Demonstration of conditional quantum phase shift between ions in a solid

A conditional quantum phase shift in a two-qubit system based on an optical transition of europium ions in a solid was demonstrated. It was seen that the ions possessed a permanent electric dipole moment which depended on their electronic state. Each europium ions had a unique optical transition frequency which is determined by the local crystal environment. It was found that at the end of the pulse sequence used the target ions had a spread in-phase caused by their differing interaction with the control.