Generation of counterpropagating paired Stokes and anti-Stokes photons at the two-photon level in an electromagnetically induced transparency system is examined in quantum theory. In particular, we focus on the transverse effects of generated entangled photon pairs. Using first-order perturbation theory, we have studied the two-photon state including the phase matching conditions. The comparison of single photon counting and two-photon coincidence counting measurement is provided, which show some interesting properties.

Generation of counterpropagating paired Stokes and anti-Stokes photons in a double-$\Lambda$- (or $M$-) type electromagnetically induced transparency (EIT) system is examined in quantum theory in the three-dimensional space. We use the Maxwell-Bloch equations to study the transverse effects of generated entangled photon pairs via such an EIT medium. We reexamine correlation measurements for both amplitude and intensity correlations. In the low parametric gain region $[\sqrt{v_g∕8{\gamma }_{31}L}\gg \sqrt{k_s∕k_{as}}(\mid {\Omega }_p\mid ∕\mid {\Gamma }_p\mid \left)\right]$, when the paired Stokes and anti-Stokes are at the single-photon level, we obtain the results shown in Wen and Rubin, Phys. Rev. A 74, 023807 (2006). If $\sqrt{k_s∕k_{as}}(\mid {\Omega }_p\mid ∕\mid {\Gamma }_p\mid )$ is comparable to or greater than $\sqrt{v_g∕8{\gamma }_{31}L}$, i.e., in the high parametric gain regime, the system may not reach the single-photon level, and accidental coincidences occur which cause loss of visibility in the interference experiments.

We investigate semiclassical dynamics and quantum properties of light beams generated in time-modulated nondegenerate optical parametric oscillator (NOPO). Having in view production of continuous-variable (CV) entangled states of light beams we propose two experimentally feasible schemes of NOPO: (i) driven by continuously modulated pump field; (ii) under action of a periodic sequence of identical laser pulses. It is shown that the time modulation of pump field amplitude essentially improves the degree of CV entanglement in NOPO. On the whole the level of integral two-mode squeezing, which characterizes the degree of CV entanglement, goes below the standard limit established in an ordinary NOPO with monochromatic pumping. We develop semiclassical and quantum theories of these devices for both below- and above-threshold regimes of generation. Properties of CV entanglement for various operational regimes of the devices are discussed in the time domain in application to time-resolved quantum information technologies. Our analytical results are in well agreement with the results of numerical simulation and support a concept of CV entangled states of time-modulated light beams.

Laser ellipticity significantly influences optical harmonic generation in ${\mathrm{C}}_{60}$. Numerical results presented here show that a change from a linearly to circularly polarized light reduces the harmonic intensity substantially. For low-order harmonics and weak laser intensities, the reduction is monotonic, consistent with the perturbation theory prediction, but for high harmonics and strong laser fields, the reduction becomes nonmonotonic and the harmonic intensity peaks at a nonzero ellipticity. Not only is the harmonic intensity influenced, but also the harmonic ellipticity is affected. The harmonic ellipticity is normally smaller than the laser ellipticity; its linear dependence on laser ellipticity becomes highly nonlinear as the laser intensity increases. These results are testable experimentally and are critical for future manipulation of harmonic generations in ${\mathrm{C}}_{60}$.

The experimental investigation of the Casimir force between a large metallized sphere and semiconductor plate is performed using an atomic force microscope. Improved calibration and measurement procedures permitted a reduction in the role of different uncertainties. Rigorous statistical procedures are applied for the analysis of random, systematic, and total experimental errors at 95% confidence. The theoretical Casimir force is computed for semiconductor plates with different conductivity properties, taking into account all theoretical uncertainties discussed in the literature. The comparison between experiment and theory is done at both 95% and 70% confidence. It is demonstrated that the theoretical results computed for the semiconductor plate used in experiment are consistent with the data. At the same time, the theory describing a dielectric plate is excluded by experiment at 70% confidence. Thus, the Casimir force is proved to be sensitive to the conductivity properties of semiconductors.

We have performed calculations of the size of the frequency shift induced by a static electric field on the clock transition frequencies of the hyperfine splitting in ${\mathrm{Yb}}^{+}$, Rb, Cs, ${\mathrm{Ba}}^{+}$, and ${\mathrm{Hg}}^{+}$. The calculations are used to find the frequency shifts due to blackbody radiation which are needed for accurate frequency measurements and improvements of the limits on variation of the fine-structure constant $\alpha$. Our result for Cs $[\delta \nu ∕E^2=-2.26\left(2\right)\times {10}^{-10}\mathrm{Hz}∕{(\mathrm{V}∕\mathrm{m})}^2]$ is in good agreement with early measurements and ab initio calculations. We present arguments against recent claims that the actual value might be smaller. The difference $(\sim 10\%)$ is due to the contribution of the continuum spectrum in the sum over intermediate states.

The Sagnac effect in two-dimensional resonant microcavities is studied theoretically and numerically. The frequency shift due to the Sagnac effect occurs as a threshold phenomenon for the angular velocity in a rotating microcavity. Above the threshold, the eigenfunctions of a rotating microcavity become rotating waves while they are standing waves below the threshold.

An optical quantum memory scheme using two narrow-linewidth cavities and some optical fibers is proposed. The cavities are connected via an optical fiber, and the gap of each cavity can be adjusted to allow photons with a certain bandwidth to transmit through or reflect back. Hence, each cavity acts as a shutter and the photons can be stored in the optical fiber between the cavities at will. We investigate the feasibility of using this device in storing a single photon. We estimate that with current technology storage of a photon qubit for up to 50 clock cycles (round trips) could be achieved with a probability of success of 85%. We discuss how this figure could be improved.

Integrated cross sections for the electron-impact excitation of ground-state hydrogen to the $3s$, $3p$, and $3d$ final states have been calculated using propagating exterior complex scaling and convergent close-coupling methods at energies between the $n=3$ and 4 excitation thresholds. The calculations are in excellent agreement and demonstrate that exterior complex scaling methods can accurately reproduce the resonance structure and magnitude of the excitation cross sections below the ionization threshold. Measurements of the separate $3s$, $3p$, and $3d$ differential cross sections were made at $12.24\mathrm{eV}$, and are consistent with both calculations within a total experimental uncertainty of about 35%.

The properties of a vortex in a rotating superfluid Fermi gas are studied in the unitary limit. A phenomenological approach based on Ginzburg-Landau theory is developed for this purpose. The density profiles, including those of the normal fluid and superfluid, are obtained at various temperatures and rotation frequencies. The superfluid and normal fluid densities can be identified from the angular momentum density. The total free energy and angular momentum of the vortex are also obtained.

We present ab initio quantal calculations of electron capture cross sections for collisions of ground and metastable states of ${}^{14}\mathrm{N}^{2+}$ and ${}^{16}\mathrm{O}^{2+}$ ions with $\mathrm{H}\left(1s\right)$, at collision energies ${10}^{-2}<E<{10}^2\mathrm{eV}∕\mathrm{amu}$. The calculation for ${\mathrm{N}}^{2+}+\mathrm{H}$ updates the previous one of Barragán et al. [Phys. Rev. A 70, 022707 (2004)] at $0.1<E<0.3\mathrm{eV}∕\mathrm{amu}$. Total cross sections for both systems show large values of about $5\times {10}^{-15}{\mathrm{cm}}^2$ at $E<0.1\mathrm{eV}∕\mathrm{amu}$, where they exhibit resonant structures.

Two different schemes are proposed for deterministically generating a pure motion-entangled state for two well-separated ions trapped in a cavity. The first one is that through adjusting the amplitudes and the frequencies of transverse lasers, the two ions trapped in a bimodal cavity can unconditionally evolve into a two-mode squeezed vacuum state with the aid of the cavity dissipation. The second one is based on the interactions of two appropriate series of the driving laser pulses with the two ions trapped in a single-mode cavity, it allows us to produce a two-mode squeezed vacuum state for the trapped ions’ center-of-mass motion.

We investigate quantum walks in multiple dimensions with different quantum coins. We augment the model by assuming that at each step the amplitudes of the coin state are multiplied by random phases. This model enables us to study in detail the role of decoherence in quantum walks and to investigate the quantum-to-classical transition. We also provide classical analog of the quantum random walks studied. Interestingly enough, it turns out that the classical counterparts of some quantum random walks are classical random walks with a memory and biased coin. In addition random phase shifts “simplify” the dynamics (the cross-interference terms of different paths vanish on average) and enable us to give a compact formula for the dispersion of such walks.

We have measured the polarization of the $2p_{3∕2}\to 1s_{1∕2}$ Lyman-${\alpha }_1$ x-ray line of hydrogenlike ${\mathrm{Ar}}^{17+}$ and ${\mathrm{Fe}}^{25+}$ at electron-impact energies ranging from 7 to 25 threshold units. The highly charged argon and iron ions were produced using the Lawrence Livermore National Laboratory SuperEBIT electron beam ion trap. A combination of two crystal spectrometers and a microcalorimeter were used to record the Lyman-$\alpha$ x-ray emission of ${\mathrm{Ar}}^{17+}$ and ${\mathrm{Fe}}^{25+}$ and to infer the polarization of the Lyman-${\alpha }_1$ line. Our results show a systematic discrepancy with the predictions of distorted-wave calculations.

We consider a protocol recently proposed by Cardoso et al. for teleporting entangled photon states from a bimodal cavity to another one. It is shown that the proposed protocol can afford full fidelity instead of the 97% fidelity that the authors ascribed to their scheme.

We present a remarkably simple derivation of an exact time-local master equation describing the dynamics of quantum states in harmonic traps subject to arbitrary fluctuating forces. The relation between our master equation and known master equations of irreversible harmonic oscillator dynamics are established. Motivated by recent experiments, we focus on decoherence and in particular on the precise decoherence dynamics of a superposition of wave packets. We determine the decaying purity resulting from the time evolution based on our master equation and study its connection to experimentally accessible observables. Finally, we discuss the heating of the system subjected to arbitrary Gaussian noise.

We report on the experimental implementation of a polarimeter based on a scheme known to be optimal for obtaining the polarization vector of ensembles of spin-$\frac{1}{2}$ quantum systems and the alignment procedure for this polarimeter. We also show how to use this polarimeter to estimate the polarization state for identically prepared ensembles of single photons and photon pairs and extend the method to obtain the density matrix for generic multiphoton states. State reconstruction and performance of the polarimeter is illustrated by actual measurements on identically prepared ensembles of single photons and polarization entangled photon pairs.

Stark-induced amplitudes for the $6P_{1∕2}\text{−}7P_{1∕2}$ transition in $\mathrm{T}\mathrm{l}\mathrm{I}$ are calculated using the relativistic singles-doubles (SD) approximation in which single and double excitations of Dirac-Hartree-Fock levels are summed to all orders in perturbation theory. Our SD values ${\alpha }_S=368a_0^3$ and $\mid {\beta }_S\mid =298a_0^3$ are in good agreement with the measurements ${\alpha }_S=377\left(8\right)a_0^3$ and ${\beta }_S=313\left(8\right)a_0^3$ by D. DeMille, D. Budker, and E. D. Commins [Phys. Rev. A 50, 4657 (1994)]. Calculations of the Stark shifts in the $6P_{1∕2}\text{−}7P_{1∕2}$ and $6P_{1∕2}\text{−}7S_{1∕2}$ transitions are also carried out. The Stark shifts predicted by our calculations agree with the most accurate measured values within the experimental uncertainties for both transitions.