Measuring physical quantities with unprecedented precision is one of the most important paradigms to extend our fundamental understanding of nature. With the development of new quantum techniques, quantum systems have become a promising platform along the path to pursue higher accuracy and stability of measurement, while the classical methods are approaching their own limitation. Owing to its high stability, long coherence time and good controllability of quantum states, the trapped ion system has attracted much attention as a promising platform for quantum metrology. Recent progress on quantum control of trapped ions in both the scientific and technological aspects greatly advance the potential applications in precision measurement of various physical quantities. The invention of optical comb with ultra-stable laser brings us a new approach to develop a clock working on optical frequency, and features a much higher precision than microwave. This achievement has the potential reform the definition of the basic unit of the international system of units in the near future. New methods of dynamic decoupling or preparing special dressed states significantly extend the coherence time, such that an ultra-sensitive detection of magnetic field can be achieved. By introducing a spin-dependent kick in the phase space, one may also realize rotation measurement with trapped ions and obtain high accuracy with a chip-size apparatus. In this short review, we introduce the principles and designs of optical clock, magnetometer and gyroscope based on trapped ion systems. Owing to its unique features, this platform presents many advantages which can help improving sensitivity and stability, as well as building transportable devices.
Measuring physical quantities with unprecedented precision is one of the most important paradigms to extend our fundamental understanding of nature. With the development of new quantum techniques, quantum systems have become a promising platform along the path to pursue higher accuracy and stability of measurement, while the classical methods are approaching their own limitation. Owing to its high stability, long coherence time and good controllability of quantum states, the trapped ion system has attracted much attention as a promising platform for quantum metrology. Recent progress on quantum control of trapped ions in both the scientific and technological aspects greatly advance the potential applications in precision measurement of various physical quantities. The invention of optical comb with ultra-stable laser brings us a new approach to develop a clock working on optical frequency, and features a much higher precision than microwave. This achievement has the potential reform the definition of the basic unit of the international system of units in the near future. New methods of dynamic decoupling or preparing special dressed states significantly extend the coherence time, such that an ultra-sensitive detection of magnetic field can be achieved. By introducing a spin-dependent kick in the phase space, one may also realize rotation measurement with trapped ions and obtain high accuracy with a chip-size apparatus. In this short review, we introduce the principles and designs of optical clock, magnetometer and gyroscope based on trapped ion systems. Owing to its unique features, this platform presents many advantages which can help improving sensitivity and stability, as well as building transportable devices.
Recent progresses on quantum control of cold atoms and trapped ions in both the scientific and technological aspects greatly advance the applications in precision measurement. Thanks to the exceptional controllability and versatility of these massive quantum systems, unprecedented sensitivity has been achieved in clocks, magnetometers, and interferometers based on cold atoms and ions. Besides, these systems also feature many characteristics that can be employed to facilitate the applications in different scenarios. In this review, we briefly introduce the principles of optical clocks, cold atom magnetometers, and atom interferometers used for precision measurement of time, magnetic field, and inertial forces. The main content is then devoted to summarize some recent experimental and theoretical progresses in these three applications, with special attention being paid to the new designs and possibilities towards better performance. The purpose of this review is by no means to give a complete overview of all important works in this fast developing field, but to draw a rough sketch about the frontiers and show the fascinating future lying ahead.
For the past 15 years, tremendous progress within the fields of laser stabilization, optical frequency combs and atom cooling and trapping have allowed the realization of optical atomic clocks with unrivaled performances. These instruments can perform frequency comparisons with fractional uncertainties well below 10-17, finding applications in fundamental physics tests, relativistic geodesy and time and frequency metrology. Even though most optical clocks are currently laboratory setups, several proposals for using these clocks for field measurements or within an optical clock network have been published, and most of time and frequency metrology institutes have started to develop transportable optical clocks. For the purpose of this special issue, we chose to focus on trapped-ion optical clocks. Even though their short-term fractional frequency stability is impaired by a lower signal-to-noise ratio, they offer a high potential for compactness: trapped ions demand low optical powers and simple loading schemes, and can be trapped in small vacuum chambers. We review recent advances on the clock key components, including ion trap and ultra-stable optical cavity, as well as existing projects and experiments which draw the picture of what future transportable, single-ion optical clocks may resemble.
Recent development of controlling quantum systems has enabled us to utilize the systems for quantum computing, communication, and sensing. In particular, quantum sensing has attracted attention to a broad community of science and technology, as it could surpass classical limitations in measuring physical quantities such as electric and magnetic field with unprecedented precision. Among various physical platforms for quantum sensing, trapped-ion based system possesses several advantages-atomic size, outstanding quantum coherence, and quantum properties. In this review, we introduce previous research efforts to utilize the trapped-ion system for reaching ultimate sensitivity and discuss future perspective and research directions in this emerging field.
Quantum precision measurement and sensing aims to obtain a measurement accuracy beyond the limits specified by classical measurement techniques and achieve ultra-high precision measurements of physical quantities, such as magnetic field, inertia, gravity, and time by employing quantum resources and effects. With the advancement of quantum optics, atomic physics, and related fields, in addition to the incentives of the Nobel Prize and the “quantization” of the seven basic physical quantities of the International Unit, precision measurement has entered the quantum era. Compared with conventional sensors based on classical technology, quantum sensors can surpass the standard quantum limit. In addition, quantum sensors are more appropriate for precision measurements because they are not affected by manufacturing differences, defects, impurities, aging, and other factors. It has broad application potential in biomagnetism, geomagnetism, space magnetic field detection, and so on. Furthermore, its practical applications include complicated systems, poor portability and operability, high power consumption, and high cost. However, many issues remain to be addressed. Given the broad application prospect of precision measurement, certain international institutions, for instance, NIST, have begun researching chip-scale atomic sensing devices. Among the reponed chip-scale atomic systems thus far, the progress of the atomic clock and magnetometer is paramount. In this paper, we review the latest development and application of chip-scale atomic clocks and magnetometers and examine their opportunities and challenges. Finally, by taking the homebuilt microfabricated atomic magnetometer as an example, we describe the mechanism of spin squeezing-assisted quantum-enhanced metrology and provide a long-term outlook for chip-scale quantum-enhanced metrology.
Optical atomic clocks based on laser-cooled trapped ions and atoms have advanced rapidly over the past decade. With fractional frequency uncertainties now surpassing 10 −18 , they are some of the most precise measurement tools ever built. Yet researchers are still pursuing new avenues of research to explore the fundamental limits to their stability, accuracy, and reproducibility. In this mini-review, we provide a survey of the current state of the art by describing the fundamental principles and techniques that underpin this progress, the architectures used to realize optical clocks, and the supporting laser technologies that are essential to their operation. We also examine the progress that has been made toward a redefinition of the second in the International System of Units and the inclusion of optical clocks into the global time and frequency metrology infrastructure. Finally, we discuss emerging applications of optical clocks and look at the prospects for making their precision more readily accessible to end users.
The exquisite control exhibited over quantum states of individual particles has revolutionized the field of precision measurement, as exemplified by the most accurate atomic clock realized in single trapped ions. Whereas many-atom lattice clocks have shown advantages in measurement precision over trapped-ion clocks, their accuracy has remained 20 times worse. Here we demonstrate, for the first time, that a many-atom system achieves accuracy (6x10^{-18}) better than a single ion-based clock, with vastly reduced averaging times (3000 s). This is the first time a single clock has achieved the best performance in all three key ingredients necessary for consideration as a primary standard - stability, reproducibility, and accuracy. This work paves the way for future experiments to integrate many-body quantum state engineering into the frontiers of quantum metrology, creating exciting opportunities to advance precision beyond the standard quantum limit. Improved frequency standards will have impact to a wide range of fields from the realization of the SI units, the development of quantum sensors, to precision tests of the fundamental laws of nature.