Double debut for three-way quantum entanglement

We filed a post a few weeks back about research that showed it was possible to spilt a photon into three.

Now, researchers at the University of Santa Barbara (and simultaneously, a group at Yale led by Prof. Rob Schoelkopf) have gone one better and demonstrated three-way quantum entanglement.

Reported here in the journal Nature, the work shows two different ways of entangling a triplet of qubits. One, known as GHZ, is highly entangled, but very fragile. Measuring the state of just one of the trio will collapse the other two into unentangled states. The other , called W, produces a less entangled, but more robust arrangement. The researchers found that two thirds of the time, measuring one qubit leaves the other two entangled.

Lead author Matthew Neely said: "We produced both of these states with our phase qubits, and measured their fidelity compared to the theoretical ideal states. Experimentally, the fidelity is never perfect, but we showed that it is high enough to prove that the three qubits are entangled."

"Entanglement is a resource that gives quantum computers an advantage over classical computers, and so producing multipartite entanglement is an important step for any system with which we might hope to construct a quantum computer."

The university’s announcement is here.