Magnetic trapping of metastable3P2atomic strontium

Abstract

We report the magnetic trapping of metastable 3 P 2 atomic strontium. Atoms are cooled in a magneto-optical trap ͑MOT͒ operating on the dipole-allowed 1 S 0 -1 P 1 transition at 461 nm. Decay via 1 P 1 → 1 D 2 → 3 P 2 continuously loads a magnetic trap formed by the quadrupole magnetic field of the MOT. Over 10 8 atoms at a density of 8ϫ10 9 cm Ϫ3 and temperature of 1 mK are trapped. The atom temperature is significantly lower than what would be expected from the kinetic and potential energies of atoms as they are transferred from the MOT. This suggests the occurrence of thermalization and evaporative cooling in the magnetic trap. Laser-cooled alkaline-earth-metal atoms offer many possibilities for practical applications and fundamental studies. The two valence electrons in these systems give rise to triplet and singlet levels connected by narrow intercombination lines that are utilized for optical frequency standards ͓1͔.Laser cooling on such a transition in strontium may lead to a fast and efficient route to all-optical quantum degeneracy ͓2,3͔, and there are abundant bosonic and fermionic isotopes for use in this pursuit. The lack of hyperfine structure in the bosonic isotopes and the closed electronic shell in the ground states make alkaline-earth-metal atoms appealing testing grounds for cold-collision theories ͓4 -6͔, and collisions between metastable alkaline-earth-metal atoms is a relatively new and unexplored area for research ͓7͔.In this paper we characterize a technique that should benefit all these experiments-the continuous loading of metastable 3 P 2 atomic strontium ( 88 Sr) from a magneto-optical trap ͑MOT͒ into a purely magnetic trap. This idea was discussed in a recent theoretical study of alkaline-earth-metal atoms and ytterbium ͓8͔. Katori et al. ͓9͔ and Loftus et al. ͓10͔ have also reported observing this phenomenon in their strontium laser-cooling experiments. Continuous loading of a magnetic trap from a MOT was recently described for chromium atoms ͓11͔.This scheme should allow for collection of large numbers of atoms at high density since atoms are shelved in a dark state and are less susceptible to light-assisted collisional loss mechanisms ͓4,6,12͔. It is an ideal starting place for many experiments such as sub-Doppler laser cooling on a transition from the metastable state, as has been done with calcium ͓13͔, production of ultracold Rydberg gases ͓14͔ or plasmas ͓15͔, and evaporative cooling to quantum degeneracy. Optical frequency standards based on laser-cooled alkaline-earthmetal atoms, which are currently limited by high sample temperatures ͓1͔, may benefit from the ability to trap larger numbers of atoms and evaporatively cool them in a magnetic trap.We will first describe the operation of the Sr MOT and how this loads the magnetic trap with 3 P 2 atoms. Then we will characterize the loading and decay rates of atoms in the magnetic trap. Finally, we will present measurements of the 3 P 2 sample temperature.Sr atoms are loaded from a Zeeman-slowed atomic beam ͓16͔ and cooled and tr...

Tensorial analysis of the long-range interaction between metastable alkaline-earth-metal atoms

“…An interesting strategy to overcome this obstacle is to work with metastable alkaline-earth atoms in their lowest (nsnp) 3 P 2 state [18,19], which have radiative lifetimes of the order of ten minutes [20]. The experimental feasibility of magnetic trapping of metastable 88 Sr has already been demonstrated [21,22,23].…”

Magnetic relaxation in dysprosium-dysprosium collisions

“…For atoms whose outermost electronic shell has nonzero orbital angular momentum, or open-shell atoms, the electrostatic anisotropic interaction can play the determining role in trap loss and limit the efficiency of evaporative cooling. For instance, experiments with metastable Sr [12,13] and Yb [14] and theoretical studies with O [15] show that these atoms undergo magnetic moment reorientation in nearly every collision due to electron anisotropy. Consequently, collision processes in cold gases with anisotropic electrostatic interactions present a new challenge to theory and a new area of exploration for experiment [16].…”

Numerical modeling of collisional dynamics of Sr in an optical dipole trap

“…The creation of samples of 88 Sr or 84 Sr atoms in an optical dipole trap (ODT) starts with laser cooling and trapping phases that have been described in detail previously [22,[27][28][29]. Atoms are trapped in a magneto-optical trap (MOT) operating on the 461-nm 1 S 0 -1 P 1 transition (Fig.…”

“…There is a decay channel from the 1 P 1 state to the 1 D 2 state with a branching ratio of 2 × 10 −5 . 1 D 2 atoms can decay to the 3 P 1 state, which decays to the ground state to allow further cooling, or to 3 P 2 state, which can be trapped and accumulated in the magnetic trap formed by the quadrupole MOT magnets [27]. 3 P 2 atoms are repumped by applying a 3-µm laser resonant with the 3 P 2 -3 D 2 transition that returns these atoms to the ground state [30].…”