We present laser-induced electron diffraction measurements of elastic differential scattering cross sections (DCSs) of a photoelectron on the parent ion for argon, krypton, and xenon, using waveform-controlled few-cycle pulses. Considering only cutoff electrons and employing the adiabatic theory for the analysis enables us to eliminate ambiguities in extracting the DCSs from experimental spectra. Contrary to previous works, which mainly focused on the angular dependence of the DCS, our method allows us to extract also its dependence on the scattering momentum. In the case of xenon, we demonstrate how this method can be used to obtain the complete angular and momentum dependence of the DCS in a range of these variables determined by the pulse. The obtained results are compared to theoretical calculations based on the single-active-electron approximation, which shows a high level of agreement. Further investigations may provide opportunities to study multielectron effects when more advanced theoretical models become available.

Very different strongly interacting quantum systems such as Fermi gases, quark-gluon plasmas formed in high-energy ion collisions, and black holes studied theoretically in string theory are known to exhibit quantitatively similar damping of hydrodynamic modes. It is not known if such similarities extend beyond the hydrodynamic limit. Do nonhydrodynamic collective modes in Fermi gases with strong interactions also match those from string theory calculations? In order to answer this question, we use calculations based on string theory to make predictions for modes outside the hydrodynamic regime in trapped Fermi gases. These predictions are amenable to direct testing with current state-of-the-art cold atom experiments.

The sensitivity of the pinning transition (PT) as described by the sine-Gordon model of strongly interacting bosons confined in a shallow, one-dimensional, periodic optical lattice (OL), is examined against perturbations of the OL. The PT has been recently realized experimentally by Haller et al. [Nature (London) 466, 597 (2010)] and is the exact opposite of the superfluid-to-Mott-insulator transition in a deep OL with weakly interacting bosons. The continuous-space worm-algorithm (WA) Monte Carlo method [Boninsegni et al., Phys. Rev. E 74, 036701 (2006)] is applied for the present examination. It is found that the WA is able to reproduce the PT, which is another manifestation of the power of continuous-space WA methods in capturing the physics of phase transitions. In order to examine the sensitivity of the PT, it is tweaked by the addition of the secondary OL. The resulting bichromatic optical lattice (BCOL) is considered with a rational ratio of the constituting wavelengths ${\lambda }_1$ and ${\lambda }_2$ in contrast to the commonly used irrational ratio. For a weak BCOL, it is chiefly demonstrated that this PT is robust against the introduction of a weaker, secondary OL. The system is explored numerically by scanning its properties in a range of the Lieb-Liniger interaction parameter $\gamma$ in the regime of the PT. It is argued that there should not be much difference in the results between those due to an irrational ratio ${\lambda }_1/{\lambda }_2$ and those due to a rational approximation of the latter, bringing this in line with a recent statement by Boers et al. [Phys. Rev. A 75, 063404 (2007)]. The correlation function, Matsubara Green's function (MGF), and the single-particle density matrix do not respond to changes in the depth of the secondary OL $V_1$. For a stronger BCOL, however, a response is observed because of changes in $V_1$. In the regime where the bosons are fermionized, the MGF reveals that hole excitations are favored over particle excitations manifesting that holes in the PT regime play an important role in the response of properties to changes in $\gamma$.

Using the density-matrix renormalization-group method, we studied the ground state of the one-dimensional $S=1$ Bose-Hubbard model with local three-body interactions, which can be a superfluid or a Mott insulator state. We drew the phase diagram of this model for both ferromagnetic and antiferromagnetic interaction. Regardless of the sign of the spin-dependent coupling, we obtained that the Mott lobes area decreases as the spin-dependent strength increases, which means that the even-odd asymmetry of the two-body antiferromagnetic chain is absent for local three-body interactions. For antiferromagnetic coupling, we found that the density drives first-order superfluid-Mott insulator transitions for even and odd lobes. Ferromagnetic Mott insulator and superfluid states were obtained with a ferromagnetic coupling, and a tendency to a “long-range” order was observed.

We report the observation of quantum dynamical oscillations of ultracold atomic gases in the $F$ and $D$ bands of an ordinary optical lattice. We are able to control the Bragg reflections at the Brillouin-zone edge up to the third order. As a result, we can switch the quantum dynamics from oscillations across both the $F$ and $D$ bands to oscillations only within the $F$ band. Our capability to observe these oscillations comes from a nonadiabatic technique which allows us to load ultracold atoms efficiently to the $G$ band of an optical lattice.

We present an effective-medium model for a subwavelength periodically patterned metallic layer, its cavities being filled with a nonlinear dielectric material, which accounts for both the linear and second-order behavior. The effective nonlinear susceptibility for the homogenized layer is driven by the nonlinearity of the dielectric material and by the geometrical parameters, thus leading to much higher susceptibility than existing materials. This leads to a huge enhancement of nonlinear processes when used together with resonances. Furthermore, multiple resonances are taking place in the metallic cavities and we investigate the mode-matching situations for frequency conversion processes and show how it enhances further their efficiency.

The Lamb shift (self-energy) of an elliptic dielectric microcavity is studied. We show that the size of the Lamb shift, which is a small energy shift due to the system-environment coupling in the quantum regime, is dependent on the geometry of the boundary conditions. It shows a global transition depending on the eccentricity of the ellipsis. These transitions can be classified into three types of decay channels known as whispering-gallery modes, stable-bouncing-ball modes, and unstable-bouncing-ball modes. These modes are manifested through the Poincaré surface of section with the Husimi distribution function in classical phase space. It is found that the similarity (measured in Bhattacharyya distance) between the Husimi distributions below critical lines of two different modes increases as the difference of their self-energies decreases when the quality factors of the modes are on the same order of magnitude.

An exceptional point (EP) is a degeneracy occurring in a non-energy-conserving system, in which two eigenvectors of a non-Hermitian Hamiltonian coalesce. We explore how EPs can be realized in a metamaterial surface, or metasurface, consisting of a pair of lossy coupled linear antennas in each unit cell. EPs appear in the eigenvectors of the transmission matrix by tuning the frequency and the coupling and loss rates of the metasurface. Each EP is associated with the appearance of a circularly polarized transmission eigenstate; hence, within the parameter space of the system, the EPs lie along pairs of curves with distinct chirality. Our results are obtained using finite-difference time-domain simulations, as well as a fitted coupled-mode theory. The coupled-mode theory agrees well with the numerical results and is capable of accurately predicting the EP $f$ curves.

Possible paths of a photon passing through a nested Mach-Zehnder interferometer on its way to a detector are analyzed using the consistent histories formulation of quantum mechanics, and confirmed using a set of weak measurements (but not weak values). The results disagree with an analysis by Vaidman [Phys. Rev. A 87, 052104 (2013)], and agree with a conclusion reached by Li et al. [Phys. Rev. A 88, 046102 (2013)]. However, the analysis casts serious doubt on the claim of Salih et al. (whose authorship includes Li et al.) [Phys. Rev. Lett. 110, 170502 (2013)] to have constructed a protocol for counterfactual communication: a channel which can transmit information even though it contains a negligible number of photons.

The concept of weak invariant is introduced. Then the weak invariants associated with time-dependent quantum dissipative systems are discussed in the context of master equations of the Lindblad type. In particular, with the help of the $\mathit{su}$(1,1) Lie-algebraic structure, the weak invariant is explicitly constructed for the quantum damped harmonic oscillator with the time-dependent frequency and friction coefficient. This generalizes the Lewis-Riesenfeld invariant to the case of nonunitary dynamics in the Markovian approximation.

When conducting a Bell test, it is normal to assume that the preparation of the quantum state is independent of the measurements performed on it. Remarkably, the violation of local realism by entangled quantum systems can be certified even if this assumption is partially relaxed. Here, we allow such measurement dependence to correlate multiple runs of the experiment, going beyond previous studies that considered independent and identically distributed (i.i.d.) runs. To do so, we study the polytope defined by block-i.i.d. measurement-dependent local models. We prove that non-i.i.d. models are strictly more powerful than i.i.d. ones, and comment on the relevance of this work for the study of randomness amplification in simple Bell scenarios with suitably optimized inequalities.

We derive an inequality that is necessary and sufficient to show Einstein-Podolsky-Rosen (EPR) steering in a scenario employing only correlations between two arbitrary dichotomic measurements on each party. Thus the inequality is a complete steering analogy of the Clauser-Horne-Shimony-Holt (CHSH) inequality, a generalization of the result of Cavalcanti et al. [E. G. Cavalcanti, C. J. Foster, M. Fuwa, and H. M. Wiseman, JOSA B 32, A74 (2015)]. We show that violation of the inequality only requires measuring over equivalence classes of mutually unbiased measurements on the trusted party and that in fact assuming a general two-qubit system arbitrary pairs of distinct projective measurements at the trusted party are equally useful. Via this it is found that for a given state the maximum violation of our EPR-steering inequality is equal to that for the CHSH inequality, so all states that are EPR steerable with CHSH-type correlations are also Bell nonlocal.

The underlying physics behind the molecular harmonic emission in relatively long $\sin {}^2$-like laser pulses is investigated. We numerically solved the full-dimensional electronic time-dependent Schrödinger equation beyond the Born-Oppenheimer approximation for simple molecular ion ${\mathrm{H}}_2{}^{+}$. The occurrence and the effect of electron localization, nonadiabatic redshift, and spatially asymmetric emission are evaluated to understand better complex patterns appearing in the high-order harmonic generation (HHG) spectrum. Results show that the complex patterns in the HHG spectrum originate mainly from a nonadiabatic response of the molecule to the rapidly changing laser field and also from a spatially asymmetric emission along the polarization direction. The effect of electron localization on the HHG spectrum was not observed as opposed to what is reported in the literature.

Cold atomic ensembles and spinor Bose-Einstein condensates are potential candidates for quantum memories as they have long coherence times and can be coherently controlled. Unlike most candidates for quantum memories, which are genuine or effective single-particle systems, in atomic ensembles the quantum information is stored as a spin coherent state involving a very large number of atoms. A typical task with such ensembles is to drive the state towards a particular quantum state. While such quantum control methods are well developed for qubit systems, it is a nontrivial task to extend quantum control methods to the many-particle case. The objective of this work is to deterministically steer an arbitrary state of the atomic ensemble into a desired spin coherent state. To this end, we design our control law using stochastic stability theory, the quantum filtering theorem, and phase contrast imaging. We apply our control laws to different axes and show that it is possible to manipulate the atoms into different target states.

Motivated by trapping and cooling experiments with nonspherical nanoparticles, we discuss how their combined rotational and translational quantum state is affected by the interaction with a gaseous environment. Based on the quantum master equation in terms of orientation-dependent scattering amplitudes, we evaluate the localization rate for gas collisions off an anisotropic van der Waals–type potential and for photon scattering off an anisotropic dielectric. We also show how pure angular momentum diffusion arises from these open quantum dynamics in the limit of weak anisotropies.

We study the dissipative dynamics of an atom in a V-level configuration driven by lasers and coupled to a semi-infinite waveguide. The coupling to the waveguide is chiral, in that each transition interacts only with the modes propagating in a given direction, and this direction is opposite for the two transitions. The waveguide is terminated by a mirror which coherently feeds the photon stream emitted by one transition back to the atom. First, we are interested in the dynamics of the atom in the Markovian limit where the time delay in the feedback is negligible. Specifically, we study the conditions under which the atom evolves towards a pure “dark” stationary state, where the photons emitted by both transitions interfere destructively thanks to the coherent feedback, and the overall emission vanishes. This is a single-atom analog of the quantum dimer, where a pair of laser-driven two-level atoms is coupled to a unidirectional waveguide and dissipates towards a pure entangled dark state. Our setup should be feasible with current state-of-the-art experiments. Second, we extend our study to non-Markovian regimes and investigate the effect of the feedback retardation on the steady state.

We demonstrate that light is subject to anomalous (i.e., negative) diffraction when propagating in the presence of hyperbolic dispersion. We show that light propagation in hyperbolic media resembles the dynamics of a quantum particle of negative mass moving in a two-dimensional potential. The negative effective mass implies time reversal if the medium is homogeneous. Such property paves the way to diffraction compensation, i.e., spatial analog of dispersion compensating fibers in the temporal domain. At variance with materials exhibiting standard elliptic dispersion, in inhomogeneous hyperbolic materials light waves are pulled towards regions with a lower refractive index. In the presence of a Kerr-like optical response, bright (dark) solitons are supported by a negative (positive) nonlinearity.

Practical quantum communication (QC) protocols are assumed to be secure provided implemented devices are properly characterized and all known side channels are closed. We show that this is not always true. We demonstrate a laser-damage attack capable of modifying device behavior on demand. We test it on two practical QC systems for key distribution and coin tossing, and show that newly created deviations lead to side channels. This reveals that laser damage is a potential security risk to existing QC systems, and necessitates their testing to guarantee security.

In creating a large-scale quantum information processor, the ability to construct control pulses for implementing an arbitrary quantum circuit in a scalable manner is an important requirement. For liquid-state nuclear-magnetic-resonance quantum computing, a circuit is generally realized through a sequence of selective soft pulses, in which various control imperfections exist and are to be corrected. In this work, we present a comprehensive analysis of the errors arisen in a selective pulse network by using the zeroth- and first-order average Hamiltonian theory. Effective correction rules are derived for adjusting important pulse parameters such as irradiation frequencies, rotational angles, and transmission phases of the selective pulses to increase the control fidelity. Simulations show that applying our compilation procedure for a given circuit is efficient and can greatly reduce the error accumulation.