Method for adding nodes to a quantum key distribution system

A multi-client quantum key distribution system comprising:

• a quantum sender adapted to transmit a random bit sequence as a plurality of photons each having a predetermined quantum state;
• and
• a quantum receiver adapted to measure the quantum state of the plurality of photons transmitted by the quantum sender;
• and
• a quantum channel between the quantum sender and the quantum receiver, wherein the quantum channel includes a plurality of nodes adapted to perform an operation capable of altering the quantum state of at least one of the plurality of photons transmitted by the quantum sender;
• wherein first and second clients associated with first and second ones of the plurality of nodes are adapted to determine a cryptographic key with knowledge of shared information including a) the quantum state and basis of the plurality of photons at the originating node set by the quantum sender, b) the quantum state and basis of the plurality of photons measured by the quantum receiver at the terminating node, and c) the basis choice and operation performed on the plurality of photons at each of the intermediate nodes except a first intermediate node associated with the first client and a second intermediate node associated with the second client, wherein the shared information is communicated over a public communications path.

A method of quantum key distribution comprising:

• providing a quantum channel including a plurality of nodes associated with a corresponding plurality of clients, the plurality of nodes including:
• an originating node,
• a terminating node, and
• a plurality of intermediate nodes;
• transmitting a quantum signal including a plurality of photons over the quantum channel from the originating node to the terminating node;
• performing an operation on the quantum signal at each of the intermediate nodes, wherein the operation is capable of changing the quantum state of at least one of the plurality of photons in the quantum signal;
• making public to a first client associated with a first one of the plurality of nodes and a second client associated with a second one of the plurality of nodes:
• a) the quantum state and the transmission basis of the plurality of photons at the originating node,
• b) the quantum state and the measurement basis of the plurality of photons at the terminating node,
• c) the choice of basis and the operation performed on the quantum signal at each of the intermediate nodes by all except the first client and the second client;
• d) the choice of basis by the first client and the second client;
• and
• determining a cryptographic key shared between the first client and second client.

A method for generating a key among first and second designated clients in a multi-party entanglement quantum key distribution system comprising:

• providing a first quantum path including a first terminating node and a first plurality of intermediate nodes, the first plurality of intermediate nodes including intermediate node Ni associated with the first designated client;
• providing a second quantum path including a second terminating node and a second plurality of intermediate nodes, the second plurality of intermediate nodes including intermediate node Nj associated with the second designated client;
• transmitting first and second photons of an entangled photon pair over the first and second quantum paths, respectively;
• performing an operation on the entangled photon pair at each node of the first and second plurality intermediate nodes;
• measuring the quantum state of the entangled photon pair at the first and second terminating nodes;
• revealing to the first and second designated clients over a public communication path:
• a) complete information regarding the measurement of the entangled photon pair at the terminating nodes, b) complete information regarding the operations performed at the plurality of intermediates nodes, c) partial information regarding the operation performed at intermediate node Ni, and d) partial information regarding the operation performed at intermediate node Nj;
• and
• determining, at the first and second designated clients, a cryptographic key shared between the first and second designated clients based on the revealed information.