We demonstrated enhancement of fluorescence emission from helium atoms in terms of ultraviolet and infrared filaments nonlinear interaction in a mixture of argon and helium atomic gases. The seed electrons produced by ultraviolet pulses were accelerated by infrared filaments to kick a significant amount of helium atoms into high-lying excited states. This provided a method to efficiently excite helium atoms through electron collisions for further investigation on electron-ion collisions and their effects on atomic coherence behavior.

We propose a method for the generation of trains of alternating bright solitons in two-component Bose-Einstein condensates, using controlled emission of nonlinear matter waves in the uncoupled regime with spatially varying intraspecies interaction and out-of-phase oscillations of the ground states in the trap. Under this scheme, solitons are sequentially launched from the different components and interact with each other through phase-independent cross coupling. We obtain an analytical estimation of the critical condition for soliton emission using a geometric guiding model, in analogy with integrated optical systems. In addition, we show how strong initial perturbations in the system can trigger the spontaneous generation of supersolitons, i.e., localized phononlike excitations of the soliton trains. Finally, we demonstrate the controllable generation of slow and fast supersolitons by adding external localized potentials in the nonlinear region.

We investigate the generation of squeezed states in a movable mirror in dissipative optomechanics in which the oscillating mirror modulates both the resonance frequency and the linewidth of the cavity mode. Via feeding broadband squeezed-vacuum light accompanying a coherent driving laser field into the cavity, the master equation for the cavity-mirror system is derived by following the general reservoir theory. When the mirror is weakly coupled to the cavity mode, we find that the driven cavity field can effectively perform as a squeezed-vacuum reservoir for the movable mirror via utilizing the completely destructive interference of quantum noise. Efficient transfer of squeezing from the light to the movable mirror occurs, irrespective of the ratio between the cavity damping rate and the mechanical frequency. Moreover, when the mirror is moderately coupled to the cavity mode, photonic excitation can preclude the completely destructive interference of quantum noise. As a consequence, the mirror deviates from the ideal squeezed state.

We study the transverse-size effect of a quasi-one-dimensional rectangular waveguide on the single-photon scattering on a two-level system. We calculate the transmission and reflection coefficients for single incident photons using the scattering formalism based on the Lippmann-Schwinger equation. When the transverse size of the waveguide is larger than a critical size, we find that the transverse mode will be involved in the single-photon scattering. Including the coupling to a higher traverse mode, we find that the photon in the lowest channel will be lost into the other channel, corresponding to the other transverse modes, when the input energy is larger than the maximum bound-state energy. Three kinds of resonance phenomena are predicted: single-photon resonance, photonic Feshbach resonance, and cutoff (minimum) frequency resonance. At these resonances, the input photon is completely reflected.

A hybrid device consisting of a nitrogen-vacancy-center ensemble $($NVE$)$ in diamond magnetically coupled to a superconducting flux qubit is investigated. The flux qubit is suitably driven by a bichromatic microwave field to induce sidebands, which leads to the desired qubit-NVE coupling. The distinct feature of the present scheme is that the qubit decay as a resource is utilized to steer the stationary state of the NVE into a single-mode squeezed vacuum state via a dissipative repumping process.

We study the precise phase estimation using squeezed states in the presence of photon loss. Our exact quantum Fisher information calculation shows significant enhancement even though the loss is very large and sets a benchmark for experimental realization. We show that if we blindly use the existing parity measurement scheme [Anisimov et al., Phys. Rev. Lett. 104, 103602 (2010)] for the ideal case, the result will be even worse than the classical case given very small loss. Using our formulas, we can optimize the measurement result by making loss-dependent phase shift and choosing appropriate squeezed states (average photon number of squeezed states).

We examine the quantum correlations of spin pairs in the cyclic $\mathit{XX}$ spin-$1/2$ chain in a transverse field through the analysis of the quantum discord, the geometric discord, and the information deficit. It is shown that while these quantities provide the same qualitative information, being nonzero for all temperatures and separations and exhibiting the same type of asymptotic behavior for large temperatures or separations, important differences arise in the minimizing local measurement that defines them. Whereas the quantum discord prefers a spin measurement perpendicular to the transverse field, the geometric discord and information deficit exhibit a perpendicular-to-parallel transition as the field increases, which subsists at all temperatures and for all separations. Moreover, it is shown that such transition signals the change from a Bell state to an aligned separable state of the dominant eigenstate of the reduced density matrix of the pair. Full exact results for both the thermodynamic limit and the finite chain are provided through the Jordan-Wigner fermionization.

We show that the phenomenon of frozen discord, exhibited by specific classes of two-qubit states under local nondissipative decoherent evolutions, is a common feature of all known bona fide measures of general quantum correlations. All those measures, despite inducing typically inequivalent orderings on the set of nonclassically correlated states, return a constant value in the considered settings. Every communication protocol that relies on quantum correlations as a resource will run with a performance completely unaffected by noise in the specified dynamical conditions. We provide a geometric interpretation of this phenomenon.

We study measurements of single-mode phase observables with emphasis on the canonical phase. We focus on the class of phase-shift covariant phase-space observables, which then yield the phase observables as the angle margins after integrating over the radial part. We consider the possibility of measuring such observables by using a double homodyne detector and its modification. We show that, in principle, the canonical phase distribution of the signal state can be measured via double homodyne detection by first processing the state using a two-mode unitary channel.

Complexity is often invoked alongside size and mass as a characteristic of macroscopic quantum objects. In 2004, Aaronson introduced the tree size (TS) as a computable measure of complexity and studied its basic properties. In this paper, we improve and expand on those initial results. In particular, we give explicit characterizations of a family of states with superpolynomial complexity $n^{\Omega \left(\log n\right)}=\mathrm{TS}=O(\sqrt{n}!)$ in the number of qubits $n$, and we show that any matrix-product state whose tensors are of dimension $D\times D$ has polynomial complexity $\text{TS}=O\left(n^{{\log }_{2}2\text{D}}\right)$.

We propose a method for measuring the magnetic dipole ($M1$) transition moment of the $6S_{1/2}(m=-1/2)\leftrightarrow 5D_{3/2}(m=-1/2)$ transition in single trapped Ba${}^{+}$ by exploiting different symmetries in the electric quadrupole ($E2$) and $M1$ couplings between the states. The technique is adapted from a previously proposed method for measuring atomic parity nonconservation in a single trapped ion [N. Fortson, Phys. Rev. Lett. 70, 2383 (1993)]. Knowledge of $M1$ is crucial for any parity nonconservation measurement in Ba${}^{+}$, as laser coupling through $M1$ can mimic the parity-violating signal. The magnetic moment for the transition has been calculated by atomic theory and found to be dominated by electron-electron correlation effects [B. K. Sahoo et al., Phys. Rev. A 74, 062504 (2006)]. To date the value has not been verified experimentally. This proposed measurement is therefore an essential step toward a parity nonconservation experiment in the ion that will also test current many-body theory. The technique can be adapted for similar parity nonconservation experiments using other atomic ions, where the magnetic dipole moment could present similar complications.

We report the experimental determination of the scattering parameters for a $p$-wave Feshbach resonance in a single-component Fermi gas of ${}^6$Li atoms in the lowest spin state. The time scale of the cross-dimensional relaxation reflects the elastic-scattering rate of the atoms, and scattering parameters are determined from the scattering rate as a function of magnetic field by taking into account the momentum distribution and inhomogeneous density profile of the atoms in a trap. Precise determination of the scattering parameters for a $p$-wave Feshbach resonance is an important step toward the realization of a $p$-wave superfluid in an ultracold atomic gas.

Exact relativistic plane-wave Born (RPWB) matrix elements of the Møller interaction are incorporated in the “analytic Born subtraction technique” and employed in the relativistic convergent close-coupling method. Application to the calculation of high-energy electron-impact-excitation cross sections of highly charged hydrogenlike ions demonstrates the “Bethe rise,” an effect that is manifest in Bethe's original 1932 work on relativistic high-energy, electron-impact excitation. The result represents an improvement over Bethe's relativistic high-energy theory developed in the 1930s in that (i) both target and projectile electrons are represented relativistically with Dirac spinor wave functions and (ii) the dipole approximation plus additional assumptions are not employed in the RPWB scattering amplitude of the Møller interaction.

Total and partial cross sections for breakup of the ground rovibronic state of ${\mathrm{H}}_2^{+}$ by photon impact are calculated using the exact nonadiabatic nonrelativistic Hamiltonian without approximation. The converged results span six orders of magnitude. The breakup cross section is divided into dissociative excitation and dissociative ionization. The dissociative excitation channels are divided into contributions from principal quantum numbers 1–4. For dissociative ionization, the fully differential cross section is calculated using a formally exact expression. These results are compared with approximate expressions. The Born-Oppenheimer expression for the dissociative ionization amplitude is shown to be deficient near onset. A Born-Oppenheimer approximation to the final state is shown to give accurate results for the sharing of kinetic energy between the electronic and the internuclear degrees of freedom—the doubly differential cross section. To accurately calculate the triply differential cross section, including the angular behavior, it is shown that nonadiabatic wave functions for both initial and final states are required at low electron energies.

We report theoretical results for magnetic-field-induced $2p^{5}3s{}^3{P}_{0,2}-2p^6{}^1{S}_0$ $E1$ transitions in Ne-like ions with zero nuclear spin ($I=0$) between Mg iii and Zn xxi as well as in Ne i. We demonstrate that it is important to include both “perturber” states $2p^{5}3s{}^1{P}_1$ and $2p^{5}3s{}^3{P}_1$ in order to produce reliable transition rates. Furthermore, we investigate the trends of the rates along the isoelectronic sequence of the $2p^{5}3s{}^3{P}_{0,2}-2p^6{}^1{S}_0$ transitions and their competition with the $2p^{5}3s{}^3{P}_0-2p^{5}3s{}^3{P}_1$ $M1$ and the $2p^{5}3s{}^3{P}_2-2p^6{}^1{S}_0$ $M2$ decays. For the $2p^{5}3s{}^3{P}_0$ state the magnetic-field-induced transition becomes the dominant decay channel for the light elements even in a relatively weak magnetic field, and it will therefore prove useful in diagnostics of the strength of magnetic fields in different plasmas. The influence of an external magnetic field on the lifetime of the $2p^{5}3s{}^3{P}_2$ state is much smaller but still observable for the ions near the neutral end of the sequence. As a special case, the magnetic field effect on the lifetimes of $2p^{5}3s{}^3{P}_{0,2}$ states of neutral ${}^{20}$Ne is discussed. It is found that the lifetimes are drastically reduced by a magnetic field, which may be an underlying reason for the discrepancies in the lifetime of the $2p^{5}3s{}^3{P}_2$ state between experiment [14.73(14) s] and theory (17.63 s).

Motivated by the recent experiment of Choi et al. [Phys. Rev. Lett. 108, 035301 (2012)], we simulate, within the Gross-Pitaevskii equation, the process of creating a skyrmion in an antiferromagnetic spin-1 Bose-Einstein condensate via the magnetic-field rotation method. Complex skymion structures are found and the factors influencing them are discussed. The dynamics of the system is mainly quasiperiodic. When the center of the skyrmion is displaced from the trap center, half vortices can be found at an intermediate stage of the dynamical evolution, but they do not necessarily lead to the destruction of the skyrmions.

We consider optical beams with topological singularities which possess Schmidt decomposition and show that such classical beams share many features of two mode entanglement in quantum optics. We demonstrate the coherence properties of such beams through the violations of Bell inequality for continuous variables using the Wigner function. This violation is a consequence of correlations between the $(x,p_x)$ and $(y,p_y)$ spaces which mathematically play the same role as nonlocality in quantum mechanics. The Bell violation for the Laguerre-Gaussian beams is shown to increase with higher orbital angular momenta $l$ of the vortex beam. This increase is reminiscent of enhancement of nonlocality for many particle Greenberger-Horne-Zeilinger states or for higher spins. The states with large $l$ can be easily produced using spatial light modulators.

We study optical properties and coherent dynamics of a hybrid system consisting of one quantum dot and one metallic nanoparticle when its excitations are governed by its collective molecular states (dark and bright states), rather than excitons or plasmons. We predict that in the bright state the exciton states of the quantum dot are optically dressed, forming standard Mollow spectra with ac Stark shifts enhanced by plasmonic effects. In the dark state the optics of the quantum dot is dominated by a combination of two seemingly uncorrelated processes: (i) coherent generation of a superfluorescent state that supports ultranarrow gain in the absence of population inversion, and (ii) plasmonic broadening and red shifting of pure exciton states, as if the laser field does not exist. We show that the coherent exciton-plasmon coupling in such a system can form an analog of Rabi flopping in the plasmonic field, causing its ultrafast oscillation, when the laser is red detuned from the quantum dot transition. For blue-detuning we predict generation of time delay in the field experienced by the quantum dot, before the system is transferred to its dark state.

We study the collective phenomenon in the scattering of a single photon by one or two layers of two-level atoms. By modeling the photon dispersion with a two-dimensional coupled cavity array (2D CCA), we analytically derive the scattering probability of a single photon. We find that the translational symmetry of the atomic distribution leads to many important effects in the single-photon scattering. In the case with one layer of atoms, the atomic collective Lamb shift is related to the photonic density of states (DOS) of a 1D CCA, rather than the photonic DOS of a 2D CCA. As a result, the photon is effectively not cattered by the atoms when the incident momentum of the photon takes some special values. In the case with two layers of atoms, an effective coupling between two layers appears and induces an electromagnetically induced transparency like phenomenon. Our work provides a scheme of analyzing photon coherent transport in 2D and may help to understand recent experiments related to high-energy photon scattering by layered nuclei material.

We consider the ground-state energy of the electromagnetic field in a piston geometry. In the idealized case, where the piston and the walls of the chamber are taken as perfect mirrors, the Casimir pressure on the piston is finite and independent of the small-scale physics of the media that compose the mirrors; the Casimir energy of the system can be regularized and is cutoff independent. Yet we find that, when the body of the piston is filled with an inhomogeneous dielectric medium, the Casimir energy is cutoff dependent, and the value of the pressure is thus inextricably dependent on the detailed behavior of the mirror and the medium at large wave vectors. This result is inconsistent with recent proposals for regularizing Casimir forces in inhomogeneous media.