Time-sliced velocity imaging experiments have been performed for the low-energy electron dissociative attachment to CFCl${}_3$ in the gas phase. The time-sliced velocity images of the F${}^{-}$ anionic fragment, recorded at different electron attachment energies (2.0–7.0 eV), indicate image pattern evolutions. The angular and kinetic energy distributions of the F${}^{-}$ fragment are interpreted with two shape-resonant states of CFCl${}_3$${}^{-}$ and thermochemistry calculations for dissociation thresholds. The dramatic reduction of the F${}^{-}$ kinetic energy observed at higher attachment energies is possibly due to two-body dissociation with an electronically excited state of CCl${}_3$ (${}^2{A}^{\prime \prime }$) or three-body dissociations.

We investigate $p$-orbital Bose-Einstein condensates in both the square and checkerboard lattice by numerically solving the Gross-Pitaevskii equation. The periodic potential for the latter lattice is taken exactly from the recent experiment [Nature Phys. 7, 147 (2011)]. It is confirmed that the staggered orbital-current state is the lowest-energy state in the $p$ band. Our numerical calculation further reveals that for both lattices the staggered $p$-orbital state suffers Landau instability but the situation is remarkably different for dynamical instability. A dynamically stable parameter region is found for the checkerboard lattice, but not for the square.

We study the interplay of disorder with pumping and decay in coupled qubit-cavity arrays, the Jaynes-Cummings-Hubbard model. We find that relatively weak disorder can wash out the bistability present in the clean pumped system and that moreover the combination of disorder in on-site energies and decay can lead to effective phase disorder. To explore these questions, we present a nonequilibrium generalization of stochastic mean-field theory, providing a simple tool to address such questions. This technique is developed for rather general forms of light-matter coupling, driving, dissipation, and on-site disorder, making it applicable to a wide range of systems.

We present a Leggett-type model that reproduces quantum correlations for the Bell states. It cannot be falsified through known tests based on Bell-type, Leggett-type, or so-called chained Bell inequalities. The model entails partial suppression of measurement independence (free will) to a fraction of $1/4$, as quantified by a recently proposed measure that varies between 0 and 1. This is a consequence of assuming a possible nonlocal relationship between an entangler and one of two measuring stations, thereby differing from the usual nonlocal, Leggett-type models. Furthermore, the model admits arbitrary time ordering for events occurring at two spacelike separated measuring stations. The predicted correlations reproduce the quantum-mechanical ones. Thus, the model is not falsified by so-called before-before tests.

Dissipative and stochastic effects in the geometric phase of a qubit are taken into account using a geometrical description of the corresponding open-system dynamics within a canonical Langevin framework based on a Caldeira-Leggett-like Hamiltonian. By extending the Hopf fibration $S^3\to S^2$ to include such effects, the exact geometric phase for a dissipative qubit is obtained, whereas numerical calculations are used to include finite-temperature effects on it.

Zitterbewegung of neutral relativistic particles propagating along a constant magnetic and/or electric field is studied. It is shown that spin Zitterbewegung, when superimposed on the Larmor precession frequency, leads to a beating pattern. The existence of a forbidden frequency of spin precession is predicted. Modifications of position and velocity Zitterbewegung due to lifted spin degeneracy manifested in the appearance of longitudinal and transversal Zitterbewegung, each with two Zitterbewegung frequencies and resulting beating patterns, are reported.

We present a detailed investigation of the dynamics of two physically different qubit models, dephasing under the effect of an ultracold atomic gas in a Bose-Einstein-condensed (BEC) state. We study the robustness of each qubit probe against environmental noise; even though the two models appear very similar at a first glance, we demonstrate that they decohere in a strikingly different way. This result holds significance for studies of reservoir engineering as well as for use of the qubits as quantum probes of an ultracold gas. For each model we study whether and when, upon suitable manipulation of the BEC, the dynamics of the qubit can be described by a (non-)Markovian process and consider the the effect of thermal fluctuations on the qubit dynamics. Finally, we provide an intuitive explanation for the phenomena we observe in terms of the spectral density function of the environment.

We use the abstract search algorithm and its extension due to Tulsi to analyze a spatial quantum search algorithm that finds a marked vertex in Hanoi networks of degree 4 faster than classical algorithms. We also analyze the effect of using non-Groverian coins that take advantage of the small-world structure of the Hanoi networks. We obtain the scaling of the total cost of the algorithm as a function of the number of vertices. We show that Tulsi's technique plays an important role to speed up the searching algorithm. We can improve the algorithm's efficiency by choosing a non-Groverian coin if we do not implement Tulsi's method. Our conclusions are based on numerical implementations.

Symmetrically private information retrieval, a fundamental problem in the field of secure multiparty computation, is defined as follows: A database $D$ of $N$ bits held by Bob is queried by a user Alice who is interested in the bit $D_b$ in such a way that (1) Alice learns $D_b$ and only $D_b$ and (2) Bob does not learn anything about Alice's choice $b$. While solutions to this problem in the classical domain rely largely on unproven computational complexity theoretic assumptions, it is also known that perfect solutions that guarantee both database and user privacy are impossible in the quantum domain. Jakobi et al. [Phys. Rev. A 83, 022301 (2011)] proposed a protocol for oblivious transfer using well-known quantum key device (QKD) techniques to establish an oblivious key to solve this problem. Their solution provided a good degree of database and user privacy (using physical principles like the impossibility of perfectly distinguishing nonorthogonal quantum states and the impossibility of superluminal communication) while being loss-resistant and implementable with commercial QKD devices (due to the use of the Scarani-Acin-Ribordy-Gisin 2004 protocol). However, their quantum oblivious key distribution (QOKD) protocol requires a communication complexity of $O\left(N\log N\right)$. Since modern databases can be extremely large, it is important to reduce this communication as much as possible. In this paper, we first suggest a modification of their protocol wherein the number of qubits that need to be exchanged is reduced to $O\left(N\right)$. A subsequent generalization reduces the quantum communication complexity even further in such a way that only a few hundred qubits are needed to be transferred even for very large databases.

We propose a method of generating entanglement using single photons and electron spins in the regime of resonance scattering. The technique involves matching the spontaneous emission rate of the spin dipole transition in bulk dielectric to the modified rate of spontaneous emission of the dipole coupled to the fundamental mode of an optical microcavity. We call this regime resonance scattering where interference between the input photons and those scattered by the resonantly coupled dipole transition result in a reflectivity of zero. The contrast between this and the unit reflectivity when the cavity is empty allow us to perform a nondemolition measurement of the spin and to nondeterministically generate entanglement between photons and spins. The chief advantage of working in the regime of resonance scattering is that the required cavity quality factors are orders of magnitude lower than is required for strong coupling, or Purcell enhancement. This makes engineering a suitable cavity much easier particularly in materials such as diamond where etching high-quality-factor cavities remains a significant challenge.

We report measurements and first-principles calculations of the differential cross sections for elastic scattering of low-energy electrons by acetylene, C${}_2$H${}_2$, at collision energies from 1 to 100 eV, with an emphasis on energies near and below that of the ${\pi }^{*}$ shape resonance. The measurements cover angles from 5${}^{\circ }$ to 130${}^{\circ }$. We compare our results to previous experimental and theoretical values.

We show experimentally that precise phase modulation of an optical potential allows us to control quantum correlations for atomic wave packets in a way that greatly enhances momentum transport. Experimentally, this means that for the same laser power and pulse frequency, atoms are accelerated to much higher energies. We explain our results with a pseudoclassical analysis along with numerical simulations, highlighting the existence of transporting islands in phase space.

We demonstrate a horizontal, linearly guided Mach-Zehnder atom interferometer in an optical waveguide. Intended as a proof-of-principle experiment, the interferometer utilizes a Bose-Einstein condensate in the magnetically insensitive $\left|F=1,m_F=0\right.〉$ state of ${}^{87}$Rb as an acceleration-sensitive test mass. We achieve a modest sensitivity to acceleration of $\Delta a=7\times {10}^{-4}$ m/s${}^2$. Our fringe visibility is as high as 38$\%$ in this optically guided atom interferometer. We observe a time of flight in the waveguide of over 0.5 s, demonstrating the utility of our optical guide for future sensors.

We study theoretically the superfluidity and stability of a Bose-Einstein condensate (BEC) whose interatomic scattering length is periodically modulated with optical Feshbach resonance. Our numerical study finds that the properties of this periodic BEC are strongly influenced by the modulation strength. When the modulation strength is small, only the Bloch waves close to the Brillouin zone edge suffer both Landau and dynamical instabilities. When the modulation strength is strong enough, all Bloch waves become dynamically unstable. In other words, the periodic BEC loses its superfluidity completely.

The hopping dynamics of two fermionic species with different effective masses in the one-dimensional Hubbard model driven by an external field are theoretically investigated. A multiple-time-scale asymptotic analysis of the driven asymmetric Hubbard model shows that a high-frequency bichromatic external field can sustain a low-energy particle bound state (a doublon) in which two fermions of different species occupy nearest-neighbor sites and cotunnel along the lattice. The predictions of the asymptotic analysis are confirmed by direct numerical simulations of the two-particle Hubbard Hamiltonian.

The phenomenon of dynamical tunneling is investigated in asymmetric resonant cavities by exploiting the avoided resonance crossing. With the external coupling between resonances localized within different regions of phase space, we show that the tunneling rate can be dramatically reduced. The nearly complete suppression of dynamical tunneling, so-called “locking,” has been achieved under two-state weak coupling. A possible way to observe and control the coherent destruction of dynamical tunneling experimentally is also presented. Our research may find application in $Q$ switching and ultrafast beam steering of microcavity lasers.

We introduce a one-dimensional system combining the $\mathcal{PT}$-symmetric complex periodic potential and the ${\chi }^{\left(2\right)}$ (second-harmonic-generating) nonlinearity. The imaginary part of the potential, which represents spatially separated and mutually balanced gain and loss, affects only the fundamental-frequency (FF) wave, while the real potential acts on the second-harmonic (SH) component too. Soliton modes are constructed, and their stability is investigated (by means of the linearization and direct simulations) in semi-infinite and finite gaps in the corresponding spectrum, starting from the bifurcation which generates the solitons from edges of the gaps’ edges. Families of solitons embedded into the continuous spectrum of the SH component are found too, and it is demonstrated that a part of the families of these embedded solitons is stable. The analysis is focused on effects produced by the variation of the strength of the imaginary part of the potential, which is a specific characteristic of the $\mathcal{PT}$ system. The consideration is performed chiefly for the most relevant case of matched real potentials acting on the FF and SH components. The case of the real potential acting solely on the FF component is briefly considered too.

Quantum pulsed second-subharmonic generation in a planar waveguide with a small periodic corrugation at the surface is studied. Backscattering of the interacting fields on the corrugation enhances the nonlinear interaction, giving larger values of squeezing. The problem of backscattering is treated by perturbation theory, using the Fourier transform for nondispersion propagation, and by numerical approach in the general case. Optimum spectral modes for squeezed-light generation are found using the Bloch-Messiah reduction. An improvement in squeezing and increase of the numbers of generated photons are quantified for the corrugation resonating with the fundamental and second-subharmonic field. Splitting of the generated pulse by the corrugation is predicted.

In this contribution we provide an in depth theoretical analysis of the bifurcations leading to nonlinear polarization dynamics in a free-running vertical-cavity surface-emitting laser (VCSEL). We detail the sequence of bifurcations that occurs when increasing the injection current, and which brings the laser from linear to elliptical polarization emission and then self-pulsating or even more complex chaotic dynamics of the light intensity. Continuation techniques allow us to follow the stable and unstable limit cycle solutions emerging from Hopf bifurcations, and therefore to interpret the frequency of the self-pulsating polarization dynamics. The fundamental frequency of the pulsating dynamics is either close to the laser relaxation oscillation frequency or close to the linear-birefringence-induced polarization mode frequency splitting, depending on the laser parameters. A systematic analysis of the parameter space allows us to identify two scenarios that are in excellent qualitative agreement with those reported in recent experiments. Our results provide, moreover, evidence for an interesting polarization mode hopping mechanism, i.e., a so-called deterministic mode hopping where the laser exhibits a chaotic and therefore random-like hopping between two states that are elliptically polarized and nonorthogonal.

Quantum memory is one of the key components constituting a quantum network. An important step towards the successful development of such a network is the storage of single photons. Encoding photons in high-dimensional photonic states can significantly increase the network's information-carrying capacity. Furthermore, quantum memories that are able to store multiple optical modes offer advantages over single-mode memories, in terms of both speed and capacity. However, a practical implementation of such a scheme for storing and retrieving multiple images at the single-photon level has not yet been achieved. Here, we provide experimental evidence that two spatial probe fields imprinted with a real image each can be stored and retrieved with good visibility and similarity at the single-photon level in a ${}^{85}$Rb cold atomic ensemble, making use of electromagnetically induced transparency. Our results are very promising for the realization of a high-dimensional quantum network in the future.