Device for receiving cryptography key sent by transmitter, has photo diode for detecting arriving photons with beams, and evaluation unit for evaluating signal at photo diode based on required running times of photons and polarization

摘要

The device (1) has a beam splitter (PBS) coupled with two partial beams (S1, S2), which are divided into other two partial beams (S3, S4). A photo diode (PD) detects arriving photons with the latter partial beams. Paths (W1-W4) are connected in four path combinations such that running times (Li, Lk, Lm, Ln) of the photons have measurable running time difference relative together, where the running times are required for the path combinations. An evaluation unit (3) evaluates a signal at the photo diode based on the required running times of the photons and polarization. An independent claim is also included for a method for receiving a cryptography key sent by a transmitter.