Manipulating and measuring single atoms in the Maltese cross geometry

Background: Optical microtraps at the focus of high numerical aperture (high-NA) imaging systems enable efficient collection, trapping, detection and manipulation of individual neutral atoms for quantum technology and studies of optical physics associated with super- and sub-radiant states. The recently developed “Maltese cross” geometry (MCG) atom trap uses four in-vacuum lenses to achieve four-directional high-NA optical coupling to single trapped atoms and small atomic arrays. This article presents the first extensive characterisation of atomic behaviour in a MCG atom trap. Methods: We employ a MCG system optimised for high coupling efficiency and characterise the resulting properties of the trap and trapped atoms. Using current best practices, we measure occupancy, loading rate, lifetime, temperature, fluorescence anti-bunching and trap frequencies. We also use the four-directional access to implement a new method to map the spatial distribution of collection efficiency from high-NA optics: we use the two on-trap-axis lenses to produce a 1D optical lattice, the sites of which are stochastically filled and emptied by the trap loading process. The two off-trap-axis lenses are used for imaging and single-mode collection. Correlations of single-mode and imaging fluorescence signals are then used to map the single-mode collection efficiency. Results: We observe trap characteristics comparable to what has been reported for single-atom traps with one- or two-lens optical systems. The collection efficiency distribution in the axial and transverse directions is directly observed to be in agreement with expected collection efficiency distribution from Gaussian beam optics. Conclusions: The multi-directional high-NA access provided by the Maltese cross geometry enables complex manipulations and measurements not possible in geometries with fewer directions of access, and can be achieved while preserving other trap characteristics such as lifetime, temperature, and trap size.

Analyzing Ca-41 sample at 1E-15 abundance level with cold atom trap techniques

<p>On earth, Calcium-41 is produced as a cosmogenic isotope via neutron capture process, leaving a natural isotopic abundance of 10<sup>-15</sup> on earth surface. Calcium is also of vital importance for the metabolism of biological organisms. Consequently, analysis of the long lived radioactive isotope Calcium-41 is of great importance in geoscience, archeology and life sciences. The half-life of Calcium-41 is 1.03 x 10<sup>5</sup> years. It is a good candidate in dating rock and bone samples ranging from 50,000 to 1,000,000 years old.</p><p>The available techniques for trace analysis of Calcium-41 include accelerator mass spectrometry (AMS) and resonance ionization mass spectroscopy (RIMS). The detection limit of RIMS is on the level of 10<sup>-11 </sup>due to the interference of Potassium-41, which is difficult to remove from the sample. The analysis with high-energy AMS is more expensive than the table top apparatus, and it also faces similar problem as RIMS method.</p><p>We develop an atom trap trace analysis(ATTA) apparatus for Calcium-41 analysis to the sensitivity of 10<sup>-15</sup> abundance level by one hour of single atom counting. ATTA uses laser tuned at the resonant wavelength for a specific element and isotope to slow down and capture single atom by fluorescence radiation. It has a very high selectivity of element and isotope, which is more advantageous than AMS and RIMS to avoid isobar interference. ATTA has been used in analysis of Krypton-81, Argon-39 dating of the hydrological samples. This work on high sensitivity Calcium-41 analysis is very promising in dating the geochemical sample to determine the exposure ages of rocks or in cosmochemistry for investigations on terrestrial ages.</p>