Abstract: Embodiments are disclosed for facilitating quantum computing over classical and quantum communication channels. An example system includes a network interface card (NIC) apparatus. The NIC apparatus includes an optical receiver, an embedded processor, and a network switch. The optical receiver is configured to receive qubit data via a first communication channel associated with quantum communication. The embedded processor is configured to convert the qubit data into binary bit data. The network switch is configured to output the binary bit data via a second communication channel associated with classical network communication.

Abstract: A transmitter Continuous-Variable Quantum Key Distribution (CV-QKD) device stores and transmits a quantum signal over a communication channel. A receiver CV-QKD device receives the quantum signal via the communication channel and via a reception band. The receiver CV-QKD device determines a quantum communication channel. The receiver CV-QKD device communicates the determined quantum communication channel to the transmitter CV-QKD device over an authenticated communication channel. The transmitter CV-QKD device obtains a modified quantum signal by modifying the stored quantum signal based on the determined quantum communication channel. The transmitter CV-QKD device and the receiver CV-QKD device generate a secret key using the modified quantum signal and the received quantum signal.

Abstract: A transmitter Continuous-Variable Quantum Key Distribution (CV-QKD) device stores and transmits a quantum signal over a communication channel. A receiver CV-QKD device receives the quantum signal via the communication channel and via a reception band. The receiver CV-QKD device determines a quantum communication channel. The receiver CV-QKD device communicates the determined quantum communication channel to the transmitter CV-QKD device over an authenticated communication channel. The transmitter CV-QKD device obtains a modified quantum signal by modifying the stored quantum signal based on the determined quantum communication channel. The transmitter CV-QKD device and the receiver CV-QKD device generate a secret key using the modified quantum signal and the received quantum signal.

Abstract: A method and a system for generating independent coherent photons frequency-stabilized to transition of atoms for long-distance quantum communication are provided. The method for generating independent coherent photons frequency-stabilized to transition of atoms for long-distance quantum communication according to the present disclosure, includes generating a photon in a quantum state from a first quantum light source including an alkali atom or an ensemble of alkali atoms therein as a medium, further generating a photon in a quantum state from a second quantum light source spatially separated from the first quantum light source, including the same medium as that of the first quantum light source therein, and oscillating a photon pair obtained by coupling the photons generated by the first and second quantum light sources as a continuous wave coherent photon (CWCP) for quantum communication.

Abstract: A receiver for recognizes blinding attacks in a quantum encrypted channel having an optical fiber. The receiver includes a multipixel detector having a plurality of pixels, and configured to be illuminated by a light beam outputted by the optical fiber. A processing unit connects to the multipixel detector and is configured to determine the presence of a blinding attack if a predetermined number of pixels detects light within a predetermined interval. The receiver recognizes blinding attacks in a quantum encrypted channel and implements a method for recognizing blinding attacks in a quantum encrypted channel.

Abstract: An imaging and quantum cryptography apparatus comprising alight-refracting optical setup (101), a light-directing optical setup (102), an imaging sensor (103) capturing light refracted from the light-refracting optical setup and directed to the imaging sensor by the light-directing optical setup and at least one of a quantum key distribution (QKD) transmitter (104) generating a QKD light signal and transmitting the QKD light signal via the light-directing optical setup and through the light-refracting optical setup and a QKD receiver (105) acquiring and decoding light signals refracted from the light-refracting optical setup and directed to the QKD receiver by the light-directing optical setup. The imaging sensor, the at least one of QKD transmitter and QKD receiver, and the alignment unit, all use the same light-directing optical setup and the same light-refracting optical setup.

Abstract: The invention is directed to a Quantum Random Number Generator comprising an emitting device (110) triggered by a signal representing an input bit x and adapted to generate and send a physical system (130) characterized by one of two possible quantum states determined by said input bit x, a measurement device (120) adapted to detect said physical system, to identify the quantum state of said physical system through an unambiguous state discrimination measurement and to generate an output b first representing whether the quantum state has been identified or not and, if it has been identified, which quantum state among the two possible quantum states was detected by the unambiguous state discrimination measurement to a processing device (140), the processing device (140) being adapted to estimate the entropy of the output b given the probabilities p(b|x) representing the probability of observing output b for a state preparation x, and a randomness extraction device (150) adapted to extract final random bit stre

Abstract: Systems and methods include, responsive to obtaining measurement data from an optical network and determining viability of a plurality of paths based on Signal-to-Noise Ratio (SNR) and availability of the plurality of paths, providing a User Interface (UI) that displays one or more photonic services and a path viability visualization for each of the one or more photonic services, wherein the path viability visualization, for each photonic service, includes visual elements for available paths of the plurality of paths and an indicator associated with each visual element indicative of path viability; and updating the UI responsive to a change in any of the viability and the availability of the plurality of paths. The steps can further include periodically obtaining the measurement data from the optical network and determining the viability of the plurality of paths.

Abstract: A free space optical communications transmitter terminal including an optical source arranged to provide a first beam of light encoding information to be communicated; an optical source arranged to provide photons encoding bits of a key of a Quantum Key Distribution protocol; and an optics arrangement. The first beam and the photons are linearly polarised. The optics arrangement is configured to combine the first beam and the photons into a single, second, beam to be transmitted to a receiver terminal; and transform the linear polarisation of the first beam into one of left and right circular polarisation and transform the linear polarisation of the photons into the other of left and right circular polarisation. A receiver terminal receives the second beam, transforms the circular polarisations into orthogonal linear polarisations, and filters out the linear polarisation of the first beam to allow the photons to pass to a single photon detector.

Abstract: A method includes receiving Bell pairs. Photons are obtained in a Greenberger-Hom-Zeilinger (GHZ) state by providing, to a first beam splitter, a photon from a first Bell pair and a photon from a second Bell pair. The first beam splitter is coupled with a first output channel and a second output channel. Obtaining the photons in the GHZ state further includes providing, to a second beam splitter, a photon from a third Bell pair and a photon from a fourth Bell pair. The second beam splitter is coupled with a third output channel arid a fourth output channel. Obtaining the photons in the GHZ state further includes providing a photon output from the second output channel as a first input to a detector and a photon output in the third output channel a second input to the first detector.

Abstract: An example described herein may involve receiving a temperature measurement associated with an input component, wherein the temperature measurement is received from a temperature sensor, and wherein the temperature measurement indicates a temperature of an input element of the input component; determining that the temperature of the input element satisfies a threshold temperature; and causing an infrared element to emit infrared light in association with a position of the input component. While the infrared element is emitting the infrared light, capture information associated with a user interacting with the input component may be obfuscated.

Abstract: A communications system receives a plurality of input data streams and applies a different orthogonal function to each of the plurality of input data streams. The system processes each of the plurality of input data streams to spatially locate a first group of the plurality of input data streams onto a first carrier signal and to spatially locate a second group of the plurality of input data streams onto a second carrier signal. The system temporally locates the first carrier signal and the second carrier signal onto a third carrier signal and transmits the third carrier signal over a communications link.

Abstract: A security code input may be obfuscated from a thermal imaging device by randomly heating a random set of inputs of an input device. The security code is inputted on an input device, which communicates with a security system to grant or deny access to a user based on an entry of the security code. The input device includes a plurality of hearing elements. The input device may receive an input from the user. A random set of heating elements including one or more heating elements, are generated from the plurality of heating elements. A temperature is determined for the one or more heating elements of the random set of heating elements. The temperature is then applied to the one or more heating elements of the random set of heating elements of the input device.

Abstract: The invention relates to a method for monitoring a detachable fiber-optic connection, especially in a fiber-optic transmission device or system, comprising the steps of transmitting a wanted optical transmission signal carrying information data to be transmitted to at least one fiber-optic connection, a predetermined portion of the power of said optical transmission signal being reflected at the at least one fiber-optic connection depending on the status and properties of the at least one fiber-optic connection, creating a detection signal by detecting said reflected predetermined portion of the power of said optical transmission signal, monitoring and evaluating the detection signal as a function of time and creating a “DETECT” signal if the detection signal or a signal derived from the detection signal reveals a characteristic change in its course in time. Further, the invention relates to a corresponding device adapted to realize this method.

Abstract: A bandwidth control method used in a case where, for example, a first communication device (OLT) allocates a bandwidth for signal transmission to each of a plurality of second communication devices (ONUs) connected to the OLT in a communication system having the OLT and the ONUs includes a sleep controlling of shifting devices among the ONUs that satisfy a predetermined condition into a power saving state, a control-target selecting of selecting control target devices among the ONUs based on a result of performing the sleep controlling, and a bandwidth determining of determining a bandwidth to be allocated to the selected control target devices.

Abstract: An optical network including at least one optical network node that receives an optical signal for either transmission or reception. The optical network node analyzes the optical signal and applies communication protocols necessary for optical transmission or reception of the optical signal to or from the optical network. At least one communication module is coupled to the at least one optical network node either decodes or encodes the optical signal by identifying or adding at least one wavelength to the optical signal for security.

Abstract: The present disclosure relates to fiber optic networks carrying sensitive information such as classified government communications, sensitive financial information, proprietary corporate information, and associated systems and methods for secure transmission where fiber tampering is easily detected. The present invention provides improved security systems and methods for fiber optic communication links. Specifically, a hollow-core photonic bandgap fiber is deployed as a transmission medium. A secure fiber optic communication link is established over the hollow-core photonic bandgap fiber with a monitoring mechanism. The monitoring mechanism is configured to detect large losses and large spectral variability each indicative of loss introduced by malicious intrusion attempts. Further, the monitoring mechanism allows easy differentiation of intrusion relative to normal system variations thereby reducing false positives and missed intrusions.

Abstract: The first photon in single-photon state is divided into two components by the half beam splitter, and the first component is sent to the sender while the second component is sent to the receiver. The sender measures the first component of the first photon when he sends “1”. The sender doesn't measure the first component of the first photon when he sends “0”. The receiver makes the second component of the first photon enter into the Sagnac interferometer, and the receiver also makes the reference light enter into the Sagnac interferometer at the same time. The receiver makes the second component of the first photon interact with the reference light in the nonlinear optical medium arranged in the Sagnac interferometer. The receiver knows the signal from the phase modulation of the reference light caused by the interaction with the second component of the first photon.

Abstract: A communication system comprising an emitter of weak light pulses, a detector which is capable of detecting single photons, and a source of a clock signal, wherein said emitter and detector are synchronized using said clock signal, the system further comprising a frequency divider for said clock signal to produce a reduced frequency clock signal and a clock regenerator for regenerating the original clock signal from the reduced frequency clock signal, the system further comprising a communication channel configured to communicate the clock signal between the emitter and detector, the clock signal being reduced before sending through said channel and reconstructed after it has exited said channel.

Abstract: A method for protecting a data entry device from eavesdropping includes masking a signature of entry resulting from entry of data by a user of the data entry device so as to reduce the detectability of the signature by eavesdropping. The signature may include a temperature differential in the data entry device from data entry by the user and the masking may include controlling the external temperature of the data entry device to reduce temperature differentials left in the data entry device by the user. Alternatively, the signature may include sound waves emitted from the data entry device and the masking may include masking sound waves emitted from the data entry device to reduce the detectability of the sound waves. A system may also be employed for protecting data entry to a data entry device from eavesdropping.

Abstract: In one embodiment, an event impact signature detector may analyze a time series with external events. A data interface 250 may receive a data set 310 representing the time series with external events. A processor 220 may fit the data set 310 into a baseline time series model 330. The processor 220 may iteratively determine each event location 352 for multiple external events 350 affecting the baseline time series model 330. The processor 220 may iteratively solve for each event impact 354 of the multiple external events 350 factoring in interactions between the multiple external events 350.

Abstract: In a PON system in which communication is performed at a plurality of types of transmission rate (L, M, and H) in an upstream direction from a plurality of terminals connected to a station apparatus through optical fibers, within a discovery period for allowing an unregistered terminal to be recognized by station apparatus, the terminal makes a discovery response at one type of transmission rate (L). With this configuration, station apparatus can wait for a discovery response with a receive function being allowed to support transmission rate (L).

Abstract: In a PON system in which communication is performed at a plurality of types of transmission rate (L, M, and H) in an upstream direction from a plurality of terminals connected to a station apparatus through optical fibers, within a discovery period for allowing an unregistered terminal to be recognized by station apparatus, the terminal makes a discovery response at one type of transmission rate (L). With this configuration, station apparatus can wait for a discovery response with a receive function being allowed to support transmission rate (L).

Abstract: The present invention provides methods to mitigate the problems associated with MAC address spoofing and denial of service attacks in an FTTH network system. The MAC address spoofing attack may occur when a computer hacker configures his computer to change the MAC address of a data signal to deceive the receiver of the signal's source address. The denial of service may occur when a computer hacker floods a file server with data packets. The present invention mitigates these attacks by modifying the software of certain components of the FTTH network system to enable the components to insert virtual MAC addresses, tags and codes into the data packets that identify a component of the communication related to the address of the source computer.

Abstract: A technique for securing data transmission via an optical communication line comprising an optical fiber extending between a first network element and a second network element; the technique comprises conveying a first optical signal carrying data via the optical fiber from the first network element towards the second network element at a predetermined optical wavelength, and conveying a second optical signal at the same predetermined optical wavelength via the same fiber in the opposite direction to create within the optical fiber a combined optical signal such that combination of the first and second optical signals is adapted to hamper an unauthorized non-intrusive extraction of the first optical signal from the combined optical signal.

Abstract: Data is encrypted onto an electromagnetic beam by providing an electromagnetic beam having a signal component having a modal state, wherein the signal component is susceptible to accumulation of a geometric phase, and a reference component, transmitted along a path over at least part of which the signal component accumulates a geometric phase by transformation of its modal state from a first to a second modal state, from the second to at least one further modal state, and then back to the first modal state; and modulating with the data the geometric phase so accumulated, by modulating the modal state transformations. Data is decrypted from a received electromagnetic beam by corresponding processing of the received electromagnetic beam and by comparing an overall phase of the signal component with an overall phase of the reference component so as to retrieve the modulation.

Abstract: A system is provided for intercepting signals transmitted between a target served by a fiber optic network and a subscriber. A network is described having a phone switch at a central office configured to receive signals for transmission to and from a target, such as the target of a criminal investigation. A signal received at the central office is assigned to an analog circuit, and a monitoring device configured to intercept and monitor the signal is installed along the analog circuit at a location that allows the monitoring of communications without notifying the target that he is under surveillance. After the signal has been monitored, it is converted to a digital signal for transmission. A method is also provided for intercepting a signal transmitted between the target served by a fiber optic network and a subscriber, such that a monitoring device may be installed without alerting the target.

Abstract: In a PON system in which communication is performed at a plurality of types of transmission rate (L, M, and H) in an upstream direction from a plurality of terminals connected to a station apparatus through optical fibers, within a discovery period for allowing an unregistered terminal to be recognized by station apparatus, the terminal makes a discovery response at one type of transmission rate (L). With this configuration, station apparatus can wait for a discovery response with a receive function being allowed to support transmission rate (L).

Abstract: A secure optical communication system and method are disclosed. Short optical pulses are first modulated with data, then dispersed in time so that they spread out over multiple bit periods, then the desired code is applied to the dispersed pulses. The encoding may include frequency shifts or phase shifts or other. The dispersed optical symbols overlap in time so an applied code chip thus acts on multiple symbols simultaneously. There are generally multiple code chips per dispersed symbol. The coding device does not need to be synchronized to the data rate. Multiple wavelength division multiplexed channels may be encoded simultaneously. The signal propagates to a decoder that is synchronized with encoder to apply a complementary code thereby canceling out the effect of the encoder. The encoder and decoder can be realized by varying the wavelength of an optical pump to a parametric amplifier, allowing for a wide-band frequency shift.

Abstract: A quantum repeater includes a transmitter portion including a source, a set of matter systems, and an optical system. The source produces a probe pulse in a probe state having components with different photon numbers, and each matter system has at least one state that interacts with photons in the probe pulse to introduce a change in a phase space location of the probe state. The optical system can direct the probe pulse for interaction with one of the matter systems and direct light from the matter system for transmission on a first channel.

Abstract: A system is provided for intercepting signals transmitted between a target served by a fiber optic network and a subscriber. A network is described having a phone switch at a central office configured to receive signals for transmission to and from a target, such as the target of a criminal investigation. A signal received at the central office is assigned to an analog circuit, and a monitoring device configured to intercept and monitor the signal is installed along the analog circuit at a location that allows the monitoring of communications without notifying the target that he is under surveillance. After the signal has been monitored, it is converted to a digital signal for transmission. A method is also provided for intercepting a signal transmitted between the target served by a fiber optic network and a subscriber, such that a monitoring device may be installed without alerting the target.

Abstract: A method for protecting a data entry device from eavesdropping includes masking a signature of entry resulting from entry of data by a user of the data entry device so as to reduce the detectability of the signature by eavesdropping. The signature may include a temperature differential in the data entry device from data entry by the user and the masking may include controlling the external temperature of the data entry device to reduce temperature differentials left in the data entry device by the user. Alternatively, the signature may include sound waves emitted from the data entry device and the masking may include masking sound waves emitted from the data entry device to reduce the detectability of the sound waves. A system may also be employed for protecting data entry to a data entry device from eavesdropping.

Abstract: A method and apparatus for securing an optical communication link includes the step of identifying a profile of the link by measuring, at the transmitter, optical back-reflections from optical pulses forwarded to a receiver. The profile is stored at the transmitter. Periodically during operation, such as during key exchange, more optical pulses are forwarded to the receiver, and the back reflections are collected as periodic profiles. The periodic profiles are compared against the stored profiles. Eavesdroppers, such as those who cut the fiber, tap the fiber, or implement a man in the middle attack, may be easily identified because the losses caused by their interference with the fiber will be evident in the periodic profiles.

Abstract: To achieve secure optical communications, a messaging encoding scheme is utilized in which optical communication signals are encoded based upon a known unique code. This encoding methodology allows for the broad transmission across an optical network which will include intended destination. Only the intended destination or destinations will include the necessary unique codes to allow recognition and decoding of the optically encoded message. By providing security in this optical encoding manner, the need for additional message overhead and/or additional systems is thus avoided, thereby providing efficient communication in a secure manner.

Abstract: Photonic signals are tagged with a pre-selected modification, such as a polarization signature to carry data across an obstructed path between sender and receiver. Communication authentication through polarization variation allows for Yuen-Kumar or entangled photon quantum communication protocols to propagate through environmental scattering media such as air, smoke, fog, rain, and water. While ultraviolet light photons are well suited as a carrier for quantum communication signals scattered in air, it is appreciated that visible wavelengths have longer propagation paths in water to convey non-line-of-sight data. A secure signal is scattered by the media and simultaneously communicated to a single recipient or multiple recipients exposed to scattered signal portions. A process of solving the scattering processes through a random scattering media is provided to reconstruct a quantum keyed message at a receiver.

Abstract: A fiber optic communication system including a fiber optic link, a transmitter system and a receiver system. The transmitter system includes a laser source producing a light beam, and a polarization controller receiving the light beam and providing an expected pattern of changing states of polarization to the light beam to output light signals into the fiber optic link to cause the expected pattern of changing states of polarization to be transmitted along the fiber optic link. The receiver system is provided with a polarization analyzer, and a light detector. The light detector receives the light signals transmitted by the transmitter, and forwards data indicative of the light signals to the polarization analyzer. The polarization analyzer analyzing the data with an inverse polarization reference frame and generates an alert based on deviations of the data from the expected pattern of changing states of polarization.

Abstract: Embodiments of optical network evaluation systems and methods are disclosed. One system embodiment, among others, comprises a processor configured with logic to provide a cross layer model of disturbance propagation in an optical network based on a combination of a physical layer model and a network layer model, the physical layer mode based on the disturbance propagation having a threshold effect only on nodes along a route followed by the disturbance.

Abstract: A method for protecting a data entry device from eavesdropping includes masking a signature of entry resulting from entry of data by a user of the data entry device so as to reduce the detectability of the signature by eavesdropping. The signature may include a temperature differential in the data entry device from data entry by the user and the masking may include controlling the external temperature of the data entry device to reduce temperature differentials left in the data entry device by the user. Alternatively, the signature may include sound waves emitted from the data entry device and the masking may include masking sound waves emitted from the data entry device to reduce the detectability of the sound waves. A system may also be employed for protecting data entry to a data entry device from eavesdropping.

Abstract: A system is provided for intercepting signals transmitted between a target served by a fiber optic network and a subscriber. A network is described having a phone switch at a central office configured to receive signals for transmission to and from a target, such as the target of a criminal investigation. A signal received at the central office is assigned to an analog circuit, and a monitoring device configured to intercept and monitor the signal is installed along the analog circuit at a location that allows the monitoring of communications without notifying the target that he is under surveillance. After the signal has been monitored, it is converted to a digital signal for transmission. A method is also provided for intercepting a signal transmitted between the target served by a fiber optic network and a subscriber, such that a monitoring device may be installed without alerting the target.

Abstract: A system is provided for intercepting signals transmitted between a target served by a fiber optic network and a subscriber. A network is described having a phone switch at a central office configured to receive signals for transmission to and from a target, such as the target of a criminal investigation. A signal received at the central office is assigned to an analog circuit, and a monitoring device configured to intercept and monitor the signal is installed along the analog circuit at a location that allows the monitoring of communications without notifying the target that he is under surveillance. After the signal has been monitored, it is converted to a digital signal for transmission. A method is also provided for intercepting a signal transmitted between the target served by a fiber optic network and a subscriber, such that a monitoring device may be installed without alerting the target.

Abstract: An optical communication system is provided. In one embodiment, a source creates a multiplicity of photon pairs, with each photon pair comprising a first photon and a second photon. The first photon is sent to a transmitter, and either remains in the transmitter or is transmitted by the transmitter to a receiver. The second photon is sent to the receiver. Data is decoded by determining a polarization direction and a time of detection of any photon pairs detected at the receiver.

Abstract: An open-path/free-space optical communication system using reflected light has modulated optical or laser sources and provides communication between the modulated source and a detector in an obstructed line-of-sight relationship. The system detects backscattered light impinging on a target illuminated by the source of light. Barrier objects positioned in a line-of-sight path between the source and detector are circumvented and a first device that provides the modulation signal for the source controls a remote second device.

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: An embodiment of the present invention provides an apparatus, comprising a radio frequency identification transceiver adapted for self jammer suppression. The transceiver may further comprise a phase shifter and variable attenuator/variable amplifier adjusted to minimize the power injected into a receive chain by the self jammer. In an embodiment of the present invention the present transceiver may further comprise at least one RF peak power detector to determine the power injected into the receive chain.

Abstract: An optical network monitoring system and method provide for optical network diverting or further legal intercept, operational and/or other monitoring of general or specific transmission information that may be transmitted via a network optical branch. In one embodiment, a splitter within a diverter assembly diverts a portion of a received transmission signal (strength) to an optical receiver or re-transmitter, and outputs a further portion of the signal via a diverter assembly output or further via a re-transmitter or booster. In another embodiment, the splitter is generally matched to the receiver. A further embodiment provides for transferring the diverted portion to a monitoring assembly with which the diverting assembly may be matched, disposed or otherwise integrated, and which may provide for configuring the diverting assembly.

Abstract: A method for creating a logic state for teleporting quantum information using a single photon is described. The method includes receiving a photon with an initial polarization and causing a first semiconductor crystal to have a first spin orientation. The photon interacts with the first semiconductor crystal for producing a resulting polarization dependent upon the first spin orientation. Causing the photon to interact with the first semiconductor crystal generates a maximally entangled state.

Abstract: The subject invention pertains to a method and apparatus for multiplexing in optical fiber communications. The subject invention relates to a method and apparatus for spatial domain modulation in optical wavelengths. In a specific embodiment, the subject invention relates to a spatial domain multiplexer (SDM) for use with an optical fiber. Preferably, the input channels coupled into the fiber optic cable include collimated laser beams. The techniques of the subject invention can be utilized with single mode and multi mode waveguide structures, for example, single mode and multi mode optical fibers. The subject invention is applicable to step index optical fiber and to graded index optical fiber. Applications of the subject technology can include secure data links, for example, which can modulate data such that if the data is intercepted, the data cannot be interpreted. The subject methods and apparatus can also be used in conjunction with other multiplexing techniques such as time-domain multiplexing.

Abstract: A method and apparatus for securing an optical communication link includes the step of identifying a profile of the link by measuring, at the transmitter, optical back-reflections from optical pulses forwarded to a receiver. The profile is stored at the transmitter. Periodically during operation, such as during key exchange, more optical pulses are forwarded to the receiver, and the back reflections are collected as periodic profiles. The periodic profiles are compared against the stored profiles. Eavesdroppers, such as those who cut the fiber, tap the fiber, or implement a man in the middle attack, may be easily identified because the losses caused by their interference with the fiber will be evident in the periodic profiles.

Abstract: The invention provides systems and methods enabling high fidelity quantum communication over long communication channels even in the presence of significant loss in the channels. The invention involves laser manipulation of quantum correlated atomic ensembles using linear optic components (110, 120), optical sources of low intensity pulses (10), interferers in the form of beam splitters (150), and single-photon detectors (180, 190) requiring only moderate efficiencies. The invention provides fault-tolerant entanglement generation and connection using a sequence of steps that each provide built-in entanglement purification and that are each resilient to realistic noise levels. The invention relies upon collective rather single particle excitations in atomic ensembles and results in communication efficiency scaling polynomially with the total length of the communication channel.

Abstract: A method and apparatus for securing an optical communication link includes the step of identifying a profile of the link by measuring, at the transmitter, optical back-reflections from optical pulses forwarded to a receiver. The profile is stored at the transmitter. Periodically during operation, such as during key exchange, more optical pulses are forwarded to the receiver, and the back reflections are collected as periodic profiles. The periodic profiles are compared against the stored profiles. Eavesdroppers, such as those who cut the fiber, tap the fiber, or implement a man in the middle attack, may be easily identified because the losses caused by their interference with the fiber will be evident in the periodic profiles.