Do you have to use a Beta-barium borate crystal in order to entangle photons?

[ice909]

im just curious and i just want to know, do you need a Beta-barium borate crystal to entangle photons? are there any alternatives? can you use sodium chloride crystals as a possible option? what makes a Beta-barium borate so special and different from any other crystals? please provide good info and please no negative comments. thank you.

 

[skippy1729]

I am not an expert in quantum optics but I believe any birefringent crystal will do.

 

[Cthugha]

Yes, in principle any material showing strong birefringence and having a certain symmetry making them attractive for nonlinear optics could be used. However in practice you of course also want them to be transparent for the wavelengths of interest and the damage threshold should be rather high, too. The most common non-linear crystals besides BBO are potassium titanyl phosphate (KTP), (potassium dihydrogen phosphate (KDP) and lithium niobate.