Sergey V. Polyakov is a physicist in Quantum Measurement Division at the National Institute of Standards and Technology (NIST), whose mission is the study and use of quantum light sources and single-photon detectors for advancing novel, quantum-enabled measurements, quantum information, and tests of fundamental physics. Recently, Sergey has developed new characterization techniques for classical and non-classical light sources, which were successfully applied for an in-depth analysis of a range of optical sources: from quantum dots to parametric down-conversion single-photon sources, to faint lasers and thermal sources. He demonstrated indistinguishability of single photons generated by single photon sources of different nature. He also holds an accuracy record in comparing absolute calibrations of single-photon detectors using a quantum two-photon method and a more traditional radiant-power measurement and detector substitution method. As a postdoctoral fellow of California Institute of Technology, he contributed in development of early ensemble-based sources of single photons, and he co-authored first demonstration of entanglement in remote atomic ensembles, published by Nature.