Ultracold Calcium Atoms Research Articles

Evidence for sympathetic vibrational cooling of translationally cold molecules

Compared with atoms, molecules have a rich internal structure that offers many opportunities for technological and scientific advancement. The study of this structure could yield critical insights into quantum chemistry, new methods for manipulating quantum information, and improved tests of discrete symmetry violation and fundamental constant variation. Harnessing this potential typically requires the preparation of cold molecules in their quantum rovibrational ground state. However, the molecular internal structure severely complicates efforts to produce such samples. Removal of energy stored in long-lived vibrational levels is particularly problematic because optical transitions between vibrational levels are not governed by strict selection rules, which makes laser cooling difficult. Additionally, traditional collisional, or sympathetic, cooling methods are inefficient at quenching molecular vibrational motion. Here we experimentally demonstrate that the vibrational motion of trapped BaCl(+) molecules is quenched by collisions with ultracold calcium atoms at a rate comparable to the classical scattering, or Langevin, rate. This is over four orders of magnitude more efficient than traditional sympathetic cooling schemes. The high cooling rate, a consequence of a strong interaction potential (due to the high polarizability of calcium), along with the low collision energies involved, leads to molecular samples with a vibrational ground-state occupancy of at least 90 per cent. Our demonstration uses a novel thermometry technique that relies on relative photodissociation yields. Although the decrease in vibrational temperature is modest, with straightforward improvements it should be possible to produce molecular samples with a vibrational ground-state occupancy greater than 99 per cent in less than 100 milliseconds. Because sympathetic cooling of molecular rotational motion is much more efficient than vibrational cooling in traditional systems, we expect that the method also allows efficient cooling of the rotational motion of the molecules. Moreover, the technique should work for many different combinations of ultracold atoms and molecules.

Influence of Chirped Excitation Pulses in an Optical Clock With Ultracold Calcium Atoms

We have investigated the influence of frequency chirps of the excitation pulses in a time-domain optical Ramsey-Borde/spl acute/ atom-interferometer used in an optical clock with ultracold calcium atoms. With optical interferometry, we identify a ringing in the excitation pulses to be responsible for the observed frequency shifts. Using these results, the uncertainty of the latest frequency measurement could be reduced to 1.2/spl middot/10/sup -14/.

Sub-Doppler magneto-optical trap for calcium

We explore an efficient method for preparing large samples of ultracold calcium atoms. An optimized conventional (Doppler-limited) magneto-optical trap collects atoms from a Zeeman cooled atomic beam using a strong dipole transition within the singlet system. This transition is not completely closed thus yielding an intense flux of atoms into the metastable triplet state ${}^{3}{P}_{2}.$ A second magneto-optical trap sharing the same magnetic-field gradient is superimposed which captures and further cools the metastables using the narrow-band infrared transition ${}^{3}{\stackrel{\ensuremath{\rightarrow}}{{P}_{2}}}^{3}{D}_{3}.$ In our present experiment we were able to prepare $3\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at temperatures below 20 microkelvin within 250 ms. Minor technical improvements of our setup promise to yield above ${10}^{10}$ atoms at submicrokelvin temperatures within 1 s.