We show through modeling the effect of pulse propagation upon the evolution of coherence and nonlinear frequency mixing in an ionizing three-level medium. This work extends earlier studies, in which the coherence dephasing due to photoelectrons was considered, by including the effects of pulse reshaping as the coupled fields propagate through the medium. In this way we establish a realistic model that enables us to predict qualitatively the performance of experimental coherence enhanced frequency mixing schemes.

We present a Gaussian-state description of squeezed light generated in an optical parametric oscillator. Using the Gaussian-state description we describe the dynamics of the system conditioned on homodyne detection on the output field. Our theory shows that the output field is squeezed only if observed for long enough times or by a detector with finite bandwidth. As an application of the present approach we consider the use of finite bandwidth squeezed light together with a sample of spin-polarized atoms to estimate a magnetic field.

A two-photon mechanism for cooling atoms below the Doppler temperature is analyzed. We consider the magnesium ladder system $\left(3s^2\right){}^{1}S_0\to \left(3s3p\right){}^{1}P_1$ at $285.2\mathrm{nm}$ followed by the $\left(3s3p\right){}^{1}P_1\to \left(3s3d\right){}^{1}D_2$ transition at $880.7\mathrm{nm}$. For the ladder system quantum coherence effects may become important. Combined with the basic two-level Doppler cooling process this allows for reduction of the atomic sample temperature by more than a factor of 10 over a broad frequency range. First experimental evidence for the two-photon cooling process is presented and compared to model calculations. Agreement between theory and experiment is excellent. In addition, by properly choosing the Rabi frequencies of the two optical transitions a velocity independent atomic dark state is observed.

A new gyroscopic interference effect stemming from the Galilean translational factor in the matter wave function is pointed out. In contrast to the well-known Sagnac effect that stems from the geometric phase and leads to a shift of interference fringes, this effect causes slanting of the fringes. We illustrate it by calculations for two split cigar-shaped Bose-Einstein condensates under the conditions of a recent experiment, see Y. Shin et al., Phys. Rev. Lett. 92, 050405 (2004). Importantly, the measurement of slanting obviates the need of a third reference cloud.

We discuss the possibility of measuring nuclear anapole moments in atomic Zeeman transitions and perform the necessary calculations. Advantages of using Zeeman transitions include variable transition frequencies and the possibility of enhancement of parity nonconservation effects.

Complementarity was originally introduced as a qualitative concept for the discussion of properties of quantum mechanical objects that are classically incompatible. More recently, complementarity has become a quantitative relation between classically incompatible properties, such as the visibility of interference fringes and “which-way” information, but also between purely quantum mechanical properties, such as measures of entanglement. We discuss different complementarity relations for systems of two-, three-, or $n$ qubits. Using nuclear magnetic resonance techniques, we have experimentally verified some of these complementarity relations in a two-qubit system.

We extend exact deterministic remote state preparation (RSP) with minimal classical communication to quantum systems of continuous variables. We show that, in principle, it is possible to remotely prepare states of an ensemble that is parametrized by infinitely many real numbers—i.e., by a real function—while the classical communication cost is one real number only. We demonstrate continuous variable RSP in three examples using (i) quadrature measurement and phase-space displacement operations, (ii) measurement of the optical phase and unitaries shifting the same, and (iii) photon counting and photon number shift.

Elastic and excitation (single and double) cross sections $(n⩽3)$ of orthopositronium-orthopositronium $(o\text{−}\mathrm{Ps}–o\text{−}\mathrm{Ps})$ scattering system are predicted using eigenstate close-coupling approximation at medium energies. The partial wave cross sections have shown a peculiar feature. The static exchange results and other inelastic cross sections for even parity transitions only survive for even values of partial wave and vice versa like Born-Oppenheimer (BO) cross sections. To the best of our knowledge, this feature has not been noticed for other systems. Our results are nearly convergent with added eigenstates and elastic and excitation cross sections are compared with their corresponding BO predictions.

The $s$-wave elastic phase shifts and cross sections for the $\overline{\mathrm{H}}\text{−}\mathrm{Li}$ system are predicted using an ab initio and nonadiabatic quantal method at very low energies. The smooth and monotonic change of the phase shifts with added eigenstates indicates that the leptonic potential for the present system has no barrier as noticed in the case of the $\overline{\mathrm{H}}\text{−}\mathrm{He}$ system, or even a hump which is present in $\overline{\mathrm{H}}\text{−}\mathrm{H}$ interaction. The very high value of the $s$-wave elastic cross section at zero or near zero energy implies that Li will be a more efficient buffer gas in cooling the antiatom to ultralow temperatures. This study may stimulate new experiments in thermalizing $\overline{\mathrm{H}}$ atom.

A calculation of the one-loop self-energy and vacuum-polarization corrections to the hyperfine splitting of the $1s$ and $2s$ states in light H-like ions is carried out to all orders in the parameter $Z\alpha$. Using the known values for the $Z\alpha$-expansion coefficients, the numerical data obtained are extrapolated from $Z=5$ and higher to $Z=0$, 1, and 2, with the resulting accuracy being significantly better than in previous evaluations. Our calculation shifts the theoretical value of the normalized difference of the $1s$ and $2s$ hyperfine-structure intervals in ${}^3\mathrm{He}^{+}$ by $0.056\mathrm{kHz}$ and improves its accuracy.

Relative cross sections for the $4\mathrm{MeV}$ ${\mathrm{H}}^{+}+{\mathrm{D}}_2$ $\left({}^1\Sigma _g^{+}\right)\to {\mathrm{H}}^{+}+{\mathrm{D}}_2^{+}\left(1s\sigma \right)+e^{-}$ ionization process were measured as a function of the molecular alignment during the interaction. The angle between the molecular axis and the projectile was obtained by using a momentum imagining technique and isolating the events in which the ${\mathrm{D}}_2^{+}\left(1\mathrm{s}\sigma \right)$ ions are excited to the vibrational continuum and subsequently dissociate. While anisotropic cross sections have been observed in the past for a number of collision processes involving both target electrons, the one electron process investigated here is isotropic within our experimental uncertainties.

The measurements of electron density distributions and binding-energy spectrum of the complete valence shell of cyclopentene $\left({\mathrm{C}}_5{\mathrm{H}}_8\right)$ using a binary $(e,2e)$ electron momentum spectrometer are reported. The experimental momentum profiles of the valence orbitals are compared with the theoretical distributions calculated using Hartree-Fock and density-functional-theory (DFT) methods with various basis sets. The agreement between theory and experiment for the shape and intensity of the orbital electron momentum distributions is generally good. The DFT calculations employing B3LYP hybrid functional with a saturated and diffuse AUG-CC-PVTZ basis set provide the better descriptions of the experimental data. Some “turn up” effects in the low momentum region of the measured $(e,2e)$ cross section compared with the calculations of $3a^{″}$, $2a^{″}$, and $3a^{\prime }$ orbitals could be mainly attributed to distorted-wave effects. The pole strengths of the main ionization peaks from the orbitals in the inner valence are estimated.

We study three-body recombination in the gas of spin-polarized atomic hydrogen adsorbed on the surface of superfluid helium at temperatures from $45\text{to}130\mathrm{mK}$. The two-dimensional gas is thermally compressed to densities up to $\approx 4\times {10}^{12}{\mathrm{cm}}^{-2}$ using the “cold spot” method which makes the three-body process the dominant decay channel in the system. We measure the loss rate and surface density of atoms directly and independently and observe the former to be proportional to the third power of the latter. The result for the surface three-body recombination rate constant at $4.6\mathrm{T}$, $L_s=2.0\left(7\right)\times {10}^{-25}{\mathrm{cm}}^4∕\mathrm{s}$, significantly reduces the discrepancy between the theory and earlier measurements where the surface density was inferred from the adsorption isotherm. We also measured the three-body rate constant on a 0.1% ${}^3\mathrm{He}\text{−}{}^4\mathrm{He}$ film and found $L_s=1.3\left(4\right)\times {10}^{-24}{\mathrm{cm}}^4∕\mathrm{s}$. This larger value is attributed to an increased delocalization of adsorbed hydrogen atoms in the direction normal to the surface.

We optimize the turning on of a one-dimensional optical potential, $V_L(x,t)=S\left(t\right)V_0{\cos }^2\left(kx\right)$ to obtain the optimal turn-on function $S\left(t\right)$ so as to load a Bose-Einstein condensate into the ground state of the optical lattice of depth $V_0$. Specifically, we minimize interband excitations at the end of the turn-on of the optical potential at the final ramp time $t_r$, where $S\left(t_r\right)=1$, given that $S\left(0\right)=0$. Detailed numerical calculations confirm that a simple unit cell model is an excellent approximation when the turn-on time $t_r$ is long compared with the inverse of the band excitation frequency and short in comparison with nonlinear time $\hslash ∕\mu$ where $\mu$ is the chemical potential of the condensate. We demonstrate using the Gross-Pitaevskii equation with an optimal turn-on function $S\left(t\right)$ that the ground state of the optical lattice can be loaded with no significant excitation even for times $t_r$ on the order of the inverse band excitation frequency.

We investigate the temporal fluctuations characteristic of the formation of molecular dimers from ultracold fermionic atoms via Raman photoassociation. The quantum fluctuations inherent to the initial atomic state result in large fluctuations in the passage time from atoms to molecules. Assuming degeneracy of kinetic energies of atoms in the strong coupling limit, we find that a heuristic classical stochastic model yields qualitative agreement with the full quantum treatment in the initial stages of the dynamics. We also show that in contrast to the association of atoms into dimers, the reverse process of dissociation from a condensate of bosonic dimers exhibits little passage time fluctuations. Finally, we explore effects due to the nondegeneracy of atomic kinetic energies.

The atom-photon controlled phase-flip gates using vacuum Rabi splitting proposed by Duan and Kimble [Phys. Rev. Lett. 92, 127902 (2004)] are simulated by a quantum trajectory approach. Atomic nonradiative dephasing and intracavity loss due to absorption and scattering by cavity mirrors are taken into account in addition to atomic spontaneous emission. The gate fidelity calculated by the trajectory approach is compared with that obtained by a simple amplitude-damping model. The gate fidelity under the condition of no photon loss is also discussed.

Exact three-dimensional quantum calculations of muon exchange between muonic hydrogen and carbon for collision energies in the range ${10}^{-3}–100\mathrm{eV}$, are presented. Muon transfer rates at thermal and epithermal energies are calculated including partial waves up to $J=7$. The relative populations of the final states are also given. The results show that above $1\mathrm{eV}$, the relative population of ${\left(\mu \mathrm{C}\right)}_{n=5}^{5+}$ can reach up to 30%.

We describe situations in which appreciable radiation-induced excitation is predicted to occur in a two-state quantum system even though the radiation has no frequency component at the Bohr transition frequency. These are illustrated with numerical simulations and analytical results of first- and third-order time-dependent perturbation theory for an example, in which frequencies are limited to a finite range and the carrier frequency may or may not fall within this interval. For appropriate pulse areas and detunings complete excitation is possible, even when the pulse has no resonant frequencies.

We report on a measurement of splitting in the excitation spectrum of a condensate driven by an optical traveling wave. Experimental results are compared to a numerical solution of the Gross-Pitaevskii equation, and analyzed by a simple two-level model and by the more complete band theory, treating the driving beams as an optical lattice. In this picture, the splitting is a manifestation of the energy gap between neighboring bands that opens on the boundary of the Brillouin zone.

Chaos-pass filtering (CPF) of semiconductor lasers has been studied theoretically. CPF is a phenomenon which occurs in laser chaos synchronization by injection locking and is a fundamental technique for the extraction of messages at the receiver laser in chaotic communications systems. We employ a simple theory based on driven damped oscillators to clarify the physical background of CPF. The receiver laser is optically driven by injection from the transmitter laser. We have numerically investigated the response characteristics of the receiver when it is driven by periodic (message) and chaotic (carrier) signals. It is thereby revealed that the response of the receiver laser in the two cases is quite different. For the periodic drive, the receiver exhibits a response depending on the signal frequency, while the chaotic drive provides a frequency-independent synchronous response to the receiver laser. We verify that the periodic and chaotic drives occur independently in the CPF response, and, consequently, CPF can be clearly understood in the difference of the two drives. Message extraction using CPF is also examined, and the validity of our theoretical explanation for the physical mechanism underlying CPF is thus verified.