  Current photon entangling schemes require resources that grow with the photon
number. We present a new approach that generates quantum entanglement between
many photons, using only a single source of entangled photon pairs. The
different spatial modes, one for each photon as required by other schemes, are
replaced by different time slots of only two spatial modes. States of any
number of photons are generated with the same setup, solving the scalability
problem caused by the previous need for extra resources. Consequently,
entangled photon states of larger numbers than before are practically
realizable.
