ABSTRACT
Entanglement is one of the essential resources of quantum information and
communication technology. The non-local nature of entanglement con-
flicts with classical local realism, as pointed out by Einstein, Podolsky and
Rosen [1]. The existence criterion of the non-local quantum correlation
was formalized by Bell’s inequality [2] and by its generalization known
as CHSH-Bell’s inequality [3]. From the 1960s through the 80s several
experiments [4-9] had been carried out to test Bell’s inequality; they had
demonstrated the violation of Bell’s inequality and thus manifested the exis-
tence of non-local quantum correlations brought by entanglement. In these
early experiments, photon pairs emitted from atomic cascades are used to
hold entanglement in their polarization states. Following to such pioneer-
ing works, a number of methods to generate entangled photons have been
proposed. To date, parametric down-conversion (PDC) has been being the
most popular and powerful method to obtain entangled photons [10, 11].
Most recently, entangled photon generation using semiconductor materi-
als [12-16] attracts attention because of its potential for the realization
of entangled photon emitting diodes in the near future. In these experi-
ments, cascaded photon emission from a biexciton, a solid state analogue
of the atomic cascade, was used to generate polarization entanglement [17].
In this chapter, we review the experimental results on the generation of
polarization-entangled photons from a biexciton in a CuCl crystal via res-
onant hyperparametric scattering [12, 16], and discuss the quantum state
of the generated photon pairs.
