We investigate theoretic high-order harmonic generation and single attosecond pulse generation in an orthogonally polarized two-color laser field, which is synthesized by a mid-infrared (IR) pulse ($12.5$ fs, $2000$ nm) in the $y$ component and a much weaker ($12$ fs, $800$ nm) pulse in the $x$ component. We find that the width of the harmonic plateau can be extended when a static electric field is added in the $y$ component. We also investigate emission time of harmonics in terms of a time-frequency analysis to illustrate the physical mechanism of high-order harmonic generation. We calculate the ionization rate using the Ammosov-Delone-Krainov model and interpret the variation of harmonic intensity for different static electric field strengths. When the ratio of strengths of the static and the $y$-component laser fields is 0.1, a continuous harmonic spectrum is formed from $220$ to $420$ eV. By superposing a properly selected range of the harmonic spectrum from $300$ to $350$ eV, an isolated attosecond pulse with a duration of about $75$ as is obtained, which is near linearly polarized.

A standing-wave light-pulse sequence is demonstrated that places atoms into a superposition of wave packets with precisely controlled displacements that remain constant for times as long as 1 s. The separated wave packets are subsequently recombined, resulting in atom interference patterns that probe energy differences of $\approx {10}^{-34}$ J and can provide acceleration measurements that are insensitive to platform vibrations.

In this article we discuss possibilities for manipulating a matter wave with time-dependent potentials. Assuming a specific setup on an atom chip, we explore how one can focus, accelerate, reflect, and stop an atomic wave packet, with, for example, electric fields from an array of electrodes. We also utilize this method to initiate coherent splitting or an arbitrary wave form. Special emphasis is put on the robustness of the control schemes. We begin with the wave packet of a single atom and extend this to a Bose-Einstein condensate in the Gross-Pitaevskii picture. In analogy to laser pulse shaping with its wide variety of applications, we expect this work to form the base for more complex time-dependent potentials, eventually leading to matter-wave pulse shaping with numerous applications.

Every measurement of the population in an uncorrelated ensemble of two-level systems is limited by what is known as the quantum projection noise limit. Here, we present quantum-projection-noise-limited performance of a Ramsey-type interferometer using freely propagating coherent atoms. The experimental setup is based on an electro-optic modulator in an inherently stable Sagnac interferometer, optically coupling the two interfering atomic states via a two-photon Raman transition. Going beyond the quantum projection noise limit requires the use of reduced quantum uncertainty (squeezed) states. The experiment described demonstrates atom interferometry at the fundamental noise level and allows the observation of possible squeezing effects in an atom laser, potentially leading to improved sensitivity in atom interferometers.

We use the diagrammatic $T$-matrix approach to analyze the three-body scattering problem between two identical fermions and a third particle (which could be a different species of fermion or a boson). We calculate the $s$-wave dimer-atom scattering length for all mass ratios, and our results exactly match the results of Petrov. In particular, we list the exact dimer-atom scattering lengths for all available two-species Fermi-Fermi and Bose-Fermi mixtures. In addition, unlike that of the equal-mass-particles case where the three-body scattering $T$ matrix decays monotonically as a function of the outgoing momentum, we show that, after an initial rapid drop, this function changes sign and becomes negative at large momenta and then decays slowly to zero when the mass ratio of the fermions to the third particle is higher than a critical value (around $6.5$). As the mass ratio gets higher, modulations of the $T$ matrix become more apparent with multiple sign changes, related to the “fall of a particle to the center” phenomenon and to the emergence of three-body Efimov bound states.

We derive the steady-state solution of the Fokker-Planck equation that describes the dynamics of the nondegenerate optical parametric oscillator in the truncated Wigner representation of the density operator. We assume that the pump mode is strongly damped, which permits its adiabatic elimination. When the elimination is correctly executed, the resulting stochastic equations contain multiplicative noise terms and do not admit a potential solution. However, we develop a heuristic scheme leading to a satisfactory steady-state solution. This provides a clear view of the intracavity two-mode entangled state valid in all operating regimes of the optical parametric oscillator. A non-Gaussian distribution is obtained for the above threshold solution.

The population distribution within the ground state of an atomic ensemble is of great significance in a variety of quantum-optics processes. We present a method to reconstruct the detailed population distribution from a set of absorption measurements with various frequencies and polarizations, by utilizing the differences between the dipole matrix elements of the probed transitions. The technique is experimentally implemented on a thermal rubidium vapor, demonstrating a population-based analysis in two optical-pumping examples. The results are used to verify and calibrate an elaborated numerical model, and the limitations of the reconstruction scheme, which result from the symmetry properties of the dipole matrix elements, are discussed.

Simulations show that intense plasma-amplified pulses of 100 fs duration and below are feasible by seeding specifically tailored plasma with an ultrashort pulse of high harmonic radiation. Seeding overcomes gain narrowing by driving amplifying media into saturation earlier, and compensates for reduced gain resulting from boosting the lasing transition linewidth. We conclude that ultrahigh intensities (above ${10}^{16}$ W cm${}^{-2}$) could be reached.

We demonstrate by experiment and theory that a light pulse propagating through a Si-based photonic-crystal waveguide is adiabatically blueshifted when the refractive index of the Si is reduced on a femtosecond time scale. Thanks to the use of slow-light modes, we are able to shift a $1.3$-ps pulse at telecom frequencies by 0.3 THz with an efficiency as high as $80\%$ in a waveguide as short as $19\mu$m. An analytic theory reproduces the experimental data excellently, which shows that adiabatic dynamics are possible even on the femtosecond time scale as long as the external stimulus conserves the spatial symmetry of the system.

We demonstrate controlled polarization rotation of an optical field conditional on the presence of a second field. Induced rotations of greater than $\pi /2$ rad are seen with a transmission of $95\%$, corresponding to a ratio of phase shift to absorption of $40\pi$. This combination of large, controlled rotation and low loss is well suited for the manipulation of light pulses.

Efficient collection of fluorescence from trapped ions is crucial for quantum optics and quantum computing applications, specifically for qubit state detection and in generating single photons for ion-photon and remote ion entanglement. In a typical setup, only a few percent of the ion fluorescence is intercepted by the aperture of the imaging optics. We employ a simple metallic spherical mirror integrated with a linear Paul ion trap to achieve a photon collection efficiency of at least $10\%$ from a single Ba${}^{+}$ ion. An aspheric corrector is used to reduce the aberrations caused by the mirror and achieve high image quality.

We suggest and demonstrate a novel source of two-photon multipartite entangled states which exploits the transverse spatial structure of spontaneous parametric down-conversion together with a programmable spatial light modulator (SLM). The one-dimensional SLM is used to perform polarization entanglement purification and to realize arbitrary phase gates between polarization and momentum degrees of freedom of photons. We experimentally demonstrate our scheme by generating two-photon three-qubit linear cluster states with high fidelity using a diode laser pump with a limited coherence time and power on the crystal as low as $~2.5$ mW.

We propose a scheme to achieve a strong coupling between two distant symmetrically placed electronic spins (such as nitrogen-vacancy centers in diamonds) by using a quantized nanomechanical resonator (NAMR) as a data bus. These distant spins (without any direct interaction) simultaneously couple to a common NAMR. When the detunings between effective spin transition frequencies and the fundamental frequency of the NAMR are large enough, an effective coupling could be induced between the two distant electronic spins. The value of such a coupling could be significantly large (i.e., up to a few kilohertz). This induced interaction between the two spins can be used to implement an iSWAP quantum gate, and to probabilistically prepare two-spin maximal entangled states by detecting the frequency shifts of the NAMR.

The reduced-added Green’s function technique in the quantum defect theory combines the advantages of analytical and ab initio methods in calculating frequency-dependent (dynamic) polarizabilities of atoms and molecules, providing an exact account for the high-excited and continuum electronic states. In the present paper this technique is modified to take into account the long-range dipole potential of a polar molecule core. The method developed is applied to calculation of the dynamic polarizability tensors of alkali-metal hydrides LiH and NaH as well as to some fluorides (CaF and BF) in the frequency range up to the first resonances. The results are in good agreement with ab initio calculations available for some frequencies.

Resonance states of a two-electron quantum dots are studied using a variational expansion with both real basis-set functions and complex scaling methods. The two-electron entanglement (linear entropy) is calculated as a function of the electron repulsion at both sides of the critical value, where the ground (bound) state becomes a resonance (unbound) state. The linear entropy and fidelity and double orthogonality functions are compared as methods for the determination of the real part of the energy of a resonance. The complex linear entropy of a resonance state is introduced using complex scaling formalism.

With the aim of describing real-time electron dynamics, we introduce an adiabatic approximation for the equation of motion of the one-body reduced density matrix (one-matrix). The eigenvalues of the one-matrix, which represent the occupation numbers of single-particle orbitals, are obtained from the constrained minimization of the instantaneous ground-state energy functional rather than from their dynamical equations. The performance of the approximation vis-à-vis nonadiabatic effects is assessed in real-time simulations of a two-site Hubbard model. Due to Landau-Zener-type transitions, the system evolves into a nonstationary state with persistent oscillations in the observables. The amplitude of the oscillations displays a strongly nonmonotonic dependence on the strength of the electron-electron interaction and the rate of variation of the external potential. We interpret an associated resonance behavior in the phase of the oscillations in terms of “scattering” with spectator energy levels. To clarify the motivation for the minimization condition, we derive a sequence of energy functionals $E_v^{(n)}$, for which the corresponding sequence of minimizing one-matrices is asymptotic to the exact one-matrix in the adiabatic limit.

Quantum-scattering calculations at ultralow (close to ${10}^{-6}$ cm${}^{-1}$) collision energies are carried out for the Cs dimer in its spin-stretched triplet state, interacting with helium. An ab initio potential energy surface is computed and employed, while the target molecule is kept in its ground vibrational state and several excitated initial rotational states are considered in the quantum dynamics. The highly anisotropic interaction is seen to cause, in spite of its weakness, internal energy quenching rates comparable with the efficiency of the collisional cooling of relative kinetic energies. The rates of spin-flip processes are also analyzed and compared with pure rotational quenching events.

Hyperpolarized K-${}^3\mathrm{He}$ comagnetometers have been used for tests of fundamental physics and inertial rotation sensing. These experiments will demonstrate increased sensitivity if the ${}^3\mathrm{He}$ buffer gas is replaced with ${}^{21}\mathrm{Ne}$. We measure the parameters necessary to realize implementation of an alkali-metal–${}^{21}\mathrm{Ne}$ comagnetometer for two promising alkali-metal species, Rb and K. The spin-exchange rate constant for K with ${}^{21}\mathrm{Ne}$ and Rb with ${}^{21}\mathrm{Ne}$ are measured using two different methods. We also make the first measurement of the K-${}^{21}\mathrm{Ne}$ contact spin interaction. Measurements for the Rb-${}^{21}\mathrm{Ne}$ contact spin interaction, as well as the spin-destruction coefficients for ${}^{21}\mathrm{Ne}$ with both alkali-metal species are consistent with previous measurements. Additionally the quadrupolar spin-relaxation rate of ${}^{21}\mathrm{Ne}$ is measured. Finally, the feasibility of utilizing polarized ${}^{21}\mathrm{Ne}$ for operation in a comagnetometer is discussed.

The angular distribution of the Kr $4p$ photoelectrons was investigated in the photon energy range of the $(3d){}^{-1}\to \mathit{np}$ resonant excitations. The experimental dipole ($\beta$) and nondipole ($\gamma$ and $\delta$) anisotropy parameters were determined for the spin-orbit components of the Kr $4p$ shell. A simple theoretical model was developed for the description of the photoionization and excitation processes. An interference effect was observed between the direct photoionization and the resonant excitation participator Auger decay processes in the photon energy dependence of the experimental anisotropy parameters.