Figure 1: Schematic of the single photon source and multiport waveguide circuit.
From: Multiphoton quantum interference in a multiport integrated photonic device
We generate two pairs of single photons by spontaneous parametric down conversion in two non-linear crystals (potassium dihydrogen phosphate, KDP), driven by a frequency doubled (second-harmonic generation, SHG) femtosecond laser (Ti:sapph) - see methods. The circuit consists of eight modes labelled a to h, 10 beam splitters labelled η1 to η10, and three variable phase shifters labelled φ1 to φ3. Single photons are launched into a subset of b to g and the output of each mode was monitored by a single-photon detector. The ancillary modes a and h were not accessible for coupling.
