We present a novel source of highly correlated atom pairs, which we use for the first realisation of ghost imaging of an object using massive particles [1]. Until now ghost imaging has only been demonstrated with photons.

Ghost imaging is a surprising, counter-intuitive phenomenon -- first realized in quantum optics -- which allows the image of an object to be reconstructed from the spatio-temporal properties of a beam that never interacts with it.  Two beams of correlated particles are used, one of which passes through the object to a bucket (single-pixel) detector, while the spatial profile of the second beam is measured by a high resolution (multi-pixel) detector, although this beam never interacts with the object. Neither detector can reconstruct the image independently, but rather the image emerges from temporal cross-correlation between the two separate beams.

In our experiments, the two beams are formed by correlated pairs of ultracold metastable helium atoms, originating from two colliding Bose-Einstein condensates (He* BEC) via s-wave scattering [2].
We use higher-order Kapitza-Dirac diffraction to generate the large number of correlated atom pairs required, enabling the creation of a ghost image with good visibility and sub-millimetre resolution.

As well as demonstrating complementarity for this phenomena using matter waves, realising ghost imaging with atoms is a potential precursor to experiments that test fundamental concepts in quantum mechanics with massive particles, such as ghost interference, Einstein-Podolsky-Rosen entanglement and Bell's inequalities.

[1] Khakimov R., et al., arXiv:1607.02240, doi:10.1038/nature20154
[2] Perrin A., et al., Phys. Rev. Lett. 99, 150405 (2007)