Advance opens door for secure quantum applications without specialized infrastructure
But can you detect the link being broken by someone other than your intended communication partner?
Yes, because breaking the entanglement destroys the link between the photons received at either end.
Observing an entangled photon requires extremely precise timing, the lightspeed lag on the line has to be known down to the nanosecond to ensure that the photon received is paired with the photon at the other end. Even if a MitM wanted to try retransmitting the quantum states it observes on the line, they wouldn’t be able to do so without introducing enough lag to desync the connection.
Alternatively, if M tried sending their own random data in sync with the expected timing, then the bits received by B would only have a 50-50 chance of matching the bits sent from A. Any encryption based on that data would almost immediately begin to suffer a 100% error rate.
