Complex sentence: As already mentioned above, for the implementation of a boson sampling machine one necessitates a reliable source of many indistinguishable photons, and this requirement currently remains one of the main difficulties in scaling up the complexity of the device.
Split into simpler sentences: As already mentioned above, for the implementation of a boson sampling machine one necessitates a reliable source of many indistinguishable photons. And this requirement currently remains one of the main difficulties in scaling up the complexity of the device.