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: 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 nod

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 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 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 apparatus for use in assessing strength of at least one knee flexor muscle of a subject, the apparatus including a support, two securing members, each securing member securing a respective lower leg of the subject in a position that in use is substantially fixed relative to the support and at least one sensor, which in use senses a force indicative of the strength of the at least one knee flexor muscle in at least one leg of the subject while the subject performs an eccentric contraction of the at least one knee flexor muscle.

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 apparatus for use in assessing strength of at least one knee flexor muscle of a subject, the apparatus including a support, two securing members, each securing member securing a respective lower leg of the subject in a position that in use is substantially fixed relative to the support and at least one sensor, which in use senses a force indicative of the strength of the at least one knee flexor muscle in at least one leg of the subject while the subject performs an eccentric contraction of the at least one knee flexor muscle.

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: 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: 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 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: 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: A method for using a photon source, which includes a semiconductor structure having a first light emitting diode region, a second region including a quantum dot, a first voltage source, and a second voltage source, is provided. The method includes steps of applying an electric field across said first light emitting diode region to cause light emission by spontaneous emission, wherein the light emitted from said first light emitting diode region is absorbed in said second region and produces carriers to populate said quantum dot; and applying a tuneable electric field across said second region to control the emission energy of said quantum dot, wherein the light emitted from the second region exits said photon source.

Abstract: An optical source including: a phase-randomised light source including a master light source configured to intermittently generate master light pulses; a slave light source optically coupled to the master light source and configured to receive the master light pulses, and that generates a sequence of slave light pulses during each period of time that a master light pulse is received; and an interferometer optically coupled to the slave light source and configured to receive sequences of slave light pulses, delay the received sequences by the first time interval to form delayed sequences of slave light pulses, interfere the received sequences with the delayed sequences, such that pulses from a received sequence interfere with adjacent pulses of the delayed sequence, and output interfered pulses including first and second output pulses that have a first and second predetermined amplitude respectively and a predetermined relative phase between them.

Abstract: An optical system comprising a first emitter and a receiver, said first emitter comprising an encoding unit configured to encode information using phase on a first optical information signal, said first information signal having a single first wavelength, said emitter being configured to output a reference signal, said reference signal having a reference wavelength which is different to the first wavelength, the emitter further comprising a multiplexer configured to multiplex the first information signal and the reference signal to produce a multiplexed first signal and output the multiplexed first signal to a communication channel said receiver comprising: a de-multiplexer configured to de-multiplex the multiplexed first signal received from the emitter to extract the first information signal and the reference signal; a decoder configured to decode the phase information in the first information signal; and a phase compensation unit configured to estimate the phase change of the first information signal c

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.