  The integration of entangled photon emitters in nanophotonic structures
designed for the broadband enhancement of photon extraction is a major
challenge for quantum information technologies. We study the potential of
quantum dot (QD) microlenses to act as efficient emitters of maximally
entangled photons. For this purpose, we perform quantum tomography measurements
on InGaAs QDs integrated deterministically into microlenses. Even though the
studied QDs show non-zero excitonic fine-structure splitting (FSS),
polarization entanglement can be prepared with a fidelity close to unity. The
quality of the measured entanglement is only dependent on the temporal
resolution of the used single-photon detectors compared to the period of the
excitonic phase precession imposed by the FSS. Interestingly, entanglement is
kept along the full excitonic wave-packet and is not affected by decoherence.
Furthermore, coherent control of the upper biexcitonic state is demonstrated.
