To acquire the best path-entangled photon Fock states for robust quantum-optical metrology with parity detection, we calculate phase information from a lossy interferometer by using twin entangled Fock states. We show that $\left(\text{a}\right)$ when loss is less than 50$\%$ twin entangled Fock states with large photon number difference give higher visibility, while when loss is higher than 50$\%$, the ones with less photon number difference give higher visibility; and $\left(\text{b}\right)$ twin entangled Fock states with large photon number difference give sub–shot-noise limit sensitivity for phase detection in a lossy environment. This result provides a reference on what particular path-entangled Fock states are useful for real world metrology applications.

The dynamics of vector vortex pairs with explicit and hidden vorticity in nonlocal media with an arbitrary degree of nonlocality is investigated analytically and numerically. We show that the stability dynamics of the vortex pairs depends crucially upon their total angular momentum, the topological charge, and the degree of nonlocality. In particular, we show that nonlocality eliminates the splitting of the vortex pairs, improves their propagation stability, and leads to formation of stationary bound states of vortex pairs.

Approximated formulas for real quasimomentum and the associated energy spectrum are presented for one-dimensional Bose gas with weak attractive contact interactions. On the basis of the energy spectrum, we obtain the equation of state in the high-temperature region, which is found to be the van der Waals equation without volume correction.

Quantum discord, an information-theoretic quantum correlation measure, can satisfy as well as violate monogamy for three-party quantum states. We quantify the feature using the concept of discord monogamy score. We find a necessary condition of a vanishing discord monogamy score for arbitrary three-party states. A necessary and sufficient condition is obtained for pure states. We prove that the class of states having a vanishing discord monogamy score cannot have arbitrarily high genuine multipartite entanglement, as quantified by generalized geometric measure. In the special case of three-qubit pure states, their classification with respect to the discord monogamy score reveals a rich structure that is different from that which had been obtained by using the monogamy score corresponding to the entanglement measure called concurrence. We investigate properties like genuine multipartite entanglement and violation of the multipartite Bell inequality for these states.

Quantum Fisher information, which plays a central role in parameter estimation theory, is a useful quantity for metrological applications. We use quantum Fisher information to distinguish and characterize behaviors of the evolved state for Bose-Einstein condensates in a symmetric double well, which display a classical bifurcation and a transition from Josephson oscillation to self-trapping. We find that the precision of the parameter estimation on the evolved state in the unstable regime is much higher than that in the stable regime, which lies at the shot-noise level. We also show that the parameter sensitivity of the evolved state approaches the Heisenberg limit in the Josephson oscillation regime, while it is just scaled as the shot-noise limit in the self-trapping regime. Finally, we discuss the relation between the parameter sensitivity of the evolved state and the entanglement entropy.

The Aharon-Vaidman (AV) game exemplifies the advantage of using simple quantum systems to outperform classical strategies. We present an experimental test of this advantage by using a three-state quantum system (qutrit) encoded in a spatial mode of a single photon passing through three slits. The preparation of a particular state is controlled as the photon propagates through the slits by varying the number of open slits and their respective phases. The measurements are achieved by placing detectors in the specific positions in the near and far fields after the slits. This set of tools allowed us to perform tomographic reconstructions of generalized qutrit states, and to implement the quantum version of the AV game with compelling evidence of the quantum advantage.

We employ the Loschmidt echo, i.e., the signal recovered after the reversal of an evolution, to identify and quantify the processes contributing to decoherence. This procedure, which has been extensively used in single-particle physics, is employed here in a spin ladder. The isolated chains have $1/2$ spins with $XY$ interaction and their excitations would sustain a one-body-like propagation. One of them constitutes the controlled system $\mathcal{S}$ whose reversible dynamics is degraded by the weak coupling with the uncontrolled second chain, i.e., the environment $\mathcal{E}$. The perturbative $\mathcal{SE}$ coupling is swept through arbitrary combinations of $XY$ and Ising-like interactions, that contain the standard Heisenberg and dipolar ones. Different time regimes are identified for the Loschmidt echo dynamics in this perturbative configuration. In particular, the exponential decay scales as a Fermi golden rule, where the contributions of the different $\mathcal{SE}$ terms are individually evaluated and analyzed. Comparisons with previous analytical and numerical evaluations of decoherence based on the attenuation of specific interferences show that the Loschmidt echo is an advantageous decoherence quantifier at any time, regardless of the $\mathcal{S}$ internal dynamics.

We present high-resolution crystal spectroscopy measurements of the $n=3\to n=2$ $L$-shell x-ray transitions of neonlike W${}^{64+}$, which include seven electric-dipole–allowed transitions, two electric quadrupole transitions, and one magnetic quadrupole transition. The resulting wavelength data are compared to recent calculational results, allowing us to clearly distinguish between different theoretical approaches which need to take into account not only substantial electron correlations effects but also radiative contributions, which in case of the transition from the upper level ${\left(1s^{2}2s_{1/2}2p^{6}3p_{3/2}\right)}_{J=1}$ to the closed-shell neonlike ground state exceeds 20 eV. Best agreement is found with calculations utilizing the relativistic multireference Møller-Plesset approach. In addition to the emission from W${}^{64+}$, we observed several inner-shell collisional satellite lines associated with oxygenlike W${}^{66+}$, fluorinelike W${}^{65+}$, sodiumlike W${}^{63+}$, and magnesiumlike W${}^{62+}$, which provide benchmarks for future calculations as well as for recent calculations using the relativistic many-body perturbation theory. The present measurements also provide accurate rest wavelengths for establishing the instrumental dispersion needed for future measurements of the core plasma motion in the ITER tokamak and show that the candidate W${}^{64+}$ line for such measurements remains well isolated from neighboring collisional satellite lines even when broadened by the expected high temperatures in this device.

We have used the ab initio R-matrix formalism at low impact energies (below the ionization threshold of the target) and the spherical complex optical potential methodology above the ionization threshold to generate total cross sections for $e$-SO${}_2$ scattering over the energy range from 0.1 to 2000 eV. The eigenphase diagram and total cross section indicate a structure at 3.4 eV which is ascribed to a shape resonance, evidence for which appears in earlier experimental studies.

We traced the femtosecond nuclear-wave-packet dynamics in ionic states of oxygen and nitrogen diatomic molecules employing 38-eV XUV-pump–XUV-probe experiments at the free-electron laser in Hamburg (FLASH). The nuclear dynamics is monitored via the detection of coincident ionic fragments using a reaction microscope and a split-mirror setup to generate the pump and probe pulses. By comparing measured kinetic-energy-release spectra with classical and quantum-mechanical simulations, we identified electronic states of the molecular ions that are populated by ionization of the neutral molecule. For specific fragment charge states, this comparison allows us to assess the relevance of specific dissociation paths.

We use a ${\mathcal{L}}^2$-discretization technique for solving the time-dependent Schrödinger equation for H${}_2^{+}$ interacting with a short vuv laser pulse, in the Born-Oppenheimer approximation. The calculations include the electronic three-dimensional and vibrational one-dimensional motions. In this approach, we use the prolate spheroidal coordinate system to describe the electronic functions and a basis of Laguerre and Legendre functions [Phys. Rev. A 71, 053407 (2005)]. The vibrational motion is treated by using a basis of Sturmian functions. We consider the problem of two-photon dissociation of H${}_2^{+}$ with photons ranging from 0.32 to 0.4 a.u corresponding to wavelengths from 143 to 114 nm. The initial vibrational wave packet results from a vertical (Franck-Condon) transition from the H${}_2$ ground state towards a superposition of vibrational states in the $1s{\sigma }_g$ electronic state of H${}_2^{+}$. The effects of various types of nuclear interference on the population of the dissociative channels $2s{\sigma }_g$ and $3d{\sigma }_g$ are discussed in detail. In addition, we show that for 0.32-a.u. photon energy, the interference effects in the $3d{\sigma }_g$ channel whose existence has been demonstrated previously [Phys. Rev. Lett. 102, 123001 (2009)] can be observed in the total kinetic energy release spectrum.

The famous Hanbury Brown and Twiss type experiments are performed with optical vortices. Though the intensity correlation for vortices are found to be similar to that of the TEM${}_{00}$ mode of the He-Ne laser used to generate the vortices, an interesting difference is observed when they are scattered through a rotating ground glass plate. For smaller time delays, correlations for vortices follow the same pattern as the scattered Gaussian beam of light except that the vortices decay faster and the rate of decay depends on the order of the vortex. For longer time delays, however, the intensity correlation curves for vortices are found to be modulated and this modulation becomes more prominent as the order of the vortex is increased. This seemingly counterintuitive observation is supported by exact analytical results.

We theoretically show that the topology of a nonsimply connected annular atomic Bose-Einstein condensate enforces the inner surface waves to be always excited with outer surface excitations and that the inner surface modes are associated with induced vortex dipoles unlike the surface waves of a simply connected one with vortex monopoles. Consequently, under stirring to drive an inner surface wave, a peculiar population oscillation between the inner and outer surface is generated regardless of annulus thickness. Moreover, a vortex nucleation process by stirring is observed that can merge the inner vortex dipoles and outer vortex into a single vortex inside the annulus. The energy spectrum for a rotating annular condensate with a vortex at the center also reveals the distinct connection of the Tkachenko modes of a vortex lattice to its inner surface excitations.

We investigate universal thermodynamics and quantum criticality of spin-1 bosons with strongly repulsive density-density and antiferromagnetic spin-exchange interactions in a one-dimensional harmonic trap. From the equation of state, we find that a partially polarized core is surrounded by two wings composed of either spin-singlet pairs or a fully spin-aligned Tonks-Girardeau gas depending on the polarization. We describe how the scaling behavior of density profiles can reveal the universal nature of quantum criticality and map out the quantum phase diagram. We further show that at quantum criticality the dynamical critical exponent $z=2$ and correlation length exponent $\nu =1/2$. This reveals a subtle resemblance to the physics of the spin-1/2 attractive Fermi gas.

We present an experimental feasible scheme to synthesize two-mode continuous-variable entangled states of two superconducting resonators that are interconnected by two gap-tunable superconducting qubits. We show that, with each artificial atom suitably driven by a bichromatic microwave field to induce sidebands in the qubit-resonator coupling, the stationary state of the photon fields in the two resonators can be cooled and steered into a two-mode squeezed vacuum state via a dissipative quantum dynamical process, while the superconducting qubits remain in their ground states. In this scheme the qubit decay plays a positive role and can help drive the system to the target state, which thus converts a detrimental source of noise into a resource.

The Voigt profile—a convolution of a Gaussian and a Lorentzian—accurately describes the absorption lines of atomic and molecular gases at low probe powers. Fitting experimental absorption data to such a Voigt profile yields both the Lorentzian natural linewidth and the Gaussian Doppler broadening. However, as the probe power increases, saturation effects change the absorption line shape, such that it is no longer accurately described by a Voigt profile. Naively fitting a simple Voigt profile to the absorption line therefore introduces spurious power dependence into the extracted Doppler component. Using a simple atomic model, we calculate power-dependent corrections to the Voigt profile, which are parametrized by the Gaussian Doppler width, the Lorentzian natural linewidth, and the optical depth. We show numerically and experimentally that including the correction term substantially reduces the spurious power dependence in the fitted Gaussian width.

The primary dynamical Dirac relativistic effects can only be seen in hydrogenic systems without the complications introduced by electron-electron interactions in many-electron systems. They are known to be the contraction towards the origin of the electronic charge in hydrogenic systems and the nodal disappearance (because of the raising of all the nonrelativistic minima) in the electron density of the excited states of these systems. In addition we point out the (largely ignored) gradient reduction of the charge density near and far from the nucleus. In this work we quantify these effects by means of single (Fisher information) and composite [Fisher-Shannon complexity and plane, López-Ruiz, Mancini, and Calbet (LMC) complexity] information-theoretic measures. While the Fisher information measures the gradient content of the density, the (dimensionless) composite information-theoretic quantities grasp twofold facets of the electronic distribution: The Fisher-Shannon complexity measures the combined balance of the gradient content and the total extent of the electronic charge, and the LMC complexity quantifies the disequilibrium jointly with the spreading of the density in the configuration space. Opposite to other complexity notions (e.g., computational and algorithmic complexities), these two quantities describe intrinsic properties of the system because they do not depend on the context but are functionals of the electron density. Moreover, they are closely related to the intuitive notion of complexity because they are minimum for the two extreme (or least complex) distributions of perfect order and maximum disorder.

Using the cumulant decomposition of the two-body reduced density matrix (two-matrix) for a spin-unpolarized homogeneous electron gas, it is shown that both the momentum distribution and the structure factors follow from one two-body quantity, namely, the cumulant two-matrix. The random phase approximation serves as a test example.

We study quasi-one-dimensional atomic gases across wide and narrow confinement-induced resonances (CIRs). We show using the virial expansion that, by tuning the magnetic field, the repulsive scattering branch initially prepared at low fields can continuously go across CIRs without decay; instead, the decay occurs when the noninteracting limit is approached. The interaction properties essentially rely on the resonance width of the CIR. Universal thermodynamics holds for the scattering branch right at a wide CIR, but is smeared out in a narrow CIR due to the strong energy dependence of the coupling strength. In wide and narrow CIRs, the interaction energy of the scattering branch shows different types of strong asymmetry when the decay is approached from opposite sides of the magnetic field. Finally, we discuss the stability of the repulsive branch for a repulsively interacting Fermi gas in different trapped geometries at low temperatures.