Fig. 1

Experimental schematic for the generation and detection of entangled pairs of atoms. a A Raman pulse (two green arrows) initiates the collision of oppositely spin-polarised BECs (coloured ellipsoids), which scatter pairs of atoms into opposite momenta and entangled in spin as \(|{\Psi }^{+}\rangle\) (see right inset). Spin-\(\uparrow\) (\(\downarrow\)) state is labelled blue (red) and correspond to the \({m}_{J}=1\) (0) state of He*. b The scattered pairs form a spherical shell as antipodal points in momentum, where the BECs lie on the two poles along the collision axis. Pairs spatially separate in time at which point each individual atom’s spin (indicated by hollow-headed arrows) is rotated by an angle \(\theta\) using co-propagating Raman beams (green arrow). The Raman transition level scheme is shown on the right (see main text for details). c An applied magnetic field gradient spatially separates the atoms by spin, which are detected with single-atom precision after 416 ms free-fall with full 3D momentum and spin resolution. The images on the right show the atom count density (averaged over 1000 shots) in the \(zx\)-plane when the spins were rotated uniformly by \(\theta =\pi /2\). Spin correlations between the back-to-back scattered pairs exhibit quantum nonlocality