US Patent 9219605 Quantum key distribution

An apparatus including: an input optical interface configured to receive a series of optical input signals each including photons; an encoder configured to encode a quantum key for distribution by encoding each of the series of received optical input signals with a measurable state; an attenuator configured to attenuate each of the encoded optical input signals to create a series of quantum optical signals; and an output optical interface configured to send the series of quantum optical signals to the remote apparatus via a quantum communication channel.