==See also==*SI unit* Orders of magnitude (time)* Becquerel*Coordinated Universal Time*Hertz*International Atomic Time*International System of Units*Leap second*Magneto-optical trap* Specific impulse*Time standard* Femtosecond* Microsecond* Millisecond* Nanosecond* Picosecond== Notes and references ====External links==* National Physical Laboratory: "Trapped ion optical frequency standards"* "High-accuracy strontium ion optical clock"; National Physical Laboratory (2005)* National Research Council of Canada: "Optical frequency standard based on a single trapped ion"* NIST: "Definition of the second"; notice the cesium atom must be in its ground state at 0 K* Official BIPM definition of the second* The leap second: its history and possible future* "What is a Cesium atom clock?
* National Physical Laboratory: "Trapped ion optical frequency standards"* "High-accuracy strontium ion optical clock"; National Physical Laboratory (2005)* National Research Council of Canada: "Optical frequency standard based on a single trapped ion"* NIST: "Definition of the second"; notice the cesium atom must be in its ground state at 0 K* Official BIPM definition of the second* Seconds and leap seconds by the USNO* The leap second: its history and possible future* "What is a Cesium atom clock?