Generation and detection of entangled single-photon pairs

Sammanfattning: Quantum information technology is an emerging field with important applications such as quantum cryptography and teleportation, quantum imaging and lithography. These applications make use of single photons and pairs of entangled photons. In this work, we experimentally generate and attempt to detect the entangled photons. The entangled photon pairs are produced using a nonlinear crystal of beta bariumborate through a process of spontaneous parametric down-conversion (SPDC). Alignment necessary to detect the entangled photon pairs is implemented using a HeNe laser. The experimental results reveal key signatures of the down-converted photons: (i) energy conservation as the wave length of generated photons (810 nm) is two times larger than that of the photons used to optically pump SPDC (405 nm), which is shown by using a 10-nm band-pass filter centred around 810 nm; (ii) the angles between the two photons of a pair correspond to the configuration of momentum conservation calculated analytically;(iii) the photons arrived at the detectors within the jitter time of those; and (iv) orthogonal polarisation of down-converted photons (810 nm) with respect to pump photons (405 nm). These findings show the consequences of SPDC.