Abstract: A quantum cryptographic key distribution system, including: an optical source, which generates a plurality of optical pulses; an optical beam splitter, which generates, starting from each optical pulse, a first and a second optical sub-pulse; a first and a second peripheral device; and an optical path having a first and a second end connected to the optical beam splitter, the optical path extending through the first and second peripheral devices and being traversed in opposite directions by the first and second optical sub-pulses. The peripheral device randomly phase shifts the second optical sub-pulse by a first phase, and the second peripheral device randomly phase shifts the first optical sub-pulse by a second phase. Furthermore, the optical path is such as to cause interference in the first optical beam splitter between the first and second optical sub-pulses, as a function of first and second phases.

Abstract: A method for estimating the noise of a two-photon entangled state, including generating pairs of photons; for each pair of photons, defining a first polarization measurement, associated with a first angle, and defining a second polarization measurement, associated with a second angle. The method includes generating a first string of polarization measurements and a first string of angles; generating a second string of polarization measurements and a second string of angles; generating a first uncorrelated substring, formed by the polarization measurements of the first string associated with angles that are different from the corresponding angles of the second string of angles; generating a second uncorrelated substring, formed by the polarization measurements of the second string associated with angles that are different from the corresponding angles of the first string of angles; and determining an estimate of the noise on the basis of the first and the second uncorrelated substrings.

Abstract: An interferometer for controlling the coalescence of a pair of photons, including: an optical source, which generates a first and a second pump pulse coherent with each other and shifted in time by a delay; and a first interferometric stage, which receives the first pump pulse and generates an antisymmetric state with two coalescent photons (1/?{square root over (2)}(|21,02?|01,22)). The interferometer also includes a second interferometric stage, which receives the second pump pulse and generates a symmetric state with two coalescent photons (1/?{square root over (2)}·(|21,02+|01,22)), the first and the second interferometric stages being connected in a manner such that the interferometer outputs a final state equal to a weighted sum of the antisymmetric state and of the symmetric state (1/?{square root over (2)}·(|21,02+|01,22)+ei?·1/?{square root over (2)}·(|21,02?|01,22)), the weights of the sum being a function of the delay.

Abstract: A quantum cryptographic key distribution system, including: an optical source which generates a plurality of optical pulses; an optical beam splitter, which generates, starting from each optical pulse, a first and a second optical sub-pulse; a first and a second peripheral device; and an optical path having a first and a second end connected to the optical beam splitter, the optical path extending through the first and second peripheral devices and being traversed in opposite directions by the first and second optical sub-pulses. The peripheral device randomly phase shifts the second optical sub-pulse by a first phase, and the second peripheral device randomly phase shifts the first optical sub-pulse by a second phase. Furthermore, the optical path is such as to cause interference in the first optical beam splitter between the first and second optical sub-pulses, as a function of first and second phases.

Abstract: Described herein is a method for determining second-order nonlinear optical coefficients of a material. The method envisages the steps of providing a specimen made at least in part of the material, causing a first optical signal and a second optical signal having, respectively, a first pulsation and a second pulsation, and a first polarization state and a second polarization state, to impinge upon the specimen in such a way that the specimen generates a second-harmonic optical signal having a third pulsation equal to the sum of the first and second pulsations, and a third polarization state that is a function of the first and second polarization states. The method further envisages the step of determining a plurality of measurements of power corresponding to the second-harmonic optical signal, and the step of determining the second-order nonlinear optical coefficients on the basis of the plurality of measurements of power.

Abstract: A method for estimating the noise of a two-photon entangled state, including generating pairs of photons; for each pair of photons, defining a first polarization measurement, associated with a first angle and defining a second polarization measurement, associated with a second angle. The method includes generating a first string of polarization measurements and a first string of angles; generating a second string of polarization measurements and a second string of angles; generating a first uncorrelated substring, formed by the polarization measurements of the first string associated with angles that are different from the corresponding angles of the second string of angles; generating a second uncorrelated substring, formed by the polarization measurements of the second string associated with angles that are different from the corresponding angles of the first string of angles; and determining an estimate of the noise on the basis of the first and the second uncorrelated substrings.

Abstract: The invention concerns a cryptographic key distribution system comprising a server node, a repeater network connected to the server node through a quantum channel, and a client node connected to the repeater network through a quantum channel; wherein in use: the repeater network and the client node cooperatively generate a transfer quantum key which is supplied to a system subscriber by the client node; the server node and the repeater network cooperatively generate a link quantum key; the repeater network encrypts the link quantum key based on the transfer quantum key and sends the encrypted link quantum key to the system subscriber through a public communication channel; the server node encrypts a traffic cryptographic key based on the link quantum key and a service authentication key and sends the encrypted traffic cryptographic key to the system subscriber through a public communication channel.

Abstract: Optical logic gate having a second-harmonic generator element that receives a first and a second optical input signal respectively having a first and a second angular frequency and respectively having a first and a second polarization, and which provides a second-harmonic optical signal having a third angular frequency and a third polarization. The third angular frequency is equal to the sum of the first and the second angular frequency. The third polarization is a function of the first and the second polarization. The second-harmonic generator element includes a second-harmonic generator layer in a material having a non-null second-order optical tensor.

Abstract: The invention concerns a or key distribution system comprising a server node, a repeater network connected to the server node through a quantum channel, and a client node connected to the repeater network through a quantum channel; wherein in use the repeater network and the client node cooperatively generate a transfer quantum key which is supplied to a system subscriber by the client node; the server node and the repeater network cooperatively generate a link quantum key; the repeater network encrypts the link quantum key based on the transfer quantum key and sends the encrypted link quantum key to the system subscriber through a public communication channel; the node encrypts a traffic cryptographic key based on the link quantum key and a service an key and sends the encrypted traffic cryptographic key to the system subscriber through a public communication channel.

Abstract: An interferometer for controlling the coalescence of a pair of photons, including: an optical source, which generates a first and a second pump pulse coherent with each other and shifted in time by a delay; and a first interferometric stage, which receives the first pump pulse and generates an antisymmetric state with two coalescent photons (1/?{square root over (2)}(|21,02?|01,22)). The interferometer also includes a second interferometric stage, which receives the second pump pulse and generates a symmetric state with two coalescent photons (1/?{square root over (2)}·(|21,02+|01,22)), the first and the second interferometric stages being connected in a manner such that the interferometer outputs a final state equal to a weighted sum of the antisymmetric state and of the symmetric state (1/?{square root over (2)}·(|21,02+|01,22)+ei?·1/?{square root over (2)}·(|21,02?|01,22)), the weights of the sum being a function of the delay.

Abstract: Described herein is a method for determining second-order nonlinear optical coefficients of a material. The method envisages the steps of providing a specimen made at least in part of the material, causing a first optical signal and a second optical signal having, respectively, a first pulsation and a second pulsation, and a first polarization state and a second polarization state, to impinge upon the specimen in such a way that the specimen generates a second-harmonic optical signal having a third pulsation equal to the sum of the first and second pulsations, and a third polarization state that is a function of the first and second polarization states. The method further envisages the step of determining a plurality of measurements of power corresponding to the second-harmonic optical signal, and the step of determining the second-order nonlinear optical coefficients on the basis of the plurality of measurements of power.

Abstract: Optical logic gate having a second-harmonic generator element that receives a first and a second optical input signal respectively having a first and a second angular frequency and respectively having a first and a second polarization, and which provides a second-harmonic optical signal having a third angular frequency and a third polarization. The third angular frequency is equal to the sum of the first and the second angular frequency. The third polarization is a function of the first and the second polarization. The second-harmonic generator element includes a second-harmonic generator layer in a material having a non-null second-order optical tensor.