Mode-resolved photon counting via cascaded quantum frequency conversion

Resources for the manipulation and measurement of high-dimensional photonic signals are crucial for implementing qudit-based applications. Here we propose potentially high-performance, chip-compatible devices for such purposes by exploiting quantum frequency conversion in nonlinear optical media. Specifically, by using sum-frequency generation in a χ(2) waveguide, we show how mode-resolved photon counting can be accomplished for telecom-band photonic signals subtending multiple temporal modes. Our method is generally applicable to any nonlinear medium with arbitrary dispersion properties.