Laser Cooling of Molecular Anions (original) (raw)
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Challenges of laser-cooling molecular ions
New Journal of Physics, 2011
The direct laser cooling of neutral diatomic molecules in molecular beams suggests that trapped molecular ions can also be laser cooled. The long storage time and spatial localization of trapped molecular ions provides the opportunity for multi-step cooling strategies, but also requires a careful consideration of rare molecular transitions. We briefly summarize the requirements that a diatomic molecule must meet for laser cooling, and we identify a few potential molecular ion candidates. We then perform a detailed computational study of the candidates BH + and AlH + , including improved ab initio calculations of the electronic state potential energy surfaces and transition rates for rare dissociation events. Based on an analysis of population dynamics, we determine which transitions must be addressed for laser cooling and compare experimental schemes using continuous-wave and pulsed lasers.
Physical Review A, 2021
Despite the fact that the laser cooling method is a well-established technique to obtain ultra-cold neutral atoms and atomic cations, it has so far never been applied to atomic anions due to the lack of suitable electric-dipole transitions. Efforts of more than a decade currently have Laas the only promising candidate for laser cooling. Our previous work [Tang et al., Phys. Rev. Lett. (2019) accept] showed that This also a potential candidate. Here we report on a combination of experimental and theoretical studies to determine the relevant transition frequencies, transition rates, and branching ratios in Th-. The resonant frequency of the laser cooling transition is determined to be /c= 4118.0 (10) cm-1. The transition rate is calculated as A=1.1710 4 s 1. The branching fraction to dark states is very small, 1.47×10-10 , thus this represents an ideal closed cycle for laser cooling. Since Th has zero nuclear spin, it is an excellent candidate to be used to sympathetically cool antiprotons in a Penning trap. The achievement of Bose-Einstein condensation, precision spectroscopy, and tests of fundamental symmetries has opened a new chapter in atomic and molecular physics. The main driving force behind this achievement is the ability to cool atoms and positive ions to K or even lower temperatures via laser cooling techniques. Although laser cooling is a well-established technique for producing ultracold neutral atoms and positive ions, it has not yet been achieved for negative ions. In principle, once we produce ultracold ensembles of a specific anion system, we can use them to sympathetically cool any anions, ranging from elementary particles to molecular anions, which will promote the research of cold plasma[1], ultracold chemistry[2], and fundamental-physics tests[3-8]. In contrast to neutral atoms and positive ions, which have an infinite number of bound states, negative ions have only a single bound state in most cases. The reason is that in atomic anions, the excess
ACS Omega
The ground and excited electronic states of the diatomic molecules CaCs and CaNa have been investigated by implementing the ab initio CASSCF/(MRCI + Q) calculation. The potential energy curves of the doublet and quartet electronic low energy states in the representation 2s+1 Λ (±) have been determined for the two considered molecules, in addition to the spectroscopic constants T e , ω e , B e , R e , and the values of the dipole moment μ e and the dissociation energy D e. The determination of vibrational constants E v , B v , D v , and the turning points R min and R max up to the vibrational level v = 100 was possible with the use of the canonical functions schemes. Additionally, the transition and the static dipole moments curves, Einstein coefficients, the spontaneous radiative lifetime, the emission oscillator strength, and the Franck−Condon factors are computed. These calculations showed that the molecule CaCs is a good candidate for Doppler laser cooling with an intermediate state. A "four laser" cooling scheme is presented, along with the values of Doppler limit temperature T D = 55.9 μK and the recoil temperature T r = 132 nK. These results should provide a good reference for experimental spectroscopic and ultra-cold molecular physics studies.
Laser cooling and slowing of CaF molecules
We demonstrate slowing and longitudinal cooling of a supersonic beam of CaF molecules using counter-propagating laser light resonant with a closed rotational and almost closed vibrational transition. A group of molecules are decelerated by about 20 m/s by applying light of a fixed frequency for 1.8 ms. Their velocity spread is reduced, corresponding to a final temperature of about 85 mK. The velocity is further reduced by chirping the frequency of the light to keep it in resonance as the molecules slow down.
Blackbody-radiation-assisted molecular laser cooling
The translational motion of molecular ions can be effectively cooled sympathetically to temperatures below 100 mK in ion traps through Coulomb interactions with laser-cooled atomic ions. The distribution of internal rovibrational states, however, gets in thermal equilibrium with the typically much higher temperature of the environment within tens of seconds. We consider a concept for rotational cooling of such internally hot, but translationally cold heteronuclear diatomic molecular ions. The scheme relies on a combination of optical pumping from a few specific rotational levels into a "dark state" with redistribution of rotational populations mediated by blackbody radiation.
Laser cooling of CaF molecules
2014
Cold and ultracold molecules are highly desirable for a diverse range of applications such as precision measurements, tests of fundamental physics, quantum simulation and information processing, controlled chemistry, and the physics of strongly correlated quantum matter. Although laser cooling has been enormously successful in cooling atomic species to extremely low temperatures, this technique has long been thought to be infeasible in molecules because their complex structure makes it difficult to find a closed cycling transition. Recently, however, several diatomic molecules, one of which is CaF, have been shown to possess a convenient electronic structure and highly diagonal Franck-Condon matrix and thus be amenable to laser cooling. This thesis describes experiments on laser cooling of CaF radicals produced in a supersonic source. We first investigate the increased fluorescence when multi-frequency resonant light excites the molecules from the four hyperfine levels of the ground...
Journal of The Optical Society of America B-optical Physics, 2003
Trapped and laser-cooled ions are increasingly used for a variety of modern high-precision experiments, for frequency standard applications, and for quantum information processing. Therefore laser cooling of trapped ions is reviewed, the current state of the art is reported, and several new cooling techniques are outlined. The principles of ion trapping and the basic concepts of laser cooling for trapped atoms are introduced. The underlying physical mechanisms are presented, and basic experiments are briefly sketched. Particular attention is paid to recent progress by elucidating several milestone experiments. In addition, a number of special cooling techniques pertaining to trapped ions are reviewed; open questions and future research lines are indicated.