M.A. Lawn

Laser cooling of 171Yb+ ions in a linear paul trap

We report laser cooling of trapped 171Yb+ ions. The ions are confined in a linear Paul trap. Temperatures below 1 K have been achieved, and evidence of a phase transition to a crystal-like state has been observed. The metastable 2D3/2 level is drained using a transition at 609.1 nm not previously used for this purpose. Laser cooling of 171Yb+ may be of importance to the development of new microwave frequency standards.

Very high Q microwave spectroscopy on trapped /sup 171/Yb/sup +/ ions: application as a frequency standard

A microwave frequency standard based on buffer-gas cooled /sup 171/Yb/sup +/ ions confined in a linear Paul trap has been demonstrated in prototype form. The standard exhibits a fractional frequency instability characterized by an Allan deviation /spl sigma//sub y/(/spl tau/)=3.7/spl times/10/sup -13//spl tau//sup -1/2/ for /spl tau/ >

Performance of a prototype microwave frequency standard based on laser-detected, trapped171Yb+ ions

A microwave frequency standard based on buffer gas-cooled171Yb+ ions confined in a linear Paul trap has been demonstrated in prototype form. The standard exhibits a fractional frequency instability characterised by an Allan deviation of σ(y(τ) = 2.9 × 10−13τ−1/2 for τ < 2 × 104 s. Factors affecting the stability of the standard have been systematically investigated.

Temperature of laser-cooled /sup 171/Yb/sup +/ ions and application to a microwave frequency standard

Microwave frequency standards based on buffer gas-cooled /sup 171/Yb/sup +/ ions have demonstrated high stability but are limited in accuracy by the second-order Doppler shift caused by thermal motion. We have previously obtained near shot noise-limited Ramsey fringes with a laser-cooled ion cloud. Here, we present measurements confirming that the ion temperature remains <1 K throughout the microwave interrogation period for a Ramsey pulse separation of up to 10 s and longer. The potential stability of the ions as a frequency standard is better than /spl sigma//sub y/ (/spl tau/)=5/spl times/10/sup -14/ /spl tau//sup -1/2/, and estimates of the systematic offsets to the clock frequency and their uncertainties indicate that a total uncertainty of four parts in 10/sup 15/ or better is achievable.

The CSIRO trapped /sup 171/Yb/sup +/ ion clock: improved accuracy through laser-cooled operation

The microwave frequency standard based on buffer gas-cooled /sup 171/Yb/sup +/ ions at the CSIRO National Measurement Laboratory has demonstrated high stability, but has an accuracy limited by the second-order Doppler shift due to the thermal motion of the ions. We report measurements obtained with a cloud of approximately 10/sup 4/ ions laser-cooled to below 1 K, including near shot noise-limited Ramsey fringes with a pulse separation up to 10 s. Estimates indicate that a potential stability of /spl sigma//sub y/(/spl tau/)=5/spl times/10/sup -14/ /spl tau//sup -1/2/ and a total uncertainty of 5 parts in 10/sup 15/ or better are achievable for this system.

Performance of a prototype microwave frequency standard based on trapped /sup 171/Yb/sup +/ ions

A microwave frequency standard based on buffer-gas cooled /sup 171/Yb/sup +/ ions confined in a linear Paul trap has been demonstrated in prototype form. The standard exhibits a fractional Allan deviation /spl sigma//sub y/(/spl tau/)=3.7/spl times/10/sup -13/ /spl tau//sup -1/2/ for /spl tau/<3000 s.<<ETX>>

Development of a /sup 171/Yb/sup +/ microwave frequency standard at the National Measurement Institute, Australia

Microwave frequency standards based on the 12.6 GHz ground state hyperfine transition in 171Yb+ have been under development at the National Measurement Institute, Australia, for many years. Using a laser-cooled ion cloud, the transition frequency was measured in 2001 to an accuracy of 8 parts in 1014, limited by the homogeneity of the magnetic field due to the stainless-steel vacuum chamber. We have designed and commissioned a new chamber in the alloy CrCu, which is non-magnetic and has good vacuum properties. The design incorporates large viewports and high-quality quartz windows for optical access. Uncertainties associated with field inhomogeneity in the new vacuum system are now below 1 part in 1015, a significant reduction which permits operation in the 10-15 accuracy range. We have also demonstrated the use of photoionization to load the trap in a preliminary experiment, including isotope-selective loading

171Yb+ Microwave Frequency Standard

Microwave frequency standards based on the 12.6 GHz ground state hyperfine transition in 171Yb+ have been under development at the National Measurement Institute, Australia, for many years. Using a laser-cooled ion cloud, the transition frequency was measured in 2001 to an accuracy of 8 parts in 1014 , limited by the homogeneity of the magnetic field. Uncertainties associated with field inhomogeneity in the new vacuum system are now below 1 part in 1015. We demonstrate that other systematic uncertainties such as AC Zeeman shift, microwave imperfections and pressure shifts permit operation in the 10-15 accuracy range. The performance of the 171Yb+ microwave standard can therefore be comparable to that of a caesium fountain.

GPS activities at the National Measurement Institute, Australia

The National Measurement Institute, Australia, (NMIA) is continuing the development of reliable, high-integrity and remotely-operable GPS-based systems for precise time and frequency transfer. These systems combine an OEM receiver with a PC and support a variety of applications, of which we describe three: the intercomparison of receiver internal delays among laboratories in the Asia-Pacific, using a portable time-transfer system; a geodetic monitoring station, contributing data to Australian and international geodetic reference networks; and delivery of traceable time and frequency to a distant location, or equivalently continuous remote calibration of a frequency standard at a clients premises

A microwave frequency standard based on laser-cooled /sup 171/Yb/sup +/ ions

We report operation of a microwave frequency standard based on the 12.6 GHz ground-state hyperfine transition in a cloud of laser-cooled /sup 171/Yb/sup +/ ions. The projected performance of this standard (frequency uncertainty /spl les/ 4 /spl times/ 10/sup -15/ and stability 5 /spl times/ 10/sup -14/ /spl tau//sup -1/2/ for a 10 s Ramsey time) is comparable to that of a cesium fountain.