Abstract
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.
Highlights
SYSTEM DESCRIPTIONThe system employs a small magneto-optical trap (MOT) to collect and cool a cloud of 87Rb atoms from background vapor in an ultrahigh vacuum enclosure, and load them into a faroff-resonance trap (FORT) located within the MOT volume
Optical microtraps at the focus of high numerical aperture imaging systems enable efficient collection, trapping, detection and manipulation of individual neutral atoms
The article is organized as follows: In section I we describe the experimental system, including magneto-optical trap (MOT), faroff-resonance trap (FORT), and atomic fluorescence collection
Summary
The system employs a small MOT to collect and cool a cloud of 87Rb atoms from background vapor in an ultrahigh vacuum enclosure, and load them into a FORT located within the MOT volume. In the presence of cooler light, e.g. if the MOT is on, light-assisted collisions (LACs) [17] rapidly remove any pairs of atoms in this small volume This ensures the presence of no more than one atom in the trap. Based on the reported parameters of Volz et al [27], where a single atom trap with similar characteristics and FORT light wavelength is described, we predicted a value of wFORT = 1.6 μm. For this value of wFORT, the transverse and axial trap frequencies are ωr = 4U0/m87wF2ORT ≈ 56 kHz and ωz = 2U0/m87zR2 ≈ 6.7 kHz, respectively, where m87 is the 87Rb mass
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