Broadening the bandwidth of entangled photons: a step towards the   generation of extremely short biphotons
  We demonstrate a technique that allows to fully control the bandwidth of entangled photons independently of the frequency band of interest and of the nonlinear crystal. We show that this technique allows to generate nearly transform-limited biphotons with almost one octave of bandwidth (hundreds of THz) which corresponds to correlation times of just a few femtoseconds. The presented method becomes an enabling tool for attosecond entangled-photons quantum optics. The technique can also be used to generate paired photons with a very high degree of entanglement. 
M. Hendrych, X. Shi, A. Valencia, and J. P. Torres