According to scientists at Massachusetts Institute of Technology's Research Laboratory of Electronics in Cambridge, parametric down-conversion of short-pulse laser radiation in a periodically poled KTP crystal should yield a source of frequency-entangled pairs of photons with the same frequencies for experimenters. Such photon pairs, said Franco N.C. Wong, one of the researchers on the project, are the first step toward boosting the accuracy of various N-photon experiments by a factor of (check)N.The scientists calculate that a 2-cm-long crystal with a grating period of 47.7 µm should produce the pairs when exposed to 170-fs pulses of 790-nm radiation. They described their work in the May 6 issue of Physical Review Letters.