Ph.D. Student Paolo Barigelli

Generation and characterization of polarization-entangled states using quantum dot single- photon sources

The generation of entangled states is the fundamental step in most of the quantum information applications. The sources based on spontaneous parametric down-conversion can be employed to obtain high-fidelity entangled photons, but have an intrinsic trade-off between the brightness and quality of the state. In this work, we implement and characterize a method for the creation of entangled states based on probabilistic interference of identical photons emitted from the same single-photon source; Semiconductor Quantum Dots are the ideal candidates due to their high single-photon indistinguishability, on-demand generation and low multiphoton emission. The generation scheme has been implemented via a simple, compact design that produces entangled photon pairs in the polarization degree of freedom. The proposed platform has been tested and analysed with single photons produced through two different pumping schemes, the resonant excited one and the longitudinal-acoustic phonon-assisted configuration. A novel theoretical model has been developed to characterize the entangled two-photon states and determine the experimental variables limiting Bell’s inequality’s maximum violation. The source shows long-term stability in terms of fidelity and Bell’s parameter, thus constituting a reliable building block for optical quantum technologies and communications protocols.