Abstract
Semiconductor Bragg-reflection waveguides are well-established sources of correlated photon pairs as well as promising candidates for building up integrated quantum optics devices. Here, we use such a source with optimized non-linearity for preparing time-bin entangled photons in the telecommunication wavelength range. By taking advantage of pulsed state preparation and efficient free-running single-photon detection, we drive our source at low pump powers, which results in a strong photon-pair correlation. The tomographic reconstruction of the state's density matrix reveals that our source exhibits a high degree of entanglement. We extract a concurrence of $88.9\pm 1.8\%$ and a fidelity of $94.2 \pm 0.9\%$ with respect to a Bell state.
Highlights
Robust entangled photon sources are vital for performing quantum optics tasks fast and reliably
Braggreflection waveguides (BRWs) based on semiconductor materials are good candidates to become truly practical as integrated quantum photonic components
We used a BRW sample with a simplified epitaxial structure designed for having a larger nonlinearity and for simplifying the fabrication process to produce cross-polarized signal and idler beams via parametric down-conversion (PDC)
Summary
Robust entangled photon sources are vital for performing quantum optics tasks fast and reliably. The pulsed operation is convenient for performing quantum optics tasks fast, and when being transmitted over long distances in optical fibers, time-bin entangled photons are more robust against decoherence than the polarization-entangled ones due to the inevitable polarization-mode dispersion.[31] In the past, these types of entanglement have been demonstrated on various quantum photonic platforms ranging from PDC in bulk crystals[32,33,34] and waveguides[35,36] and spontaneous four wave mixing (FWM) in silicon waveguides and optical fibers[37,38] to photon emission from quantum dots.[39,40] While the latter work only in a highly controlled environment, FWM sources suffer from low conversion and background suppression efficiencies. With the help of the achieved concurrence, we can validate the quality of the entangled state and predict that a violation of Bell’s inequality is possible with our source
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