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