High-performance quantum entanglement generation via cascaded second-order nonlinear processes

In this paper, we demonstrate the generation of high-performance entangled photon-pairs in different degrees of freedom from a single piece of fiber pigtailed periodically poled LiNbO$_3$ (PPLN) waveguide. We utilize cascaded second-order nonlinear optical processes, i.e. second-harmonic generation (SHG) and spontaneous parametric down conversion (SPDC), to generate photon-pairs. Previously, the performance of the photon pairs is contaminated by Raman noise photons from the fiber pigtails. Here by integrating the PPLN waveguide with noise rejecting filters, we obtain a coincidence-to-accidental ratio (CAR) higher than 52,600 with photon-pair generation and detection rate of 52.3 kHz and 3.5 kHz, respectively. Energy-time, frequency-bin and time-bin entanglement is prepared by coherently superposing correlated two-photon states in these degrees of freedom, respectively. The energy-time entangled two-photon states achieve the maximum value of CHSH-Bell inequality of S=2.708$\pm$0.024 with a two-photon interference visibility of 95.74$\pm$0.86%. The frequency-bin entangled two-photon states achieve fidelity of 97.56$\pm$1.79% with a spatial quantum beating visibility of 96.85$\pm$2.46%. The time-bin entangled two-photon states achieve the maximum value of CHSH-Bell inequality of S=2.595$\pm$0.037 and quantum tomographic fidelity of 89.07$\pm$4.35%. Our results provide a potential candidate for quantum light source in quantum photonics.Comment: 29 pages,7 figure

InGaAs Quantum Dots Embedded in p-n Junction on GaAs(311)B Substrate

ABSTRACTWe have evaluated the photoluminescence (PL) properties of quantum dots (QDs) embedded in a p-n junction on GaAs(311)B and were compared with the identical structure grown on GaAs(001). The QDs on these two surfaces were fabricated with a similar size and density by optimizing the growth conditions. The PL emission from the QDs grown on GaAs(001) rapidly disappeared when the excitation power was decreased below 0.4W/cm2, while that from on GaAs(311)B was clearly observable even at a lower excitation power of 0.1W/cm2. From the measurements of PL intensity dependence on temperature and applied electric field, it was found that there are clear differences between the QDs grown on (001) and the QDs grown on (311)B in the recombination rates through non-radiative processes and/or the escape rates of carriers out of QDs to the GaAs host through a tunneling process.</jats:p