We study the Floquet-surface bound states embedded in the continuum (BICs) and bound states out the continuum in a resonantly driven one-dimensional tilted defect-free lattice. In contrast to fragile single-particle BICs assisted by specially tailored potentials, we find that Floquet-surface BICs, stable against structural perturbations, can exist in a wide range of parameter space. By using a multiple-time-scale asymptotic analysis in the high-frequency limit, the appearance of Floquet-surface bound states can be analytically explained by effective Tamm-type defects at boundaries induced by the resonance between the periodic driving and tilt. The phase boundary of existing Floquet-surface states is also analytically given. Based on the repulsion effect of surface states, we propose to detect transition points and measure the number of Floquet-surface bound states by quantum walk. Our work opens a door to experimental realization of BICs in a quantum system.

We report on a study of a one-dimensional linear photonic lattice hosting, simultaneously, fundamental and dipolar modes at every site. We show how, thanks to the coupling between different orbital modes, this minimal model exhibits rich transport and topological properties. By varying the detuning coefficient we find a regime where bands become flatter (with reduced transport) and a second regime, where both bands connect at a gap-closing transition (with enhanced transport). We detect an asymmetric transport due to the asymmetric intermode coupling and a linear energy exchange mechanism between modes. Further analysis shows that the bands have a topological transition with a nontrivial Zak phase which leads to the appearance of edge states in a finite system. Finally, for zero detuning, we found a symmetric condition for coupling constants, where the linear spectrum becomes completely flat, with states fully localized in space occupying only two lattice sites.

Efficient circularly polarized terahertz (THz) emission is important for THz imaging technology and basic scientific research. In order to achieve this, we have made a simple, all-passive design to achieve collinear and corotating circularly polarized two-color laser fields. The collinearity allows us to manipulate accurately the relative phase between two-color lasers. For a given relative phase, our experiments show that efficient nearly-circularly-polarized THz emission can be generated from an air plasma pumped by the two-color fields. The emitted THz power is ∼2.5 times that pumped by linear-polarized two-color laser fields. Our results also indicate that nearly circularly polarization is stable against different pump power and plasma distance.

In a recent work Brunner and Vertesi [Phys. Rev. A 86, 042113 (2012)] the question of persistency of entanglement and nonlocality of multiparty systems under particle loss has been addressed. This question is of immense importance considering the practical realization of the information theoretic tasks which make use of the power of quantum correlations. But in the multipartite scenario more interesting cases arise since subsystems can also possess genuineness in correlation which is prevalently inequivalent to the bipartite scenario. In this paper we investigate the persistency of such genuine correlations under particle loss. Keeping in mind the practical importance, considerable attention has been devoted to find the multiparty states which exhibit maximal persistency of genuine correlations.

Quantum communication through spin chains has been extensively investigated. In this scenario, state transfer through linearly arranged spins connected by uniform nearest-neighbor couplings qualifies as a natural choice, with minimal control requirements. However, quantum states usually cannot be perfectly transferred through a uniformly coupled chain due to the dispersion of the chain. Here, we propose an effective quantum control technique to realize almost exact state transfer (AEST) in a quantum spin chain. The strategy is to add a leakage elimination operator Hamiltonian to the evolution, which implements a sequence of pulse control acting on a perfect state transfer subspace. By using the one-component Feshbach PQ partitioning technique, we obtain the conditions over the required pulses. AEST through a spin chain can then be obtained under a suitable pulse intensity and duration.

We present angle-integrated and angle-differential cross sections for electron-impact excitation of the $\left(5s^{2}5p\right){}^{2}P_{1/2}\to \left(5s^{2}6s\right){}^{2}S_{1/2}$ transition in atomic indium. Experimental data for six incident electron energies between 10 and 100 eV are compared with predictions from semirelativistic and fully relativistic $B$-spline $R$-matrix calculations, as well as a fully relativistic convergent close-coupling model. Agreement between our measured and calculated data is, with a few exceptions, found to be typically very good. Additionally, the agreement between the present theoretical predictions is generally excellent, with the remaining small deviations being associated with the slightly different, although still very accurate, descriptions of the target structure. Agreement between the present results and an earlier relativistic distorted-wave computation [T. Das, R. Srivastava, and A. D. Stauffer, Phys. Lett. A 375, 568 (2011)] was, however, found to be marginal, particularly at 10 and 20 eV.

Over the past three decades numerous numerical methods for solving the time-dependent Schrödinger equation within the single-active electron approximation have been developed for studying ionization of atomic targets exposed to an intense laser field. In addition, various numerical techniques for extracting the photoelectron spectra from the time-dependent wave function have emerged. In this paper we compare photoelectron spectra obtained by either projecting the time-dependent wave function at the end of the laser pulse onto the continuum state having the proper incoming boundary condition or by using the window-operator method. Our results for three different atomic targets show that the boundary condition imposed onto the continuum states plays a crucial role for obtaining correct spectra accurate enough to resolve fine details of the interference structures of the photoelectron angular distribution.

We report on the static and dynamical properties of multiple dark-antidark solitons (DADs) in two-component, repulsively interacting Bose-Einstein condensates. Motivated by experimental observations involving multiple DADs, we present a theoretical study which showcases that bound states consisting of dark (antidark) solitons in the first (second) component of the mixture exist for different values of interspecies interactions. It is found that ensembles of few DADs may exist as stable configurations, while for larger DAD arrays, the relevant windows of stability with respect to the interspecies interaction strength become progressively narrower. Moreover, the dynamical formation of states consisting of alternating DADs in the two components of the mixture is monitored. A complex dynamical evolution of these states is observed, leading either to sorted DADs or to beating dark-dark solitons depending on the strength of the interspecies coupling. This study demonstrates clear avenues for future investigations of DAD configurations.

We propose a scheme for simulating a momentum dependent non-Hermitian Hamiltonian term by adding loss in the hopping process in a one-dimensional array of optical cavities, which leads to a one-band topological nontrivial non-Hermitian model. We find that there is a kind of transition from all real energy spectrum to all imaginary one under open boundary conditions: the eigenvalues are all real or imaginary dependent on which amplitude of the Hermitian or non-Hermitian part is dominant even though the eigenvalues of the bulk system are complex under the periodic boundary condition. In addition, for such a non-Hermitian Hamiltonian, the left eigenvectors are the mirror symmetry of the right eigenvectors. Finally, by using the input-output formula, we show that the distribution of the boundary states can be directly observed by detecting the optical transmission in both cases.

We show through rigorous calculation that optical binding can organize hyperbolic metamaterial slabs into one-dimensional photonic hypercrystals. It was reported that a photonic hypercrystal can possess an angle-independent band gap and blueshifting and redshifting band gaps. We find that an angle-independent band gap could lead to angle-independent optical binding, where light can organize a collection of hyperbolic slabs into one mechanically stable photonic hypercrystal, irrespective of the angle of incidence of the incident plane wave. We call such a phenomenon incident angle-independent optical binding. In addition, the evolution of the lattice constants of the self-organized photonic hypercrystals with blueshifting and redshifting band gaps is also investigated.

We theoretically demonstrate that an especially tuned degenerate optical parametric amplifier (OPA) inside a cavity can lead to the momentum squeezing of a moving membrane in a dissipative optomechanical system. The momentum squeezing of the membrane depends on the parametric gain and the parametric phase of the OPA, the power of the external laser driving the cavity, and the temperature of the environment. The best achievable momentum squeezing is about 2.53 dB, which is limited by the OPA. Moreover, we show that the momentum squeezing of the membrane can be detected by directly measuring the cavity output field. In addition, we find that the mechanical squeezing can be enhanced to about 10.36 dB under the joint effect of the OPA and an input broadband squeezed vacuum field.

The scattering of high-power probe laser pulses by tightly focused ultrastrong laser pulses has been investigated through a semiclassical approach using a perturbative method based on the Born approximation. Under a $4\pi$-spherically-focused ultrastrong light field, the electric permittivity and magnetic permeability tensors for vacuum are calculated from the Euler-Heisenberg Lagrangian to show the nonlinear birefringent property of vacuum. And, from permittivity and permeability tensors, the scattering potential is derived for the Born approximation. The first-order solution of the Born approximation is taken as an electric field scattered from the $4\pi$-spherically-focused laser pulse when a probe laser pulse propagates through the focused laser field. The differential cross section of the nonlinear birefringent vacuum is derived, and the number of photons scattered from the nonlinear birefringent vacuum is analyzed in the laser power range of 10–1000 PW.

We propose a scheme called the weak measurement with two pointers to measure time delays in a large dynamic range with high precision. One pointer with the light frequency and the other pointer with the postselected probability play a complementary role in the dynamic range of the time-delay estimation. By inserting the main systematic errors, we study the antierror capability and the amplification behavior of two types of pointers, where the pointer with the postselected probability shows stronger robustness against systematic errors and larger working range in general. The proof-of-principle experiments together with the Fisher information metric analysis show that high precision can be effectively retained in a large dynamic range of the time-delay estimation. Further implementation strategy of this scheme is also provided, which may promote the precise estimation of other parameters in a large dynamic range.

We discuss the properties of bound states in finite-bandwidth waveguide QED beyond the rotating wave approximation or excitation-number-conserving light-matter coupling models. Therefore, we extend the standard calculations to a broader range of light-matter strengths, in particular, in the so-called ultrastrong coupling regime. We do this using the polaron technique. Our main results are as follows: We compute the spontaneous emission rate, which is renormalized as compared with the Fermi golden rule formula. We generalize the existence criteria for bound states, their properties, and their role in the qubit thermalization. We discuss effective spin-spin interactions through both vacuum fluctuations and bound states. Finally, we sketch a perfect state-transfer protocol among distant emitters mediated by bound states.

The projection method with explicitly correlated Gaussians is used to demonstrate the existence of two doubly excited states of the positronium molecule (${\mathrm{Ps}}_2$). One is below the $\mathrm{Ps}(n=2)+\mathrm{Ps}(n=2)$ threshold, with $A_1$ symmetry, and the other is below the $\mathrm{Ps}(n=2)+\mathrm{Ps}(n=3)$ threshold, with $E$ symmetry. These states exist as resonances in the Ps-Ps continuum. Moreover, the resonance positions and resonance widths of the two states are calculated using the complex rotation method with basis sets obtained via the orthogonalizing pseudoprojector method. The resonance positions obtained using the complex rotation method agree with the results of the orthogonalizing pseudoprojector method. We also investigate the various structural properties of these states as well as the decay probabilities of $2\gamma$ emission due to electron-positron annihilation.

Attoclock is a powerful technique to resolve laser-driven electron dynamics on an attosecond time scale. Previously, it was mainly limited to atomic targets. Here we apply the attoclock technique to aligned molecules to study the subcycle ionization dynamics. By controlling the alignment of the molecule relative to the major axis of a strong elliptically polarized laser field, we demonstrate that the electron ionization time in aligned molecules can be precisely resolved by the attoclock technique. We find that the ionization time corresponding to the peak of the photoelectron momentum distribution shifts several tens of attoseconds relative to the laser field peak depending on the molecular orientation and molecular orbital structure. A significant difference between the measurement and molecular Ammosov-Delone-Krainov model is found. We further show that the photoelectron ionization time of molecules is sensitive to angular-dependent ionization rate, opening up opportunities for probing attosecond electron dynamics in complex polyatomic molecules.

In this paper, we implement a scheme to combine six coherent, spatially separated Raman sidebands generated in single-crystal diamond into a collinear beam. With appropriate phase tuning, this results in a pulse much shorter than the generating pump. We elucidate the characteristics of the synthesized pulse by using an interferometric collinear cross-correlation frequency-resolved optical gating setup. The beating of the synchronized sidebands results in an additional component in the signal, which we use to optimize the relative phases of our sidebands. In this way, we synthesize and measure visible-range, nearly single-cycle isolated pulses of approximately 5-fs total pulse duration.

Non-Markovian time evolution of quantum systems is a challenging problem, often mitigated by employing numerical methods or making simplifying assumptions. In this work, we address this problem in waveguide quantum electrodynamics (QED) by developing a diagrammatic approach, which performs fully analytical non-Markovian time evolution of single-photon states. By revisiting Fermi's two-atom problem, we tackle the impeding question of whether the rotating-wave approximation violates causality in single-photon waveguide QED. Afterward, we introduce and prove the no upper half-plane poles (no-UHP) theorem, which connects the poles of scattering parameters to the causality principle. Finally, we visualize the time-delayed coherent quantum feedback mediated by the field and discuss the Markovian limit for microscopically separated qubits where short-distance causality violations occur and the emergence of collective decay rates in this limit. Our diagrammatic approach is a method to perform exact and analytical non-Markovian time evolution of multiemitter systems in waveguide QED.