Concurrence of a pair of time-bin entangled photons
Manuél Ávila, J.A. Morales-Cadena · Journal of Modern Optics · 2015
A metastable state m subjected to a couple of pulses transits to an excited level α of an atom with probabilities p1 and p2, respectively. One photon is emitted in the transition from the level α to a lower atomic level η. A second photon is emitted in the transition from the level η to a lowest atomic level β. The first photon must be emitted before than the second one so they are both time ordered (time-bin) and entangled. It is calculated that the concurrence of the two produced time-bin photons as a function of p1, p2 and the branching ratios of the two transitions α→η and (η→β). It is found that the two produced photons are maximally entangled if the branching ratios are greater than 80%. It is also found that certain values of p1, p2 and the branching ratios preclude entanglement between the two produced photons. Intervals of values for p1 and p2 where the concurrence is large enough and then two-qubit quantum information processing protocols can be optimally implemented are found.