Entangled Photons Pairs

Entangled photon pairs are special cases of correlated photon pairs which are superimposed in a non-separate manner by their quantum states. They are linked in a nonlocal manner although they are spatially separated. An example of generating polarization entanglement (Bell quantum states) of photons by SPDC process: The upper figure shows the generation of an entangled qubit pair. The quantum state described is the quantum superposition of two states. If we measure the horizontal H polarization of a photon in spatial mode a we determine that the state of the second photon is vertical V in spatial mode b. Measuring the quantum system collapses the wave function to |H,V> The two photons are unseparated, measuring the state of one photon in a two-particle entangled state defines the state of the second photon instantaneously, whereas neither particle possesses its own well-defined state before the measurement. An efficient entangled source can be used in many important applications such as quantum key distribution (QKD), quantum computing, quantum computing, etc.