonics against detuning frequency are calculated both analytically and numerically by varying the external electric field and the modulation of two pump beams. It is found that the results of our theoretical calculations for the frequency detuning curves of subharmonic intensity agree with the experimental data very well. © 1996 The American Physical Society.

Previous applications of neoclassical radiation theory (NCT) have been limited to nonrelativistic effects involving electric dipole radiation. Here a relativistic extension of NCT that takes into account the intrinsic spin of the electron will be presented. In relativistic NCT the charge current, which is used as a source term in Maxwell’s equations, is assumed to be proportional to the Dirac probability current. The presence of Zitterbewegung requires a careful approach to the approximations used to extract radiative level shifts and spontaneous decay from the dynamical equations. Some of the new terms that result from the inclusion of spin can be identified with the energy of interaction of a classical magnetic dipole with its own field. The contribution of these terms should already be included in the value of the experimentally observed mass of the electron. When this identification is made, inclusion of spin in NCT is found not to significantly alter the earlier predictions of radiative level shifts. This observation answers a criticism of the NCT theory by van den Doel and Kokkedee [R. van den Doel and J. J. J. Kokkedee, Phys. Rev. 9, 1468 (1974)]. © 1996 The American Physical Society.

We investigate theoretically and experimentally breakup and subsequent spatial dynamics of (1+1)- and (2+1)-dimensional beams in bulk media with an anisotropic photorefractive nonlinear response. © 1996 The American Physical Society.

The transverse patterns of an active resonator with cylindrical optics are investigated. This resonator configuration corresponds to a ‘‘channel’’ form of the potential for the ‘‘photon fluid.’’ Simultaneous emission of different transverse modes along the channel, periodic nucleation of vortices in the form of a vortex street (vortices of alternating senses of rotation appearing in a flow behind an obstacle), accelerated flow in a ‘‘tilted channel,’’ and destabilization of the one-directional flow in the channel are demonstrated and interpreted in terms of tilted waves and beating of channel modes, as well as in fluid terms, illustrating the fluid dynamics correspondence of class-A lasers. © 1996 The American Physical Society.

We report the measurement of nonclassical photon statistics at the outputs of 2×2 and 3×3 fiber couplers resulting from quantum-mechanical second-order interference of entangled photon pairs from a parametric down-conversion source. This is a demonstration of the bunching of bosons at the outputs of fiber multiports. Single-mode fibers provide precise wavelength selection from the down-conversion source spectrum, thus yielding very long coherence times and good collection efficiency without the need of interference filters. Two-photon interference visibilities close to the theoretical maximum were achieved in the experiments. © 1996 The American Physical Society.

A mesoscopic beam of two-level Rydberg atoms, prepared in the lower state, interacts with a coherently driven cavity mode. The dynamics is described by Maxwell-Bloch equations with atomic propagation. On resonance, the system was predicted to exhibit multistability, upper-branch instabilities, and self-pulsing. In the presence of atomic detuning its dynamical behavior is shown to include in addition period doubling, frequency locking, quasiperiodicity, and chaos, thus providing a remarkable example of nonlinear dynamics of a passive autonomous atomic system with propagation. © 1996 The American Physical Society.

Dicke superradiance (SR) and stimulated electronic Raman scattering (SERS) have been observed at 451.1 nm in atomic indium following optical excitation at the resonance line 410.2 nm. The SR and SERS characteristics have been studied. The coherent population trapping state was observed. The pump to Raman conversion efficiency is found to be up to 40% and a range of tunability of 30 ${\mathrm{cm}}^{\mathrm{-}1}$. The SR and SERS processes have shown different optimum densities of indium atoms. © 1996 The American Physical Society.

In this paper we analyze theoretically the influence of the local-field effects on reflection spectra of a degenerate four-wave mixing in a dense medium of two-level atoms. We discuss the spectral dependence of the nonlinear absorption and dispersion of the signal and probe fields as well as their coupling for various strengths of the external field and atomic densities. For weak external fields the local-field effects reduce to the well known Lorentz redshift of the reflection spectra. When the external field saturates the transition in a dense sample significant modifications of the probe reflectivity and of the wave mixing spectra occur, resulting in asymmetric, multipeak line shapes. © 1996 The American Physical Society.

To test the application of solid-state lasers to intracavity laser absorption spectroscopy (ICLAS), we studied a neodymium-doped glass laser, in the presence of extreme relaxation oscillations (up to ${10}^8$ intensity contrast). The contrast of these oscillations could be varied by changing the Q-switch transition time. The recorded absorption spectra accurately follow the regular ICLAS behavior except when the intensity in the first relaxation oscillation minimum becomes too low. In such a case, we find that the ICLAS absorption spectrum accumulated during the first spike is ‘‘forgotten’’ by the system. Numerical simulations were done which accurately describe the observed transition to a regime of memory loss, when the number of photons circulating in each mode drops close to 1. These simulations show that the mechanism of memory loss is the prevailing of spontaneous over stimulated emission. This effect sets the fundamental limit of the sensitivity of an ICLAS spectrometer where the nonlinear mode interactions are negligible. This effect was observed before only in a diode laser system with high internal losses. In this paper we report an observation of ICLAS sensitivity saturation by spontaneous emission during relaxation oscillations in a laser with low cavity losses. © 1996 The American Physical Society.

We study the scattering of light by a single ultracold trapped atom initially in the ground state of the trapping harmonic potential. We have found interesting features of scattering in the regime where the atomic recoil energy is much larger than the separation between oscillatory trap levels. Although we present the quantum-mechanical expression for the scattering cross section, special attention is paid to the semiclassical analysis of the process. We show that the major characteristics of the scattering might be deduced from two conservation laws: conservation of energy and momentum in absorption and emission of photon process separately. These conservation laws impose a strong correlation between scattered light characteristics and the position of the trapped atom at the moment of photon emission. © 1996 The American Physical Society.

We present the definition of the angular velocity in quantum mechanics. To accomplish this, first we show that quantum-mechanical description of rotation angles proposed by Barnett and Pegg [Phys. Rev. A 41, 3427 (1990)] (the BP formalism) possesses a q-deformation structure inherently in itself. Based on this idea, we then construct the angular velocity operator via the q-deformed Heisenberg equation of motion. It is found that this operator exhibits a physically plausible behavior in the semiclassical regime of large angular momenta. This gives a resolution to the problem of anomalous properties of the angular velocity dynamically defined from the BP angle operator. We discuss in detail how the classical-quantum correspondence is established for the angular velocity variable if the q-deformation structure is introduced. Our result can also be seen as an example of the physical reality of the q-deformation prescription. © 1996 The American Physical Society.

We propose the use of a single trapped and laser-cooled ion for vibrational amplification assisted by stimulated emission of radiation. This quantum-mechanical counterpart of the micromaser allows one to modify the fundamental vibronic coupling externally. In particular, a vibrational number state can be prepared in a coherent interaction regime, whereas incoherent interaction may yield a sub-Poissonian, binomial number distribution. © 1996 The American Physical Society.

The Gaussian effective potential (GEP) is an approximation to quantum mechanics that semiquantitatively estimates quantum effects such as zero-point fluctuations and tunneling. We show how to use the GEP to compute semiclassical eigenvalues. It is well known that the GEP provides very accurate variational approximations to the ground-state energy of simple quantum systems; our results show that it also provides accurate excited-state energies. We also show how this method is related to the first-order Bargmann-Voros coherent-state representation of quantum mechanics, and that our results improve upon those derived from the latter method. © 1996 The American Physical Society.

Exactness of the lowest-order supersymmetric WKB (SWKB) quantization condition ${\mathrm{\int }}_{{\mathit{x}}_1}^{{\mathit{x}}_2}$√E-${\mathrm{\omega }}^2$(x)dx=nħπ, for certain potentials, is examined, using the complex integration technique. Comparison of the above scheme with a similar, but exact quantization condition, ${\mathrm{\oint }}_{\mathit{cp}}$(x,E)dx=2πnħ, originating from the quantum Hamilton-Jacobi formalism, reveals that the locations and the residues of the poles that contribute to these integrals match identically for both of these cases. As these poles completely determine the eigenvalues in these two cases, the exactness of the SWKB for these potentials is accounted for. Three nonexact cases are also analyzed; the origin of this nonexactness is shown to be due to the presence of additional singularities in √E-${\mathrm{\omega }}^2$(x), like branch cuts in the complex x plane. © 1996 The American Physical Society.