Quantum cryptography takes advantage of quantum physics theory to create what many believe are unbreakable codes. Quantum theory explores interactions between electromagnetic radiation and matter. It differs from classical physics theory in that energy at the subatomic level is neither radiated nor absorbed continuously, but moves sporadically in multiples of discrete, indivisible units called quanta. These quanta, typically in the form of photons, units of light, are used in quantum cryptography in place of the ones and zeroes that make up binary number sequences in digital communications. Los Alamos quantum cryptography uses photons randomly polarized to states representing ones and zeroes.
Polarization refers to the direction of oscillation for the electromagnetic wave of a photon.
These polarized photons are transmitted between sender and receiver to create a random string of numbers known only to the sender and receiver. This string of numbers becomes a quantum cryptographic key that locks or unlocks the encrypted messages that are sent via normal communication channels. Because the photons cannot be intercepted without tipping off the receiver, the quantum cryptographic key is secure and the data is secure. While this distance is far enough to create networks connecting closely spaced government offices or local branches of a bank, at greater distances the signal loss in optical fiber increases until the photons are absorbed. For longer distances, Los Alamos researchers developed free-space quantum cryptography which allows codes to be sent through the air.