The security of many encryption codes relies on the difficulty of factoring large numbers. For now, however, Shor's algorithm is the only quantum algorithm of practical importance. None of the quantum computers that have been built to date can be scaled to a practical-size device. The NRO suggested that clock synchronization has uses in spy satellites, but didn't give any more specifics. Dowling, however, speculated that the technique would be useful for calibrating signals from two different spy satellites and for global positioning systems.
Spy satellites bounce light waves off objects to gather intelligence about the objects.
Typically, two satellites will send light from different angles. When the signals bounce back to the satellite, one signal is subtracted from the other and the difference gives detailed information about the makeup of the object. In order to use this technique accurately, however, beams of light from the two different satellites have to be synchronized. Similarly, global positioning systems pinpoint a location by sending information from two different satellites some distance apart. Current clock synchronization techniques for these systems can lead to errors of up to several meters.