Neodymium-doped crystal. Neodymium is a rare earth element, here being added to a crystal used in quantum memory experiments, part of research into quantum computing. Selective laser excitation in the crystal permits high accuracy operations on groups of single ions (qubits). The interaction between neighbouring ions in the host crystal allow implementation of quantum gates. Photographed in April 2011, at the applied optical physics department of the University of Geneva, Switzerland.