We discuss a method for creating bright matter solitons by loading a Bose-Einstein condensate of atoms in a driven tilted optical lattice. It is shown that one can realize the self-focusing regime for the wave-packet dynamics by properly adjusting the phase of the driving field with respect to the phase of Bloch oscillations. If atom-atom interactions are larger than some critical value $g_{\min }$, this self-focusing regime is followed by the formation of bright solitons. Increasing the interactions above another critical value $g_{\max }$ makes this process unstable. Instead of soliton formation one now meets the phenomenon of incoherent self-trapping. In this regime a fraction of atoms is trapped in incoherent localized wave packets, while the remaining atoms spread ballistically.

In a strongly pumped nondegenerate traveling-wave optical parametric amplifier, we produce a two-color squeezed vacuum with up to millions of photons per pulse. Our approach to registering this macroscopic quantum state is direct detection of a large number of transverse and longitudinal modes, which is achieved by making the detection time and area much larger than the coherence time and area, respectively. Using this approach, we obtain a record value of twin-beam squeezing for direct detection of bright squeezed vacuum. This makes direct detection of macroscopic squeezed vacuum a practical tool for quantum information applications.

We present rigorous performance bounds for the optimal dynamical decoupling pulse sequence protecting a quantum bit (qubit) against pure dephasing. Our bounds apply under the assumption of instantaneous pulses and of bounded perturbing environment and qubit-environment Hamiltonians such as those realized by baths of nuclear spins in quantum dots. We show that if the total sequence time is fixed the optimal sequence can be used to make the distance between the protected and unperturbed qubit states arbitrarily small in the number of applied pulses. If, on the other hand, the minimum pulse interval is fixed and the total sequence time is allowed to scale with the number of pulses, then longer sequences need not always be advantageous. The rigorous bound may serve as a testbed for approximate treatments of optimal decoupling in bounded models of decoherence.

Accurate quantum-mechanical calculations are carried out for antiproton capture by singly ionized He ions, that is, $\mathrm{p̄}+{\mathrm{He}}^{+}\to \mathrm{p̄}{\text{He}}^{2+}+e$, by the combined use of an $R$-matrix method and direct numerical solution. The total capture cross sections (or collision strengths) and the state distributions of the capture products, $\mathrm{p̄}{\mathrm{He}}^{2+}$, are calculated at collision energies ranging from 0 to $4$ eV. The present system is rich in resonances, which appear as a Rydberg series and are characterized as an electron attached to an ion core, $\mathrm{p̄}{\mathrm{He}}^{2+}$. Some resonance levels can be reproduced by a reasonable model based on molecular-quantum-defect theory. The capture into the highest energetically possible state of the products, $\mathrm{p̄}{\mathrm{He}}^{2+}$, always takes place overwhelmingly in the presence or absence of the resonances. However, owing to the resonances, the angular momentum distribution of the products varies considerably depending on the collision energy. The energy-averaged capture cross sections and the capture rate coefficients are also presented for the convenience of future experiments.

A multicoincidence velocity-map-imaging technique was employed to study the fragmentation of inner-shell excited furan molecules for the photon energies encompassing the C and O $K$ edges. We have analyzed the kinetic energy distributions and the momentum correlations of detected ionic fragments. Comparisons of our experimental observations with predictions of a Coulomb explosion model elucidate possible fragmentation pathways.

By the exchange of virtual microwave photon induced by a stripline cavity, we present a collective spin-qubit model for the indirect interaction between a superconducting charge-phase qubit and an ensemble of the polar molecules. More importantly, the high-order nonlinear interaction among the polar molecules is generated successfully by using the SU(2) commutation relations of the qubit. Numerical simulation shows that this high-order nonlinear interaction can lead to a strong macroscopic quantum coherent effect, even if the parameters including the molecular number are small. For a large molecular number, the Kerr nonlinear interaction is also obtained. Moreover, it is found that this Kerr nonlinear parameter depends linearly on the molecular number, and as a result, has a giant value, which is 2 to 3 orders of magnitude larger than that in the other proposal schemes of the solid-state systems. Our results present a way to investigate the quantum nonlinear dynamics of the polar molecules.

We conduct a numerical study on the giant optical resonances near the split photonic band edges of two-dimensional square lattices. Their quality factors are $1$ order of magnitude higher than those near the regular band edges. Such enhancement results from the efficient interference of multiple Bloch waves, which minimizes light leakage from the periodic pattern of finite size. The variation of the quality factor with the pattern size is nonmonotonic for the split band edge resonance, leading to an optimal size for the maximal quality factor.

The classical Lorentz oscillator model of bound electron motion ordinarily excludes magnetic forces at nonrelativistic intensities for the simple reason that their magnitude is small. However, perturbative and numerical results show that when the $\mathrm{v⃗}\times \mathrm{B⃗}$ term is retained, dynamically enhanced terms give rise to large amplitude, magnetically induced charge displacements at zero frequency and at twice the driving frequency in the Cartesian laboratory frame. Numerical simulations of electron motion are in accord with the predictions of perturbative theory for steady-state motion in the classical picture. Direct integration shows that magnetic response which is comparable to electric dipole response can arise in transparent dielectrics at optical frequencies. Parametric instability in the equations of motion is implicated as the source of rapid energy transfer from electric to magnetic motions by reduction of the equations to a complex Mathieu equation.

The cross section for double charge transfer between ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^{-}$ at low collision energies ($E⩽90$ eV) is calculated using a many-state molecular close-coupling model. The wave function is expanded in a diabatic representation of the seven lowest ${}^1{\Sigma }_g^{+}$ and the six lowest ${}^1{\Sigma }_u^{+}$ states of the hydrogen molecule. The calculated cross section shows clear oscillations as a function of the collision energy, similar to those observed experimentally. However, the magnitude of the calculated cross section is larger than found in experiments. Also, the cross section for double charge transfer in collisions between ${\mathrm{D}}^{+}$ and ${\mathrm{H}}^{-}$ is calculated.

A formalism based on a combination of differential geometry and perturbation theory is used to obtain analytic expressions for confined eigenmode changes due to general curvature effects. In cases of circular-shaped and helix-shaped structures, where alternative analytic solutions can be found, the perturbative solution is shown to yield the same result. The present technique allows the generalization of earlier results to arbitrary boundary conditions. The power of the method is illustrated using examples based on Maxwell’s and Schrödinger’s equations for applications in photonics and nanoelectronics.

We construct a quantum algorithm that creates the Laughlin state for an arbitrary number $n$ of particles for a filling fraction of one. This quantum circuit is efficient since it only uses $n(n-1)/2$ local qudit gates and its depth scales as $2n-3$. Furthermore, we prove the optimality of the circuit using permutation theory arguments and we compute exactly how entanglement develops along the action of each gate. Finally, we discuss its experimental feasibility by decomposing the qudits and the gates in terms of qubits and two qubit-gates, as well as its generalization to arbitrary filling fraction.

The stability of a one-parameter family of dissipative solitons seen in the cubic-quintic complex Ginzburg-Landau equation is studied. It is found that an unusually strong stability occurs for solitons controlled by the spectral filtering and nonlinearity saturation simultaneously, consistently with the linear stability analysis and confirmed by large-perturbation numerical simulations. Two universal types of bifurcations in the spectrum structure are demonstrated.

Optical aberrations are usually considered a drawback in optical systems. Here we show that through them a net cubic phase modulation can be imprinted on the wave front of a light beam, which after spatial Fourier transformation creates Airy beams. Experiments and supporting simulations demonstrate that appropriately adjusted cylindrical lenses can produce both one- and two-dimensional tunable Airy beams. The use of simple optical elements makes the approach attractive and convenient for generating intense femtosecond Airy beams and filaments. Moreover, we show that the Airy tunability is an excellent means of obtaining tailored filaments in both size and intensity.

We study the Zeno and anti-Zeno effects in a superconducting qubit interacting strongly and ultrastrongly with a microwave resonator. Using a model of a frequently measured two-level system interacting with a quantized mode, we predict different behaviors and total control of the Zeno times depending on whether the rotating-wave approximation can be applied in the Jaynes-Cummings model. As an example, we show the dependence of our results with the properties of the initial field states.

We describe a method that allows transient suppression of spontaneous emission-induced diffusion in the atom-optics realization of the kicked rotor. The system is prepared in an initial state with a momentum distribution concentrated in an interval much sharper than the Brillouin zone; the measure of the momentum distribution is restricted to this interval of quasimomenta. Because most of the atoms undergoing decoherence processes fall outside this detection range and thus are not detected, the measured signal is effectively free of decoherence-induced diffusion effects.

I report a tight upper bound of the maximum speed of evolution from one quantum state $\rho$ to another ${\rho }^{\prime }$ with fidelity $F(\rho ,{\rho }^{\prime })$ less than or equal to an arbitrary but fixed value under the action of a time-independent Hamiltonian. Since the bound is directly proportional to the average absolute deviation from the median of the energy of the state $\mathcal{D}E$, one may interpret $\mathcal{D}E$ as a meaningful measure of the maximum information-processing capability of a system.

We investigate general probabilistic theories in which every mixed state has a purification, unique up to reversible channels on the purifying system. We show that the purification principle is equivalent to the existence of a reversible realization of every physical process, that is, to the fact that every physical process can be regarded as arising from a reversible interaction of the system with an environment, which is eventually discarded. From the purification principle we also construct an isomorphism between transformations and bipartite states that possesses all structural properties of the Choi-Jamiołkowski isomorphism in quantum theory. Such an isomorphism allows one to prove most of the basic features of quantum theory, like, e.g., existence of pure bipartite states giving perfect correlations in independent experiments, no information without disturbance, no joint discrimination of all pure states, no cloning, teleportation, no programming, no bit commitment, complementarity between correctable channels and deletion channels, characterization of entanglement-breaking channels as measure-and-prepare channels, and others, without resorting to the mathematical framework of Hilbert spaces.

The asymptotic behavior of the quantum walk on the line is investigated, focusing on the probability distribution of chirality independently of position. It is shown analytically that this distribution has a longtime limit that is stationary and depends on the initial conditions. This result is unexpected in the context of the unitary evolution of the quantum walk as it is usually linked to a Markovian process. The asymptotic value of the entanglement between the coin and the position is determined by the chirality distribution. For given asymptotic values of both the entanglement and the chirality distribution, it is possible to find the corresponding initial conditions within a particular class of spatially extended Gaussian distributions.

We study reduced fidelity and reduced fidelity susceptibility in the Kitaev honeycomb model. It is shown that the nearest-two-site reduced fidelity susceptibility manifests itself as a peak at the quantum phase transition point, although the one-site reduced fidelity susceptibility vanishes. Our results directly reveal that the reduced fidelity susceptibility can be used to characterize the quantum phase transition in the Kitaev honeycomb model, which suggests that, despite its local nature, the reduced fidelity susceptibility is an accurate marker of the topological phase transition when it is properly chosen.