  We report on an experiment demonstrating entanglement swapping of
time-frequency entangled photons. We perform a frequency-resolved Bell-state
measurement on the idler photons from two independent entangled photon pairs,
which projects the signal photons onto a two-color Bell state. We verify
entanglement in this heralded state using two-photon interference and observing
quantum beating without the use of filters, indicating the presence of
two-color entanglement. Our method could lend itself to use as a highly-tunable
source of frequency-bin entangled single photons.
