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IEEJ Transactions on Fundamentals and Materials

Recent Research Activities on Atomic Time & Frequency Standards

Shinichi Ohshima

Published Jan 1, 2005• 0 citations
Publisher

Abstract

Recent research activities on atomic time and frequency standards are introduced. Especially two topics are selected and explained in detail. One topic is “accurate optical frequency standards" which may be a primary standard of “one second" in the next generation. Another is “chip-scale atomic clocks" which may be useful for industries, communications and various scenes in our daily life.

DOI
10.1541/ieejfms.125.491

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Recent research activities on atomic time and frequency standards are introduced. Especially two topics are selected and explained in detail. One topic is “accurate optical frequency standards" which may be a primary standard of “one second" in the next generation. Another is “chip-scale atomic clocks" which may be useful for industries, communications and various scenes in our daily life.
The SI second is the most accurately realized of the base units, and time intervals can therefore be measured more precisely than any other fundamental quantity. Precision timing information from atomic clocks provides the backbone of such ubiquitous technologies as electrical power grids, wireless phone networks and the global positioning system. Today's best time and frequency standards, cesium fountain atomic clocks, have uncertainty at the level of about two nanoseconds per month. The search for yet more accurate and stable frequency standards has now led to the development of optical-frequency atomic clocks.
Frequency and its inverse, time, are the most accurately measured quantities. Historically, improvements in the accuracy of clocks have enabled advances in navigation, communication, and science. Since 1967, the definition of the International System (SI) second has been based on the frequency of a microwave transition in cesium, and present day cesium atomic clocks have a fractional uncertainty near 10-16. Recently, a new type of atomic clock based on optical transitions has been developed, with a current fractional uncertainty near 10-18 (approximately one second divided by the age of the universe), and they are rapidly improving. This talk presents a brief summary of the development of optical atomic clocks, with a focus on the Al+ quantum-logic clock developed at NIST. We discuss the current state-of-the-art in optical clock performance, and describe new applications in sensing and fundamental physics. Future directions in optical atomic clock research are also considered.
The stability and accuracy of atomic microwave frequency standards (atomic clocks) have been improving at a rate exceeding one order of magnitude per decade for the past 30 years. This sustained improvement has been driven mainly by the many and diverse technological applications requiring highly stable and accurate time and frequency standards. There is no reason to suspect that this rate of progress is slowing. Over the last decade, research and development in atomic frequency standards has tended increasingly towards the use of atom and ion trapping technologies to approach the supposedly ideal unperturbed atomic frequency reference consisting of a single atom or ion either motionless or in free-fall in a perfect, field-free vacuum. This work has been facilitated by the relatively recent development of techniques whereby laser light is used to cool, confine and manipulate atoms or ions. This paper reviews the current status of atomic microwave frequency standards based on trapped atoms and trapped ions, and attempts to explain the motivation for their development and the principles of their operation, with particular emphasis on the physics of factors which limit their performance.
With timekeeping being of paramount importance for modern life, much research and major scientific advances have been undertaken in the field of frequency metrology, particularly over the last few years. New Nobel-prize winning technologies have enabled a new era of atomic clocks; namely the optical clock. These have been shown to perform significantly better than the best microwave clocks reaching an inaccuracy of 1.6 10^-18. With such results being found in large lab based apparatus, the focus now has shifted to portability - to enable the accuracy of various ground based clocks to be measured, and compact autonomous performance - to enable such technologies to be tested in space. This could lead to a master clock in space, improving not only the accuracy of technologies on which modern life has come to require such as GPS and communication networks. But also more fundamentally, this could lead to the redefinition of the second and tests of fundamental physics. Within the European collaboration, Space Optical Clocks (SOC2) consisting of various institutes and industry partners across Europe we have tried to tackle this problem of miniaturisation whilst maintaining stability, accuracy (5 10^-17) and robustness whilst keeping power consumption to a minimum -- necessary for space applications. We will present the most recent results of the Sr optical clock in SOC2 and also the novel compact design features, new methods employed and outlook.