Optimizing time-entanglement between two sources

Abstract: We demonstrate a compact source of four entangled telecommunication wavelength photons, which is used to generate a GHZ state, with minimal spectral and spatial entanglement. The spatial and spectral degree of freedom are minimized by careful source design. To optimize the entanglement between the two sources, distinguishing temporal information must be removed. We demonstrate this high degree of coherence, between pairs of sources, by performing a Hong-Ou-Mandel measurement. This measurement enables the optical path lengths within the system to be equalized, removing timing information from photons. We also measure the second order correlation function to test the rate of multi-pair production from a single pump pulse. With these optimizations completed, we measure a count rate of 13,600 counts/s per mW of pump power.