Five photons linked

Quantum computing another step closer: error correction.

Researchers from the University of Science and Technology of China, the University of Innsbruck in Austria, and the University of Heidelberg in Germany have entangled five photons. “Our experiment demonstrated for the first time the ability to manipulate five-particle entanglement,” said Jianwei Pan, a physics professor at the University of Science and Technology of China and a fellow at the University of Heidelberg in Germany.

Error correction uses mathematical codes to detect when a bit has been accidentally flipped, and is widely used in classical computing because electronic and magnetic bits occasionally switch accidentally from a 1 to a 0 or vice versa. Quantum bits are more delicate and require an error correction method to be feasible.

Quantum computers have the potential to be blazingly fast because a string of quantum bits, or qubits, that store the ones and zeros of computer information can represent all the numbers possible within that string at once. This would make it possible for a quantum computer to check every potential answer to a problem with a single set of operations.

Qubits take advantage of the quantum phenomenon of superposition. A photon can be polarized in one of two orientations, but when it is in superposition it is in a mix of both orientations at once.

The challenge in building computers to take advantage of the phenomenon is that superposition is a fragile condition, and interactions with the environment can knock a particle out of superposition and into one definite state. Interactions with the environment can also have more subtle effects that can result in the equivalent of a qubit being flipped from a 1 to a 0 or vice versa.