In the field of "quantum communication"—that is, performing communication by means of one-to-one interaction of photons—"quantum cryptography" is technique that achieves encryption by applying Heisenburg's Uncertainty Principle (namely, a theory stating that if one kind of physical quantity from among multiple kinds of physical quantities possessed by a single photon is measured, the other kinds of physical quantity become no longer measurable). Differing from the common type of encryption using a sequence of numbers—for example, in that attempted eavesdropping along the communication route renders the contents meaningless and instances of eavesdropping can be detected—quantum cryptography is said to be the ultimate encryption technology.
