Quantum physics: Entanglement beyond identical ions.

Abstract

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 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 9Be+ and 25Mg+, and Christopher Ballance et al. achieved entanglement between different atomic isotopes, 40Ca+ and 43Ca+. 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.