Joint spectrum of photon pairs measured by coincidence Fourier   spectroscopy
  We propose and demonstrate a method for measuring the joint spectrum of photon pairs via Fourier spectroscopy. The biphoton spectral intensity is computed from a two-dimensional interferogram of coincidence counts. The method has been implemented for a type-I downconversion source using a pair of common-path Mach-Zender interferometers based on Soleil compensators. The experimental results agree well with calculated frequency correlations that take into account the effects of coupling into single-mode fibers. The Fourier method is advantageous over scanning spectrometry when detectors exhibit high dark count rates leading to dominant additive noise. 
Wojciech Wasilewski, Piotr Wasylczyk, Piotr Kolenderski, Konrad   Banaszek, Czeslaw Radzewicz