Patent ID: 8781334

Claim:
A quantum repeater optically couplable to first and second neighbour nodes through local-link optical channels; the repeater comprising: quantum physical hardware providing first and second repeater portions (L, R) respectively arranged to support first and second qubits for entanglement with qubits in the first and second neighbour nodes respectively by light fields transmitted over the local-link channels thereby to form respective local link entanglements, herein “LLE”s; the quantum physical hardware being operable to merge two entanglements respectively involving a first and a second qubit, by locally operating on these qubits; first and second LLE control units for controlling the quantum physical hardware to effect creation of first and second LLEs in cooperation with the first and second neighbour nodes; and a top-level control arrangement operative to initiate a merging of entanglements respectively involving a first and a second qubit when both a token has been received from the first neighbour node, and there exists a condition that the second qubit concerned is at least expected to have been entangled with a qubit of the second neighbour node; the top-level control arrangement being arranged, in the case where the token is received before the said condition involving the second qubit exists, to await the existence of that condition before initiating the merging of entanglements; and the top-level control arrangement being further operative to send on the token to the second neighbour node following successful completion of said merging of entanglements.