Abstract: A system for generating a biased random bit stream, wherein said biased bit stream has different predetermined probabilities of occurrence for bit “0” and bit “1”, said system comprising: a true random generator unit configured to output a true random bit stream, a pseudo random generator unit configured to output a pseudo random bit stream, said pseudo random bit stream comprising n bit words, where n is an integer of at least two; a combining unit configured to combine a bit from said true random generator unit with an n-bit word from said pseudo random generator unit to output a processed n-bit word; and an output unit configured to generate an output bit value from said processed n-bit word using a function, wherein said function is selected to control the probabilities of occurrence of the bit “0” values and bit “1” values to be the predetermined probabilities of occurrence.

Abstract: An optical device comprises a light source, an intensity control element (adjustable between an on-state and an off-state), an optical channel, and an optical component. The light source supplies an optical pulse to the intensity control element, which modulates an intensity of the received pulse and to provides the modulated pulse to the channel. The intensity of the modulated pulse is higher when the intensity control element is in the on-state than in the off-state. The optical component receives the modulated pulse from the channel. The optical intensity modulator is configured such that at least a portion of the pulse is modulated in the on-state, the leading edge of said portion exits the intensity modulator at a first time, and the intensity modulator is in the off-state at a second time which is twice the propagation time measured from to the first time.

Abstract: A combining unit for combining a first optical input and a second optical input, the first optical input comprising a first polarisation maintaining fibre “PMF” having a fast optical axis and a slow optical axis, the second optical input comprising a second PMF having a fast optical axis and a slow optical axis, the combining unit being configured to combine the first optical input with the second optical input in free space such that the fast and slow optical axis of the first PMF and the second PMF are rotated with respect to one another by a non-zero angle to produce a combined signal.

Abstract: A photonic assembly comprising: a first section, the first section comprising a first substrate; and a second section, the second section comprising a second substrate; wherein the photonic assembly comprises an interferometer, the interferometer comprising a plurality of passive photonic elements and a phase modulator; wherein the phase modulator is provided on the second section; and wherein the plurality of passive photonic elements are provided on the first section.

Abstract: A photon detection system comprising an avalanche photodiode configured to generate a photodiode signal in response to an incident photon. The photon detection system also comprises a biasing circuit configured to supply a gating signal to the avalanche photodiode. The gating signal is a periodic signal configured to reverse bias the avalanche photodiode above and below its breakdown voltage for photon detection during each period. The photon detection system further comprises a non-reflective filter circuit configured to receive, at an input port, the photodiode signal, and provide, at a first output port, a first filtered output signal by applying a low-pass filter with a first cut-off frequency to the received photodiode signal.

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: 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: 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: 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: 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.