Physics World wrote about this breakthrough:

To Chris Ballance and colleagues at the University of Oxford and Ting Rei Tan and colleagues at NIST in Boulder, Colorado, for creating and measuring quantum entanglement between pairs of two different kinds of ions. The work - which was done independently by the two groups - is an important step towards the creation of ion-based quantum computers based on two or more different kinds of ion. Such hybrid systems would take advantage of the fact that some ions are better than others at performing specific quantum-computing tasks. The Oxford team entangled ions of two different isotopes of the same element - calcium-40 and calcium-43 - whereas the NIST group used beryllium-9 and magnesium-25 as their ions.

This achievement was "highly commended" in the list drawn up by the magazine of the Institute of Physics. The top 10 breakthroughs are chosen by a panel of four Physics World editors and reporters, and the criteria for judging include:

• fundamental importance of research;
• significant advance in knowledge;
• strong connection between theory and experiment; and
• general interest to all physicists.

The overall winner this year was "the LIGO Scientific Collaboration for its revolutionary, first-ever direct observations of gravitational waves".

Read more about this on the Physics World website:

• LIGO's gravitational-wave discovery is Physics World 2016 Breakthrough of the Year
• Physicists take entanglement beyond identical ions