Magneto-optical traps have been used for several decades. Among fundamental mechanisms occurring in such traps, the magnitude of the multiple scattering is still unclear. Indeed, many experimental situations cannot be modeled easily, different models predict different values of the reabsorption cross section, and no simple experimental measurements of this cross section are available. We propose in this paper a simple measurement of this cross section through the size and the shape of the cloud of cold atoms. We apply this method to traps with a configuration where theoretical values are available and show that the measured values are compatible with some models. We also apply the method to configurations where models are not relevant and show that the reabsorption is sometimes much larger than the usually assumed value.

Assemblies of Rydberg atoms subject to resonant dipole-dipole interactions exhibit Frenkel excitons. We show that van der Waals shifts can significantly modify the exciton wave function, whenever atoms approach each other closely. As a result, attractive dipole-dipole potentials and repulsive van der Waals interactions can be combined to form stable one-dimensional atom chains, akin to bound aggregates. Here the van der Waals shifts ensure a stronger homogeneous delocalization of a single excitation over the whole chain, enabling it to bind several atoms. When brought into unstable configurations, such Rydberg aggregates allow the direct monitoring of their dissociation dynamics.

We propose a scheme to decelerate polar molecules by using traveling microwave lattices in a waveguide. Two counterpropagating microwave fields with different frequencies create a traveling microwave lattice and decelerate polar molecules by exploiting their first-order ac Stark shift. During deceleration, molecules are always close to the field maximum, thus reducing the potential particle loss due to nonadiabatic transitions occurring in the low-field region. The method can be used for molecules in a rotational ground state, which is suitable for further sympathetic or evaporative cooling. Numerical trajectory simulations are carried out, and the results show that the phase-space acceptance area is comparable to that of some other deceleration methods.

We investigate the finite-lifetime effects on first-order correlation functions of dissipative Bose-Einstein condensates. By taking into account the phase fluctuations up to all orders, we show that the finite-lifetime effects are negligible for the spatial first-order correlation functions, but have an important effect on the temporal correlations. As an application, we calculate the one-particle density matrix of a quasicondensate of photons. Finally, we also consider the photons in the normal state and we demonstrate that the finite-lifetime effects decrease both the spatial and temporal first-order correlation functions.

We consider the total density and spin density fluctuations of a uniform spin-1 Bose-Einstein condensate within the Bogoliubov formalism. We present results for the total density and spin density static structure factors for all four magnetic phases. A key result of our work is a set of analytic predictions for the structure factors in the large- and small-momentum limits. These results will be useful in current experiments aiming to develop a better understanding of the excitations and fluctuations of spinor condensates.

We have observed nonlinear transduction of the thermomechanical motion of a nanomechanical resonator when detected as laser transmission through a sideband unresolved (stationary) optomechanical cavity. Nonlinear detection mechanisms are of considerable interest as special cases allow for quantum nondemolition measurements of the mechanical resonator's energy. We investigate the origin of the nonlinearity in the optomechanical detection apparatus and derive a theoretical framework for the nonlinear signal transduction, and the optical spring effect, from both nonlinearities in the optical transfer function and second-order optomechanical coupling. By measuring the dependence of the linear and nonlinear signal transduction—as well as the mechanical frequency shift—on laser detuning from optical resonance, we provide estimates of the contributions from the linear and quadratic optomechanical couplings.

We show that when a single vortex convected by a flowing background collides with an oblique dark soliton in a defocusing Kerr-type medium, it passes through the oblique soliton. However, this process is accompanied by a considerable vertical shift of the vortex that grows with decrease of the inclination angle of the dark soliton with respect to the direction of the flow and decreases with increase of the flow (or collision) velocity. In the parameter range where the interaction with a vortex does not lead to drastic deformations of the shape of the oblique dark soliton, this shift can be estimated analytically under the assumption that the vortex soliton moves along the “streamlines” that exhibit vertical shift in the vicinity of the oblique dark soliton. A similar effect was observed upon collision of dark solitons with moving vortex dipoles or rotating pairs of vortices with equal topological charges.

Recently reported anomalies in the photo-double-ionization spectra of the aromatic molecules partially deuterated benzene, naphthalene, anthracene, pentacene, azulene, phenanthrene, pyrene, and coronene are attributed to Coulomb-pair resonances of π electrons. The properties of the resonance in benzene are investigated in detail. The quasilinear behavior in the 2+/1+ ion ratio above the resonance is attributed to a transition associated with excitation from the ground state to a two-electron continuum. A similar explanation applies to the quasilinear behavior seen in the pentagonal rings pyrrole, furan, selenophene, and thiophene which do not display resonance peaks.

We propose and experimentally demonstrate an approximate universal-not (unot) operation that is robust against operational errors. In our proposal, the unot operation is composed of stochastic unitary operations represented by the vertices of regular polyhedrons. The operation is designed to be robust against random operational errors by increasing the number of unitary operations (i.e., reference axes). Remarkably, no increase in the total number of measurements nor additional resources are required to perform the unot operation. Our method can be applied in general to reduce operational errors to an arbitrary degree of precision when approximating any antiunitary operation in a stochastic manner.

We investigate the time evolution of the chirality reduced density matrix for a discrete-time quantum walk on a one-dimensional lattice. The matrix is obtained by tracing out the spatial degree of freedom. We analyze the standard case, without decoherence, and the situation in which decoherence appears in the form of broken links in the lattice. By examining the trace distance for possible pairs of initial states as a function of time, we conclude that the evolution of the reduced density matrix is non-Markovian, in the sense defined by Breuer, Laine, and Piilo [Phys. Rev. Lett. 103, 210401 (2009)]. As the level of noise increases, the dynamics approaches a Markovian process. The highest non-Markovianity corresponds to the case without decoherence. The reduced density matrix tends always to a well-defined limit that we calculate, but only in the decoherence-free case is this limit nontrivial.

An electron-nucleus Colle-Salvetti-type correlation functional for multicomponent density-functional theory is proposed. We demonstrate that our correlation functional quantitatively reproduces the quantum mechanical effects of protons; the mean absolute deviation value is 2.8 millihartrees for the optimized structures of hydrogen-containing molecules, and the effective potential energy curve of the hydrogen molecule is well reproduced. Since this functional is derived without any unphysical assumption, the strategy taken in this development will be a promising recipe to make new functionals for the potentials of other particles' interactions, such as electron-positron and electron-muon.

We explore a method, named energy-resolved population imaging (EPI), to analyze on an equal footing the temporary electronic transition and nuclear motion during laser-molecular interaction. By using EPI we have intuitively demonstrated the population transfer in vibrational ${{\text{H}}_2}^{+}$ exposed to extreme ultraviolet pulses, revealing the energy-sharing rule for the correlated electron and nuclei. We further show that EPI can be extended to uncover the origins of the distinct energy-sharing mechanisms in multiphoton and tunneling regimes. The present study has clarified a long-standing issue about the dissociative ionization of ${{\text{H}}_2}^{+}$ and paves the way to identify instantaneous molecular dynamics in strong fields.

We present a scheme for engineering the extended two-component Bose-Hubbard model using polariton condensate supported by an optical microcavity. Compared to the usual two-component Bose-Hubbard model with only Kerr nonlinearity, our model includes a nonlinear tunneling term which depends on the number difference of the particle in the two modes. In the mean-field treatment, this model is an analog to a nonrigid pendulum with a variable pendulum length whose sign can be also changed. We study the dynamic and ground-state properties of this model and show that there exists a first-order phase transition as the strength of the nonlinear tunneling rate is varied. Furthermore, we propose a scheme to obtain the polariton condensate wave function.

We study the vortex dynamics and vortex pinning effect in Bose-Einstein condensates in a rotating double-well trap potential and corotating optical lattice. We show that the vortex number does not diverge when the rotational frequency $\Omega \to 1$ if the trap potential is of anisotropic double-well type. The critical rotational frequency as obtained from numerical simulations agrees very well with the value $\sqrt{l}/l$ for $l=4$, which supports the conjecture that surface modes with angular momentum $l=4$ are excited when the rotating condensate is trapped in a double-well potential. The vortex lattice structure in a rotating triple-well trap potential and its pinning show very interesting features. We show the existence and pinning of hidden vortices whose phase profile is similar to that of the visible vortices.

We study the spreading of the wave function of a Bose-Einstein condensate accelerated by a constant force both in the absence and in the presence of atom-atom interactions. We show that, despite the initial velocity dispersion, the local velocity dispersion defined at a given position downward can reach ultralow values and be used to probe very narrow energetic structures. We explain how one can define quantum mechanically and without ambiguities the different velocity moments at a given position by extension of their classical counterparts. We provide a common theoretical framework for interacting and noninteracting regimes based on the Wigner transform of the initial wave function that encapsulates the dynamics in a scaling parameter. In the absence of interaction, our approach is exact. Using a numerical simulation of the one-dimensional Gross-Pitaevskii equation, we provide the range of validity of our scaling approach and find a very good agreement in the Thomas-Fermi regime. We apply this approach to the study of the scattering of a matter wave packet on a double barrier potential. We show that a Fabry-Perot resonance in such a cavity with an energy width below the pK range can be probed in this manner. We show that our approach can be readily transposed to a large class of many-body quantum systems that exhibit self-similar dynamics.

We present a high-order harmonic generation theory which generalizes the strong-field approximation to the resonant case when the harmonic frequency is close to that of the transition from the ground state to an autoionizing state of the generating system. We show that the line shape of the resonant harmonic is a product of the Fano-like factor and the harmonic line which would be emitted in the absence of the resonance. The theory predicts rapid variation of the harmonic phase in the vicinity of the resonance. The calculated resonant harmonic phase is in reasonable agreement with recent measurements. Predicting the phase locking of a group of resonantly enhanced harmonics, our theory allows us to study the perspectives of producing an attosecond pulse train using such harmonics.

The filamentation of ultraviolet and infrared nanosecond light pulses in fused silica is investigated theoretically and numerically. Emphasis is put on the action of a dynamical plasma response on two counterpropagating waves, amplified by Kerr self-focusing and stimulated Brillouin scattering (SBS). For a single unperturbed wave, laser filamentation takes place through a quasistationary balance between Kerr self-focusing and plasma defocusing, for which a variational approach reproduces global propagation features. However, such a quasistationary balance cannot hold as temporal modulational instability breaks up the pulse over electron recombination times. For two counterpropagating waves, we report similar instabilities which are justified through a plane-wave stability analysis. These instabilities originate from an intense backscattered wave that induces strong plasma contribution and thus destabilizes the pump near the entrance face of the material. Rapid phase modulations are then applied to suppress backscattering. We show that pump waves with broad enough bandwidths can inhibit SBS and thus prevent instability. The robustness of phase modulations against random fluctuations in the input pump pulse is finally addressed.

We investigate the coherent control of the quantum optical properties of a quantum dot coupled to a metallic nanoparticle using a photon Green's function method, which is based on the exact quantization of the electromagnetic fields in a dissipative medium. The properties of the spontaneous emission spectra of such a system are studied in detail with and without involving the coherent field. The Rabi splitting effect in the spectrum emitted by the quantum dot under particular conditions is predicted for different sizes of the metal nanoparticles. We show that the spontaneous emission spectra of the transition coupled to surface plasmons may be further modified by adjusting the external coherent control on the adjacent transitions. Furthermore, the pronounced oscillatory behavior for the quantum-dot dynamics is demonstrated with the presence of the metal nanoparticle by the non-Markovian treatment. Our results may have potential applications in plasmonic-based quantum manipulation.

Optomechanical detectors have reached the standard quantum limit in position and force sensing where measurement backaction noise starts to be the limiting factor for the sensitivity. A strategy to circumvent measurement backaction and surpass the standard quantum limit has been suggested by M. Tsang and C. Caves [Phys. Rev. Lett. 105, 123601 (2010)]. We provide a detailed analysis of this method and assess its benefits, requirements, and limitations. We conclude that a proof-of-principle demonstration based on a micro-optomechanical system is demanding but possible. However, for parameters relevant to gravitational-wave detectors, the requirements for backaction evasion appear to be prohibitive.