Entanglement beyond identical ions

Control of quantum particles has been extended to enable different types of ion to be entangled — correlated in a non-classical way. This opens up opportunities for the development of new quantum technologies. See Letters p.380 & p.384 A mixed bag of entangled particles In quantum-computing architectures, not all physical systems are equally good at completing each task. For example, in trapped-ion quantum computers, one specific element might be an excellent memory qubit, while another element is more suited to transporting information between nodes. However, a crucial prerequisite to harness these advantages is the entanglement of different atomic species. Now, two groups have independently achieved this. Ting Rei Tan et al . showed entanglement between different elements 9 Be + and 25 Mg + , and Christopher Ballance et al . achieved entanglement between different atomic isotopes, 40 Ca + and 43 Ca + . These studies represent a first step towards mixed-species quantum logic, and from a fundamental perspective they show that particles that are distinguishable by many internal properties can indeed be entangled and violate Bell's inequality.