NIST cesium fountains: current status and future prospects

We review the current status of the U.S. Primary Frequency Standard, NIST-F1. NIST-F1 is a laser-cooled cesium fountain based frequency standard with an inaccuracy of less than δ f / f ≤ 5x10-16 limited mainly by the radiation field in the room-temperature fountain (blackbody shift). NIST-F1 is one of the best cesium fountains currently contributing to international atomic time, but has reached a point that it is impractical to improve its accuracy substantially. Therefore we are building a new fountain, imaginatively named NIST-F2, with a cryogenic (77 K) Ramsey interrogation zone that lowers the blackbody shift by several orders of magnitude. NIST-F2 is currently undergoing final assembly, and we will discuss our planned (hoped for) performance, which includes frequency inaccuracy of δ f / f < 1x10-16

[1]  Steven R. Jefferts,et al.  Time Measurement at the Millennium , 2001 .

[2]  Steven R. Jefferts,et al.  Operation of the NIST-F1 Cesium Fountain Primary Frequency Standard with a Maser Ensemble , 2005 .

[3]  G. Dick,et al.  Power dependence of distributed cavity phase-induced frequency biases in atomic fountain frequency standards , 2005, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[4]  Dai-Hyuk Yu,et al.  Microwave leakage-induced frequency shifts in the primary frequency Standards NIST-F1 and IEN-CSF1 , 2006, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[5]  James A. Barnes.  BASIC CONCEPTS OF PRECISE TIME AND FREQUENCY , 1973 .

[6]  Jon H. Shirley,et al.  Accuracy evaluation of NIST-F1 , 2002 .

[7]  Wayne M. Itano,et al.  Shift of 2 S 12 hyperfine splittings due to blackbody radiation , 1982 .

[8]  Dai-Hyuk Yu,et al.  Power dependence of the frequency bias caused by spurious components in the microwave spectrum in atomic fountains , 2006, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[9]  Verhaar,et al.  Spin-exchange frequency shift in a cesium atomic fountain. , 1992, Physical review. A, Atomic, molecular, and optical physics.

[10]  Jon H. Shirley,et al.  NIST-F1: recent improvements and accuracy evaluations , 2005 .

[11]  Moore,et al.  Quantum projection noise: Population fluctuations in two-level systems. , 1993, Physical review. A, Atomic, molecular, and optical physics.

[12]  Steven R. Jefferts,et al.  Operation of the NIST-F1 caesium fountain primary frequency standard with a maser ensemble, including the impact of frequency transfer noise , 2005 .