Abstract: An optical power limiter, a method of fabricating the optical power limiter, a method of limiting optical power, a method of upper bounding information leakage in quantum cryptography, and a quantum cryptography system. The optical power limiter comprises an optical input port; an optical output port; an effective medium disposed between the input port and the output port; and a diaphragm disposed between the effective medium and the output port; wherein the effective medium has a thermo-optic coefficient such that a light beam entering the effective medium from the direction of the input port experiences a refractive index gradient in a direction perpendicular to a propagation direction in the effective medium as a result of absorption; and wherein the diaphragm is disposed in a path of the light beam for limiting how much of the light beam reaches the output port.

Abstract: An optical power limiter, a method of fabricating an optical power limiter, an optical device or system comprising an optical power limiter, and a method of limiting optical power using on optical power limiter.

Abstract: A method may include: a first verifier receiving a request for position verification comprising a claimed position from a prover electronic device; the first verifier generating two first bitstrings and sending one of the bitstrings to a second verifier; the prover preparing two entangled quantum systems and sending one of the quantum systems to the first verifier; the first verifier measuring the first quantum system; each of the first verifier and the second verifier sending one of the bitstrings to the prover electronic device so that they arrive at the claimed position at the same time; the prover electronic device measuring the second quantum system and sending responses to the two verifiers with the measurement; the first verifier confirming that the responses were received within an expected time window and are valid.

Abstract: A method may include: a first verifier receiving a request for a claimed position verification from a prover; the first verifier randomly generating a first bitstring and a second bitstring; the first verifier sending the first bitstring and the second bitstring to a second verifier; the first verifier preparing a quantum system and sending the quantum system to the prover; the first verifier sending the first bitstring to the prover; the second verifier sending the second bitstring to the prover such that the first bitstring and the second bitstring arrive at the claimed position at the same time; the first verifier validating a response received from the prover; and the first verifier confirming that the response was received within an expected time window.

Abstract: A system may include: a first electronic device that receives service classical data and key management system classical data from a first quantum layer, and classical data from a classical data layer, a first multiplexer/demultiplexer that multiplexes the service classical data, the key management system classical data, and the classical data into multiplexed classical data, and the first circulator receives the multiplexed classical data at a first port and routes the multiplexed classical data to a fiber optic channel via a second port. A second circulator at a second electronic device receives the multiplexed classical data from the fiber optic channel on a second port, and routes the multiplexed classical data to the second multiplexer/demultiplexer on a third port, and a second multiplexer/demultiplexer demultiplexes and outputs the service classical data, the key management system classical data, and the classical data.

Abstract: A method of using a quantum random number generator, QRNG, for security applications, a system for security applications, and a user device for a system for security applications. The method comprises the steps of generating one or more quantum keys using the QRNG; storing, using a secure network, corresponding sets of the quantum keys in a server located at a controlled access location and in a quantum key token, QKT, for a user, respectively; and using the corresponding sets of quantum keys for secure transmission between the server and a user device comprising the QKT when outside the secure network or for access control to the controlled access location.

Abstract: A method of encoding quantum information on one or several degrees of freedom of coherent states of photons of a baseband input optical signal, a quantum transmitter, and a computer-readable medium. The quantum transmitter comprises a modulator configured to encode quantum information on one or several degrees of freedom of coherent states of photons of a baseband input optical signal using sideband modulation of the baseband optical input signal.

Abstract: A method for providing a semi-device-independent random output signal, and a system for providing a semi-device-independent random output signal. The method comprises the steps of providing respective coherent laser signals of a same optical mode in a signal arm and a local oscillator arm between a quantum signal source, Alice, and at a quantum signal detector, Bob; Alice and Bob randomly selecting operation in a test mode or a randomness generation mode for each of n rounds; generating a raw random string from bit values bi of rounds in which randomness generation mode was chosen, and using rounds in which test mode was chosen to estimate an entropy of the raw random string.

Abstract: A method of using a quantum random number generator, QRNG, for security applications, a system for security applications, and a user device for a system for security applications. The method comprises the steps of generating one or more quantum keys using the QRNG; storing, using a secure network, corresponding sets of the quantum keys in a server located at a controlled access location and in a quantum key token, QKT, for a user, respectively; and using the corresponding sets of quantum keys for secure transmission between the server and a user device comprising the QKT when outside the secure network or for access control to the controlled access location.

Abstract: A method of encoding quantum information on one or several degrees of freedom of coherent states of photons of a baseband input optical signal, a quantum transmitter, and a computer-readable medium. The quantum transmitter comprises a modulator configured to encode quantum information on one or several degrees of freedom of coherent states of photons of a baseband input optical signal using sideband modulation of the baseband optical input signal.

Abstract: An optical power limiter, a method of fabricating the optical power limiter, a method of limiting optical power, a method of upper bounding information leakage in quantum cryptography, and a quantum cryptography system. The optical power limiter comprises an optical input port; an optical output port; an effective medium disposed between the input port and the output port; and a diaphragm disposed between the effective medium and the output port; wherein the effective medium has a thermo-optic coefficient such that a light beam entering the effective medium from the direction of the input port experiences a refractive index gradient in a direction perpendicular to a propagation direction in the effective medium as a result of absorption; and wherein the diaphragm is disposed in a path of the light beam for limiting how much of the light beam reaches the output port.

Abstract: A measurement-device-independent (MDI) quantum key distribution (QKD) network, a method of operating an MDI QKD network comprising a common server and a plurality of user systems, a user system for a MDI QKD network, and a method of operating a user system for a MDI QKD network. The method of operating an MDI QKD network comprising a common server and a plurality of user systems comprises the steps of performing optical pulse generation and distribution using a laser source at the common server; receiving the optical pulses at the user systems from the common server; modulating the optical pulses at the user systems for quantum communication; re-transmitting the modulated optical pulses from the user systems to the common server; and using an energy bounding component at each of the user system for limiting Trojan horse attack (THA).

Abstract: A quantum random number generation (QRNG) system includes a single-photon or equivalent single-photon light source; a beam splitter arranged to direct output from the light source to a first homodyne detector having a first local oscillator and a second homodyne detector having a second local oscillator; and a signal control and processing unit. The signal control and processing unit is configured to: vary the phases of the first and second local oscillators; receive, from the first and second homodyne detectors, a plurality of measurements of the output, said plurality of measurements being dependent on the intensity of the light source and the phases of the first and second local oscillators; determine, from the plurality of measurements, whether the CHSH inequality is satisfied; and output one or more random numbers based on whether the CHSH inequality is satisfied.