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

Abstract

Using the type-I SPDC process in BBO nonlinear crystal, we generate a polarization-entangled state near to the maximally-entangled Bell-state with high-visibility (high-brightness) 98.50 ± 1.33% (87.71 ± 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, S = 2.71 ± 0.10. Via measuring the coincidence count rate in the SPDC process, we obtain the quantum efficiency of single-photon detectors around (25.5 ± 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, 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.

Linear Entropy in the Atom-Field Interaction at Finite Temperature

“…To achieve this it is necessary to perform a partial trace on the system, such that we remain with only one subsystem described by its density matrix which is, in the most general case, a so-called "statistical mixture" state. It is more difficult the calculation of the entropy when one studies statistical mixtures [5,6] because it is a (logarithmic) function of the density matrix and the calculation may become extremely complicated [7,8].…”

Comparative Analysis of Spin, Paths, Temporal, and Spatial Modes

“…New modes impacted quantum information for the opportunity coding qubits [1] in new physical modes. It also extends the use of polarization and interferometry devices from wave-plates or splitters [2].…”