Ultracold temperatures in dilute quantum gases opened the way to an exquisite control of matter at the quantum level. Here we focus on the control of ultracold atomic collisions using a laser to engineer their interactions at large interatomic distances. We show that the entrance channel of two colliding ultracold atoms can be coupled to a repulsive collisional channel by the laser light so that the overall interaction between the two atoms becomes repulsive: this prevents them to come close together and to undergo inelastic processes, thus protecting the atomic gases from unwanted losses. We illustrate such an optical shielding (OS) mechanism with 39 K and 133 Cs atoms colliding at ultracold temperature (<1 μK). The process is described in the framework of the dressed-state picture and we then solve the resulting stationary coupled Schrödinger equations. The role of spontaneous emission and photoinduced inelastic scattering is also investigated as possible limitations of the shielding efficiency. We predict an almost complete suppression of inelastic collisions over a broad range of Rabi frequencies and detunings from the 39 K D2 line of the OS laser, both within the [0, 200 MHz] interval. We found that the polarization of the shielding laser has a minor influence on this efficiency. This proposal could easily be formulated for other bialkali-metal pairs as their long-range interaction are all very similar to each other.
We discuss the use of a region of uniform and constant magnetic field in order to implement a two-state atomic polarizer for an H(2S) beam. We have observed that a device with such field configuration is capable of achieving an efficient polarization for a wide range of magnetic field intensities and atomic velocities. In addition, we establish a criterion that must be met to confirm a successful polarization. That is possible due to a specific beating pattern for the Lyman-α radiation expected for the outgoing two-state atomic beam.
We present a thorough analysis of a Zeeman slower for sodium atoms made of permanent magnets in a Halbach configuration. Due to the orientation of the magnetic field, the polarization of the slowing laser beam cannot be purely circular, leading to optical leakages into dark states. To circumvent this effect, we propose an atomic state preparation stage that is. able to significantly increase the performance. of the Zeeman slower. After a careful theoretical analysis of the problem, we experimentally implement an optical pumping stage leading to an increase in. the magneto-optical trap loading rate by 3.5. Such a. method is easy to set up and could be extended to other Zeeman slower architectures.
Heteronuclear alkali-metal dimers represent the class of molecules of choice for creating samples of ultracold molecules exhibiting an intrinsic large permanent electric dipole moment. Among them, the KCs molecule, with a permanent dipole moment of 1.92 Debye still remains to be observed in ultracold conditions. Based on spectroscopic studies available in the literature completed by accurate quantum chemistry calculations, we propose several optical coherent schemes to create ultracold bosonic and fermionic KCs molecules in their absolute rovibrational ground level, starting from a weakly bound level of their electronic ground state manifold. The processes rely on the existence of convenient electronically excited states allowing an efficient stimulated Raman adiabatic transfer of the level population.
We study spin chains submitted to disturbed kick trains described by classical dynamical processes. The spin chains are coupled by Heisenberg and Ising-Z models. We consider chaotic processes by using the kick irregularity in the multipartite system (the spin chain). We show that the both couplings transmit differently the chaos disorder along the spin chain but conserve the horizon of coherence (when the disorder into the kick bath is transmitted to the spin chain). An example of information transmission between the spins of the chain coupled by a Heisenberg interaction shows the interest of the horizon of coherence. The use of some chosen stationary kicks disturbed by a chaotic environment allows to modify the information transmission between the spins and to perform a free control during the horizon of coherence.
We examine atomic line shapes in a magnetized hydrogen plasma. The Lorentz electric field v × B present in the emitters' frame of reference yields a perturbation of the atomic energy levels, which is commonly referred to as a 'motional' Stark effect. This effect results in a broadening of the lines owing to the statistical repartition of the atoms' velocities. We address this line broadening mechanism with numerical simulations. It is shown that Balmer line shapes can be affected at plasma conditions relevant to magnetic fusion experiments. An application to the diagnostic of an atomic temperature is suggested and discussed within a line width analysis. The possibility for a modification of the Inglis–Teller limit, which provides an estimate of the principal quantum number of the last resolved line in a series, is also discussed.
In this paper, using a standard quantum chemistry approach based on pseudopotentials for atomic core representation, Gaussian basis sets and effective core polarization potentials, we investigate the electronic properties of the MgH+ ion. We first determine potential energy curves for several states using different basis sets and discuss their predicted accuracy by comparing our values of the well depths and position with other available results. We then calculate permanent and transition dipole moments for several transitions. Finally, for the first time, we calculate the static dipole polarizability of MgH+ as a function of the interatomic distance. This study represents the first step towards the modelling of collisions between trapped cold Mg+ ions and H-2 molecules.
The potential energy curves of the NS+ electronic states are computed at the aug-cc-pV5Z/CASSCF/MRCI level of theory. Using these highly correlated wavefunctions, we evaluated their mutual spin-orbit coupling terms and the transition moment evolutions. Then, we deduced an accurate set of spectroscopic constants and investigated the spin-orbit induced predissociation of the lowest electronic excited states of this cation. In particular, we identify a new well-bound quintet state, namely the NS+ (1(5)Pi). The NS+(1(5)Pi) v'(+) <= 5 levels decay radiatively to populate the NS+(1(5)Sigma(+)) state after emission of visible light, whereas the upper rovibrational levels undergo rapid spin-orbit induced predissociation processes forming S+(S-4) and N(S-4) fragments via the repulsive 1(7)Sigma(+) state. The potential energy curve of NS (X-2 Pi) is also computed and used together with those of NS+ electronic states for the prediction of the single ionization spectrum of NS.
We study the electron impact double ionization of argon in the case where two, or else, three of the outgoing electrons (one scattered and two ejected) have the same energy. Each electron in the final (continuum) state is described by a Coulomb wave and account is taken for the interaction between these three electrons. We also include exactly all the exchange effects for the first time. The results of our model are compared to the recent experiments of Catoire et al (2004, Photonic, Electronic and Atomic Collisions ed R Schuch et al (Phys. Scr. T110 228–32); 2005, Electron and Photon Impact Ionization and Related Topics ed B Piraux (Bristol: Institute of Physics) p 53).
