Measurement of entropy and quantum coherence properties of two type-I entangled photonic qubits

Using the type-I SPDC process in BBO nonlinear crystal, we generate a polarization-entangled state near to maximally-entangled Bell-state with high-visibility (high-brightness) 98.50 ± 1.33% (87.71 4.45%) for HV (DA) basis. We calculate CHSH version of Bell inequality, as nonlocal realism test, and find strong violation from classical physics or any hidden variable theory, S = 2.71 0.10. Via measuring coincidence count rate process, obtain quantum efficiency single-photon detectors around (25.5 3.4)%, which is good agreement their manufacturer company. As expected, verify linear dependency CC vs. pump power input CW-laser, may yield effective second-order susceptibility crystal. theory measurement qubits, includes tomographic reconstruction states due set 16 polarization-measurement, together maximum-likelihood-technique, based on numerical optimization, physical non-negative definite density matrices, implies non-separability entanglement prepared state. By having maximum likelihood operator, precisely measures such Concurrence, formation, tangle, logarithmic negativity, different entropies entropy, Von-Neumann Renyi 2-entropy. Finally, this high-brightness low-rate entangled photons source can be used short-range measurements Lab.