Physicists at the Max Planck Institute have developed an efficient new method to drive the quantum entanglement of photons, and demonstrated it by entangling a record number of photons. The technique could be a boon for quantum computers.
Quantum entanglement is a phenomenon that sounds like it should be impossible. Essentially, particles can become so intertwined that they can no longer be described individually, and changing a specific property of one particle will instantly cause a change in its entangled partner, no matter how far apart they may be. The implications of this unsettled even Einstein himself, who famously described it as “spooky action at a distance.”
As counter-intuitive as it may sound, quantum entanglement has been experimentally demonstrated for decades. The phenomenon even underpins emerging commercial technologies like quantum computers, where entangled particles can be used as quantum bits (qubits) that store and process information.
To work best, large groups of particles need to be produced and entangled together, but this is tricky to do. So for the new study the Max Planck researchers investigated a more reliable method of quantum entanglement, and used it to successfully entangle 14 photons together – the largest group of photons entangled so far.
The team started with a single rubidium atom, trapped in an optical cavity that bounces electromagnetic waves around in certain patterns. The atom is struck by a laser at a particular frequency, which prepares the atom to have a given property. Then another control pulse is beamed at it, which causes the atom to emit a photon that’s entangled with the atom.
This process is repeated, with the atom rotated between each photon emission, until a whole chain of photons are produced that are all entangled with each other. The process is far more efficient than existing techniques, producing photons more than 43% of the time, or almost one photon for every two laser pulses.
If you've been following quantum records for a while, 14 entangled particles might not sound like a whole lot – scientists have managed to entangle literally trillions of atoms in a gas in previous experiments. But we're not going to be able to harness a system like that for quantum communications or computers. Photons are far simpler to produce and use in everyday technology, and the efficiency of this new technique should be relatively simple to scale up for increased photon production.
To that end, the team says that the next step is to experiment using at least two atoms as sources.
The research was published in the journal Nature.