Practical quantum cryptography

A quantum cryptography system based on a 4-basis protocol with geometrically uniform states is tested in a series of experiments. Quantum states of light transmitted through real fiber optic communication channels to a distance of 32 km in the presence of uncontrolled external actions are prepared, transformed, and measured. It is shown that the chosen algorithms of processing quantum information are adequate and can be used as foundations of practical devices in protected communication lines.