The CIPM list of recommended frequency standard values: guidelines and procedures

Abstract

A list of standard reference frequency values (LoF) of quantum transitions from the microwave to the optical regime has been recommended by the International Committee for Weights and Measures (Comité international des poids et mesures, CIPM) for use in basic research, technology, and for the metrology of time, frequency and length. The CIPM LoF contains entries that are recommended as secondary representations of the second in the International System of Units, and entries that can be used to serve as realizations of the definition of the metre. The historical perspective that led to the CIPM LoF is outlined. Procedures have been developed for updating existing, and validating new, entries into the CIPM LoF. The CIPM LoF might serve as an entry for a future redefinition of the second by an optical transition.

A Unique System for Registering One‐Photon Signals in the Ultraviolet Range from An Isomeric 229mTh Nucleus Implanted on Thin SiO2/Si Films

“…Considering the Zeeman and Stark shifts, the Doppler effect, the black body radiation shift, and ion micromotion, the relative frequency uncertainty was estimated to be <10 19 . This is significantly lower than the value estimated by the best known state‐of‐the art optical clocks that are based on electronic transitions . One of the approaches to the direct excitation of the low‐lying isomeric state with photons was developed by Jeet et al and by Stellmer et al 229 Th ions were implanted in transparent crystals such as LiCaAlF 6 , LiSrAlF 6 , CaF 2 , and other samples and then illuminated by intensive ultraviolet (UV) radiation.…”

High‐stability optical frequency transfer with all‐fiber architecture for optical lattice clocks

“…9.2 GHz). The current definition of the second goes back half a century; the attainable accuracy has improved at a pace of one digit in 10 years, and now is 16 digits (uncertainty: 10 −16 ) . However, aiming at further improvement of frequency standards in terms of accuracy and stability, researchers explore optical frequency standards in an optical frequency band (10 15 Hz) exceeding the conventional microwave frequency (10 10 Hz) .…”

“…Particularly, optical lattice clocks use multiple atoms so that quantum projection noise‐limited stability determined by the number of atoms can be improved, and high‐accuracy frequency can be realized within a short averaging time. Frequency evaluation of optical lattice clocks is performed worldwide, and optical lattice clocks using strontium, ytterbium, and mercury have been adopted as a secondary representation of the second …”

“…The current definition of the second goes back half a century; the attainable accuracy has improved at a pace of one digit in 10 years, and now is 16 digits (uncertainty: 10 −16 ). 1 However, aiming at further improvement of frequency standards in terms of accuracy and stability, researchers explore optical frequency standards in an optical frequency band (10 15 Hz) exceeding the conventional microwave frequency (10 10 Hz). 2 Research in frequency standards was spurred with realization of optical frequency measurement using optical frequency combs around 2000, 3,4 and there already appeared optical atomic clocks with uncertainty of 10 −18 , 5-8 thus outperforming cesium atomic clocks in attainable accuracy.…”

“…Frequency evaluation of optical lattice clocks is performed worldwide, and optical lattice clocks using strontium, ytterbium, and mercury have been adopted as a secondary representation of the second. 1 In evaluation of such high-accuracy atomic clocks, one must compare frequency of atomic clocks to verify frequency values and their repeatability all over the world. In addition, one can expect for geodetic applications using clock frequency shift due to the gravitational potential, and experiments are conducted to precisely compare frequencies of high-accuracy atomic clocks placed at distant locations.…”