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: 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 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 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.

Abstract: For distributing a sequence of symbols, an emitter station transmits to a receiver station quantum systems through a quantum channel. Each of the quantum systems belongs to a set of at least two non-orthogonal quantum states and comprises a group of at least two weak coherent states of an electromagnetic field. Each weak coherent state is in a time bin of duration t. Centers of neighboring weak coherent states in a group are separated by a time T1, with T1 greater than t. Centers of neighboring weak coherent states in adjacent quantum systems are separated by a time T2, with T2 greater than t. In addition, any two weak coherent states separated by T1+T2 are phase coherent. The receiver station comprises an optical subsystem configured to check, for received quantum systems, phase coherence of two weak coherent states of time bins separated by T1+T2.