Abstract: According to one embodiment, a transmitting device for a quantum key distribution system includes a light source, a beam splitter, an encoder, and a beam combiner. The light source is configured to generate an optical pulse. The beam splitter is configured to split the optical pulse into a signal pulse that travels through a first path and a polarization control pulse that travels through a second path, the second path being different in an optical path length from the first path. The encoder is provided at the first path and is configured to encode information with respect to the signal pulse. The beam combiner is configured to combine the signal pulse passing through the encoder and the polarization control pulse.

Abstract: A coil includes first and second segment conductors, and a welded metal portion where the first and second segment conductors are welded. The first and second segment conductors each include: a fixed portion held in a stator core to extend in a first direction; an inclined portion protruding from the stator core, extending in a second direction inclined with respect to the first direction, and including side surfaces covered with an insulative coating film; and a weld portion that is at a tip of the inclined portion and includes a first surface located within an extension plane in the second direction of one surface of the side surfaces, a second surface contacting the first surface, and a third surface contacting the second surface. The welded metal portion contacts the first, second, and third surfaces of the first segment conductor, and the first and second surfaces of the second segment conductor.

Abstract: A method for welding copper-including members includes laser-welding a first member that includes copper, and a second member that includes copper and is located adjacent to the first member. A welding surface of the first member and a welding surface of the second member are melted by moving an irradiation position of a laser to turn in a spiral shape while approaching a center of the spiral when irradiating the laser on the welding surface of the first member and the welding surface of the second member.

Abstract: According to one embodiment, a quantum communication system includes a transmitting apparatus and a receiving apparatus. The transmitting apparatus includes a plurality of light sources configured to generate a plurality of optical pulses having different wavelengths, an encoder including a single first modulator configured to modulate the optical pulses to encode information, and a transmitting part configured to transmit an optical pulse train including the modulated optical pulses to the receiving apparatus. The receiving apparatus includes a receiving part configured to receive the optical pulse train from the transmitting apparatus, and a decoder configured to obtain information based on the received optical pulse train.

Abstract: According to one embodiment, a quantum communication system includes a transmitting apparatus and a receiving apparatus. The transmitting apparatus includes a plurality of light sources configured to generate a plurality of optical pulses having different wavelengths, an encoder including a single first modulator configured to modulate the optical pulses to encode information, and a transmitting part configured to transmit an optical pulse train including the modulated optical pulses to the receiving apparatus. The receiving apparatus includes a receiving part configured to receive the optical pulse train from the transmitting apparatus, and a decoder configured to obtain information based on the received optical pulse train.

Abstract: According to one embodiment, a transmitting device for a quantum key distribution system includes a light source, a beam splitter, an encoder, and a beam combiner. The light source is configured to generate an optical pulse. The beam splitter is configured to split the optical pulse into a signal pulse that travels through a first path and a polarization control pulse that travels through a second path, the second path being different in an optical path length from the first path. The encoder is provided at the first path and is configured to encode information with respect to the signal pulse. The beam combiner is configured to combine the signal pulse passing through the encoder and the polarization control pulse.