Correlated Photons

Quantum correlated photons (photon pairs) used as central building block of quantum light sources. They are important for various quantum applications. Do to physical conservation laws, SPDC process outcome photons are naturally correlated in many physical entities: momentum, energy, arrival time. Simultaneous arrival time of photons can be measured by coincidence detection. Photon pairs generated in SPDC process are correlated in completing momentum and frequency. Photon pairs with different frequencies can be used for quantum sensing without direct detection of low frequency photons.