Accurate transport cross sections for the Lennard-Jones potential

It is well-known that in open quantum systems resonances can coalesce at an exceptional point, where both the energies and the wave functions coincide. In contrast to the usual behaviour of the scattering amplitude at one resonance, the coalescence of two resonances invokes a pole of second order in the Green’s function, in addition to the usual first order pole. We show that the interference due to the two pole terms of different order gives rise to patterns in the scattering cross section which closely resemble Fano-Feshbach resonances. We demonstrate this by extending previous work on the analogy of Fano-Feshbach resonances to classical resonances in a system of two driven coupled damped harmonic oscillators.     

Interference phenomena at the elastic collision of atoms with formation of the Feshbach resonance in the presence of laser radiation field

Resonant scattering of atoms with formation of the Feshbach resonance in the presence of a laser radiation coupling the levels of two bound atoms (a molecule) is considered. The laser field leads to a second resonance in scattering and broadening of resonances, which facilitates the possibility of experimental observation of asymmetry of the total scattering cross-section arising because of interference between resonant and potential scatterings. The effects associated with interference of the two channels of decay of a bound system of two atoms (a molecule) in the laser field are studied. An expression is obtained for the scattering length in collision of two cold atoms in the field of laser radiation.     

Decay of an ultracold fermionic lithium gas near a Feshbach resonance

We studied the magnetic field dependence of the inelastic decay of an ultracold, optically trapped fermionic 6Li gas of different spin compositions. The spin mixture of the two lowest hyperfine states showed two decay resonances at 550 and 680 G, consistent with the predicted Feshbach resonances for elastic s-wave collisions. The observed lifetimes of several hundred ms are much longer than the expected time for Cooper pair formation and the phase transition to superfluidity in the vicinity of the Feshbach resonance.     

Proposal for a laser control of vibrational cooling in Na(2) using resonance coalescence

With a specific choice of laser parameters resulting in a so-called exceptional point (EP) in the wavelength-intensity parameter plane, it is possible to produce the coalescence of two Floquet resonances describing the photodissociation of the Na(2) molecule, which is one of the candidates for the formation of samples of translationally cold molecules. By appropriately tuning laser parameters along a contour encircling the exceptional point, the resonances exchange their quantum nature. Thus a laser-controlled transfer of the probability density from one field-free vibrational level to another is achieved through adiabatic transport involving these resonances. We propose an efficient scenario for vibrational cooling of Na(2) referring to cascade transfers involving multiple EPs and predicted to be robust up to a 78% rate against laser-induced dissociation.     

Perspective to search for sub-eV neutral boson resonances with stimulated laser colliders

We present a novel approach to search for sub-eV neutral bosons coupling to two photons which can be candidates for dark fields in the universe. Similarly to conventional particle colliders, the search aims at detection of resonance states of these dark fields produced by photon-photon scattering, however, the interaction rate is enhanced by the stimulated decay of resonances into two photons under a background coherent laser field. We discuss the future experimental strategy to explore a large mass-coupling parameter space with high-intensity lasers.     

Formation of metastable molecular states at the resonance scattering of two atoms in a laser radiation field

Using the Dirac’s method, the formation of metastable molecular states at the resonance scattering of two atoms in the laser radiation field is considered. Expressions for the metastable level populations and the resonance scattering cross sections are obtained. In the case of an exact resonance with the laser radiation, the graphs for populations and resonance scattering cross sections, which have two peaks due to the Autler–Townes effect, are obtained. These results play an important role in the study of the controlled chemical reaction and for the understanding of the processes in the quantum systems of the Bose–Einstein condensate at low temperatures, as well as in the various optical processes in atomic gases.     

Baryon resonance analysis from SAID

We discuss the analysis of data from πN elastic scattering and single pion photo- and electropro-duction. The main focus is a study of low-lying non-strange baryon resonances. Here we concentrate on some difficulties associated with resonance identification, in particular the Roper and higher P_(11) states.     

On the possibility of high-energy neutron diffraction in a crystal in the field of laser radiation

For the first time the high-energy neutrons scattering in a crystal is considered under the influence of an external laser wave field. The process is inelastic with respect to the laser wave and at the same time it is elastic with respect to a crystal. The possibility of high-energy neutron diffraction is illustrated—wavelength of neutrons is less than the lattice period. The method is based on the multiphoton interaction of the neutron anomalous magnetic moment with the field of laser radiation by using the Farri representation. The neutron-phonon interaction is considered to be a perturbation described by the Fermi pseudopotential.     

The prospects of sympathetic cooling of NH molecules with Li atoms

We calculate the quartet potential energy surface for Li+NH and use it to calculate elastic and spin-relaxation cross sections for collisions in magnetically trappable spin-stretched states. The potential is strongly anisotropic but spin-relaxation collisions are still suppressed by centrifugal barriers when both species are in spin-stretched states. In the ultracold regime, both the elastic and inelastic cross sections fluctuate dramatically as the potential is varied because of Feshbach resonances. The potential-dependence is considerably reduced at higher energies. The major effect of using an unconverged basis set in the scattering calculations is to shift the resonances without changing their general behaviour. We have calculated the ratio of elastic and spin-relaxation cross sections, as a function of collision energy and magnetic field, for a variety of potential energy surfaces. Most of the surfaces produce ratios that are favorable for sympathetic cooling, at temperatures below about 20 mK.     

Laser-induced radiative recombination of antihydrogen in a magnetic field through a quasi-stationary state

To increase the efficiency of laser-induced recombination of antihydrogen from cold antihydrogen—positron plasma in a trap, it is proposed to use a new resonance mechanism with the participation of positron quasi-stationary states, arising under the joint action of an antiproton Coulomb field and a strong magnetic field of the trap. The recombination rate is expressed through the atomic laser ionization cross section whose frequency dependence is nonmonotonic due to the presence of quasi-stationary states against the background of the continuum. The estimates with the use of the ionization cross sections calculated earlier demonstrate the possibility of improving the efficiency of the laser-induced recombination at an optimally selected laser frequency.     

Tailoring magnetic and electric resonances with dielectric nanocubes for broadband and high-efficiency unidirectional scattering

The interference of optically induced electric and magnetic resonances in high-refractive-index dielectric nanoparticles provides a new approach to control and shape the scattering patterns of light in the field of nanophotonics. In this Letter, we spectrally tune the electric and magnetic resonances by varying the geometry of a single isolated lead telluride(Pb Te) dielectric nanocube. Then, we overlap the electric dipole resonance and magnetic dipole resonance to suppress backward scattering and enhance forward scattering in the resonance region.Furthermore, a broadband unidirectional scattering is achieved by structuring the dielectric nanocuboids as a trimer antenna.     

Efimov Effect in 2-Neutron Halo Nuclei

We provide a brief overview of our theoretical investigations, carried out in recent years, to study Efimov effect in 2-n halo nuclei. The calculations provide the evidence for the occurrence of at least two Efimov states in ²⁰C. These states disappear one by one as the two-body binding energy is increased and show up as asymmetric resonances in the elastic scattering cross section of n–¹⁹C system. The asymmetric nature of the resonances is explained by invoking the mechanism of Fano resonance.     

Cascade coherence transfer and magneto-optical resonances at 455 nm excitation of cesium

We present an experimental and theoretical study of nonlinear magneto-optical resonances observed in the fluorescence to the ground state from the 7P_3/2 state of cesium, which was populated directly by laser radiation at 455 nm, and from the 6P_1/2 and 6P_3/2 states, which were populated via cascade transitions that started from the 7P_3/2 state and passed through various intermediate states. The laser-induced fluorescence (LIF) was observed as the magnetic field was scanned through zero. Signals were recorded for the two orthogonal, linearly polarized components of the LIF. We compared the measured signals with the results of calculations from a model that was based on the optical Bloch equations and averaged over the Doppler profile. The calculations agree quite well with the measurements, especially when taking into account the fact that some experimental parameters were only estimated in the model.     

Resonant scattering of phonons by adsorbates on clean silicon surfaces

We used Phonon Surface Scattering Spectroscopy (PSSS) to study excitations of adsorbates in the far infrared region from 100 eV up to 3 meV. We investigated the scattering of pulses of monochromatic phonons by thin films of H₂O, D₂O and Ne deposited in situ onto laserannealed Si(100)-surfaces. For all substances we observed a broad scattering at coverages below one monolayer and a strong resonant scattering at about 3 monolayers. The resonance frequency decreased with increasing coverage. The reasons for the resonances are discussed. Because of the lack of any observable isotope effect between H₂O and D₂O, the possibility of tunneling states in these layers can be excluded. Instead, we conclude that a lateral vibrational mode of the adlayer is responsible for the resonance effect. Corresponding calculations by means of continuum elasticity theory describe the scattering behaviour very well if similar elastic constants are used for all film substances.     

Photoassociation spectroscopy of laser-cooled ytterbium atoms

We report the photoassociation spectroscopy of laser-cooled ytterbium atoms in an optical trap. We observed more than 90 photoassociation resonances of vibrational levels in the (1)Sigma(+)(u) state, including 80 consecutive series, up to 490 GHz detuning with respect to the atomic resonance. From the resonance frequencies we derived the atomic radiative lifetime of the (6s6p) 1P1 state to be 5.464+/-0.005 ns, which is about 2 orders of magnitude improvement over previous results. We also observed line broadening of resonances, which is ascribed to the predissociation to the triplet states, and estimated the transition probability to be 0.2. Furthermore, we observed the decrease of the photoassociation signal intensity, from which the scattering length is estimated to be equal to or less than 3 nm.     

Few-cycle attosecond pulses via periodic resonance interaction with hydrogenlike atoms

We show that it is possible to produce nearly bandwidth-limited few-cycle attosecond pulses based on periodic resonance interaction of a quasi-monochromatic radiation with the bound states of hydrogenlike atoms. A periodic resonance is provided by a far-off-resonant laser field with intensity much below the atomic ionization threshold via periodic tunnel ionization from the excited states and adiabatic Stark splitting of the excited energy levels. Without external synchronization of the spectral components, it is possible to produce 135 as pulses at 13.5 nm in Li2?-plasma controlled by radiation of a mode-locked Nd:YAG laser, as well as 1.25 fs pulses at 122 nm in atomic hydrogen controlled by radiation of a CO? laser.     

Resonance of exchange amplitude of Compton effect in the circularly polarized laser field

We present, for general relativistic case, a theoretical study of resonance of exchange amplitude when a photon is scattered by an electron in the field of a circularly polarized wave. Resonances are related to a virtual intermediate particle that falls within the mass shell. We find conditions when resonances occur in exchange amplitude. We derive the expressions for the resonant amplitudes and the differential cross-sections when the invariant intensity parameter of the laser field is small (η≪1) and the interference of direct and exchange amplitudes is absent. It is demonstrated that the resonant cross-section of scattering may be several orders of magnitude higher than the cross-section of Compton effect in the absence of the external field.     

Spin-polarized transport through a time-periodic non-magnetic semiconductor heterostructure

Spin-dependent Floquet scattering theory is developed to investigate the photon-assisted spin-polarized electron transport through a semiconductor heterostructure in the presence of an external electric field. Spin-dependent Fano resonances and spin-polarized electron transport through a laser irradiated time-periodic non-magnetic heterostructure in the presence of Dresselhaus spin-orbit interaction and a gate-controlled Rashba spin-orbit interaction are investigated. The electric field due to laser along with the spin-orbit interactions help to get spin-dependent Fano resonances in the conductance, whereas the external bias can be appropriately adjusted to get a near 80% spin-polarized electron transmission through heterostructures. The resultant nature of the Floquet scattering depends on the relative strength of these two electric fields.     

Incoherent properties of induced radiation

The evolution of a quantized electromagnetic field in a thermally excited dispersion medium is determined by two scattering channels. The coherent channel is formed exclusively by the elastic scattering of quanta. The incoherent channel, along with elastic scattering processes, necessarily contains inelastic scattering processes, including induced radiation. Interference between the channels is absent because of the orthogonality of the wave functions of the medium in its final states, which correspond to different scattering channels. Therefore, in an excited medium, interference processes that are not described by its refractive index may arise. An interference pattern of this kind can be formed, in particular, as a result of the superposition of the resonance radiation incident on an excited medium and the radiation reflected from this medium. In this case, the conventional perturbation theory proves to be inadequate.     

Spectroscopy on two coupled superconducting flux qubits

We have performed spectroscopy measurements on two coupled flux qubits. The qubits are coupled inductively, which results in a sigma(z)(1)sigma(z)(2) interaction. By applying microwave radiation, we observe resonances due to transitions from the ground state to the first two excited states. From the position of these resonances as a function of the applied magnetic field, we observe the coupling of the qubits. The coupling strength agrees with calculations of the mutual inductance.