We present a dual isotope magneto-optical trap (MOT), simultaneous sub-Doppler laser cooling, and magnetic trapping of a spin-polarized 39K-40K Bose-Fermi mixture realized in a single-chamber setup with an unenriched potassium dispenser as the source of atoms. We are able to magnetically confine more than 2.2 × 105 fermions (F = 9/2 , m F = 9/2) and 1.4 × 107 bosons (F = 2 , m F = 2) with a lifetime exceeding 1.2 s. For this work, we have developed a versatile laser tailored for sub-Doppler cooling of all naturally occurring potassium isotopes and their mixtures. This laser system incorporates innovative features, such as the capability to select an isotope by activating or deactivating specific acousto-optic modulators that control the light seeding tapered amplifiers. Switching between isotopes takes ∼1 µs without any mechanical adjustment of the components.
Abstract We demonstrate the largest number of 40K atoms that has ever been cooled to deeply sub-Doppler temperatures in a single-chamber apparatus without using an enriched source of potassium. With gray molasses cooling on the D 1-line following a standard D 2-line magneto-optical trap, we obtain 3 × 10 5 atoms at 10(2) µK. We reach densities high enough to measure the temperature via absorption imaging using the time-of-flight method. We magnetically trap a mixture of m F = − 3 / 2 , − 5 / 2 and − 7 / 2 Zeeman states of the F = 7 / 2 hyperfine ground state confining 5 × 10 4 atoms with a lifetime of 0.6 s or ∼ 10 3 atoms with a lifetime of 2.8 s—depending on whether the temperature of the potassium dispensers was chosen to maximize the atom number or the lifetime. The background pressure-limited lifetime of 0.6 s is a reasonable starting point for proof-of-principle experiments with atoms and/or molecules in optical tweezers as well as for sympathetic cooling with another species if transport to a secondary chamber is implemented. Our results show that unenriched potassium can be used to optimize experimental setups containing 40K in the initial stages of their construction, which can effectively extend the lifetime of enriched sources. Moreover, the demonstration of sub-Doppler cooling and magnetic trapping of a relatively small number of potassium atoms might influence experiments with laser-cooled radioactive isotopes of potassium.
We report simultaneous sub-Doppler cooling and optical dipole trapping of
39K-Cs and
41K-Cs mixtures. Both mixtures are cooled to temperatures
∼10 μK, achieving performance comparable to that obtained with each species individually. To the best of our knowledge, this constitutes the first realization of a laser-cooled and optically trapped
41K-Cs mixture. For the
39K-Cs mixture, we additionally implement parallel spin-resolved Feshbach spectroscopy enabled by Stern-Gerlach separation. For potassium isotopes, we implement sub-Doppler cooling with
D1-line gray molasses, while for cesium the entire cooling sequence is implemented using
D2 transitions. We spin-polarize the atoms and confine Bose-Bose mixtures in a 1064 nm optical dipole trap. Using the resulting
39K-Cs samples, we observe 14 heteronuclear Feshbach loss features. Five agree with resonances reported previously, while nine have, to the best of our knowledge, not been observed experimentally before, including
p-wave features and resonances in additional spin channels. The shorter lifetime of the
41K-Cs mixture in the optical dipole trap currently hinders systematic Feshbach spectroscopy, which we therefore do not pursue in this work. To characterize this limitation quantitatively, we study the decay dynamics of
39K-Cs and
41K-Cs mixtures under comparable temperature and density conditions, revealing a substantially stronger nonexponential loss in the
41K-Cs mixture. The demonstrated preparation of ultracold
41K-Cs mixtures provides a starting point for Feshbach-resonance and photoassociation spectroscopy of this previously unexplored isotopologue. Such measurements are essential for identifying suitable pathways for magnetoassociation and coherent optical transfer, and ultimately for the production of ultracold ground-state
41KCs molecules.
We report the sub-Doppler deep-cooled three-dimensional magneto-optical trap (3D MOT) of the fermionic 40K and bosonic 39K isotopes of potassium loaded by a very compact 2D+ MOT with a novel optical design feature. The set-up is meant for studies on the quantum dynamics of a few fermionic and bosonic atoms in an optical dipole trap near and well within quantum degeneracy. The loading rate and atom numbers achieved in the compact simple set-up are comparable to those in the previous set-ups with more elaborate vacuum design. We attained relatively low temperatures of 34 and 30 µK for 39K and 40K after the sub-Doppler cooling process.
The main goal of this research is to cool potassium-41 atoms to ultracold temperatures (<10 μK) in order to study the spin dynamics of atom to atom interactions. However, our current goal is to finish constructing the apparatus that will allow us to confine and cool these atoms in three dimensions. This apparatus will cool and confine the potassium atoms in 3 steps. First, the atoms will be cooled and trapped in our 3D magneto-optical trap. This step of the experiment will cool the atoms near the Doppler-cooling limit, which for potassium atoms is 145 μK. Second, atoms will be loaded into a FORT (far off resonance trap) with an expected depth of 25 μK. In order to cool the atoms below the Doppler-cooling limit, we will use sub-Doppler cooling techniques. What is particularly unique about our experiment is that we plan to use an octupole magnetic field to achieve sub-Doppler cooling. In typical laser cooling experiments sub-Doppler temperatures are achieved when the quadrupole magnetic field is off, which leaves the atoms untrapped. Third, once the atoms have been loaded into the FORT one last cooling mechanism will be implemented. This mechanism is referred to as evaporative cooling and will cool the atoms below 10 μK.