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 source comprising: a phase-randomised light source, the phase randomised light source further comprising: a master light source configured to intermittently generate master light pulses, wherein the phase of each generated master light pulse has a random relationship with the phase of each subsequently generated master light pulse, and wherein a first control signal is applicable to the master light source such that the master light source intermittently generates master light pulses, wherein the first control signal comprises a first and a second modulation feature in the period of time that one master light pulse is generated, wherein each phase modulation feature comprises a perturbation in the control signal applied to the master light source; a slave light source, wherein the slave light source is optically coupled to the master light source and is configured to receive master light pulses, and wherein a second control signal is applicable to the slave light source to cause the slave light so

Abstract: A transmitter for a quantum communication system, comprising: a photon source unit comprising a photon source; a first intensity modulator, configured to receive an input light pulse from the photon source unit, the first intensity modulator comprising: a first element, configured to split the input light pulse into two components; a phase modulator, configured to apply a phase shift between the two components; and a second element, configured to interfere the two components; wherein at least one of the first element and the second element is asymmetric.

Abstract: An apparatus for measuring an input signal, the apparatus comprising: a first light source configured to output a sequence of pulses of light, wherein there is a random relationship between the phase of the pulses; a beam splitter having first and second inputs and first and second outputs, said first input being arranged to receive light pulses from said first light source and the second input being arranged to receive said input signal; a differencing circuit adapted to subtract signals obtained from the first and second outputs from each other; and output a value; and a processing circuit adapted to estimate the minimum entropy of said input signal, from the output of the differencing circuit corresponding to a sequence of said light pulses from the first light source.

Abstract: A quantum communication system for distributing a key between first and second units, the system being configured to implement phase-based measurement device independent quantum cryptography, the system comprising first and second units adapted to apply phase shifts to light pulses and a detection unit adapted to cause interference between light pulses received from the first and second units and measure said interference, wherein the first and second units each comprise at least one phase modulator adapted to apply a phase shift, said phase shift comprising a global phase component and a relative phase component, wherein said global phase component represents a phase shift selected randomly in the range from 0° to 360° from a fixed phase reference and said relative phase component is a phase shift selected randomly from 0°, 90°, 180° and 270° from the phase shift introduced by the global phase component.

Abstract: An apparatus for measuring an input signal, the apparatus comprising: a first light source configured to output a sequence of pulses of light, wherein there is a random relationship between the phase of the pulses; a beam splitter having first and second inputs and first and second outputs, said first input being arranged to receive light pulses from said first light source and the second input being arranged to receive said input signal; a differencing circuit adapted to subtract signals obtained from the first and second outputs from each other; and output a value; and a processing circuit adapted to estimate the minimum entropy of said input signal, from the output of the differencing circuit corresponding to a sequence of said light pulses from the first light source.

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: A transmitter for a quantum communication system, comprising: a photon source unit comprising a photon source; a first intensity modulator, configured to receive an input light pulse from the photon source unit, the first intensity modulator comprising: a first element, configured to split the input light pulse into two components; a phase modulator, configured to apply a phase shift between the two components; and a second element, configured to interfere the two components; wherein at least one of the first element and the second element is asymmetric.

Abstract: A component for a quantum communication system, the component comprising: an input section and a decoder section, the input section comprising n waveguides, where n is an integer of at least 2, the decoder section comprising m decoders, where m is an integer of at least 2, each decoder comprising at least one waveguide, the input section and the decoder section being provided on a single substrate such that the waveguides are continuous and integrated between the input section and the decoder section, the waveguides of the input section and the decoder section being arranged such that light pulses enter the waveguides of the decoder section via the waveguides of the input section and the m decoders operate in parallel.

Abstract: A component for a quantum communication system, the component comprising: an input section and a decoder section, the input section comprising n waveguides, where n is an integer of at least 2, the decoder section comprising m decoders, where m is an integer of at least 2, each decoder comprising at least one waveguide, the input section and the decoder section being provided on a single substrate such that the waveguides are continuous and integrated between the input section and the decoder section, the waveguides of the input section and the decoder section being arranged such that light pulses enter the waveguides of the decoder section via the waveguides of the input section and the m decoders operate in parallel.

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: According to one embodiment is a string processor configured to output a biased output string having a first output value and a second output value. The string processor is given an unbiased input string of at least two input values. The string processor has a processing unit and a memory device, the memory device stores a code-word set. The code-word set has a plurality of code-words, each code-word having at least one input value, and each output value has at least one corresponding code-word. The processing unit is configured to: compare a comparison string to the code-word set, wherein the comparison string includes an input from the input string; and assign an output value to the output string when the comparison string matches a code-word. The assigned output value is that to which the matched code-word corresponds.

Abstract: A quantum communication system for distributing a key between first and second units, the system being configured to implement phase-based measurement device independent quantum cryptography, the system comprising first and second units adapted to apply phase shifts to light pulses and a detection unit adapted to cause interference between light pulses received from the first and second units and measure said interference, wherein the first and second units each comprise at least one phase modulator adapted to apply a phase shift, said phase shift comprising a global phase component and a relative phase component, wherein said global phase component represents a phase shift selected randomly in the range from 0° to 360° from a fixed phase reference and said relative phase component is a phase shift selected randomly from 0°, 90°, 180° and 270° from the phase shift introduced by the global phase component.

Abstract: A random number generation system, comprising: a light source configured to generate light pulses and a driving unit configured to drive said light source such that the phase of each light pulse has a random relationship to the phase of each subsequently generated light pulse, and such that each light pulse is generated with at least two local maxima in the temporal intensity profile.

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 detection system for monitoring the intensity of a stream of modulated pulses, the system comprising a controller configured to provide a control signal to a component outputting modulated pulses the control signal controlling the level of modulation for each pulse exiting the component and a detector configured to measure the intensity of the pulses in the stream of pulses exiting the component outputting modulated pulses, wherein the detector comprises a gated detector, the controller being configured to send a gating signal to said detector, wherein said gating signal varies the gain of the detector with the control signal, such that pulses with a selected modulation level can be detected.

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 transmitter for a quantum communication system, the transmitter comprising an interferometer, the interferometer having a first path with a phase modulator and a second path configured such that light pulses entering the interferometer follow either the first path or the second path, the output of the first and second paths being combined, the transmitter further comprising an optical filter positioned such that photons exiting the interferometer pass through the optical filter, the optical filter being configured to restrict the frequency range of pulses passing through the optical filter and temporally broaden the pulses.