A high-resolution photoelectron velocity-map-imaging study is reported for the photodetachment of the atomic oxygen anion at $532\mathrm{nm}$, where five of the six possible spin-orbit fine-structure transitions have been resolved. A resolution of $\Delta E∕E=0.38\%$ was achieved. Within the experimental uncertainty, each of the fine-structure transitions has the same anisotropy, the averaged $\beta =-0.89\left(1\right)$ consistent with previous, fine-structure-unresolved, experimental and theoretical determinations.

Intrashell transitions in Rydberg atoms with a nonhydrogenic core were studied. The degeneracy of the energy shell was lifted by constant electric and magnetic fields and transitions from initial coherent elliptic states (CES) were driven by a harmonic electric field. Evenly spaced hydrogenic resonances dominate at low eccentricities $e$ of the CES. At high $e$, the hydrogenic structures disappear and new structures of a more irregular nature emerge. Classical and quantal calculations are described and are shown to agree fairly well with the experiment. Further, the classical calculations suggest that many of the observed phenomena are a consequence of the underlying classical dynamics being chaotic.

In many instances, networks of dynamical elements are subject to distributed input signals that enter the network through different nodes. In these cases, processing of the input signals may be mediated by coupling, in what constitutes an emerging property of the network. Here we study experimentally this effect in two mutually injected semiconductor lasers with optical feedback, operating in an excitable regime. The lasers are subject to different periodic input signals in their pump current, with distinct frequencies. Our results show that when the signals are harmonics of an absent fundamental, the laser array is able to process these signals and respond at the missing fundamental frequency. When the input frequencies are rigidly shifted from their harmonic values, the response frequency follows a simple law derived from a linear sum of the inputs, even though the array integrates the electrical inputs after having transduced them optically. The results are reproduced numerically with a dynamical model of the laser array.

We propose a quantum theory of rotating light beams and study some of its properties. Such beams are polychromatic and have either a slowly rotating polarization or a slowly rotating transverse mode pattern. We show that there are, for both cases, three different natural types of modes that qualify as rotating, one of which is a type not previously considered. We discuss differences between these three types of rotating modes on the one hand and nonrotating modes as viewed from a rotating frame of reference on the other. We present various examples illustrating the possible use of rotating photons, mostly for quantum information processing purposes. We introduce in this context a rotating version of the two-photon singlet state.

We investigate theoretically dark resonance spectroscopy for a dilute atomic vapor confined in a thin (micrometric) cell. We identify the physical parameters characterizing the spectra and study their influence. We focus on a Hanle-type situation, with an optical irradiation under normal incidence and resonant with the atomic transition. The dark resonance spectrum is predicted to combine broad wings with a sharp maximum at line center, which can be singled out when detecting a derivative of the dark resonance spectrum. This narrow signal derivative, shown to broaden only sublinearly with the cell length, is a signature of the contribution of atoms slow enough to fly between the cell windows in a time as long as the characteristic ground state optical pumping time. We suggest that this dark resonance spectroscopy in micrometric thin cells could be a suitable tool for probing the effective velocity distribution in the thin cell arising from the atomic desorption processes, and notably to identify the limiting factors affecting desorption under a grazing incidence.

We investigated Berry’s phase for noncyclic evolution using the rotation of a polarization azimuth of linearly polarized light in a partially wound optical fiber over the surface of a cylinder. Using a rotation gauge around the rotation axis, the observed rotation of the polarization azimuth corresponds to the area of a spherical rectangle over the surface enclosed by the contour $C$ of actual evolution, a large circle on the equator, and a longitudinal line connecting them, whereas the rotation of the polar gauge encloses a spherical triangle connecting the zenith of the sphere. The observed values were converted to Berry’s phase by transformation from the rotation gauge to the geodesic gauge. Consequently, we could confirm that Berry’s phase for a noncyclic evolution is given by the geodesic rule proposed by Samuel and Bhandari.

Measurements transfer information about a system to the apparatus and then, further on, to observers and (often inadvertently) to the environment. I show that even imperfect copying essential in such situations restricts possible unperturbed outcomes to an orthogonal subset of all possible states of the system, thus breaking the unitary symmetry of its Hilbert space implied by the quantum superposition principle. Preferred outcome states emerge as a result. They provide a framework for “wave-packet collapse,” designating terminal points of quantum jumps and defining the measured observable by specifying its eigenstates. In quantum Darwinism, they are the progenitors of multiple copies spread throughout the environment—the fittest quantum states that not only survive decoherence, but subvert the environment into carrying information about them—into becoming a witness.

Photonic entanglement has a wide range of applications in quantum computation and communication. Here we introduce a device: the photonic module, which allows for the rapid, deterministic preparation of a large class of entangled photon states. The module is an application independent, “plug and play” device, with sufficient flexibility to prepare entanglement for all major quantum computation and communication applications in a completely deterministic fashion without number-discriminated photon detection. We present two alternative constructions for the module, one using free-space components and one in a photonic band-gap structure. The natural operation of the module is to generate states within the stabilizer formalism and we present an analysis on the cavity requirements to experimentally realize this device.

We examine the problem of estimating the expectation values of two observables when we have a finite number of copies of an unknown qubit state. Specifically we examine whether it is better to measure each of the observables separately on different copies or to perform a separable nonadaptive joint measurement of the observables on each copy. We find that joint measurements can sometimes provide an advantage over separate measurements, but only if we make estimates of an observable based solely on the results of measurements of that observable. If we instead use both sets of results to estimate each observable then we find that individual measurements will be better. Finally we consider estimating the expectation values of three complementary observables for an unknown qubit.

A classical ensemble is employed to investigate double ionization of helium for laser wavelength 390 nm and intensity $1.1\text{PW}∕{\text{cm}}^2$, below the threshold for recollision impact ionization. Significant numbers of trajectories that lead to electron energy above $2U_p$ are shown to be present and to feature a time delay between recollision and final ionization. Processes through which nuclear and laser forces combine to give an electron final energy above $2U_p$ are identified.

We investigate the rotational dynamics of heteronuclear diatomic molecules possessing a ${{}^1\Sigma }^{+}$ electronic ground state exposed to a strong external time-dependent homogeneous electric field. An exponential switching on and off is employed for the electric field. We analyze the orientation and hybridization of the angular motion, together with the population of pendular and rotational states in the constant-field and field-free regimes, as the switching times are modified. Exact results are compared with those of an $N$-mode approach to the rotational dynamics derived within the effective rotor approximation. It is demonstrated that robust predictions are possible with respect to the number of pendular states and partial waves involved in the constant and postpulse regimes, respectively. The final wave packet shows a wide variety of localization and orientation phenomena arranged in characteristic patterns, which alternate between two angular hemispheres and are periodic in time.

The response of ultracold atomic Bose gases in time-dependent optical lattices is discussed based on direct simulations of the time-evolution of the many-body state in the framework of the Bose-Hubbard model. We focus on small-amplitude modulations of the lattice potential as implemented in several recent experiments and study different observables in the region of the first resonance in the Mott-insulator phase. In addition to the energy transfer we investigate the quasimomentum structure of the system which is accessible via the matter-wave interference pattern after a prompt release. We identify characteristic correlations between the excitation frequency and the quasimomentum distribution and study their structure in the presence of a superlattice potential.

The excitation spectrum for symmetric two-component Bose-Einstein condensate (BECs) in optical lattices is obtained, with emphasis on its quantitative dependence on intercomponent interaction parameter. The resulting two branches of the excitation spectrum have a linear spectrum asymptotically in the low momentum limit, which is expected as a behavior of superfluid. The critical superfluid velocity, depending on the intercomponent interaction parameter, is then obtained, which is quite different from the result obtained in other reference. A requirement of real excitation spectrum also results in a condition on the interaction parameters, which coincides with the phase separation condition. Hence in real spectrum excitation, it is proposed that there should be two branches of superfluid with different critical superfluid velocities, while in the complex spectrum it is predicted that there should be phase separation in the two-branch superfluid system. The excitation spectrum for an asymmetric two-component BEC system is also presented and analyzed.

We developed a theoretical model for the spatial mode dynamics of an optical parametric oscillator under injection of orbital angular momentum. This process is interpreted in terms of a Poincaré representation of first order spatial modes. The spatial properties of the down-converted fields can be easily understood from their symmetries in this geometric representation. By considering an adiabatic mode conversion of the injected signal, we calculate the evolution of the down-converted beams. A phase conjugation effect is predicted which is a consequence of the symmetry in the Poincaré sphere. We also propose an experiment to measure this effect.

We consider the propagation of slow light with an orbital angular momentum (OAM) in a moving atomic medium. We have derived a general equation of motion and applied it in analyzing propagation of slow light with an OAM in a rotating medium, such as a vortex lattice. We have shown that the OAM of slow light manifests itself in a rotation of the polarization plane of linearly polarized light. To extract a pure rotational phase shift, we suggest to measure a difference in the angle of the polarization plane rotation by two consecutive light beams with opposite OAM. The differential angle $\Delta {\alpha }_l$ is proportional to the rotation frequency of the medium ${\omega }_{\text{rot}}$ and the winding number $l$ of light, and is inversely proportional to the group velocity of light. For slow light the angle $\Delta {\alpha }_l$ should be large enough to be detectable. The effect can be used as a tool for measuring the rotation frequency ${\omega }_{\text{rot}}$ of the medium.

An optical lattice loaded with cold atoms can exhibit a tunable photonic band gap for a weak probe field under the conditions of electromagnetically induced transparency. This system possesses a number of advantageous properties, including reduced relaxation of Raman coherence and the associated probe absorption, and simultaneous enhancement of the index modulation and the resulting reflectivity of the medium. This flexible system has the potential to serve as a test bed for various designs of linear and nonlinear photonic band gap materials at very low light level and can be employed to realize deterministic entanglement between weak quantum fields.

An attack strategy was recently proposed by Chau [Phys. Rev. A 75, 012327 (2007)], which was claimed to be able to break all quantum string seal protocols. Here it will be shown that the attack cannot obtain nontrivial information and escape the detection simultaneously in a class of quantum string seal, including the one proposed by He [Int. J. Quantum Inf. 4, 677 (2006)]. Thus it is insufficient to conclude that all quantum string seals are insecure.

In Phys. Rev. A 76, 056301 (2007), He claimed that the proof in my earlier paper [Phys. Rev. A 75, 012327 (2007)] is insufficient to conclude the insecurity of all quantum string seals because my measurement strategy cannot obtain nontrivial information on the sealed string and escape detection at the same time. Here, I clarify that our disagreement comes from our adoption of two different criteria on the minimum amount of information a quantum string seal can reveal to members of the public. I also point out that He did not follow my measurement strategy correctly.

We report the observation of a Bose-Einstein condensate in a bosonic isotope of ytterbium $\left({}^{170}\mathrm{Yb}\right)$. More than ${10}^6$ atoms are trapped in a crossed optical dipole trap and cooled by evaporation. Condensates of approximately ${10}^4$ atoms have been obtained. From an expansion of the condensate, we have extracted the scattering length $a_{170}=3.6\pm 0.9\mathrm{nm}$.