We present a numerical scheme to study the dynamics of slow light and light storage in an electromagnetically-induced-transparency (EIT) medium at finite temperatures. Allowing for the motional coupling, we derive a set of coupled Schrödinger equations describing a boosted closed three-level EIT system according to the principle of Galilean relativity. The dynamics of a uniformly moving EIT medium can thus be determined by numerically integrating the coupled Schrödinger equations for atoms plus one ancillary Maxwell-Schrödinger equation for the probe pulse. The central idea of this work rests on the assumption that the loss of ground-state coherence at finite temperatures can be ascribed to the incoherent superposition of density matrices representing the EIT systems with various velocities. Close agreements are demonstrated in comparing the numerical results with the experimental data for both slow light and light storage. In particular, the distinct characters featuring the decay of ground-state coherence can be well verified for slow light and light storage. This warrants that the current scheme can be applied to determine the decaying profile of the ground-state coherence as well as the temperature of the EIT medium.

Refraction of black and gray solitons at boundaries separating different defocusing Kerr media is analyzed within a Helmholtz framework. A universal nonlinear Snell’s law is derived that describes gray soliton refraction, in addition to capturing the behavior of bright and black Kerr solitons at interfaces. Key regimes, defined by beam and interface characteristics, are identified, and predictions are verified by full numerical simulations. The existence of a unique total nonrefraction angle for gray solitons is reported; both internal and external refraction at a single interface is shown possible (dependent only on incidence angle). This, in turn, leads to the proposal of positive or negative lensing operations on soliton arrays at planar boundaries.

We analyze the asymptotic behavior of the cross-polarized enhancement factor in the framework of the standard low-packing-density theory of coherent backscattering by discrete random media composed of spherically symmetric particles. It is shown that if the particles are strongly absorbing or if the smallest optical dimension of the particulate medium (i.e., the optical thickness of a plane-parallel slab or the optical diameter of a spherically symmetric volume) approaches zero, then the cross-polarized enhancement factor tends to its upper-limit value 2. This theoretical prediction is illustrated using direct computer solutions of the Maxwell equations for spherical volumes of discrete random medium.

In this article, we derive the general exact solution of the modulation instability gain. The solution described here is valid for 1-D, 2-D, and 3-D cases considering any temporal response function of the medium and with possible higher order Kerr nonlinearities. In particular, we show that the gain induced by modulation instability is initial condition dependent, while the usual calculations do not lead to such a dependence. Applications for current and high-interest nonlinear propagation problems, such as 1-D optical fiber propagation with delayed Raman response and 2-D filamentation in gases, are investigated in detail. More specifically, we demonstrate that the 2-D model of filamentation based on the balance between higher order Kerr terms leads to a modulation instability window. The impact of both self-steepening and space-time defocusing effects is also highlighted. Finally, we discuss the influence of the finite-time response of the different order electronic Kerr effects on the growth of the expected modulation instability bands.

We investigate the nature of the pulse sequence so that unwanted transitions in quantum systems can be inhibited optimally. For this purpose we show that the sequence of pulses proposed by Uhrig [Phys. Rev. Lett. 98, 100504 (2007)] in the context of inhibition of environmental dephasing effects is optimal. We derive exact results for inhibiting the transitions and confirm the results numerically. We posit a very significant improvement by usage of the Uhrig sequence over an equidistant sequence in decoupling a quantum system from unwanted transitions. The physics of inhibition is the destructive interference between transition amplitudes before and after each pulse.

Single-shot carrier-envelope-phase (CEP) tagging is combined with a reaction mircoscope (REMI) to investigate CEP-dependent processes in atoms. Excellent experimental stability and data acquisition longevity are achieved. Using this approach, we study the CEP effects for nonsequential double ionization of argon in 4-fs laser fields at 750 nm and an intensity of $1.6\times {10}^{14}$ W/cm${}^2$. The Ar${}^{2+}$ ionization yield shows a pronounced CEP dependence which compares well with recent theoretical predictions employing quantitative rescattering theory [S. Micheau et al., Phys. Rev. A 79, 013417 (2009)]. Furthermore, we find strong CEP influences on the Ar${}^{2+}$ momentum spectra along the laser polarization axis.

We study the collapse and revival of coherence induced by dipolar spin waves in a trapped gas of ${}^{87}\mathrm{Rb}$ atoms. In particular, we observe spatially localized collapse and revival of Ramsey fringe contrast and show how the pattern of coherence depends on the strength of the spin-wave excitation. We find that the spatial character of the coherence dynamics is incompatible with a simple model based only on position-space overlap of wave functions. We show that this phenomenon requires a full phase-space description of the atomic spin using a quantum Boltzmann transport equation, which highlights spin-wave-induced coherent spin currents and the ensuing dynamics they drive.

Independently, in the mid-1980s, several groups proposed to bosonize the density-functional theory (DFT) for fermions by writing a Schrödinger equation for the density amplitude $\rho (\mathbf{r}){}^{1/2}$, with $\rho (\mathbf{r})$ as the ground-state electron density, the central tool of DFT. The resulting differential equation has the DFT one-body potential $V(\mathbf{r})$ modified by an additive term $V_P(\mathbf{r})$ where $P$ denotes Pauli. To gain insight into the form of the Pauli potential $V_P(\mathbf{r})$, here, we invoke the known Coulombic density, ${\rho }_{\infty }(r)$ say, calculated analytically by Heilmann and Lieb (HL), by summation over the entire hydrogenic bound-state spectrum. We show that $V_{P\infty }(r)$ has simple limits for both $r$ tends to infinity and $r$ approaching zero. In particular, at large $r$, $V_{P\infty }(r)$ precisely cancels the attractive Coulomb potential $-{\mathit{Ze}}^2/r$, leaving $V(r)+V_{P\infty }(r)$ of $O(r^{-2})$ as $r$ tends to infinity. The HL density ${\rho }_{\infty }(r)$ is finally used numerically to display $V_{P\infty }(r)$ for all $r$ values.

The valence photoionization and resonant Auger decay at $4d$ resonances below the $4d$ ionization threshold in ${\mathrm{Sb}}_4$ clusters have been studied experimentally by means of photoelectron spectroscopy. The $4d$ absorption spectrum in the photon energy region from 30 to 36 eV has been recorded using the constant ionic state (CIS) partial electron yield (PEY), and the CIS spectra for various ionic states are presented. The photoelectron spectra at various resonant positions are recorded, and the results and their interpretation are presented. The findings provide experimental proof of the previous assignment of the various structures of the inner valence photoelectron spectrum.

Recently, position-based quantum cryptography has been claimed to be unconditionally secure. On the contrary, here we show that the existing proposals for position-based quantum cryptography are, in fact, insecure if entanglement is shared among two adversaries. Specifically, we demonstrate how the adversaries can incorporate ideas of quantum teleportation and quantum secret sharing to compromise the security with certainty. The common flaw to all current protocols is that the Pauli operators always map a codeword to a codeword (up to an irrelevant overall phase). We propose a modified scheme lacking this property in which the same cheating strategy used to undermine the previous protocols can succeed with a rate of at most $85\%$. We prove the modified protocol is secure when the shared quantum resource between the adversaries is a two- or three-level system.

We present a detailed rate analysis for a hybrid quantum repeater assuming perfect memories and using optimal probabilistic entanglement generation and deterministic swapping routines. The hybrid quantum repeater protocol is based on atomic qubit-entanglement distribution through optical coherent-state communication. An exact, analytical formula for the rates of entanglement generation in quantum repeaters is derived, including a study on the impacts of entanglement purification and multiplexing strategies. More specifically, we consider scenarios with as little purification as possible and we show that for sufficiently low local losses, such purifications are still more powerful than multiplexing. In a possible experimental scenario, our hybrid system can create near-maximally entangled ($F=0.98$) pairs over a distance of 1280 km at rates of the order of 100 Hz.

We have used velocity-map imaging to measure the three-dimensional momenta of electrons rescattered from Xe and Ar following the liberation of the electrons from these atoms by 45 fs, 800 nm intense laser pulses. Strong structure in the rescattering region is observed in both angle and energy, and is interpreted in terms of quantitative rescattering (QRS) theory. Momentum images have also been taken with two-color (800 nm $+$ 400 nm) pulses on Xe targets. A strong dependence of the spectra on the relative phase of the two colors is observed in the rescattering region. Interpretation of the phase dependence using both QRS theory and a full solution to the time-dependent Schrödinger equation shows that the rescattered electrons provide a much more robust method for determining the relative phase of the two colors than do the direct electrons.

Electronic reorganization during and after excitation by an intense ultrashort pulse is computed for LiH in a many-electron multireference time-dependent approach at a fixed nuclear geometry. The electronic dipole moment is used to probe the temporal response of the charge density. Above a field-strength threshold, there is an extensive Stark shifting and Rabi broadening of levels with corresponding distortion of the charge distribution whose response at strong fields is neither adiabatic nor diabatic. A nonresonant IR pulse is more effective in inducing charge shake-up during the pulse.

We study subsystem codes whose gauge group has local generators in two-dimensional (2D) geometry. It is shown that there exists a family of such codes defined on lattices of size $L\times L$ with the number of logical qubits $k$ and the minimum distance $d$ both proportional to $L$. The gauge group of these codes involves only two-qubit generators of type $\mathit{XX}$ and $\mathit{ZZ}$ coupling nearest-neighbor qubits (and some auxiliary one-qubit generators). Our proof is not constructive as it relies on a certain version of the Gilbert-Varshamov bound for classical codes. Along the way, we introduce and study properties of generalized Bacon-Shor codes that might be of independent interest. Secondly, we prove that any 2D subsystem $[n,k,d]$ code with spatially local generators obeys upper bounds $\mathit{kd}=O(n)$ and $d^2=O(n)$. The analogous upper bound proved recently for 2D stabilizer codes is ${\mathit{kd}}^2=O(n)$. Our results thus demonstrate that subsystem codes can be more powerful than stabilizer codes under the spatial locality constraint.

We propose an experimentally feasible scheme to produce bright quadricolor continuous-variable (CV) entanglement by a four-wave mixing process (FWM) with four-level atoms inside the optical ring cavities operating above threshold. The Stokes and anti-Stokes beams are generated via the pump beam (tuned close to one atomic transition) and the coupling beam (tuned to the resonance of another atomic transition), respectively. The quadruply resonant and narrowed linewidth of the cavity fields with different frequencies are achieved and quadricolor CV entanglement among the four cavity fields is demonstrated according to the criterion proposed by van Loock and Furusawa [Phys. Rev. A 67, 052315 (2003)]. This scheme provides a way to generate bright quadricolor CV entanglement and will be significant for applications in quantum information processing and quantum networks.

The transition energies and rates for the $2s^{2}2p^2$ ${}^3{P}_{1,2}$–$2s2p^3$ ${}^5{S}_2^o$ and $2s^{2}2p3s$–$2s^{2}2p3p$ intercombination transitions have been calculated using term-dependent nonorthogonal orbitals in the multiconfiguration Hartree-Fock approach. Several sets of spectroscopic and correlation nonorthogonal functions have been chosen to describe adequately term dependence of wave functions and various correlation corrections. Special attention has been focused on the accurate representation of strong interactions between the $2s2p^3$ ${}^{1,3}{P}_1^o$ and $2s^{2}2p3s$ ${}^{1,3}{P}_1^o$levels. The relativistic corrections are included through the one-body mass correction, Darwin, and spin-orbit operators and two-body spin-other-orbit and spin-spin operators in the Breit-Pauli Hamiltonian. The importance of core-valence correlation effects has been examined. The accuracy of present transition rates is evaluated by the agreement between the length and velocity formulations combined with the agreement between the calculated and measured transition energies. The present results for transition probabilities, branching fraction, and lifetimes have been compared with previous calculations and experiments.

We have measured double differential cross sections (DDCS) for proton fragment formation for fixed projectile energy losses as a function of projectile scattering angle in 75 keV $p$ $+$ ${\mathrm{H}}_2$ collisions. An oscillating pattern was observed in the angular dependence of the DDCS with a frequency about twice as large as what we found earlier for nondissociative ionization. Possible origins for this frequency doubling are discussed.

We have measured the reaction rates of trapped, buffer gas cooled ${\mathrm{Th}}^{3+}$ and various gases and have analyzed the reaction products using trapped ion mass spectrometry techniques. Ion trap lifetimes are usually limited by reactions with background molecules, and the high electron affinity of multiply charged ions such as ${\mathrm{Th}}^{3+}$ make them more prone to loss. Our results show that reactions of ${\mathrm{Th}}^{3+}$ with carbon dioxide, methane, and oxygen all occur near the classical Langevin rate, while reaction rates with argon, hydrogen, and nitrogen are orders of magnitude lower. Reactions of ${\mathrm{Th}}^{3+}$ with oxygen and methane proceed primarily via charge exchange, while simultaneous charge exchange and chemical reaction occurs between ${\mathrm{Th}}^{3+}$ and carbon dioxide. Loss rates of ${\mathrm{Th}}^{3+}$ in helium are consistent with reaction with impurities in the gas. Reaction rates of ${\mathrm{Th}}^{3+}$ with nitrogen and argon depend on the internal electronic configuration of the ${\mathrm{Th}}^{3+}$.