Abstract: A photon emitter including a photon generator configured to generate photons having a first polarization state or a second polarization state, the first polarization state being orthogonal to the second polarization state; and a time delay device which delays photons having the second polarization state with respect to those having the first polarization state.

Abstract: A system for transmitting quantum information comprising a sending unit and a receiving unit, said sending unit comprising an encoder configured to encode a carrier with quantum information by setting a quantum state of the carrier, the quantum state determined according to a first component and a second component, the receiving unit comprising a decoder configured to cancel said second component and decode said quantum information from the carrier.

Abstract: An encoding method, decoding method and a communication method using single photons where information is directly encoded into each photon. In one embodiment at least two out of the three parameters of phases, polarization, and energy are used to encode information. In another embodiment, three or more non-orthogonal states with respect to each parameter are used. A further embodiment is also described which uses selective grouping of the results in order to more clearly detect the presence of an eavesdropper. Apparatus capable of performing the methods are also provided.

Abstract: A semiconductor device comprising a vertical stack of layers, comprising: an active layer configured to support a two dimensional carrier gas having an excess of carriers; source and drain contacts provided to said active layer such that a current can flow between said source and drain contacts through said two dimensional carrier gas; a lower conducting region, wherein said lower contact conducting region is a patterned lower conducting region such that said active layer is suspended across gaps in said lower conducting region and said active layer is physically supported by and suspended between parts of said lower conducting region.

Abstract: A circuit for conditioning the output of a single photon detector, the output of said detector having a stepped electrical output signal with respect to time, the circuit comprising a band pass amplifier, said band pass amplifier having a 3 dB breakpoint equal to and less than the inverse of the expected duration of the rising or falling step of said detector output.

Abstract: A photon source comprising a quantum dot comprising a confined conduction band energy level capable of being populated with at least one carrier and a confined valence band energy level capable of being populated by at least one carrier is provided, the source further comprises supply means for intermittently supplying at least one carrier to the energy levels to create an exciton in the quantum dot, wherein the supply means are configured to regulate the supply of carriers such that as the exciton decays either a single photon or a plurality of single photons each having different distinct energies are emitted during a predetermined time interval. The source is configured to be able to enhance the production of a desired type of exciton and can also be configured to exploit the use of higher order excitons such as biexcitons.

Abstract: A photon source comprising a quantum dot layer having a plurality of quantum dots with an n-modal distribution in emission wavelength, said n-modal distribution in emission wavelength comprising n peaks in a plot of dot density as a function of emission wavelength where n is an integer of at least 2, the photon source further comprising isolating means for isolating the emission from a predetermined number of quantum dots.

Abstract: A photon source for emitting entangled photons, the source comprising: at least one quantum dot having a degenerate exciton level; and exciton creation means to create a biexciton or higher order exciton within the at least one quantum dot.

Abstract: An optical device such as a radiation detector or an optically activated memory includes a barrier region located between two active regions. One or more quantum dots are provided such that a change in the charging state of the quantum dot or dots affects the flow of current through the barrier region. The charging states of the quantum dot is changed by an optical device.

Abstract: A photon source includes a photon source body including quantum dots, a non-insulating layer overlying and in contact with the quantum dots, and an electrical contact that allows electrically activated emission of radiation from at least one of the quantum dots. An active region is defined within the photon source body such that emission is only collected from a dot or a limited number of dots within the active region.

Abstract: A photon emitter comprising:

Abstract: Semiconductor devices are provided which can be configured as optically activated memories or single photon detectors. The devices comprise an active layer with a plurality of quantum dots and an active layer. The devices are configured so that charge stored in the quantum dots affects the transport and/or optical characteristics etc of the active layer.

Abstract: An optical device such as a radiation detector or an optically activated memory comprises a barrier region (11) located between two active regions (9, 15). One or more quantum dots (21) are provided such that a change in the charging state of the quantum dot or dots (21) affects the flow of current through the barrier region (11). The charging states of the quantum dot is changed by optical means.

Abstract: A photon source for emitting entangled photons, the source comprising:

Abstract: A photon source comprising a photon source body, said photon source body comprising a plurality of quantum dots and at least one electrical contact, configured to allow electrically activated emission of radiation from at least one of the quantum dots, the photon source further comprising means for defining an active region within said photon source body such that emission is only collected from a dot or a limited number of dots within said active area.

Abstract: An optical device which can operate as a single photon emitter 1, comprising a three dimensional optical cavity 7 which spatially confines a photon to the order of the photon wavelength in all three dimensions. The cavity 7 is configured to define preferred emission direction for photons entering the cavity. A photon ca be supplied to the cavity using a quantum dot 5. Strong coupling can occur between the cavity 7 and the quantum dot 5 which causes the formation of two hybridised modes. Switching on an off the coupling by irradiating the device with radiation having an energy equal to that of one of the hybridised modes allows the device to act as an optical switch.

Abstract: A photon source comprising a quantum dot comprising a confined conduction band energy level capable of being populated with at least one carrier and a confined valence band energy level capable of being populated by at least one carrier is provided, the source further comprises supply means for intermittently supplying at least one carrier to the energy levels to create an exciton in the quantum dot, wherein the supply means are configured to regulate the supply of carriers such that as the exciton decays either a single photon or a plurality of single photons each having different distinct energies are emitted during a predetermined time interval. The source is configured to be able to enhance the production of a desired type of exciton and can also be configured to exploit the use of higher order excitons such as biexcitons.

Abstract: An encoding method, decoding method and a communication method using single photons where information is directly encoded into each photon. In one embodiment at least two out of the three parameters of phases, polarisation, and energy are used to encode information. In another embodiment, thee or more non-orthogonal states with respect to each parameter are used. A further embodiment is also described which uses selective grouping of the results in order to more clearly detect the presence of an eavesdropper. Apparatus capable of performing the methods are also provided.

Abstract: An optical device for efficient radiation emission having a modulation region with phase matching means (1) for enhancing the phase matching between two different frequency signals propagating in the optical modulation region (1) in response to illumination by at least one incident beam (7, 8), the phase matching means (1), having a spatial variation in its refractive index (5) along the path of the incident radiation beam (7, 8). The device may be configured as a radiation source comprising a frequency conversion member (C2) for emitting a beam of radiation (553) in response to irradiation by one or more input beams (507), the emitted beam (553) having a frequency different to that of the one or more input beams (507), the one or more input beams (507) all being produced within a lasing cavity (defined by M3, M4, M5, M6 and output coupler (523)) and said frequency conversion member (C2) being located within said lasing cavity. The invention also extends to an imaging system using the radiation source.