A new technique that keeps two photons entangled while greatly increasing the frequency of one of them has been demonstrated by researchers in Germany. The work could prove useful in quantum computation, imaging and quantum communications.
Two particles are considered entangled if their quantum states are correlated to such an extent that they cannot be described independently. This property is central to many areas of quantum technology, including schemes that use photons to exchange keys in quantum cryptography. Entanglement is, however, fragile, meaning that changing the frequency of one photon risks destroying its entanglement with another.
