Dissociative electron attachment (DEA) to gas phase ${\mathrm{CO}}_2$ has been probed using a velocity slice imaging technique. DEA to ${\mathrm{CO}}_2$ produces only an ${\mathrm{O}}^{-}$ ionic fragment and shows two major resonances located at 4.4 and 8.2 eV, respectively. The kinetic energy and angular distribution of the ${\mathrm{O}}^{-}$ ions are measured around the second resonance with higher efficiency and sensitivity that provide details of the DEA dynamics. The kinetic energy distributions are in good agreement with the previous reports. However, the distinct angular distributions show substantial difference from the two recent studies within the limited electron energies. Our angular distribution results show two negative ion resonant states are involved in the underlying DEA process at the entire electron energies over the second resonance. We discussed the recent conflicting findings in the angular distribution results. The forward-backward asymmetry observed in the angular distributions is explained due to the interference effect of different partial waves associated with the attaching electron.

Stimulated by the experimental realization of spin-dependent tunneling via a gradient magnetic field [C. J. Kennedy et al., Phys. Rev. Lett. 111, 225301 (2013); M. Aidelsburger et al., Phys. Rev. Lett. 111, 185301 (2013)], we investigate the dynamics of Bloch oscillations and Landau-Zener tunneling of single spin-half particles in a periodic potential under the influence of a spin-dependent constant force. In analogy to the Wannier-Stark system, we call our system the Wannier-Zeeman system. If there is no coupling between the two spin states, the system can be described by two crossing Wannier-Stark ladders with opposite tilts. The spatial crossing between two Wannier-Stark ladders becomes a spatial anticrossing if the two spin states are coupled by external fields. For a wave packet away from the spatial anticrossing, due to the spin-dependent constant force, it will undergo spatial Landau-Zener transitions assisted by the intrinsic intraband Bloch oscillations, which we call the Bloch-Landau-Zener dynamics. If the interspin coupling is sufficiently strong, the system undergoes adiabatic Bloch-Landau-Zener dynamics, in which the spin dynamics follows the local dressed states. Otherwise, for nonstrong interspin couplings, the system undergoes nonadiabatic Bloch-Landau-Zener dynamics.

In ferromagnetic Bose-Einstein condensates (BECs), the quadratic Zeeman effect controls magnetic anisotropy, which affects magnetic domain pattern formation. While the longitudinal magnetization is dominant (similar to the Ising model) for a negative quadratic Zeeman energy, the transverse magnetization is dominant (similar to the $XY$ model) for a positive one. When the quadratic Zeeman energy is positive, the coarsening dynamics is driven by vortex-antivortex annihilation in the same way as the $XY$ model. However, due to a superfluid flow of atoms, there exist several combinations of vortex-antivortex pairs in ferromagnetic BECs, which makes the coarsening dynamics more complicated than that of the $XY$ model. We propose a revised domain growth law, which is based on the growth law of the two-dimensional $XY$ model, for a two-dimensional ferromagnetic BEC with a positive quadratic Zeeman energy.

We propose to experimentally realize an odd-parity eigenstate $|b\rangle$ of two atoms in a double well. The occupation probability of this state shows evident dependence on the interaction, distinct from the result of two-mode model adopted in the Heidelberg experiment. The tunneling dynamics of two atoms starting from the NOON state with infinite barrier height can be derived from the exactly solved model of a $\delta$-barrier split double well based on a Bethe ansatz type hypothesis of the wave functions. We find that the single-particle tunneling shifts between the probability of double occupancy in the same well and that of single occupancy in different wells.

Light transport in a dense and disordered cold atomic ensemble, where the cooperation of atomic dipoles essentially modifies their coupling with the radiation modes, offers an alternative approach to light-matter interfacing protocols. Here, we show how the cooperativity and quasistatic dipole interaction affect the process of light propagation under the conditions of electromagnetically induced transparency (EIT). We perform comparative analysis of the self-consistent approach with ab initio microscopic calculations and emphasize the role of the interatomic interaction in the dipoles' dynamics. Our results show that in such a dense and strongly disordered system the EIT-based light storage protocol stays relatively insensitive to configuration variations and can be obtained with essentially fewer atoms than are normally needed for dilute systems.

We theoretically study the formation of Brillouin precursors in Debye media. We point out that the precursors are visible only at propagation distances such that the impulse response of the medium is essentially determined by the frequency dependence of its absorption and is practically Gaussian. By simple convolution, we then obtain explicit analytical expressions of the transmitted waves generated by reference incident waves, distinguishing precursor and main signal by a simple examination of the long-time behavior of the overall signal. These expressions are in good agreement with the signals obtained in numerical or real experiments performed on water in the radio-frequency domain and explain in particular some observed shapes of the precursor. Results are obtained for other remarkable incident waves. In addition, we show quite generally that the shape of the Brillouin precursor appearing alone at sufficiently large propagation distance and the law giving its amplitude as a function of this distance do not depend on the precise form of the incident wave but only on its integral properties. The incidence of a static conductivity of the medium is also examined and explicit analytical results are again given in the limit of weak and strong conductivities.

By means of numerical simulations and the input-output formalism, we study photon transport through a chain of coupled nonlinear optical cavities subject to uniform dissipation. Photons are injected from one end of the chain by means of a coherent source. The propagation through the array of cavities is sensitive to the interplay between the photon hopping strength and the local nonlinearity in each cavity. We characterize photon transport by studying the populations and the photon correlations as a function of the cavity position. When complemented with input-output theory, these quantities provide direct information about photon transmission through the system. The position of single-photon and multiphoton resonances directly reflects the structure of the many-body energy levels. This shows how a study of transport along a coupled cavity array can provide rich information about the strongly correlated (many-body) states of light even in presence of dissipation. The numerical algorithm we use, based on the time-evolving block decimation scheme adapted to mixed states, allows us to simulate large arrays (up to 60 cavities). The scaling of photon transmission with the number of cavities does depend on the structure of the many-body photon states inside the array.

We explore the phase diagram of interacting spin-$1/2$ systems in the presence of anisotropic interactions, spontaneous decay, and driving. We find a rich phase diagram featuring a limit-cycle phase in which the magnetization oscillates in time. We analyze the spatiotemporal fluctuations of this limit-cycle phase based on a Gaussian-Floquet analysis. Spatial fluctuations destroy long-range limit-cycle ordering for dimension $d\le 2$, as a time-dependent generalization of the Mermin-Wagner theorem. This result can be interpreted in terms of a spatiotemporal Goldstone mode corresponding to phase fluctuations of the limit cycle. We also demonstrate that the limit-cycle phase exhibits an asymmetric power spectrum measurable in fluorescence experiments.

The dynamics of quantum Fisher information (QFI) of the phase parameter in a driven two-state system is studied within the framework of the non-Markovian dissipative process. The influences of memory effects, classical driving, and detunings on the parameter-estimation precision are demonstrated by exactly solving the Hamiltonian under rotating-wave approximation. In sharp contrast with the results obtained in the presence of Markovian dissipation, we find that classical driving can drastically enhance the QFI, namely, the precision of parameter estimation in the non-Markovian regime. Moreover, the parameter-estimation precision may even be preserved from the influence of surrounding non-Markovian dissipation with the assistance of classical driving. Remarkably, we reveal that the enhancement and preservation of QFI highly depend on the combination of classical driving and non-Markovian effects. Finally, a phenomenological explanation of the underlying mechanism is presented in detail via the quasimode theory.

We study statistical properties of states of massive quantized charged Dirac and Klein-Gordon fields interacting with a background that violates the vacuum stability, first in general terms and then for a special electromagnetic background. As a starting point, we use a nonperturbative expression for the density operators of such fields derived by Gavrilov et al. [Gavrilov, Gitman, and Tomazelli, Nucl. Phys. B 795, 645 (2008)]. We construct the reduced density operators for electron and positron subsystems and discuss a decoherence that may occur in the course of the evolution due to an intermediate measurement. By calculating the entropy we study the loss of the information in QED states due to partial reductions and a possible decoherence. We consider the so-called $T$-constant external electric field as an external background. This exactly solvable example allows us to calculate explicitly all statistical properties of various quantum states of the massive charged fields under consideration.

We geometrically characterize one-qubit dissipators of a Lindblad type. An efficient parametrization in terms of 6 linear parameters opens the way to various optimizations with local dissipation. As an example, we study maximal steady-state singlet fraction that can be achieved with an arbitrary local dissipation and two-qubit Hamiltonian. We show that this singlet fraction has a discontinuity as one moves from unital to nonunital dissipators and demonstrate that the largest possible singlet fraction is $\approx 0.654$. This means that for systems with a sufficiently entangled ground state there is a fundamental quantum limit to the lowest attainable energy. With local dissipation one is unable to cool the system below some limiting nonzero temperature.

A quantum error-correcting code is a subspace $\mathcal{C}$ such that allowed errors acting on any state in $\mathcal{C}$ can be corrected. A quantum code for which state recovery is only required up to a logical rotation within $\mathcal{C}$ can be used for the detection of errors, but not for quantum error correction. Such a code with a stabilizer structure, which we call an “ambiguous stabilizer code” (ASC), can nevertheless be useful for the characterization of quantum dynamics (CQD). The use of ASCs can help lower the size of CQD probe states used, but at the cost of an increased number of operations.

We measure the differential cross sections (DCSs) for the electron-impact excitation of the combined (two fine-structure levels) resonant $4d^{10}5p{}^{2}P_{1/2,3/2}$ and $4d^{9}5s^2{}^{2}D_{5/2}$ states in silver from the $4d^{10}5s{}^{2}S_{1/2}$ ground state. A comparison with the predictions of the relativistic distorted-wave (RDW) approximation model is carried out. Relativistic distorted-wave calculations are performed for each level separately and are combined to compare with the measurements. Both the experimental and theoretical results are obtained at incident electron energies $E_0$ of 10, 20, 40, 60, 80, and 100 eV and scattering angles θ from 10° up to 150° (experiment) and from 0° to 180° (calculations). Absolute values for the experimental DCSs are obtained by normalizing relative DCSs to theoretical RDW results at 40° at all energies except at 10 eV, where we performed the normalization of the relative DCSs at 10° to our previous small-angle experimental DCS values [S. D. Tošić et al., Nucl. Instrum. Methods Phys. Res. Sect. B 279, 53 (2012)]. The integrated cross sections, which include integral $Q_{\mathrm{I}}$, momentum transfer $Q_{\mathrm{M}}$, and viscosity $Q_{\mathrm{V}}$ cross sections, are determined by numerical integration of the absolute DCSs.

We propose a directional coupler exploiting the framework of adiabatic passage for two-level atomic systems with a configuration-dependent complex-hyperbolic-secant scheme. A recently developed Shortcut to Adiabatic passage method (STA), which uses a transitionless quantum driving algorithm, is applied to the coupler. The study shows that it is possible to reduce the device length significantly using STA, keeping the efficiency of power transfer at 100%. This shortcut approach shows much superiority in terms of robustness and fidelity in power switching compared to the adiabatic approach.

Photoelectron spectroscopy studies earlier probed oscillations in $\text{C}{}_{60}$ valence emissions, producing a series of minima whose energy separation depends on the molecular cavity. We show here that the quantum phase at these cavity minima exhibits variations from strong electron correlations in $\text{C}{}_{60}$, causing rich structures in the emission time delay. Hence, these minima offer unique spectral zones to directly explore multielectron forces via attosecond RABITT interferometry not only in fullerenes, but also in clusters and nanostructures for which such minima are likely abundant.

Nonadiabatic orientation and alignment of hexapole rotational-state-selected methyl bromine $\left({\mathrm{CH}}_3\mathrm{Br}\right)$ molecules is studied. The temporal evolution of the mixed dc field and laser-induced orientation and alignment is measured by a pump-probe method. The temporal orientation and alignment transients are in good agreement with the time-dependent Schrödinger equation calculation we perform. We show that the degree of orientation and alignment is strongly dependent on the selected initial rotational state. The temporal transients originating from two different initial states, the $|111\rangle$ state and the mixed $|111\rangle +|212\rangle$ state, are discussed. Our results show a maximum degree of $\langle cos\theta \rangle =-0.7$ for the orientation of ${\mathrm{CH}}_3\mathrm{Br}$ molecules in the $|111\rangle$ state.

We consider quantum quenches of harmonically trapped one-dimensional bosons from repulsive-to-attractive interactions. We study the resulting breathing dynamics of the so-called “super-Tonks-Girardeau” (STG) state at large attraction, or of its analog at moderate or small attraction. This state is highly excited compared to the ground state of the attractive gas, and is the lowest eigenstate where the particles are not bound or clustered. We analyze the dynamics from a spectral point of view, identifying the relevant eigenstates of the interacting trapped many-body system, and analyzing the nature of these quantum eigenstates. To obtain explicit eigenspectra, we use Hamiltonians with finite-dimensional Hilbert spaces to approximate the Lieb-Liniger system. We employ two very different approximate approaches: an expansion in a truncated single-particle harmonic-trap basis and a lattice (Bose-Hubbard) model. We show how the breathing frequency, identified with the energy difference between the sTG state and another particular eigenstate, varies with interaction.

We solve the Gross-Pitaevskii (GP) and Bogoliubov equations to investigate the metastability of superfluidity in a Bose-Einstein condensate in the presence of a uniformly moving defect potential in a two-dimensional torus. We calculate the total energy and momentum as functions of the driving velocity of the moving defect and find metastable states with negative effective mass near the critical velocity. We also find that the first excited energy (energy gap) in the finite-sized torus closes at the critical velocity, that it obeys one-fourth power-law scaling, and that the dynamical fluctuation of the density (amplitude of the order parameter) is strongly enhanced near the critical velocity. We confirm the validity of our results near the critical velocity by calculating the quantum depletion. We find an unconventional swallowtail structure (multiple-swallowtail structure) through calculations of the unstable stationary solutions of the GP equation.

The Rabi model describes the simplest interaction between light and matter via a two-level quantum system interacting with a bosonic field. We demonstrate that the fully quantized version of the Rabi model is integrable in the Yang-Baxter sense at two parameter values. The model is argued to be not Yang-Baxter integrable in general. This is in contrast to the claim that the quantum Rabi model is integrable based on a phenomenological criterion of quantum integrability not presupposing the existence of a set of commuting operators. Similar Yang-Baxter integrable points are identified for the generalized Rabi model and the fully quantized Dicke model. The integrable points have particular implications for the level statistics of the Dicke model.

We propose an experimental setup that should make it possible to reveal the frictionless flow of a superfluid of light from the suppression of the drag force that it exerts on a material obstacle. In the paraxial-propagation geometry considered here, the photon-fluid dynamics is described by a wave equation analogous to the Gross-Pitaevskii equation of dilute Bose-Einstein condensates and the obstacle consists in a solid dielectric slab immersed into a nonlinear optical liquid. By means of an ab initio calculation of the electromagnetic force experienced by the obstacle, we anticipate that superfluidity is detectable in state-of-the-art experiments from the disappearance of the optomechanical deformation of the obstacle.