When two atoms bind to form a molecule, the size of the resulting compound is typically smaller than a nanometer. Excited to their Rydberg states, atoms are expected to feature an additional binding mechanism that leads to exaggerated bond lengths that can be a 1000 times larger than this. These exotic molecules, termed “macrodimers”, are held together by feeble polarization forces, active even when the atoms' electronic clouds do not overlap, and they can only persist at very low temperatures. Recently, a team of international researchers at the Max-Planck-Institute for Quantum Optics (Garching, Germany), in collaboration with Valentin Walther and Thomas Pohl from IFA, succeeded to optically excite pairs of macrodimers from a regular array of ultracold atoms held in an optical lattice. Owing to the enormous size of the macrodimers the team succeeded to directly image the formed molecules and achieved selective preparation of more than 50 internal vibrational states for the first time in experiments. These breakthroughs open up new possibilities for molecular quantum control and quantum simulations with ultracold matter.

 The paper was published in Science 364, 664 (2019) titled: “Quantum gas microscopy of Rydberg macrodimers”