At Swiss Federal Institute of Technology (ETH) in Zurich, scientists have employed laser spectroscopy and scanning probe microscopy to resolve two molecules 12 nm apart in a crystal host. The technique, which also detected dipole-dipole coupling in the molecules, promises to enable the controlled manipulation of the entanglement between such samples, opening the door to nanoscale quantum-state engineering and to a better understanding of light-harvesting complexes.

In the work, which appeared in the Oct. 11 issue of Science, the researchers used a dye laser with a tunable wavelength near 578 nm to address single terrylene molecules in a 250-nm-thick para-terphenyl crystal at a temperature of 1.4 K. They generated a local electric field in the sample with a 3-µm-diameter, silver-coated micro-sphere on a fiber tip, which induced local inhomogeneous Stark shifts in the fluorescent response that enabled them to deduce the position of the molecules.