Security loophole in free-space quantum key distribution due to spatial-mode detector-efficiency mismatch

  title={Security loophole in free-space quantum key distribution due to spatial-mode detector-efficiency mismatch},
  author={Shihan Sajeed and Poompong Chaiwongkhot and Jean-Philippe Bourgoin and Thomas Jennewein and Norbert Lutkenhaus and Vadim Makarov},
  journal={Physical Review A},
In free-space quantum key distribution (QKD), the sensitivity of the receiver's detector channels may depend differently on the spatial mode of incoming photons. Consequently, an attacker can control the spatial mode to break security. We experimentally investigate a standard polarization QKD receiver and identify sources of efficiency mismatch in its optical scheme. We model a practical intercept-and-resend attack and show that it would break security in most situations. We show experimentally… 

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