IMAGINE having two coins, both equally likely to give heads or tails when flipped, but which amazingly always give the same result no matter how far apart they are. This is the strange world of quantum entanglement – a phenomenon widely considered fundamental for quantum computing to become a reality.
Quantum computing relies on information being stored in quantum bits, or qubits, which can exist in two states at once and could therefore do multiple calculations simultaneously. Researchers have already created particles in which one or two properties such as energy or momentum are entangled. Now Paul Kwiat and his colleagues at the University of Illinois at Urbana-Champaign have created the first ever hyper-entangled particles – pairs of photons for which every possible quantum property is entangled.
They produce the pairs using a quantum splitting process in which a single photon enters an optical crystal sandwich and is spontaneously broken into two lower-energy photons. Previously, researchers had sent photons into a single crystal, but the use of two crystals adds extra degrees of entanglement because of the uncertainty about which crystal the individual photons are produced in.
Advertisement
These hyper-entangled states could make it possible to store multiple qubits on the same photon, reducing the number of photons required and making the system easier to manipulate. Their work will be published in Physical Review Letters.
