Abstract: An electronic package comprising: an active element; a first substrate; and a second substrate, the first substrate comprising a plurality of conductive tracks on a first surface, the second substrate comprising a plurality of conductive tracks on a second surface, the active element being provided on the first surface of the first substrate, the second substrate being provided overlying the first surface of the first substrate such that a face of the second substrate which is opposite to the second surface is in contact with the first surface, the second substrate having an opening to allow access to the active element and being positioned on the first substrate such that at least some of the plurality of conductive tracks on the first surface are exposed, the active element being electrically connected to at least some of the plurality of tracks on the first substrate and the plurality of tracks on the second substrate.

Abstract: An optical transmitter for a Quantum Key Distribution (QKD) system, the transmitter comprising: a multi-modal laser; a wavelength tuneable laser arranged to inject light into a cavity of the multi-modal laser, so as to cause the multi-modal laser to output light at a selected wavelength for use in generating pulses to be output by the transmitter; and a modulator for controlling a phase shift between successive pulses output from the transmitter.

Abstract: An optical device comprising: a light routing element coupled to a first optical path and a second optical path such that light received by the light routing element is directed into one of the first optical path or the second optical path; a combiner coupling the first optical path and second optical path into a single output path; a controller applying a control signal to said light routing element, the control signal indicating whether a portion of the light received by the light routing element is directed into the first optical path or into the second optical path; a phase controlling element provided in the first optical path such that there is provided a pre-determined fixed phase difference between a light pulse routed through the first optical path and a light pulse routed through the second optical path.

Abstract: A quantum communication system comprising: an transmitter and a receiver, the transmitter comprising transmitter components the transmitter components comprising a source of pulsed radiation and a modulation unit, the modulation unit being configured to randomly encode pulses of radiation; and a receiver comprising receiver components, the receiver components comprising a demodulator and detector configured to decode and detect said randomly encoded pulses, the system further comprising a control unit and an optimisation unit, the control unit being configured to apply a plurality of control signals defined by a set of control parameters to at least one of said transmitter components and receiver components, the optimization unit being configured to tune the set of control parameters, wherein the optimisation unit sets the control parameters by: obtaining a score indicating the quality of the system corresponding to a first set of control parameters; and estimating a further set of control parameters suita

Abstract: An authentication method for quantum communication between two nodes, the method comprising: applying a hash function to a message to obtain a hash code, wherein the hash function is a Poly1305; applying a one-time pad cipher to the hash code to obtain a message authentication code (MAC); and authenticating the message exchanged between the two nodes using the MAC.

Abstract: A server configured to provide a pre-shared key “PSK” with a first user node, to allow a first user node and a second user node to share a PSK, the server comprising: a network interface; an authentication unit; an encryption unit; a key management system and a quantum key distribution unit, the authentication unit being configured to receive a request for authentication, via the network interface, of a first channel between a first user node and the server, the quantum key distribution unit being configured to allow a quantum key to be distributed between the first user node and the server, the quantum key being sifted using communication over the authenticated first channel to establish a first quantum key for the first user and server, the key management system being configured to provide a first PSK for the first user to allow the first user to authenticate with the second user, the encryption unit being configured to encrypt the first PSK with the quantum key to send to the first user node via the net

Abstract: A method for use in a quantum communication network comprising a first node, a second node and a third node, the method performed by the third node, the method comprising: receiving, from the first node, a request for authentication key data for authenticating communication with the second node; in response to the request: generating the first authentication key data; sending, to the first node, a first message comprising first authentication key data for authenticating communication between the first node and the second node, wherein the first message is authenticated using second authentication key data stored on the first node and the third node, and wherein the first message is encrypted using a first cryptographic key exchanged with the first node on the quantum communication network; and sending, to the second node, a second message comprising the first authentication key data, wherein the second message is authenticated using third authentication key data stored on the second node and the third node,

Abstract: An optical emitter comprising a primary laser and a plurality of secondary lasers wherein each secondary laser is optically injection locked to said primary laser, the emitter further comprising at least one polarisation controller configured to control the polarisation of the output of at least one of the secondary lasers, the emitter further comprising a combination unit that is configured to combine the outputs of the secondary laser modules into an output signal.

Abstract: A method of exchanging a combined cryptographic key between a first node and a second node, the first node and the second node being connected through a first communication and a second communication network, wherein the first communication network is a quantum communication network wherein information is encoded on weak light pulses; and the first node and the second node being configured to: exchange one or more first cryptographic keys on the first communication network; exchange one or more second cryptographic keys using the second communication network; and form the combined cryptographic key by combining the one or more first cryptographic keys and the one or more second cryptographic keys, such that the first node and the second node share knowledge of the combined cryptographic key.

Abstract: A photon source comprising: a quantum dot; and an optical cavity, the optical cavity comprising: a diffractive Bragg grating “DBG”; and a planar reflection layer, the DBG comprising a plurality of concentric reflective rings surrounding a central disk and at least one conductive track extending from the central disk across the plurality of concentric rings, the quantum dot being provided within the central disk and the planar reflection layer being provided on one side of the DBG to cause light to be preferentially emitted from the opposing side of the DBG.

Abstract: An emitter configured to output a sequence of periodic light pulses with different polarisations, the emitter comprising: a beam splitter configured to divide the pulses of a first sequence of pulses, such that each pulse is split between a first path and a second path, the first sequence of pulses having a varying phase and a first polarisation; a polarisation rotator configured to rotate the polarisation state of pulses in one of the first path or the second path with respect to the polarisation state of pulses in the other path; a time delay component configured to provide a time delay such that the first sequence of pulses in the first arm are delayed by one period with respect to the first sequence of pulses in the second arm; an optical combination component configured to combine the delayed first sequence of pulses from the first path with the first sequence of pulses from the second path to produce an output sequence of pulses where each pulse in the output sequence is a combination of a pulse from

Abstract: An emitter configured to output a sequence of periodic light pulses with different polarisations, the emitter comprising: a beam splitter configured to divide the pulses of a first sequence of pulses, such that each pulse is split between a first path and a second path, the first sequence of pulses having a varying phase and a first polarisation; a polarisation rotator configured to rotate the polarisation state of pulses in one of the first path or the second path with respect to the polarisation state of pulses in the other path; a time delay component configured to provide a time delay such that the first sequence of pulses in the first arm are delayed by one period with respect to the first sequence of pulses in the second arm; an optical combination component configured to combine the delayed first sequence of pulses from the first path with the first sequence of pulses from the second path to produce an output sequence of pulses where each pulse in the output sequence is a combination of a pulse from th

Abstract: An optical emitter comprising a primary laser and a plurality of secondary lasers wherein each secondary laser is optically injection locked to said primary laser, the emitter further comprising at least one polarisation controller configured to control the polarisation of the output of at least one of the secondary lasers, the emitter further comprising a combination unit that is configured to combine the outputs of the secondary laser modules into an output signal.

Abstract: A photon detection device, configured to couple to a multicore optical fibre, the device comprising a plurality of detection regions, each detection region being arranged to align with just a single core of the multicore optical fibre when the device is coupled to the multicore optical fibre.

Abstract: An optical module includes: a quantum photonic integrated circuit; a temperature controller; and a housing configured to house the photonic integrated circuit and the temperature controller. The photonic integrated circuit is attached to the temperature controller, such that the photonic integrated circuit is in thermal communication with the temperature controller, and the temperature controller is attached directly to the housing, such that the temperature controller is in direct thermal communication with the housing.

Abstract: An optical system, comprising: an emitter configured to output a first optical signal along a first optical path to an interference unit and to output a second optical signal along a second optical path to the interference unit, the interference unit being configured to interfere the first and second optical signals, wherein the coherence length of the optical signal is longer than the path difference between first and second optical paths, and there is a path difference between the first and second paths of at least 1 km.

Abstract: An optical system, comprising: an emitter configured to output a first optical signal along a first optical path to an interference unit and to output a second optical signal along a second optical path to the interference unit, the interference unit being configured to interfere the first and second optical signals, wherein the coherence length of the optical signal is longer than the path difference between first and second optical paths, and there is a path difference between the first and second paths of at least 1 km.

Abstract: A node for a quantum communication network, said node comprising: a quantum transmitter, said quantum transmitter being adapted to encode information on weak light pulses; a quantum receiver, said quantum receiver being adapted to decode information from weak light pulses; at least three ports adapted to communicate with at least one other node; and an optical switch, said optical switch being configured to selectively connect the quantum transmitter and receiver to the ports such that the switch controls which of the ports is in communication with the quantum transmitter and quantum receiver.

Abstract: An optical device includes a first semiconductor substrate, a reference laser configured to generate coherent light, a plurality of first optical components, a plurality of second optical components, one or more first controllers configured to apply phase control signals to said plurality of first optical components to apply a phase shift, and one or more second controllers configured to apply pulse control signals to said plurality of second optical components such that a light pulse is outputted during a period of time that coherent light is received. The relative phase between emitted light pulses from the plurality of second optical components is controlled by the relative phase shifts applied by the one or more first controllers.

Abstract: An optical module includes: a quantum photonic integrated circuit; a temperature controller; and a housing configured to house the photonic integrated circuit and the temperature controller. The photonic integrated circuit is attached to the temperature controller, such that the photonic integrated circuit is in thermal communication with the temperature controller, and the temperature controller is attached directly to the housing, such that the temperature controller is in direct thermal communication with the housing.