Abstract: A communication system comprising n transmitters and a receiver, where n is an integer of at least 2, each of said n transmitters comprising a light source and an encoder such that each transmitter is adapted to output an encoded pulse of light, said receiver comprising a first element, the system further comprising a timing circuit, the timing circuit being configured to synchronize the encoded pulses output by the transmitters such that interference between a light pulse sent from the first transmitter and a light pulse from the second transmitter, interfere at the first element, each transmitter further comprising a suppressing element adapted to stop light exiting one of the transmitters such that the system is switchable between a first operation mode where two transmitters output encoded pulses and where both pulses interfere at the interference element and a second mode of operation where just one transmitter transmits light pulses to said receiver, the suppressing element being controlled to stop ligh

Abstract: In a quantum communication system, each transmitter unit has a source of quantum signals. A receiver unit has a quantum receiver with at least one detector configured to detect quantum signals; a first classical communication device; and a passive optical splitter. The transmitter units are optically coupled to the receiver unit through the passive optical splitter. The passive optical splitter is optically coupled to the quantum receiver through a first spatial channel and optically coupled to the first classical communication device through a second spatial channel. The first spatial channel and second spatial channel are separate spatial channels. The passive optical splitter is configured to distribute an inputted optical signal irrespective of its wavelength.

Abstract: A transmitter for a continuous variable quantum communication system, the transmitter including a coherent light source and a first controller to apply a first signal to the coherent light source such that the coherent light source generates coherent light. The transmitter also including a first optical component to produce optical intensity modulation. The transmitter including a second controller to apply a second signal to the optical component such that a light pulse is emitted during a period of time that a first part of the generated light is received, and a light pulse is emitted during a period of time that a second part of the generated light is received. A phase control element and an intensity control element encode information in a continuum of values of the phase and amplitude of an emitted light pulse.

Abstract: An optical device, comprising an optical component, configured to produce optical amplification; a component configured to intermittently supply coherent light to said optical component; and a controller, configured to apply a time varying signal to said optical component such that a plurality of light pulses are emitted during each period of time that said coherent light is received, wherein the plurality of light pulses emitted during each period have a fixed phase relation.

Abstract: A quantum communication system, comprising: a quantum transmitter optically coupled to a first waveguide; a first communication device optically coupled to a second waveguide; a multi-core optical fiber comprising a first core and a second core; a spatial multiplexing unit, configured to optically couple the first waveguide to the first core and the second waveguide to the second core.

Abstract: A transmitter for a continuous variable quantum communication system, the transmitter comprising: a coherent light source; a first controller, configured to apply a first signal to said coherent light source such that said coherent light source generates coherent light; a phase control element, configured to apply perturbations to said first signal, each perturbation producing a phase shift between parts of the generated coherent light; a first optical component, configured to produce optical intensity modulation, wherein said coherent light source is configured to supply said generated light to said optical component; a second controller, configured to apply a second signal to said optical component such that a light pulse is emitted during a period of time that a first part of the generated light is received, and a light pulse is emitted during a period of time that a second part of the generated light is received; an intensity control element, configured to modulate the amplitude of an emitted light pulse;

Abstract: A communication system comprising n transmitters and a receiver, where n is an integer of at least 2, each of said n transmitters comprising a light source and an encoder such that each transmitter is adapted to output an encoded pulse of light, said receiver comprising a first element, the system further comprising a timing circuit, the timing circuit being configured to synchronise the encoded pulses output by the transmitters such that interference between a light pulse sent from the first transmitter and a light pulse from the second transmitter, interfere at the first element, each transmitter further comprising a suppressing element adapted to stop light exiting one of the transmitters such that the system is switchable between a first operation mode where two transmitters output encoded pulses and where both pulses interfere at the interference element and a second mode of operation where just one transmitter transmits light pulses to said receiver, the suppressing element being controlled to stop ligh

Abstract: An interference system, comprising: an interference apparatus, configured such that input light pulses interfere at an interference component; wherein the input of said interference apparatus is provided by a phase-randomized light source, said phase-randomized light source comprising: at least one slave light source; at least one master light source configured to intermittently generate master light pulses such that the phase of each master light pulse has a random relationship to the phase of each subsequently generated master light pulse, further configured to supply said master light pulses to the slave light source; and a controller, configured to apply a time varying drive signal to said at least one slave light source such that just one slave light pulse is generated during each period of time for which a master light pulse is received, such that the phase of each slave light pulse has a random relationship to the phase of each subsequently generated slave light pulse.

Abstract: A quantum communication system, comprising: a plurality of transmitter units, each transmitter unit comprising a source of quantum signals; a receiver unit, comprising: a quantum receiver, comprising at least one detector configured to detect quantum signals; and a first classical communication device; and a passive optical splitter, wherein the plurality of transmitter units are optically coupled to the receiver unit through the passive optical splitter, wherein the passive optical splitter is optically coupled to the quantum receiver through a first spatial channel and optically coupled to the first classical communication device through a second spatial channel, and wherein the passive optical splitter is configured to distribute an inputted optical signal irrespective of its wavelength.

Abstract: A quantum communication system, comprising: a quantum transmitter optically coupled to a first waveguide; a first communication device optically coupled to a second waveguide; a multi-core optical fibre comprising a first core and a second core; a spatial multiplexing unit, configured to optically couple the first waveguide to the first core and the second waveguide to the second core.

Abstract: An interference system, comprising: an interference apparatus, configured such that input light pulses interfere at an interference component; wherein the input of said interference apparatus is provided by a phase-randomised light source, said phase-randomised light source comprising: at least one slave light source; at least one master light source configured to intermittently generate master light pulses such that the phase of each master light pulse has a random relationship to the phase of each subsequently generated master light pulse, further configured to supply said master light pulses to the slave light source; and a controller, configured to apply a time varying drive signal to said at least one slave light source such that just one slave light pulse is generated during each period of time for which a master light pulse is received, such that the phase of each slave light pulse has a random relationship to the phase of each subsequently generated slave light pulse.

Abstract: An optical device, comprising an optical component, configured to produce optical amplification; a component configured to intermittently supply coherent light to said optical component; and a controller, configured to apply a time varying signal to said optical component such that a plurality of light pulses are emitted during each period of time that said coherent light is received, wherein the plurality of light pulses emitted during each period have a fixed phase relation.

Abstract: A photon detection system is provided comprising a photon detector, configured to detect photons during intervals when in a receiving state and to output a signal when a photon is received, a controller, configured to generate a time varying gating signal wherein said gating signal switches said detector between the receiving state and a non-receiving state, said controller being configured to receive and process information relating to the times photons are expected to arrive at said detector, the controller being configured to generate the gating signal such that the photon detector is in the receiving state for intervals when photons are expected and also in the receiving state for additional intervals between the intervals when the photons are expected; a detection module, configured to distinguish between when the output signal from the photon detector corresponds to an interval when photons are expected and said additional intervals.

Abstract: A modulation unit for a quantum communication system, wherein said modulation unit comprises an optical component configured to cause a delay between photons with different polarisation modes and a phase modulator, the optical component comprising a birefringent optical material, wherein the birefringent optical material supports the transmission of photons with a first polarisation mode and a second polarisation mode, wherein the optical path length for photons propagating with the first polarisation mode is different to the optical path length of photons propagating with the second polarisation mode, photons with the first polarisation mode having an orthogonal polarisation to those with the second polarisation mode, the phase modulator being configured to apply a further phase difference between photons with the first and second polarisation mode which pass through said modulation unit.