Effect of Debye plasmas on the dispersion coefficients $C_8$, $C_{10}$, and $C_{12}$ for interactions between atoms has been investigated using highly accurate correlated exponential basis functions. In the free-atom case, the dispersion $C_{12}$ coefficient and the hexadecapole polarizability for helium are reported. The dispersion coefficients, hexadecapole polarizability, and $1s5g$ ${}^1{G}^e$ state energy of helium for different screening parameters are also reported.

We report detailed measurements of high-order harmonic generation in chloromethane molecules (${\mathrm{CCl}}_4$, ${\mathrm{CHCl}}_3$, and ${\mathrm{CH}}_2$${\mathrm{Cl}}_2$) to show that fingerprints of symmetry and electronic structure can be decoded from high-order harmonic generation even in complex randomly oriented molecules. In our measurements, orbital symmetries of these molecules are manifested as both extended harmonic cutoffs and a local minimum in the ellipticity dependence of the cut-off harmonics, suggesting the occurrence of quantum interferences during ionization. The harmonic spectra exhibit distinct interference minima at $~42$ and $~60$ eV. We attribute the former to the Cooper minimum in the photoionization cross section and the latter to intramolecular interference during the recombination process.

We prove a bijective mapping between the set of $v$-representable one-particle densities and the set of $v$-representable density matrix operators for certain sets of external potentials $v$. The physically most important case is the set of all external potentials describing systems interacting with a laser in dipole approximation. No further restriction with respect to the initial configuration or time dependence of the electric field is required.

The lifetime of an unstable state or resonance formed as an intermediate state in two-body scattering is known to be related to the dwell time or the time spent within a given region of space by the two interacting particles. This concept is extended to the case of three-body systems and a relation connecting the three-body dwell time with the two-body dwell times of the substructures of the three-body system is derived for the case of separable wave functions. The Kapur-Peierls formalism is revisited to discover one of the first definitions of dwell time in the literature. An extension of the Kapur-Peierls formalism to the three-body case shows that the lifetime of a three-body resonance can indeed be given by the three-body dwell time.

Quantum Darwinism provides an information-theoretic framework for the emergence of the objective, classical world from the quantum substrate. The key to this emergence is the proliferation of redundant information throughout the environment where observers can then intercept it. We study this process for a purely decohering interaction when the environment, $\mathcal{E}$, is in a nonideal (e.g., mixed) initial state. In the case of good decoherence, that is, after the pointer states have been unambiguously selected, the mutual information between the system, $\mathcal{S}$, and an environment fragment, $\mathcal{F}$, is given solely by $\mathcal{F}$’s entropy increase. This demonstrates that the environment’s capacity for recording the state of $\mathcal{S}$ is directly related to its ability to increase its entropy. Environments that remain nearly invariant under the interaction with $\mathcal{S}$, either because they have a large initial entropy or a misaligned initial state, therefore have a diminished ability to acquire information. To elucidate the concept of good decoherence, we show that, when decoherence is not complete, the deviation of the mutual information from $\mathcal{F}$’s entropy change is quantified by the quantum discord, i.e., the excess mutual information between $\mathcal{S}$ and $\mathcal{F}$ is information regarding the initial coherence between pointer states of $\mathcal{S}$. In addition to illustrating these results with a single-qubit system interacting with a multiqubit environment, we find scaling relations for the redundancy of information acquired by the environment that display a universal behavior independent of the initial state of $\mathcal{S}$. Our results demonstrate that Quantum Darwinism is robust with respect to nonideal initial states of the environment: the environment almost always acquires redundant information about the system but its rate of acquisition can be reduced.

Decoherence for a one-dimensional coupled-resonator waveguide with a two-level system inside one of the resonators, induced by their interaction with corresponding environments, is investigated. Each environment is modeled as a continuum of harmonic oscillators. By finding the eigenstates of the hybrid system, which is the dressed state of the hybrid system, we calculate the lifetime of one excitation, which characterizes the existence of quantum coherence in such hybrid systems and the basic quantum nature.

We study entanglement degradation of two noninteracting qubits subject to independent baths with broadband spectra typical of solid-state nanodevices. We obtain the analytic form of the concurrence in the presence of adiabatic noise for classes of entangled initial states presently achievable in experiments. We find that adiabatic (low-frequency) noise affects entanglement reduction analogously to pure dephasing noise. Due to quantum (high-frequency) noise, entanglement is totally lost in a state-dependent finite time. The possibility of implementing on-chip local and entangling operations is briefly discussed.

We analyze the time-domain optical response of quantum well (QW) media in the quasiequilibrium approximation. The resulting macroscopic polarization can be expressed as a convolution integral that permits a simple and efficient numerical implementation for its use in dynamical modeling. As a practical example, the resulting polarization is used in conjunction with a travelling-wave model (TWM) for analyzing saturable absorption as a pulse propagates in a waveguide that incorporates an unpumped QW in its core. Frequency-selective saturable absorption and pulse distortion are observed.

Simple analytical approaches for implementing strong field coherent control schemes are often elusive due to the complexity of the interaction between the intense excitation field and the system of interest. Here, we demonstrate control over multiphoton excitation in a three-level resonant system using simple, analytically derived ultrafast pulse shapes. We utilize a two-dimensional spatiotemporal control technique, in which temporal focusing produces a spatially dependent quadratic spectral phase, while a second, arbitrary phase parameter is scanned using a pulse shaper. In the current work, we demonstrate weak-to-strong field excitation of ${}^{85}\mathrm{Rb}$, with a $\pi$ phase step and the quadratic phase as the chosen control parameters. The intricate dependence of the multilevel dynamics on these parameters is exhibited by mapping the data onto a two-dimensional control landscape. Further insight is gained by simulating the complete landscape using a dressed-state, time-domain model, in which the influence of individual shaping parameters can be extracted using both exact and asymptotic time-domain representations of the dressed-state energies.

We demonstrate spatially resolved, coherent excitation of Rydberg atoms on an atom chip. Electromagnetically induced transparency (EIT) is used to investigate the properties of the Rydberg atoms near the gold-coated chip surface. We measure distance-dependent shifts ($~$$10$ MHz) of the Rydberg energy levels caused by a spatially inhomogeneous electric field. The measured field strength and distance dependence is in agreement with a simple model for the electric field produced by a localized patch of Rb adsorbates deposited on the chip surface during experiments. The EIT resonances remain narrow ($<4$ MHz) and the observed widths are independent of atom-surface distance down to $~$$20$ $\mu$m, indicating relatively long lifetime of the Rydberg states. Our results open the way to studies of dipolar physics, collective excitations, quantum metrology, and quantum information processing involving interacting Rydberg excited atoms on atom chips.

Numerical solutions of the time-dependent Schrödinger equation (TDSE) for a two-dimensional ${\mathrm{H}}_2{}^{+}$ molecule excited by a bichromatic ultrashort intense circularly polarized laser pulse with frequencies ${\omega }_0$ and $2{\omega }_0$ and relative carrier envelope phase $\varphi$ are used to explore the generation of high-order elliptically polarized harmonics as a function of internuclear distance $R$. Optimal values of $\varphi$ and $R$ for efficient and maximum molecular high-order harmonic generation (MHOHG) are determined from a classical model of collision with neighboring ions and confirmed from the TDSE nonperturbative simulations. Maximum elliptically polarized harmonic energies of $I_p+13.5U_p$ are found, where $I_p$ is the ionization potential and $U_p=I_0/4m_e{\omega }_0^2$ is the ponderomotive energy at intensity $I_0$ and frequency ${\omega }_0$. The polarization properties of MHOHG, phase difference $\delta$, ellipticity $\varepsilon$, and orientation angle $\phi$ are presented as well. The high efficiency of the proposed MHOHG scheme should be useful for production of elliptically polarized attosecond extreme ultraviolet pulses.

We perform a rigorous, semianalytic study of the recollision excitation with subsequent tunneling ionization (RESI) mechanism in laser-induced nonsequential double ionization (NSDI), based on the strong-field approximation. We show that the shapes of the electron momentum distributions carry information about the bound state with which the first electron collides, the bound state to which the second electron is excited, and the type of electron-electron interaction. Furthermore, one may define a driving-field intensity threshold for the RESI physical mechanism. At the threshold, the kinetic energy of the first electron, upon return, is just sufficient to excite the second electron. We compute the distributions for helium and argon in the threshold and above-threshold intensity regimes. In the latter case, we relate our findings to existing experiments. The electron momentum distributions encountered are symmetric with respect to all quadrants of the plane spanned by the momentum components parallel to the laser-field polarization, instead of concentrating on only the second and fourth quadrants. The above-mentioned momentum constraints, together with the strong dependence of the distributions on the bound states involved, may be important for singling out the RESI mechanism in actual physical situations and using NSDI in ultrafast imaging.

We study the ground state of few bosons with repulsive dipole-dipole interaction in a quasi-one-dimensional harmonic trap by means of the exact diagonalization method. Up to three interaction regimes are found, depending on the strength of the dipolar interaction and the ratio of transverse to axial oscillator lengths: a regime where the dipolar Bose gas resembles a system of weakly $\delta$-interacting bosons, a second regime where the bosons are fermionized, and a third regime where the bosons form a Wigner crystal. In the first two regimes, the dipole-dipole potential can be replaced by a $\delta$ potential. In the crystalline state, the overlap between the localized wave packets is strongly reduced and all the properties of the boson system equal those of its fermionic counterpart. The transition from the Tonks-Girardeau gas to the solidlike state is accompanied by a rapid increase of the interaction energy and a considerable change of the momentum distribution, which we trace back to the different short-range correlations in the two interaction regimes.

We study formation of rotating three-dimensional high-order solitons (azimuthons) in Bose Einstein condensate with attractive nonlocal nonlinear interaction. In particular, we demonstrate formation of toroidal rotating solitons and investigate their stability. We show that variational methods allow a very good approximation of such solutions and predict accurately the soliton rotation frequency. We also find that these rotating localized structures are very robust and persist even if the initial condensate conditions are rather far from the exact soliton solutions. Furthermore, the presence of repulsive contact interaction does not prevent the existence of those solutions, but allows one to control their rotation. We conjecture that self-trapped azimuthons are generic for condensates with attractive nonlocal interaction.

A method is proposed to directly measure the temperature of a gas of weakly interacting fermionic atoms loaded into an optical lattice. This technique relies on Raman spectroscopy and is applicable to experimentally relevant temperature regimes. Additionally, a similar spectroscopy scheme can be used to obtain information on the quasiparticle properties and Hubbard bands of the metallic and Mott-insulating states of interacting fermionic spin mixtures. These two methods provide experimentalists with probes to accurately characterize fermionic quantum gases confined to optical lattices.

Correlation function expressions for multidimensional photoelectron signals obtained for the response of electrons and nuclei in molecules to multiple ultrafast optical or x-ray pulses are derived using a superoperator formalism. For classical fields and quantum matter, these signals are recast as modulus squares of transition amplitudes which depend on the pulse bandshapes. A vibrational wave-packet representation which does not involve amplitudes is derived when the nuclear dynamics is calculated classically. In the case of a quantum radiation field, the signals depend on multipoint correlation functions of field operators. Photoelectron spectroscopy with entangled photons may be studied using this formalism.

The steering of a self-guided beam in a dye-doped nematic liquid crystal caused by an external illumination (control beam) that induces changes in the refractive index of the medium is theoretically analyzed. The interaction between the control beam and the dye molecules modifies the anchoring of the nematic molecules, so changing the director orientation in the bulk of the medium. Beam evolution is investigated by use of a modulation theory approach. It is found that the beam trajectory is independent of the beam profile, as long as this profile is self-similar. Solutions obtained from the modulation theory approach are in excellent agreement with numerical solutions.

Exciton fine-structure splittings within quantum dots introduce phase differences between the two biexciton decay paths that greatly reduce the entanglement of photon pairs generated via biexciton recombination. We analyze this problem in the frequency domain and propose a practicable method to compensate the phase difference by inserting a spatial light modulator, which substantially improves the entanglement of the photon pairs without any loss.

By fitting the Dunham-Watson model to extensive rotational and vibrational spectroscopic data of isotopic variants of CO, and by using existing precise masses of ${}^{13}\mathrm{C}$,${}^{16}\mathrm{O}$, and ${}^{18}\mathrm{O}$ from Penning-trap mass spectrometry, we determine the atomic mass of ${}^{17}\mathrm{O}$ to be $M$[${}^{17}\mathrm{O}$] $=16.999\hspace{0.5em}131\hspace{0.5em}644(30)$ u, where the uncertainty is purely statistical. Using Penning-trap mass spectrometry, we have also directly determined the atomic mass of ${}^{17}\mathrm{O}$ with the more precise result $M$[${}^{17}\mathrm{O}$] $=16.999\hspace{0.5em}131\hspace{0.5em}756\hspace{0.5em}6(9)$ u. The Dunham-Watson model applied to the molecular spectroscopic data hence predicts the mass of ${}^{17}\mathrm{O}$ to better than 1 part in ${10}^8$.

We consider ultracold collisions of polar molecules confined in a one-dimensional optical lattice. Using a quantum scattering formalism and a frame transformation method, we calculate elastic and chemical quenching rate constants for fermionic molecules. Taking ${}^{40}\mathrm{K}$${}^{87}\mathrm{Rb}$ molecules as a prototype, we find that the rate of quenching collisions is enhanced at zero electric field as the confinement is increased but that this rate is suppressed when the electric field is turned on. For molecules with 500 nK of collision energy, for realistic molecular densities, and for achievable experimental electric fields and trap confinements, we predict lifetimes for KRb molecules to be $1$ s. We find a ratio of elastic to quenching collision rates of about $100$, which may be sufficient to achieve efficient evaporative cooling of polar KRb molecules.