Second-order photon correlation measurement with picosecond resolution using frequency upconversion

The second-order correlation function of light g⁽²⁾(τ) constitutes a pivotal tool to quantify the quantum behavior of an emitter and in turn its potential for quantum information applications. The experimentally accessible time resolution of g⁽²⁾(τ) is usually limited by the jitter of available single-photon detectors. Here, we present a versatile technique allowing g⁽²⁾(τ) to be measured from a large variety of light signals with a time resolution given by the pulse length of a mode-locked laser. The technique is based on frequency upconversion in a nonlinear waveguide, and we analyze its properties and limitations by modeling the pulse propagation and the frequency conversion process. We measure g⁽²⁾(τ) from various signals including light from a quantum emitter-a confined exciton-polariton structure-revealing its quantum signatures at a scale of a few picoseconds and demonstrating the capability of the technique.