Trapping cold molecules

Rather than attempting to cool warm molecules one can try to synthesize cold molecules by associating cold atoms. The molecules thus formed are expected to maintain the translational temperature of the recombining atoms because the center-of-mass motion remains unchanged in the association process (save for the little. momentum imparted by the photon). This idea was first proposed by Julienne and j co-workers [343, 344] who envisioned a multistep association, first involving the continuum-to-bound excitation of translational continuum states of cold trapped. atoms to an excited vibrational level in an excited electronic molecular state. This step was followed by bound-bound spontaneous emission to the ground electronic state. (I... 

This part is concerned with the quantum dynamics of molecules and ensembles of trapped cold atoms and the effect of internal-translational entanglement on interference and diffraction ... 

An elegant technique for studying van der Waals complexes at low temperatures was developed by Toennies and coworkers [442]. A beam of large He clusters (lO -lO He atoms) passes through a region with a sufficient vapor pressure of atoms or molecules. The He droplets pick up a molecule which either sticks to the surface or diffuses into the central part of the droplet, where it is cooled down to a low temperature of 100 mK up to a few Kelvin (see Fig. 4.22). Since the interaction with the He atoms is very small, the spectrum of this trapped molecule does not differ much from that of a free cold molecule. However, unlike cooling during the adiabatic expansion of a supersonic jet, where Tyib > Trot > Ttrans in this case Trot = Tyib = Thc [443 45]. This implies that all molecules are at their lowest vibration-rotational levels and the absorption spectrum becomes considerably simplified. 

One example is the spectroscopy of highly forbidden transitions, which becomes possible because of the long interaction time. Another aspect is a closer look at the chemistry of cold trapped molecules, where the reaction rates and the molecular dynamics are dominated by tunneling and a manipulation of molecular trajectories seems possible. Experiments on testing time-reversal symmetry via a search for a possible electric dipole moment of the proton or the electron [1212] are more sensitive when cold molecules are used [1213, 1214]. 

An understanding of atomic and molecular interactions and collisions is essential to the study of cold and ultracold molecules. Collisions govern the lifetime of molecules in traps and determine whether proposed cooling schemes will work. Once atoms and molecules are in the ultracold regime, the extent to which their interactions can be controlled depends on a detailed understanding of their collisional properties. The purpose of this chapter is to outline atomic and molecular collision theory and describe the special features that are important to the study of cold molecules. 

Comparat, D., Drag, C., Fioretti, A., Dulieu, O., and PUlet, R, Photoassociative spectroscopy and formation of cold molecules in cold cesium vapor Trap-loss spectrum versus ion spectrum, J. Mol. Spectrosc., 195, 229, 1999. 

A thermal Boltzmann trap distribution of molecules always contains molecules whose energies allow them to aecess the spatial edge of the trap. As molecules reach this edge and stick to the cold walls of the buffer-gas cell, a truncation of the distribution takes place. Molecules that pass the edge of the trap are lost from the distribution and... 

GUijamse, J.J., Kiipper, J., Hoekstra, S., Vanhaecke, N., van de Meerakker, S.Y.T., and Meijer, G., Optimizing the Stark-decelerator beamline for the trapping of cold molecules using evolutionary strategies, Phys. Rev. A, 73, 063410, 2006. 

We note here that other scenarios for the generation of entanglement between rotational quantum states of two polar molecules have been proposed in Ref. [13]. In that approach, the entanglement arises from dipole-dipole interaction and is controlled by a sequence of laser pulses simultaneously exciting both molecules. In addition to cold molecules trapped in optical lattices, cold molecules in solid matrices are also considered in Ref. [13]. 

ION TRAPPING AND PRODUCTION OF COLD MOLECULES 18.3.1 Radio-Frequency Ion Traps... 

It is also evident from the material expounded in this volume that the research field of cold molecules has been marching ahead with big strides. What seemed unfeasible less than ten years ago (e.g., the creation of ultracold polar molecules in the absolute ground state by photoassociation, magnetic trapping of dense molecular gases, and the collision experiments with molecules at ultracold temperatures, among others) has now been realized by multiple research groups. 

There are two key side effects of the velocity dependent force. First, kinematic cooling results in real cooling, not just a rotation of position-momentum phase space, yielding an increased phase space for the cold molecules. Second, since there is dissipation, if the collisions occur in a region containing a trap for the molecules, the trap can be continuously loaded without the worry of how to load pre-cooled molecules into a conservative potential well. 

Kinematic cooling of molecules via collisions with Magneto-Optically trapped atoms provides a straightforward, yet undemonstrated, method for producing cold molecules in environments where they can undergo thermal-izing collisions with cold atoms and potentially be further sympathetically cooled into the ultracold regime. 

Rather then actively bringing a state-selected packet of molecules from a high velocity to a standstill to load a trap, a mere selection of slow molecules from an effusive source using a bent quadrupole guide has also been used to produce translationally cold molecules. 

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