The application of squeezed light to a frontal-phase-modulated signal-recycled interferometer is considered. We present a simple model to understand the required spectrum of squeezing so as to make the interferometer more sensitive. In particular we analyze the broad- and narrow-band cases for signal recycling and find that the sensitivity of the detector can be enhanced provided an appropriate input squeezed spectrum is used. We also discuss the effect of using squeezed light on the bandwidth of the detector.

The electromagnetic field in a dielectric slab bounded by two dielectric half spaces with arbitrary refractive indices is quantized by computing the complete set of orthonormal electromagnetic modes. The zero-point fluctuations of the electromagnetic field are determined as a function of position. The dependence of the rate of spontaneous emission of thin dielectric films on the thicknesses of the films and the refractive index of the substrate is studied and compared with experimental results.

A quantization scheme for the phenomenological Maxwell theory of the full electromagnetic field in an inhomogeneous three-dimensional, dispersive, and absorbing dielectric medium is developed. The classical Maxwell equations with spatially varying and Kramers-Kronig consistent permittivity are regarded as operator-valued field equations, introducing additional current- and charge-density operator fields in order to take into account the noise associated with the dissipation in the medium. It is shown that the equal-time commutation relations between the fundamental electromagnetic fields $\mathbf{E}^$ and $\mathbf{B}^$ and the potentials $\mathbf{A}^$ and $\hat{\phi }$ in the Coulomb gauge can be expressed in terms of the Green tensor of the classical problem. From the Green tensors for bulk material and an inhomogeneous medium consisting of two bulk dielectrics with a common planar interface it is explicitly proven that the well-known equal-time commutation relations of QED are preserved.

Squeezing the quantum fluctuations of the two-mode light due to the nonstationary coupling between the quadrature components $q_1$ and $q_2$ is examined. The δ- and step-function mode couplings are considered. The conditions of weak and strong step-function coupling are distinguished, the latter being the condition of the instability for the classical counterpart of the quantum system under study. Under the conditions of weak coupling the quadrature squeezing is established in both a two-mode electromagnetic noise in thermal equilibrium (the thermal state) and a two-mode correlated coherent state (CCS). Squeezing in the thermal state is suppressed at a high temperature. The photon distribution function (PDF) in the thermal state reveals oscillatory behavior for both high and low temperature, the oscillations decrease while the temperature increases. The PDF in the CCS can be either oscillatory or smooth, whereas the photon statistics is essentially non-Poissonian. The nonclassical intermode photon-number correlations in the CCS are briefly studied.

We report on the experimental observation of a spectrally asymmetric quantum correlation between the intensities of the main mode and a large number of weakly excited side modes in a pump-noise-suppressed laser diode. The total intensity noise of the laser diode results from a generally incomplete cancellation process between these mode intensities, which influences the generation of amplitude squeezed light. Nonlinear gain due to cross mode gain saturation in the semiconductor lasing medium is found to be the origin of the asymmetric intensity noise distribution between short- and long-wavelength side modes. The experimental results are in good agreement with the predictions of a multimode Langevin rate equation model including asymmetric nonlinear gain saturation.

The nature of stimulated Brillouin scattering (SBS) temporal modulations for a focused beam in a finite-length cell with homogeneous medium is examined numerically. The finite phonon lifetime produces deterministic oscillations at the threshold while the inclusion of the random noise as an initiation source of SBS leads to stochastic fluctuations in Stokes intensity and phase. A unified study of both modulations under different parameters is presented. The results indicate a large useful parameter space for excellent Stokes beam quality.

Using a microscopic theory, we determine the entangled $n$-photon state generated both by the nonlinear process of spontaneous $n$-photon parametric down-conversion and in a cascade of $n-1$ crystals with two-photon parametric down-conversions. Expressions for the entangled $n$-photon absorption cross sections are also obtained. The absorption cross sections exhibit a linear dependence on the photon flux density, and depend on the entanglement times characterizing photons. The effect of relative path delay in the beams is discussed. It forms the basis for extracting the quadrupole moments between states involved in the interaction from the absorption cross section measured as a function of path delay. Effects competitive with entangled three-photon absorption are discussed.

Interaction-free measurements were realized using a high-finesse Fabry-Pérot cavity as a measurement apparatus. A figure of merit based on the maximum likelihood estimation, which takes into account real experimental conditions, is used to analyze the efficiency of this measurement scheme. The probability of detecting the presence of an object within the cavity without any photons actually “hitting” the object was approximately 85%. The probability of asserting the absence of the object was approximately 75%. Assuming that the a priori probability of the object being present was 1/2, the likelihood of knowing whether the object was present or not was 80%. The obtained results and the limitations of our setup are discussed.

Fourth-order interference patterns of biphotons generated by type-I spontaneous parametric downconversion are examined for beams with partial angular and spectral entanglement, both for degenerate and nondegenerate constituent photons. Two-beam configurations using a single beam-splitter interferometer and a Mach-Zehnder interferometer are explicitly studied, as are four-beam configurations using pairs of beam splitters and Mach-Zehnder interferometers. The interference pattern generally comprises a number of harmonic functions of the path-length difference with frequencies and visibilities that usually depend on direction, and may have a finite or infinite duration (fourth-order coherence length). The relation between the visibility and the spectral indistinguishability of the two beams is established. Certain components of the interference pattern are independent of direction so that they are not washed out by the use of apertures of finite size.

The feasibility of a Heisenberg-limited phase measurement using a Mach-Zehnder interferometer fed with twin photon correlated light is investigated theoretically. To take advantage of the Heisenberg limit, $1/N$, for the phase sensitivity, one wants the number of correlated photons, $N$, to be high. This favors the use of parametric oscillation rather than the weaker but better correlated source given by parametric down-conversion. In real systems, decorrelation arising from photon absorption, mode mismatch, and nonideal detectors must be considered. In this paper we address the problem of detection when correlated photons are used as the input. We study the influence of photon statistics and of imperfect quantum correlation of the input light, and show that it is still possible to break the classical $1/\sqrt{N}$ phase sensitivity limit in nonideal experimental conditions. All the results are valid in the general case of quantum correlated bosons.

Near-degenerate lower levels in a $\Lambda$ system have an additional coherence term due to interaction with the vacuum of the radiation field. We report the effects of this spontaneously generated coherence on the formation of a trapped state in the presence of two coherent fields of arbitrary intensity. We show that such coherence preserves both electromagnetically induced transparency and coherent population trapping (CPT) phenomena. However, it changes the time scales associated with the formation of the CPT state, and brings about quantitative changes in the line profiles. We present a clear analytical explanation for our numerical results. We also report the dependence of line shapes on the relative phase between the two applied fields.

In their review about intracavity laser spectroscopy, P. E. Toschek and V. Baev [in Laser Spectroscopy and New Ideas, edited by W. M. Yen and M. D. Levenson, Springer Series in Optical Science (Springer, Berlin, 1987)] have shown that multimode lasers are needed to obtain a high sensitivity. In this paper we show that two modes is enough. We discuss first the ideal case where only the spontaneous emission limits the sensitivity. In a second part we take into account the spatial hole burning, which couples the two modes and has for effect a lower limitation of the sensitivity. Analytical expressions are given for the modified absorption coefficient and the time evolution of the intensity of the two modes is calculated by numerical integration.

We establish that the energy transfer between transverse modes in nonlinear Fabry-Perot resonators with curved mirrors, having degenerate or nearly degenerate modes, is governed by selection rules. Although these rules are derived in a perturbative limit, assuming a thin medium centered in the resonator, we have found numerically and experimentally that they still account for the otherwise unexpected enhancement or suppression of certain modes in more realistic cases. The existence of selection rules constitutes a fundamental difference between standing wave and traveling wave cavities and therefore prevents, in principle, the possibility of describing experiments on transverse effects performed in Fabry-Perot cavities with (simpler) ring resonator models.

The time dependence of the decoherence rate (measuring the decay of off-diagonal matrix elements) is studied by means of the Lindblad equation for the density matrix. We derive some general estimates on the behavior of the quantum density matrix from an approximation representing the density matrix by a classical phase-space distribution of a Markov process. We suggest that the decoherence rate is determined by the variance of the Markov process.

The second-order electron self-energy counterterms are evaluated analytically using the Pauli-Villars renormalization. These counterterms generalize the Feynman result for the first-order electron self-energy and represent a necessary ingredient for the complete evaluation of the second-order Lamb shift for tightly bound electrons in highly charged ions.

The contribution of Pauli and Coulomb correlations to the asymptotic structure of the Kohn-Sham density-functional theory exchange-correlation potential in the classically forbidden region of atoms is well established. In this paper we derive the analytical asymptotic structure of the correlation-kinetic component of the potential to decay in this region as $8{\kappa }_0\chi {/5r}^5,$ where ${\kappa }_0^2/2\mathrm{}$ is the ionization potential and χ is an expectation value of the resulting ion.

Steady-state laser-induced fluorescence techniques have been used to study the rates for energy transfer between the $5{}^2{P}_{1/2,3/2}$ levels in rubidium. The cross sections for collisions with the molecular species ${\mathrm{H}}_2,$ ${\mathrm{D}}_2,$ ${\mathrm{N}}_2,$ ${\mathrm{CH}}_4,$ and ${\mathrm{CF}}_4$ have been measured as ${\sigma }_2{(}^2{\overrightarrow{P_{1/2}}}^2{P}_{3/2})=10.0,$ 21.4, 13.2, 29.5, and $9.5\times {10}^{-16}{\mathrm{cm}}^2$ and ${\sigma }_1{(}^2{\overrightarrow{P_{3/2}}}^2{P}_{1/2})=13.9,$ 29.8, 18.4, 41.0, and $13.2\times {10}^{-16}{\mathrm{cm}}^2,$ respectively. Correlation of these spin-orbit transfer probabilities with rotational-energy defect is demonstrated.

We apply a simplified description to weakly bound states and cold-collision continuum states of pairs of ground-state alkali-metal atoms, which complements the usual more elaborate coupled-channel treatment. It is based on a diabatic treatment of the transition region between the exchange-dominated interatomic distance range at small $r$ and the hyperfine-dominated range at large $r$. The models contain the degenerate internal states approximation for H atoms as a special case.

The electronic energy-loss straggling of protons and antiprotons moving at arbitrary nonrelativistic velocities in a homogeneous electron gas are evaluated within a quadratic response theory and the random-phase approximation. These results show that, at low and intermediate velocities, quadratic corrections significantly reduce the energy-loss straggling of antiprotons, these corrections being, at low velocities, more important than in the evaluation of the stopping power.

The method of phenomenological damping developed by Pitaevskii (Zh. Eksp. Teor. Fiz. 35, 408 (1958) [Sov. Phys. JETP 35, 282 (1959)]) for superfluidity near the $\lambda$ point is simulated numerically for the case of a dilute, alkali, inhomogeneous Bose-condensed gas near absolute zero. We study several features of this method in describing the damping of excitations in a Bose-Einstein condensate. In addition, we show that the method may be employed to obtain numerically accurate ground states for a variety of trap potentials.