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 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.