Jonathan D. Weinstein

Magnetic trapping of calcium monohydride molecules at millikelvin temperatures

Recent advances in the magnetic trapping and evaporative cooling of atoms to nanokelvin temperatures have opened important areas of research, such as Bose–Einstein condensation and ultracold atomic collisions. Similarly, the ability to trap and cool molecules should facilitate the study of ultracold molecular physics and collisions; improvements in molecular spectroscopy could be anticipated. Also, ultracold molecules could aid the search for electric dipole moments of elementary particles. But although laser cooling (in the case of alkali metals,,) and cryogenic surface thermalization (in the case of hydrogen,) are currently used to cool some atoms sufficiently to permit their loading into magnetic traps, such techniques are not applicable to molecules, because of the latters complex internal energy-level structure. (Indeed, most atoms have resisted trapping by these techniques.) We have reported a more general loading technique based on elastic collisions with a cold buffer gas, and have used it to trap atomic chromium and europium,. Here we apply this technique to magnetically trap a molecular species—calcium monohydride (CaH). We use Zeeman spectroscopy to determine the number of trapped molecules and their temperature, and set upper bounds on the cross-sectional areas of collisional relaxation processes. The technique should be applicable to many paramagnetic molecules and atoms.

All-optical generation and photoassociative probing of sodium Bose–Einstein condensates

We demonstrate an all-optical technique to evaporatively produce sodium Bose?Einstein condensates (BEC). We use a crossed-dipole trap formed from light near 1 ?m, and a simple ramp of the intensity to force evaporation. In addition, we introduce photoassociation as diagnostic of the trap loading process, and show that it can be used to detect the onset of BEC. Finally, we demonstrate the straightforward production of multiple traps with condensates using this technique, and that some control over the spinor state of the BEC is achieved by positioning the trap as well.

Cold TiO(X3Δ)–He collisions

We use laser ablation and cryogenic helium buffer-gas cooling to produce large numbers of X3?1?TiO molecules at a translational temperature of 5?K. We investigate their cold collisions with helium and measure elastic and inelastic scattering cross-sections. As expected for 3? molecules, which have large spin?rotation couplings, TiOs inelastic m-changing collision cross-section is large: on the same order as its momentum transfer cross-section.

Sub-natural-linewidth quantum interference features observed in photoassociation of a thermal gas

By driving photoassociation transitions, we form electronically excited molecules (Na{sub 2}{sup )} from ultracold (50-300 {mu}K) Na atoms. Using a second laser to drive transitions from the excited state to a level in the molecular ground state, we are able to split the photoassociation line and observe features with a width smaller than the natural linewidth of the excited molecular state. The quantum interference which gives rise to this effect is analogous to that which leads to electromagnetically induced transparency in three-level atomic {lambda} systems, but here one of the ground states is a pair of free atoms while the other is a bound molecule. The linewidth is limited primarily by the finite temperature of the atoms.

Towards magnetic trapping of molecules

The advent of buffer-gas loaded magnetic traps for atoms has opened the possibility of trapping paramagnetic molecules. We survey our results on the loading, trapping and spectroscopy of Eu atoms that demonstrated the technique. The principles governing molecular trapping considering in particular the O2 and NO systems are outlined. The trapping of molecules should prove particularly useful in spectroscopy, especially ultra-high resolution spectroscopy that requires cold (slow), trapped (long interaction time) samples. Similar to cold atoms, cold molecules could be interrogated at a level of detail which is likely to provide new insights into their structure and interactions.

Trapping radioactive {sup 82}Rb in an optical dipole trap and evidence of spontaneous spin polarization

Optical trapping of selected species of radioactive atoms has great potential in precision measurements for testing fundamental physics such as the electric dipole moment, atomic parity nonconservation, and parity-violating {beta}-decay correlation coefficients. We report on the trapping of 10{sup 4} radioactive {sup 82}Rb atoms (t{sub 1/2}=75 s) with a trap lifetime of {approx}55 s in an optical dipole trap. Transfer efficiency from the magneto-optical trap is {approx}14%. We further report evidence of spontaneous spin polarization of the atoms in optical dipole trap loading. These advancements are an important step toward a new generation of precision nuclear-spin-{beta}-emission direction correlation measurements with polarized {sup 82}Rb atoms.

Stimulated deceleration of diatomic molecules on multiple rovibrational transitions with coherent pulse trains

We propose a method of stimulated laser decelerating of diatomic molecules by counter-propagating π-trains of ultrashort laser pulses. The decelerating cycles occur on the rovibrational transitions inside the same ground electronic manifold, thus avoiding the common problem of radiative branching in Doppler cooling of molecules. By matching the frequency comb spectrum of the pulse trains to the spectrum of the R-branch rovibrational transitions we show that stimulated deceleration can be carried out on several rovibrational transitions simultaneously. This enables an increase in the number of cooled molecules with only a single laser source. The exerted optical force does not rely on the decay rates in a system and can be orders of magnitude larger than the typical values of scattering force obtained in conventional Doppler laser cooling schemes.

Method for traveling-wave deceleration of buffer-gas beams of CH

Cryogenic buffer-gas beams are a promising method for producing bright sources of cold molecular radicals for cold collision and chemical reaction experiments. In order to use these beams in studies of reactions with controlled collision energies, or in trapping experiments, one needs a method of controlling the forward velocity of the beam. A Stark decelerator can be an effective tool for controlling the mean speed of molecules produced by supersonic jets, but efficient deceleration of buffer-gas beams presents new challenges due to longer pulse lengths. Traveling-wave decelerators are uniquely suited to meet these challenges because of their ability to confine molecules in three dimensions during deceleration and the versatility afforded by the analog control of the electrodes. We have created ground state CH(

Inelastic collisions of CaH with He at cryogenic temperatures

X^2\Pi

Electromagetically induced transparency with nuclear spin.

) radicals in a cryogenic buffer-gas cell with the potential to produce a cold molecular beam of