Diamond qubits entangled by measurement

The entanglement of nuclear spins in diamond is reported in a paper published online this week in Nature Physics. These findings are an important technological step towards developing room-temperature solid-state quantum computers and other quantum technologies.

Entanglement is an essential resource for quantum technologies. To entangle two quantum systems, they should interact with each other. But quantum states are very fragile and need to be well isolated from the environment, ideally having no external interactions. Alternatively, the measurement of a joint property can entangle two quantum systems that do not interact with each other directly. This deceptively simple idea for creating entanglement has so far proved hard to implement in solid-state systems.

In nitrogen-vacancy centres, which are naturally or artificially created defects in the diamond lattice, information can be encoded in the quantum degrees of freedom (electron and nuclear spins) and manipulated for information processing at room temperature. Ronald Hanson and colleagues used measurements of the electron spin to entangle two nuclear spins in a nitrogen-vacancy centre. This could be a breakthrough in building quantum computers.