The quADD-ED is an experiment for the generation and analysis of polarization-entangled photon pairs. A high-power UV diode laser is focused on a nonlinear crystal. By conservation of energy and momentum, some of these pump photons are transformed into a pair of lower energy near-infrared photons.
Different phenomena can be experienced by optical elements such as polarizers. Finally, the infrared photons are coupled into optical fibers and read by the quEDU with its APDs.
This board can be extended by various optical elements, ether by adding to the board or connecting by fiber.
Key Features
| Hands-on study of quantum entanglement |
| User-friendly operation, complete system |
| Add-ons to extend experiments |
Application
| Student lab course experiments |
| Violate Bell’s inequalities |
| Heralded single photon source |
Setup of the Board with the quEDU
Setup with a Michelson Interferometer
Downloads
| quADD-ED Datasheet | 02/2026 | 0.2 MB | |
| quADD-ED Manual | 03/2026 | 7.4 MB |
quADD-ED - Entanglement Demonstrator Board without the laser safety housing
LaseriThe pump laser diode emits light with a wavelength of λ = 405 nm and vertical polarization.
HWPiThe half waveplate rotates the polarization of linearly polarized light. Here, the vertical pump light can be rotated to +45° polarized light.
YVOiThe group-velocity mismatch between the pump and the down-conversion light in the birefringent BBO crystals causes the photon pairs born in the first crystal to be advanced with regard to those originating from the second. This birefringent YVO4 pre-compensation crystal negates this effect.
YVOiThe photons originating from the first BBO crystal experience higher dispersive delay due to their pass through the second BBO crystal. Consequently, a compensation using another birefringent YVO4 crystal has to be applied.
BBOiThe optical axis of the second BBO crystal is oriented at a 90° angle in comparison to the optical axis of the first crystal. This makes the process of down-converting horizontal pump photons to vertical output photon pairs possible.
BBOiA BBO crystal is a highly non-linear medium, making spontaneous parametric down conversion possible. Conservation of energy and momentum hold when a pump photon (vertically polarized) is converted into two output photons (horizontally polarized) with half the energy at λ = 810 nm.
Optical FibersiThe fiber couplers spatially select the photons to be detected. For best entanglement quality, their position and orientation has to be fine tuned such that photons from both BBO crystals are coupled with the same probability.
Polarization:
Dirac Notation:|V⟩|V⟩+|H⟩|V⟩|V⟩|V⟩+|H⟩|H⟩|HH⟩|VV⟩|VV⟩+|HH⟩|VV⟩|HH⟩
quADD-ED - Animated Entangled Photon Source. Click on HWP, YVO or BBO to explore the different source configurations.
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quADD-ED - Animated Entangled Photon Source. Click on HWP, YVO or BBO to explore the different source configurations.
LaseriThe pump laser diode emits light with a wavelength of λ = 405 nm and vertical polarization.
HWPiThe half waveplate rotates the polarization of linearly polarized light. Here, the vertical pump light can be rotated to +45° polarized light.
YVOiThe group-velocity mismatch between the pump and the down-conversion light in the birefringent BBO crystals causes the photon pairs born in the first crystal to be advanced with regard to those originating from the second. This birefringent YVO4 pre-compensation crystal negates this effect.
YVOiThe photons originating from the first BBO crystal experience higher dispersive delay due to their pass through the second BBO crystal. Consequently, a compensation using another birefringent YVO4 crystal has to be applied.
BBOiThe optical axis of the second BBO crystal is oriented at a 90° angle in comparison to the optical axis of the first crystal. This makes the process of down-converting horizontal pump photons to vertical output photon pairs possible.
BBOiA BBO crystal is a highly non-linear medium, making spontaneous parametric down conversion possible. Conservation of energy and momentum hold when a pump photon (vertically polarized) is converted into two output photons (horizontally polarized) with half the energy at λ = 810 nm.
Optical FibersiThe fiber couplers spatially select the photons to be detected. For best entanglement quality, their position and orientation has to be fine tuned such that photons from both BBO crystals are coupled with the same probability.
Polarization:
Dirac Notation:|V⟩|V⟩+|H⟩|V⟩|V⟩|V⟩+|H⟩|H⟩|HH⟩|VV⟩|VV⟩+|HH⟩|VV⟩|HH⟩
Needed Devices
Controlled Devices