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We investigate three-body recombination loss across a Feshbach resonance in a gas of ultracold 7 Li atoms prepared in the absolute ground state and perform a comparison with previously reported results of a different nuclear-spin state [N. Gross et.al., Phys. Rev. Lett. 103 163202, (2009)]. We extend the previously reported universality in three-body recombination loss across a Feshbach resonance to the absolute ground state. We show that the positions and widths of recombination minima and Efimov resonances are identical for both states which indicates that the short-range physics is nuclear-spin independent.

Emerging quantum technologies for cryptography, computing and metrology exploit quantum mechanical effects for enhanced information processing and nanoscale sensing. Though different platform systems are currently being explored, light-based quantum technologies using single-photon emitters as the basic building block are among the frontrunners 1 . Several strategies have been used to realize deterministic single photon sources in the solid state 2 , including quantum dots 3 , single molecules 4 , and point defects in wide bandgap materials such as diamond and silicon carbide 5-9 . Single photon emitters in novel van der Waals materials have garnered recent attention due to their potential for integration with waveguides, microcavities, and other passive components typical in photonic devices. Example 2D systems hosting quantum emitters include WSe 2 and MoS 2 as well as other transition metal dichalcogenides (TMDs) 10-14 .Here we focus on hexagonal boron nitride (hBN), a wide bandgap semiconductor where defect emission has been shown to be tunable and robust at room temperature 15-22 and above 23 . We use confocal microscopy to investigate the photoluminescence (PL) of point defects within thin hBN flakes deposited on a lithographically patterned SiO 2 substrate. Due to Van der Waals forces the flake conforms to the surface topography thus accumulating significant local strain near protruding features. Using large structured arrays of different sizes and geometries we find nearly perfect correspondence between the strained areas of the flake and defect emission. Our modeling supports the notion of defect activation via charge trapping in deformation potential wells. The physics at play has some similarities with that governing the dynamics of excitons in WSe 2 monolayers subjected to comparable geometries, as reported recently 24,25 . Unlike TMDs, however, the wide bandgap of hBN can accommodate large potential modulations, sufficient to stabilize the defect charge at room temperature. In particular, we calculate deformation potential wells as deep as 500 meV confined to regions of tensile and compressive strain in the hBN flake that correlate well with the spatial localization of the emitters.For the first set of experiments we use an array of 155-nm-high nanopillars with diameters ranging from 200 to 700 nm fabricated via electron beam lithography over a large-area silica substrate (Figure 1a); the sample is a commercial, 20-nmthick flake of hBN grown via chemical vapor deposition (CVD). We follow a wet transfer protocol 26 to drape the flake on the patterned silica substrate (see Methods). This technique takes advantage of the Van der Waals forces to make the flake conform to the surface topography. As an illustration, Figure 1b shows an atomic force microscopy (AFM) image from an hBN fragment where the 20-nm-thick flake folds on itself: We identify single-and double-layer sections near the left and right areas, respectively; bare pillars -visible on the lower, right corner of the image -provide a direct view...

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