An apparatus for generating a shared quantum key between a sender and a receiver comprises a sending apparatus which generates entangled photon pairs, and a receiving apparatus. A shared quantum key can be generated using temporal coincidences between photon detection events. For example, coincidences may be determined between sender and receiver photon detection events using detection data shared through a non-secure communications link between the sender and receiver. The quantum key can be used in encrypted communications. Similar apparatus and methods can be used for quantum imaging.