JPL's Linear Ion Trap frequency Standards (LITS) are world's best for measuring times from a few hours to a few weeks. Atomic clocks such as the LITS and LITE have unique measurement capability because every atom or ion in the clock is quantum-mechanically identical to every other one; thus atomic clocks allow an absolute reference for frequency and time. Our trapped ion standards are based on the atomic characteristics of mercury and ytterbium ions which are suspended in space by radio frequency fields.

The quality of any atomic frequency standard can be judged by how well the (almost) perfectly defined internal frequency of each identical atom or ion is brought out to the everyday world. The large volume of the linear trap geometry helps to accomplish this by giving each of the ions enough room to prevent neighboring ions from causing variations or instabilities in its internal frequency.