Magnetic trapping of metastable calcium atoms

Abstract

Metastable calcium atoms, produced in a magneto-optic trap (MOT) operating within the singlet system, are continuously loaded into a magnetic trap formed by the magnetic quadrupole field of the MOT. At MOT temperatures of 3 mK and 240 ms loading time we observe 1.1 × 10 8 magnetically trapped 3 P2 atoms at densities of 2.4×10 8 cm −3 and temperatures of 0.61 mK. In a modified scheme we first load a MOT for metastable atoms at a temperature of 0.18 mK and subsequently release these atoms into the magnetic trap. In this case 240 ms of loading yields 2.4 × 10 8 trapped 3 P2 atoms at a peak density of 8.7 × 10 10 cm −3 and a temperature of 0.13 mK. The temperature decrease observed in the magnetic trap for both loading schemes can be explained only in part by trap size effects.PACS numbers: 32.80. Pj, 42.50.Vk, 42.62.Fi, Earth alkaline atoms provide a unique combination of interesting spectroscopic features connected to their two valence electrons which give rise to singlet and triplet excitations. The singlet systems possess strong principle fluorescence lines well suited for laser cooling with remarkable efficiency. Yet, temperatures are limited to the mK domain, due to the absence of ground state Zeeman structure, a prerequisite for sub-Doppler techniques. The triplet systems, however, have readily accessible narrow band optical transitions that render possible refined laser cooling schemes with the promise of temperatures even beyond the microkelvin range. In fact, such schemes have recently been experimentally realized for strontium and calcium [1,2,3,4]. Owing to their spectroscopic peculiarities such ultracold earth alkaline samples open up new prospects for ultraprecise atomic clocks [5,6,7] and cold collision studies which allow direct comparisons with ab initio theoretical calculations [8,9,10]. The formation of Bose-Einstein condensates (BEC,[11]) for this exciting group of atoms appears particularly desirable.A key technique for obtaining BEC in alkalis and nobel gases has been magnetic trapping. This trapping technique outperforms optical techniques in two ways. It provides well controllable potential wells with sufficient steepness. The regime of high elastic collision rates, a precondition for efficient evaporative cooling, is thus easily accessible. Secondly, the presence of antibinding magnetic sublevels allows to actively force evaporation in a particular effective way by selectively expelling energetic atoms from the trap. The extension of this successful trapping technique to earth alkaline atoms may pave the route to BEC in this atom group. While the singlet ground state of these species lacks magnetic substructure, the ground state of the triplet system typically offers a particularly large Zeeman effect. Specifically, the long-lived 3 P 2 , m J =2 state appears appropriate for mag- * Electronic address: dhansen@physnet.uni-hamburg.de netic trapping and the formation of BEC. Recent calculations for calcium and strontium predict a positive scattering length (and thus stable BEC) for this state [...

Sub-Doppler laser cooling and magnetic trapping of erbium

“…5 where we measure temperatures below 25 µK. Similar anomalously low temperatures have been observed in MOT-loaded, magnetically trapped Ca [24] and Sr [25] while unexpectedly high temperatures were reported in Cr [23]. In Ref.…”

Two-temperature momentum distribution in a thulium magneto-optical trap

“…Double structures were previously reported for Rb [30], Dy [21] and Ca [31] MOTs. The specific cloud density profile in the Rb MOT was caused by a bi-harmonical confining potential coming from the sub-Doppler part of a magneto-optical trapping force [30].…”

Narrow line cooling and momentum-space crystals

“…Along with contributing to 1 S 0 -1 P 1 MOT loss, 1 P 1 → 1 D 2 → 3 P 2 radiative decay continuously loads milli-Kelvin atoms in the 3 P 2 ͑m =1,2͒ states into a magnetic trap formed by the 1 S 0 -1 P 1 MOT quadrupole magnetic field [24][25][26][27][28][29][30]. Importantly, these samples are expected to display a wealth of binary collision resonances that arise due to an interplay between anisotropic quadrupole interactions and the local magnetic field [31][32][33].…”