Abstract: A photon source comprising a quantum structure capable of defining one or more quantum levels such that a photon may be emitted from the quantum structure due to a transition between at least two quantum levels, a control signal configured to vary the transition energy, the transition energy being the energy separation between the at least two quantum levels; and a laser input beam configured to irradiate the quantum structure, the control signal being configured to bring the transition energy into resonance with the laser input beam and out of resonance with the laser input beam, such that the transition energy is resonant with the energy of the laser input beam for a time less than the time to output two photons from the transition.

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 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 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: An optoelectronic system comprising a first member and a second member, said first member and said second member comprising a plurality of layers, wherein each member has a profiled mating surface, the first member being connected to the second member such that the growth direction of the layers of the first member are orthogonal to the growth direction of the layers of the second member and the profiled mating surfaces fit together, the first member comprises a waveguide circuit comprising a waveguide and the second member comprises an optoelectronic device with its own optical output which is connected to the waveguide of the first member, the first and second members also being electrically connected.

Abstract: An optical measuring device for measuring a measurement region, the optical device comprising a photonic chip with an interferometer defined on said chip, said interferometer comprising first and second waveguides on said photonic chip and an interference region, wherein the first and second waveguides carry signals from the interference region to the sample region and back to the interference region, the device further comprising a phase adjusting unit configured to vary a phase difference between the signals in the first and second waveguides reflected by the measurement region.

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 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 photon detection device and method of fabricating a photon detection device are provided. The photon detection device comprises a first input terminal for receiving a DC input voltage, a second input terminal for receiving an AC input voltage and a bias tee connected to the first and second input terminals and configured to combine the AC and DC input voltages to form a combined voltage on an output of the bias tee. A first single photon detector is connected to the output of the bias tee and configured to receive the combined voltage from the bias tee, register a detection signal based on only a single photon being incident on the first single photon detector and output the detection signal indicative of the detected photon. A first output terminal is connected to an output of the first single photon detector for outputting the detection signal. The photon detection device is formed in a single integrated circuit.

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 optical system comprising a charged quantum dot having, a charged carrier, first and second ground state levels and a plurality of excited state levels, the first and second ground state energy levels having different spin states such that the said charged carrier cannot transfer between the first and second ground state energy levels without changing its spin state, the system further comprising a controller adapted to control a first radiating beam with energy not more than 100 micro-eV from a first transition within said quantum dot from a first ground state level to a selected excited state level from the plurality of excited state levels to, the system being adapted to enhance the decay rate of a second transition within said quantum dot from the selected excited state level to a second ground state level, but not a first transition, such that a photon is produced due to scattering of a photon from the first radiating beam, wherein the controller is adapted to irradiate the quantum dot with the fir

Abstract: An optoelectronic system comprising a first member and a second member, said first member and said second member comprising a plurality of layers, wherein each member has a profiled mating surface, the first member being connected to the second member such that the growth direction of the layers of the first member are orthogonal to the growth direction of the layers of the second member and the profiled mating surfaces fit together, the first member comprises a waveguide circuit comprising a waveguide and the second member comprises an optoelectronic device with its own optical output which is connected to the waveguide of the first member, the first and second members also being electrically connected.

Abstract: A photon source, comprising: a semiconductor structure, said semiconductor structure comprising: a first light emitting diode region; and a second region comprising a quantum dot; the photon source further comprising: a first voltage source configured to apply an electric field across said first light emitting diode region to cause light emission; a second voltage source configured to apply a tuneable electric field across said second region to control the emission energy of said quantum dot; wherein the semiconductor structure is configured such that light emitted from said first light emitting diode region is absorbed in said second region and produces carriers to populate said quantum dot; and wherein the photon source is configured such that light emitted from the second region exits said photon source.

Abstract: An optical system comprising a charged quantum dot having, a charged carrier, first and second ground state levels and a plurality of excited state levels, the first and second ground state energy levels having different spin states such that the said charged carrier cannot transfer between the first and second ground state energy levels without changing its spin state, the system further comprising a controller adapted to control a first radiating beam with energy not more than 100 micro-eV from a first transition within said quantum dot from a first ground state level to a selected excited state level from the plurality of excited state levels to, the system being adapted to enhance the decay rate of a second transition within said quantum dot from the selected excited state level to a second ground state level, but not a first transition, such that a photon is produced due to scattering of a photon from the first radiating beam, wherein the controller is adapted to irradiate the quantum dot with the fir

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.