![The birth of SPDC photons](https://raicol-quantum.com/wp-content/uploads/2024/02/The-birth-of-SPDC-photons-2.png)
- February 21, 2024
- Noa Bloch
- 0
The birth of SPDC photons
In nonlinear crystals, a special nonlinear process occurs. A pump photon is spontaneously converted into two complementary photons with lower energy. In this process both energy and momentum are conserved, i.e ., ωp =ωs + ωi and kp =ks + ki
In PPKTP or APKTP Crystals the momentum mismatch of the process is compensated by the crystal reciprocal vector which is determined by the spatial frequency kp = ki +ks + kG
Vacuum energy fluctuations give rise to the spontaneous creation of many random photons. However, the output photons of the SPDC (spontaneous parametric down-conversion nonlinear process) are the ones that conserve momentum and energy.
![Spdc photons Raicol Quantum](https://raicol-quantum.com/wp-content/uploads/2024/02/Spdc-photons-Raicol-Quantum.png)
In type 1 SPDC, all the photon pairs that conserve momentum are positioned on a ring-shaped structure:
![](https://raicol-quantum.com/wp-content/uploads/2024/02/SPDC-photons-Raicol.png)
Changing the temperature of the crystal or wavelength of the pump will change the phase-matching condition thus, the radius of the rings will be changed as well, as seen in the movie.
![](https://raicol-quantum.com/wp-content/uploads/2024/02/SPDC-photons-Raicol-Quantum-1.png)
Raicol
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