Entangled erbium qubits are addressed individually in a crystal

The spin states of entangled erbium ions in a solid crystal can be controlled and read out individually  using a new technique developed by Jeff Thompson and colleagues at Princeton University in the US. In doing so, the team has overcome the important challenge of making measurements on closely spaced ions in a crystal. Their technique could lead to the creation of new quantum devices that could be integrated with existing optical telecommunications technology.