An unhackable quantum internet is being built in New York City

In an office overlooking an old shipyard in Brooklyn, I am learning that I may have walked over some entangled quantum light on my way here.

Since the previous evening, researchers at Qunnect have been sending particles of light, or photons, through a 34-kilometre-long loop of optical fibre underneath New York. Their approach preserves the special quantum property of entanglement that will allow them to eventually use this loop as a starting point for a quantum internet.

In a quantum internet, devices communicate by exchanging quantum particles, like …