(ORDO NEWS) — A new method of intertwining the fates of light fragments has overcome a number of serious obstacles to quantum computing based on photons.
Researchers from the Institute of Quantum Optics. Max Planck in Germany successfully entangled 14 photons into what is thought to be the optimum state for qubits, more than doubling previous attempts and also increasing their efficiency.
Unlike the “bits” of binary code behind more traditional forms of computing, qubits exist in a state of probability called superposition, which behaves like a tossed coin tumbling through the air.
Algorithms based on how groups of quantum coins fall can quickly deal with rather complex mathematics, but only if their collective rotation is not thrown off course by the environment.
Called decoherence, this interruption of particle superposition is a huge hurdle for engineers designing useful quantum computers.
Theoretically, just about anything can exist in a quantum superposition of states, from electrons to atoms to entire molecules (or more). But to limit decoherence, smaller and simpler objects take over.
Photons are ideal qubits. Unfortunately, practical quantum computers need a lot of qubits. Thousands. Even millions. The bigger, the better. Not only do they all have to rotate in superposition simultaneously, their destinies must be separated. Or, to use a physical term, confuse.
That’s where the problem comes in.
There are relatively simple ways to entangle pairs of photons. Make an atom emit a light wave, and then separate it using a special screen, and you get two photons with a common history.
As long as they remain in flight, their respective performance remains to be measured, they more or less act like a spinning coin. Eventually, one will come up heads and the other tails.
Entangling more than two photons becomes more difficult.
In experiments with objects called quantum dots, it was possible to entangle chains of three or four photons. Not only is it unlikely that the hundreds and thousands needed for a quantum computer will ever be created, the state of entanglement using this approach is not as reliable as engineers would like.
More recently, recent studies using atoms with large electron orbitals, called Rydberg atoms, have produced up to six entangled photons, all in an effectively entangled form. While this technique can be used for ultra-fast computing components, it is also not a highly scalable option.
This latest solution could theoretically produce any number of entangled photons, all in perfect condition.
“The trick of this experiment was that we used a single atom to emit photons and weave them in a very specific way,” says physics doctoral student and lead author Philip Thomas.
>The rubidium atom was excited to emit light waves that were directed into a cavity shaped to reflect them back and forth very accurately. a photon can be entangled with the entire state of the atom meaning that each photon hopping back and forth in the cavity has also been entangled with a significant number of its siblings.
“Because the photon chain originated from a single atom, it could be obtained in a deterministic way,” says Thomas.
In this case, the team managed to confuse 12 photos. in the less efficient linear cluster and 14 in the highly prized Greenberger-Horn-Zeilinger (GHZ) state.
“To our knowledge, 14 interconnected light particles represent the largest number of entangled photons. which have so far been generated in the lab,” says Thomas.
Not only were they able to entangle so many photons, but they improved the technique’s efficiency over past processes: nearly one out of every two photons provides neatly entangled qubits.
Future installations will need to introduce a second atom to provide the qubits needed for many quantum computing operations. Entangled photons could be the basis for technologies that go beyond computing and play a central role in quantum-encrypted communications.
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