Quantum key distribution network with centralized optical pulse generation

A node for a quantum key distribution network, comprising:

• an optical input operable to receive, from a hub of the quantum key distribution network, a user-node pulse train of optical-pulse pairs, each of the optical-pulse pairs comprising a first pulse and a second pulse that is temporally delayed relative to the first pulse, the second pulse having an optical phase shift relative to the first pulse;
• a first beamsplitter configured to split the user-node pulse train into first and second pulse trains;
• a modulator operable to block the second pulse of each of the optical-pulse pairs of the second pulse train to generate a filtered pulse train;
• a second beamsplitter configured to split the filtered pulse train into an timing pulse train and a pre-qubit pulse train;
• a photodetector operable to detect the timing pulse train to generate an electronic timing signal;
• an optical delay operable to delay the pre-qubit pulse train into a delayed pulse train;
• a qubit encoder including an asymmetric Mach-Zehnder interferometer, the qubit encoder being operable to encode, based on the electronic timing signal, the delayed pulse train into a photonic-qubit pulse train;
• a phase calibrator operable to calibrate the asymmetric Mach-Zehnder interferometer with the first pulse train such that an interferometer phase shift between first and second arms of the asymmetric Mach-Zehnder interferometer matches the optical phase shift;
• and
• an optical output operable to transmit the photonic-qubit pulse train to the hub.

A method performed by a hub of a quantum key distribution network, comprising:

• transforming, with an asymmetric Mach-Zehnder interferometer, an optical pulse train into a double pulse train of optical-pulse pairs, each of the optical-pulse pairs comprising a first pulse and a second pulse that is temporally delayed relative to the first pulse, the second pulse having an optical phase shift relative to the first pulse;
• splitting the double pulse train into a first-node pulse train and a second-node pulse train;
• transmitting the first-node pulse train to a first node of the quantum key distribution network, the first node transforming the first-node pulse train into a first photonic-qubit pulse train;
• transmitting the second-node pulse train to a second node of the quantum key distribution network, the second node transforming the second-node pulse train into a second photonic-qubit pulse train;
• receiving the first photonic-qubit pulse train from the first node;
• receiving the second photonic-qubit pulse train from the second node;
• and
• performing a partial Bell-state measurement with a first photonic qubit of the first photonic-qubit pulse train and a second photonic qubit of the second photonic-qubit pulse train, the first and second photonic qubits being at least partially indistinguishable.

A hub for a quantum key distribution network, comprising:

• an asymmetric Mach-Zehnder interferometer operable to transform an optical pulse train into a double pulse train of optical-pulse pairs, each of the optical-pulse pairs comprising a first pulse and a second pulse that is temporally delayed relative to the first pulse, the second pulse having an optical phase shift relative to the first pulse;
• a beamsplitter configured to split the double pulse train into a first-node pulse train and a second-node pulse train;
• a first optical output operable to transmit the first-node pulse train to a first node of the quantum key distribution network such that the first node transforms the first-node pulse train into a first photonic-qubit pulse train;
• a second optical output operable to transmit the second-node pulse train to a second node of the quantum key distribution network such that the second node transforms the second-node pulse train into a second photonic-qubit pulse train;
• a first optical input operable to receive the first photonic-qubit pulse train;
• a second optical input operable to receive the second photonic-qubit pulse train;
• and
• a Bell-state measurement module operable to perform a partial Bell-state measurement with a first photonic qubit of the first photonic-qubit pulse train and a second photonic qubit of the second photonic-qubit pulse train, the first and second photonic qubits being at least partially indistinguishable.