Optical properties of ensembles of realistic quantum emitters coupled to plasmonic systems are studied by using adequate models that can take into account full atomic geometry. In particular, the coherent effects such as forming “dark states,” optical pumping, coherent Raman scattering, and the stimulated Raman adiabatic passage (STIRAP) are revisited in the presence of metallic nanoparticles. It is shown that the dark states are still formed but they have more complicated structure, and the optical pumping and the STIRAP cannot be employed in the vicinity of plasmonic nanostructures. Also, there is a huge difference in the behavior of the local atomic polarization and the atomic polarization averaged over an ensemble of atoms homogeneously spread near nanoparticles. The average polarization is strictly related to the polarization induced by the external field, while the local polarization can be very different from the one induced by the external field. This is important for the excitation of single molecules, e.g., different components of scattering from single molecules can be used for their efficient detection.

We suggest and demonstrate a scheme to reconstruct the symmetric two-mode squeezed thermal states of spectral sideband modes from an optical parametric oscillator. The method is based on both a single homodyne detector and the error signal from the active stabilization of the oscillator cavity. The measurement scheme has been successfully tested on different two-mode squeezed thermal states, ranging from uncorrelated coherent states to entangled states.

High-order-harmonic generation in ZnO crystal exposed to the elliptically polarized midinfrared light is theoretically investigated upon scanning the ellipticity. We find the normalized yield of each harmonics in the plateau decreases in a form that can be well fitted to Gaussian dependence as increasing the ellipticity of driving pulse. We demonstrate primarily that the sensitivity for the ellipticity dependence of the interband harmonics above the band gap is determined by both the harmonic order and the intensity of driving light, which is interpreted in terms of the semiclassical saddle-point analysis. The effect of more laser pulse parameters on the ellipticity dependence is also investigated. Furthermore, it is shown that the ellipticity dependence of each harmonics is strongly affected by the variation of the energy band in the global and the local way. This shows that high-order-harmonic generation by an elliptically polarized driving field carries the significant signature of the band structure in solids.

A tractor beam is a traveling wave that transports illuminated objects back to its source, opposite to the wave's direction of propagation, along its entire length. The requisite retrograde force arises when an object scatters the wave's momentum density downstream into the direction of propagation and then recoils upstream by conservation of momentum. Achieving this condition imposes constraints on the structure of the wave, which we elucidate in the Rayleigh limit, when the wavelength exceeds the size of the object. Continuously propagation-invariant modes such as Bessel beams do not satisfy these conditions at dipole order in the multipole expansion and so cannot serve as general-purpose long-ranged tractor beams. Modes with discrete propagation invariance, however, can act as first-order tractor beams. We demonstrate this by introducing a class of minimal solenoidal waves together with a set of design criteria that distinguish tractor beams that pull objects from repulsor beams that push them.

Bosonic quantum conversion systems can be modeled by many-particle single-mode Hamiltonians describing a conversion of $m$ molecules of type A into $n$ molecules of type B and vice versa. These Hamiltonians are analyzed in terms of generators of a polynomially deformed su(2) algebra. In the mean-field limit of large particle numbers, these systems become classical and their Hamiltonian dynamics can again be described by polynomial deformations of a Lie algebra, where quantum commutators are replaced by Poisson brackets. The Casimir operator restricts the motion to Kummer shapes, deformed Bloch spheres with cusp singularities depending on $m$ and $n$. It is demonstrated that the many-particle eigenvalues can be recovered from the mean-field dynamics using a WKB-type quantization condition. The many-particle state densities can be semiclassically approximated by the time periods of periodic orbits, which show characteristic steps and singularities related to the fixed points, whose bifurcation properties are analyzed.

Usually, the three-tangle of a tripartite pure state of qubits can be directly measured with the simultaneous preparation of a not-less-than fourfold copy of the state. We show that the exact genuine tripartite entanglement for ($2\otimes 2\otimes n$)-dimensional pure quantum states can be measured in a similar manner, provided that only two simultaneous copies of the state are available. Lower bounds are also proposed for more convenient experimental operations. As an example, a comprehensive demonstration of the scheme is provided for the three-tangle of a three-qubit state.

We consider a system consisting of four independent chains of coupled single-mode superconducting transmission line resonators and a gap-tunable qubit. When the first four resonators of the chains are coupled to the qubit properly driven by multicolor fields, we show that the resonators can be prepared in continuous-variable quadripartite cluster states via the decay of the qubit to its ground state. Moreover, the resulting cluster states can be replicated in the other resonators in column via the nearest-neighbor swapping interaction of the resonators. This means that one can generate a set of cluster states, each of which involves the four resonators from the different chains. By a similar protocol, we show that the generation and replication of continuous-variable quadripartite Greenberger-Horne-Zeilinger states in the chains of the resonators can be achieved. The numerical simulation shows that the present scheme is realizable in current accessible on-chip quantum circuit experiments. The present result may have a potential application for the realization of a large-scale one-way quantum computation.

Although the topological order is known as a quantum order in quantum many-body systems, it seems that there is not a one-to-one correspondence between topological phases and quantum phases. As a well-known example, it has been shown that all one-dimensional (1D) quantum phases are topologically trivial [X. Chen et al., Phys. Rev. B 83, 035107 (2011)]. By such facts, it seems a challenging task to understand when a quantum phase transition between different topological models necessarily reveals different topological classes of them. In this paper, we make an attempt to consider this problem by studying a phase transition between two different quantum phases which have a universal topological phase. We define a Hamiltonian as interpolation of the toric code model with $Z_2$ topological order and the color code model with $Z_2\times Z_2$ topological order on a hexagonal lattice. We show such a model is exactly mapped to many copies of 1D quantum Ising model in transverse field by rewriting the Hamiltonian in a new complete basis. Consequently, we show that the universal topological phase of the color code model and the toric code model reflects in the 1D nature of the phase transition. We also consider the expectation value of Wilson loops by a perturbative calculation and show that behavior of the Wilson loop captures the nontopological nature of the quantum phase transition. The result on the point of phase transition also shows that the color code model is strongly robust against the toric code model.

Shake processes of different origin are identified in the $\mathit{KLL}$ Auger spectrum of ${\mathrm{H}}_2\mathrm{S}$ with unprecedented detail. The $\mathit{KLL}$ Auger spectrum is presented together with the S $1s^{-1}$ photoelectron spectrum including the S $1s^{-1}{V}^{-1}n\lambda$ and S $1s^{-1}2p^{-1}n\lambda$ shake-up satellites with $V^{-1}$ and $n\lambda$ indicating a hole in the valence shell and an unoccupied molecular orbital, respectively. By using different photon energies between 2476 and 4150 eV to record the $\mathit{KLL}$ Auger spectra two different shake-up processes responsible for the satellite lines are identified. The first process is a shake-up during the Auger decay of the S $1s^{-1}$ core hole and can be described by S $1s^{-1}\to 2p^{-2}{V}^{-1}n\lambda$. The second process is the Auger decay of the shake-up satellite in the ionization process leading to S $1s^{-1}{V}^{-1}n\lambda \to 2p^{-2}{V}^{-1}n\lambda$ transitions. By combining the results of photoelectron and Auger spectra the involved $V^{-1}n\lambda$ levels are assigned.

In this work we perform a polarization dependence study of enhanced ionization (EI) in diatomic molecules. We find that EI exists when the field polarization is parallel to the molecular axis but disappears when polarization is perpendicular. We further study EI with circular polarization and find that EI exists with circular polarization indicating that rescattering does not play a significant role for EI. Furthermore, we study molecular orbital effect on EI. We find that EI exists in σ type but not π type outmost molecular orbitals.

Level-crossing spectroscopy involves lifting the degeneracy of an excited state and using the interference of two nearly degenerate levels to measure the excited-state lifetime. Here we use the idea of interference between different pathways to study the momentum-dependent wave-packet lifetime due an excited-state level crossing (conical intersection) in a molecule. Changes in population from the wave-packet propagation are reflected in the detected fluorescence. We use a chirped pulse to control the wave-packet momentum. Increasing the chirp rate increases the transition to the lower state through the conical intersection. It also increases the interference of different pathways in the upper electronic state due to the geometric phase acquired. Therefore, increasing the chirp rate decreases the population of the upper electronic state and its fluorescence yield. This suggests that there is a finite momentum-dependent lifetime of the wave packet through the level crossing as a function of chirp. We dub this lifetime the wave-packet-momentum lifetime.

We report on a general method for the rapid production of quantum degenerate gases. Using ${}^{174}\mathrm{Yb}$, we achieve an experimental cycle time as low as 1.6–1.8 s for the production of Bose-Einstein condensates (BECs) of $(0.5–1)\times {10}^5$ atoms. While laser cooling to $30\mu \mathrm{K}$ proceeds in a standard way, evaporative cooling is highly optimized by performing it in an optical trap that is dynamically shaped by utilizing the time-averaged potential of a single laser beam moving rapidly in one dimension. We also produce large $\left(>{10}^6\right)$ atom number BECs and successfully model the evaporation dynamics over more than three orders of magnitude in phase space density. Our method provides a simple and general approach to solving the problem of long production times of quantum degenerate gases.

We show that the Gabor transform provides a convenient tool allowing one to study the origin of the low-energy structures (LES) in the process of the strong-field ionization. The classical trajectories associated with the stationary points of the Gabor transform enable us to explicate the role of the forward scattering process in forming LES. Our approach offers a fully quantum mechanical description of LES, which can also be applied for other strong-field processes.

We consider a repulsive two-component Fermi gas confined in a two-dimensional isotropic harmonic potential and subject to a large Rashba spin-orbit coupling. The single-particle dispersion can be tailored by the spin-orbit-coupling term, which provides an opportunity to study itinerant ferromagnetism in this system. We show that the interplay among spin-orbit coupling, correlation effect, and mean-field repulsion leads to a competition between ferromagnetic and nonmagnetic phases. The weakly correlated nonmagnetic and the ferromagnetic phases can be well described by the mean-field Hartree-Fock theory, while the transition between the ferromagnetic and a strongly correlated nonmagnetic phase is driven by beyond-mean-field quantum correlation effect. Furthermore, the ferromagnetic phase of this system possesses a chiral current density induced by the Rashba spin-orbit coupling, whose experimental signature is investigated.

A unit filling Bose-Hubbard Hamiltonian embedded in a strong Stark field is studied in the off-resonant regime inhibiting single- and many-particle first-order tunneling resonances. We investigate the occurrence of coherent dipole wavelike propagation along an optical lattice by means of an effective Hamiltonian accounting for second-order tunneling processes. It is shown that dipole wave function evolution in the short-time limit is ballistic and that finite-size effects induce dynamical self-interference patterns known as quantum carpets. We also present the effects of the border right after the first reflection, showing that the wave function diffuses normally with the variance changing linearly in time. This work extends the rich physical phenomenology of tilted one-dimensional lattice systems in a scenario of many interacting quantum particles, the so-called many-body Wannier-Stark system.

A major challenge for postclassical boson sampling experiments is the need for a large number of coupled optical modes, detectors, and single-photon sources. Here we show that these requirements can be greatly eased by time-bin encoding and dispersive optics-based unitary transformations. Detecting consecutively heralded photons after time-independent dispersion performs boson sampling from unitaries for which an efficient classical algorithm is lacking. We also show that time-dependent dispersion can implement general single-particle unitary operations. More generally, this scheme promises an efficient architecture for a range of other linear optics experiments.

We consider the optomechanically induced transparency in the double quadratically coupled optomechanical cavities within a common reservoir, in which the two cavities are driven by the coupling fields. It is shown that the probe transparency is improved by increasing the coupling field (the left coupling field) applied on the probing cavity, but the transparency position (the probe frequency of the maximal transparency) is shifted to high frequency. The coupling field (the right coupling field) applied on the other quadratically coupled cavity can lead to a low-frequency shift for the transparency position, which can be used to fix the transparency position by adjusting the right coupling field. We get the quantitative findings that the transparency position is exactly determined by the intensity difference between the two coupling fields. On the other hand, it is found that when the two coupled optomechanical cavities interact with their common reservoir, the cross decay induced by the common reservoir can improve the probe transparency and widen the transparency window. Finally, the effects of the environment's temperature on the transparency are investigated. This will be useful in cooling the membrane, squeezing and entangling the output fields.

We consider a bipartite quantum object, composed of a quantum system and a quantum actuator which is periodically reset. We show that the reduced dynamics of the system approaches unitarity as the reset frequency of the actuator is increased. This phenomenon arises because quantum systems interacting for a short time can impact each other faster than they can become significantly entangled. In the high reset-frequency limit, the effective Hamiltonian describing the system's unitary evolution depends on the state to which the actuator is reset. This makes it possible to indirectly implement a continuous family of effective Hamiltonians on one part of a bipartite quantum object, thereby reducing the problem of indirect control (via a quantum actuator) to the well-studied one of direct quantum control.

Quantum localization within an energy shell of a closed quantum system stands in contrast to the ergodic assumption of Boltzmann, and to the corresponding eigenstate thermalization hypothesis. The familiar case is the real-space Anderson localization and its many-body Fock-space version. We use the term Hilbert-space localization in order to emphasize the more general phase-space context. Specifically, we introduce a unifying picture that extends the semiclassical perspective of Heller, which relates the localization measure to the probability of return. We illustrate our approach by considering several systems of experimental interest, referring in particular to the bosonic Josephson tunneling junction. We explore the dependence of the localization measure on the initial state and on the strength of the many-body interactions using a recursive projection method.