An optical transmitter for quantum key distribution includes a plurality of spatially separated light sources configured to emit a light signal with the same wavelength. Each light source emits a light signal with a unique encoding. A beam combiner receives the light signals from the plurality of light sources and combines the received light signals into a combined light signal. A spatial filter is optically coupled to the beam combiner and includes an aperture that receives the combined light signal and emits a filtered light signal. The aperture has an aperture diameter less than or equal to the specified wavelength. A collimator is optically coupled to the spatial filter and receives the filtered light signal and emits a collimated light signal. An output aperture receives the collimated light signal and outputs the collimated light signal as an output light signal towards an optical receiver.

A photon entanglement system is disclosed which includes a plurality of remote nodes (Nodes A.sub.i and Node B.sub.i) each without a quantum memory; and a central entangling node (Node C) in both quantum and classical communication with the remote Nodes configured to provide photon entanglement therebetween, and includes a first and second broadband photon generators each adapted to generate sets of photon pairs at: i) random times within time-bins, and ii) random frequency bins, wherein one photon of each pair set is transmitted to an associated remote node over quantum channels, and a multiplexed Bell-state analyzer configured to receive another photon of the pair, wherein if the received photons arrive at about same time, then the received photons are marked as being entangled by the controller which communicates the associated time-bin to the associated remote nodes and thereby entangling their associated photons.

A photon entanglement system is disclosed which includes a plurality of remote nodes (Nodes A.sub.i and Node B.sub.i) each without a quantum memory; and a central entangling node (Node C) in both quantum and classical communication with the remote Nodes configured to provide photon entanglement therebetween, and includes a first and second broadband photon generators each adapted to generate sets of photon pairs at: i) random times within time-bins, and ii) random frequency bins, wherein one photon of each pair set is transmitted to an associated remote node over quantum channels, and a multiplexed Bell-state analyzer configured to receive another photon of the pair, wherein if the received photons arrive at about same time, then the received photons are marked as being entangled by the controller which communicates the associated time-bin to the associated remote nodes and thereby entangling their associated photons.

A quantum entanglement communication service can be provided by detecting a request to access data stored at a first computer. In response to detecting the data access request, a request can be generated to request that a server computer generate an entangled particle pair. Measurement data can be received, the measurement data corresponding to a measurement observed after interacting a first bit of a token stored at a second computer with a first entangled particle from the entangled particle pair. An operation to perform on a second entangled particle of the entangled particle pair at the first computer can be determined and performed. A state of the second entangled particle can be measured to obtain a value, and a bit string can be generated, where the bit string can include a number that corresponds to the value.

A quantum entanglement communication service can be provided by detecting a request to access data stored at a first computer. In response to detecting the data access request, a request can be generated to request that a server computer generate an entangled particle pair. Measurement data can be received, the measurement data corresponding to a measurement observed after interacting a first bit of a token stored at a second computer with a first entangled particle from the entangled particle pair. An operation to perform on a second entangled particle of the entangled particle pair at the first computer can be determined and performed. A state of the second entangled particle can be measured to obtain a value, and a bit string can be generated, where the bit string can include a number that corresponds to the value.

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.

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.

Disclosed is a time division quadrature homodyne CV QKD system, and a continuous variable quantum key distribution system which includes: a transmitter generating an optical pulse of quantum state data by using continuous light according to data of a transmission target encryption key; and a receiver separating the optical pulse received from a channel into two paths and fixing phases of two signals having a time difference of one period of the optical pulse to orthogonal phases, and then generating bit information through state detection by a time division homodyne detection from interacted signals.

Disclosed is a time division quadrature homodyne CV QKD system, and a continuous variable quantum key distribution system which includes: a transmitter generating an optical pulse of quantum state data by using continuous light according to data of a transmission target encryption key; and a receiver separating the optical pulse received from a channel into two paths and fixing phases of two signals having a time difference of one period of the optical pulse to orthogonal phases, and then generating bit information through state detection by a time division homodyne detection from interacted signals.

A system includes a quantum light device comprising a light source configured to emit a plurality of pairs of photons, wherein each pair of photons of the plurality of pairs of photons occupies a quantum entangled state. The system also includes optical circuitry configured to receive a first set of photons and a second set of photons. A set of photon detectors may receive the first set of photons and the second set of photons from the optical circuitry. Additionally, the system may include processing cirucitry configured to determine, based on a set of time signals corresponding to each photon detector of the set of photon detectors, whether a time delay value exists in which a Clauser, Home, Shimony and Holt (CHSH) parameter is greater than a threshold CHSH parameter value.