2016 PTTI Distinguished Service Award

Presented to: Dr. Steven Jefferts

Citation: For significant contributions to the design and development of cesium fountain primary standards, and leadership in bringing this technology to the international metrology community


Dr. Steven Jefferts currently leads the research group developing and operating cesium fountain primary frequency standards at the National Institute of Standards and Technology’s (NIST) and also leads the effort to develop other coldatom microwave frequency standards. These standards play a critical role in calibrating the rate of International Atomic Time (TAI), serve as a primary frequency reference for the USA, and are the foundation of PTTI systems.

Dr. Jefferts lead the development of NIST-F1 in 1999, and has provided several calibrations of TAI every year since the then except for 2014 when the fountain was moved to a new building. His group has made fundamental advances in the understanding of biases in the fountain PFS, including microwave leakage, sideband pulling, and the power dependence caused by spurious components in the microwave spectrum and distributed cavity phase shift. NIST-F1 played a critical role in providing one of the most stringent tests of local position invariance, as well as serving as the reference for absolute calibrations of optical frequency standards at NIST. More recently,

Dr. Jefferts led the effort to design and build the first cryogenic primary frequency standard, NIST-F2. Dr. Jefferts was the primary scientific leader on NASA’s Primary Atomic Reference Clock in Space (PARCS) program. He also designed the physics package now being used in the Italian cryogenic PFS. These two standards, along with the room temperature NIST-F1, have resulted in the most accurate direct measurement of the black body radiation shift ever performed. Dr. Jefferts is currently leading an effort at NIST to develop a microwave cold atom cesium clock for GPS.

Dr. Jefferts received his BS degree in Physics from the University of Washington, and a PhD in Atomic Physics/ Precision Metrology from JILA/University of Colorado.