Session P3: Novel Cooling and Trapping Methods

Magneto-optical trap in a vapor cell

Since the development of laser cooling, numerous applications have been developed, including atom interferometry, magnetometry, atomic clocks, quantum information, and non-linear optics. Despite the promising performance of these technologies, cold atoms have seen essentially no commercial development. One reason is the large size and complexity of the apparatus required. We discuss the development of a novel vacuum system consisting of a simple glass cell pumped only by a non-evaporable getter, and with an alkali dispenser to serve as an atom source. We have maintained a Rb magneto-optical trap in such a cell over a time scale of months, and we have developed several in situ diagnostics to monitor vacuum pressure and alkali atom density. This data reveals a great deal about how the alkali atoms interact with the glass walls and the getter material, knowledge which is needed for informed cell design.   

Ion Current as a Precise Measure of the Loading Rate of a Magneto-Optical Trap

We have demonstrated that the ion current resulting from collisions between metastable krypton atoms in a magneto-optical trap can be used to precisely measure the trap loading rate. We measured both the ion current of the abundant isotope $^{83}$Kr (isotopic abundance $=$ 11{\%}) and the single-atom counting rate of the rare isotope $^{85}$Kr (isotopic abundance $\sim$ 1 $\times$ 10$^{-11})$, and found the two quantities to be proportional at a precision level of 0.9{\%}. This work results in a significant improvement in using the magneto-optical trap as an analytical tool for noble-gas isotope ratio measurements, and will benefit both atomic physics studies and applications in the earth sciences. Reference: Opt. Lett. \textbf{39}, 409 (2014).   

Progress towards a MOT for CaF

We report on progress toward a magneto-optical trap (MOT) of CaF molecules. While following the same essential approach as that used to laser cool SrF and YO [1,2], we are developing direct MOT loading from a 2-stage cryogenic buffer gas beam (CBGB) source [3]. This source has a lower forward velocity compared to the hydrodynamic CBGB source that was employed with SrF and YO. We report the creation of the first CBGB loaded MOTs, without the use of a Zeeman slower, for Ho, Yb, Er, and Tm [4]. The slower initial beam velocity of the two-stage CBGB should aid in MOT loading of molecules, which have inherently low MOT capture velocities ($\sim 10$\,m/s). We plan to implement an AC-MOT for CaF, and report on theoretical studies and experimental progress toward that goal.\\[4pt] [1] E.~F.~Shuman, et al., Nature 467, 820 (2010)\\[0pt] [2] M.~T.~Hummon, et al., Phys. Rev. Lett. 110, 143001 (2013)\\[0pt] [3] N.~R.~Hutzler, et al., Chem. Rev. 112, 4803 (2012)\\[0pt] [4] B.~Hemmerling, et al., arXiv:1310.3239   

Grey-molasses cooling of an optically trapped Fermi gas

Robust sub-Doppler cooling has recently been demonstrated at the D1 (nS$_{1/2}$ to nP$_{1/2}$) transition of potassium [1-3] and lithium [4], atoms that are challenging to cool on the D2 cycling transition. Two mechanisms are at work: first, Sisyphus cooling in the standing-wave dipole potential, at least partially due to polarization gradients [1]; second, velocity-selective coherent population trapping (VSCPT) in a superposition of the two hyperfine ground states [2-4]. We extend this technique to the cooling of dense clouds in optical traps. Since the VSCPT dark state relies only on ground-state coherences, it is insensitive to optical shifts from far-detuned optical traps. We also observe that the molasses has sufficient cooling power to withstand light scattering on the 4S-5P transition. Together these observations indicate that D1 cooling is a promising approach to fluorescent imaging of single fermions in an optical lattice. \\[4pt] [1] D. Rio Fernandes et al., EPL, 100 63001 (2012).\\[0pt] [2] D. Nath et al., PRA, 88 053407 (2013).\\[0pt] [3] G. Salomon et al., EPL, 104 63002 (2013).\\[0pt] [4] A. T. Grier et al., PRA 87 063411 (2013).   

Sympathetic Cooling and Reordering in Multiple Trapped Ion Species Chains

Using multiple ion species allows ion-based quantum computing projects to overcome limitations of addressability and cooling in long ion chains. Namely, a single ion species would be used for quantum operations, while the other would be devoted to cooling of the entire chain. The cooling species are interspersed among the qubit ions to enable more efficient cooling while making individual addressing of the qubit ions easier. We attempt to measure and explore the effect of ion species ordering on the efficiency of the resultant cooling. Initially, the energy of spontaneous ion reordering is approximated via classical simulations. Then, the axial temperature and heating rate can be determined by measuring the time required for different length chains to reorder. Initial, approximate heating rates and work towards measuring ion species reordering effects are presented.   

Measurements of cold lithium atoms in a magneto-optical trap

We present measurements of cold $^7$Li atoms in a magneto-optical trap based on an amplified external cavity diode laser at 671~nm. The temperature of the atoms is measured to be 550 $\pm$ 70 $\mathrm{ \mu K}$ using a time-lapsed absorption imaging and cloud radius measurement technique. This temperature is confirmed using the release-and-recapture method with a trap diameter of $d=1.9~cm$. We recorded the frequency spectrum of the cold atoms at approximately 1.5~mK on the D2 unresolved lines ($2S_{1/2}\, F\!=\!2 \rightarrow 2P_{3/2}\, F'$) in $^7$Li using fluorescence imaging. The spectroscopic line width of the $F=2\rightarrow F'=3$ transition is approximately 11 MHz full-width at half-maximum, consistent with temperature measurements and a Voigt spectral line shape with natural line width $\gamma/2\pi=5.87~\mathrm{MHz}$. We observed line shape effects due to probe laser beam polarization in the presence of an equal irradiance re-pumping beam on the $F=1\rightarrow F'$ transition, which included a peak shift of approximately 1~MHz.   

Trapping Metastable Krypton Atoms for Radio-Isotope Dating

We have developed a MOT of metastable krypton atoms achieving a loading rate of 10$^{\mathrm{12}}$ s$^{\mathrm{-1}}$ for the abundant isotope $^{\mathrm{84}}$Kr. At the same time, the trap is capable of single atom detection of the rare isotopes $^{\mathrm{81}}$Kr and $^{\mathrm{85}}$Kr used for radio-isotope dating. Metastable atom production via gas discharge remains a major limit to trapping efficiency. We are exploring direct optical excitation methods to overcome this limit. This technique uses a krypton lamp to produce resonant 124 nm light and an 819 nm laser to drive the krypton from the ground state to the metastable level. These advancements would lead to a next generation ATTA instrument for $^{\mathrm{81}}$Kr dating. Improved efficiency would open up new opportunities such as dating deep ice core samples.   

Trapping of atoms with a concentric cavity

A near-concentric cavity is the only stable, linear optical resonator with a focus at its center. The concentric configuration not only enables high circulating laser intensity at the cavity center, but also provides us with a rich variety of three-dimensional optical trapping potentials. Using shadow imaging, we have measured cold-atom area density distributions that replicate the near-perfect profiles of Hermite-Gaussian and Laguerre-Gaussian modes at the cavity center. Fluorescence images exhibit strong, stable radiation of the highly elongated atomic clouds confined in the cavity modes along the axial direction of the cavity, indicating light guiding and possibly cooperative emission in that direction. We also investigate spectroscopic shifts of Rydberg transitions in the cavity-generated optical trapping potential. In the talk, I will first review our experimental results. Then I will discuss possible applications, including adiabatic compression and Rydberg-level spectroscopy in high-intensity cavity fields and radiation guiding in dense, elongated atom clouds.   

Atom chip-based ultracold potassium for microwave and radio-frequency potentials

We present progress on an experiment to manipulate and trap ultracold atoms with microwave and radio-frequency ($\mu $/RF) AC Zeeman potentials produced with an atom chip. These $\mu $/RF potentials are well suited for atom interferometry and spin-dependent trapping for 1D many-body physics studies due to their compatibility with magnetic Feshbach resonances for tuning interactions. Calculations show that $\mu $/RF potentials are expected to significantly suppress the inherent atom chip roughness associated with DC magnetic potentials. We have assembled a dual species, dual chamber apparatus that produces ultracold $^{39}$K samples and $^{87}$Rb Bose-Einstein condensates on an RF-capable atom chip, with access to other isotopes. On-chip $^{39}$K will be sympathetically cooled through the microwave evaporation of rubidium, and transferred to a co-located dipole trap for a series of spatial manipulation experiments to study the capabilities and performance of $\mu $/RF potentials.   

Magnetic Microtrap Array of Ultracold Atoms

A novel kind of magnetic microtrap has been demonstrated for ultracold neutral atoms. The microtrap consists of two concentric current loops having radii $r_1$ and $r_2$. A magnetic field minimum can be generated along the axis of the loops with oppositely oriented current flowing through the loops. Selecting $r_2:r_1 = 2.2$ maximizes the microtrap force. The strength and the position of the microtrap can be adjusted by applying an external bias magnetic field. A microtrap array can be formed by aligning individual microtraps together. A linear array of 3 microtraps having $r_1 = 300$ $\mu$m, was loaded with more than 10$^5$ $^{87}$Rb atoms using three different method: 1) from a transported quadrupole magnetic trap, 2) an optical dipole trap, or 3) directly from a spin polarized MOT.