Patent ID: 7760883
Filing Date: 2010-07-20
Classification: H04L

Abstract:
1. Apparatus for distributing a quantum key between a first node and a second node in a communications network, comprising: a photon source operable to generate a sequence of source pulses; a coupler operable to split each of the source pulses into a respective first pulse and a respective second pulse; an interface operable to: a detection unit operable to combine the received first pulses and corresponding ones of the received second pulses into corresponding composite pulses and to process the composite pulses in order to produce a sequence of detection outcomes indicative of phase mismatch between the received first pulses and corresponding ones of the received second pulses; a control unit operable to receive from at least one of the first node and the second node an indication of occurrences of a match between the encoding bases employed by the first node and the encoding bases employed by the second node, said control unit further operable to derive an XOR bit string from those detection outcomes in the sequence of detection outcomes that are associated with occurrences of a match, and to communicate said XOR bit string to at least one of the first and second nodes, the XOR bit string comprising bits each of which is either logic “0” to indicative a detection outcome produced from a composite pulse affected with constructive interference, or logic “1” to indicate a detection outcome produced from a composite pulse affected with destructive interference; wherein execution of an XOR between the XOR bit string and the respective key bit string of one of the first and second nodes allows the first and second nodes to form a shifted key.