Ions trapped in radiofrequency traps find use in quantum information processing [1,2], mass spectrometry [3,4] and time and frequency metrology [5-7]. Operating these traps require a considerable ensemble of lasers and control electronics; therefore, finding simple and user-friendly designs for the light sources will aid the development of field deployable experiments, such as relativistic geodesy using optical clocks [8].
Ions trapped in radiofrequency traps find use in quantum information processing [1,2], mass spectrometry [3,4] and time and frequency metrology [5-7]. Operating these traps require a considerable ensemble of lasers and control electronics; therefore, finding simple and user-friendly designs for the light sources will aid the development of field deployable experiments, such as relativistic geodesy using optical clocks [8].
Since the birth of ion trapping techniques in the 1960s, physics and chemistry applications have evolved fruitfully in concert, leading to the award of one-quarter of the 1989 Nobel Prize in Physics to each of W. Paul [1] and H.G. Dehmelt [2]. Although radiofrequency ion traps were used largely for high resolution atomic spectroscopy, spin exchange experiences, and lifetimes of atomic levels [3,4], the so-called ‘QUISTOR’[5] (QUadrupole Ion STORe) opened a new vista in mass spectrometry not only for component analysis but also for studies of chemical reaction paths also. Atomic excitations that are employed in lasers and the subsequent manipulation of such atomic lasers have stimulated the realization of the huge possibilities presented by ion trapping. Laser cooling, which has permitted the attainment of extreme accuracy in atomic spectroscopy measurements, has provided the means for precise internal and external ion energy manipulation thus opening the way to novel and powerful applications, such as quantum information and atomic clocks in the optical domain [6]. In general, lasers afford quite extraordinary means for both the formation of monatomic and polyatomic ions in specic excitation states and for probing such species in excited states. Recent progress in the development of a wide range of lasers, including the advent of laser diodes, offers myriad opportunities for new kinds of investigations. Another important research direction was opened by the liberties taken with the hyperboloidal geometry of the quadrupole ion trap. Enhanced understanding of the connement properties of quadrupole ion traps allowed the exploitation of new geometries that were easier to construct, such as cylindrical ion traps that permitted ready access for experimentation, exploited new characteristics such an non-linear modes of excitation, and introduced a stretched geometry that led to improvement in mass resolution. Recently, miniaturization of cages [7] or traps on micro-chips [8] have been exploited in atomic quantum physics as well as in chemistry analysis.* It is worthy to note that the extent of progress made in each of these domains was realized due to the curiosity of researchers and their desire to learn from the results of the experiments carried out. The purpose of this chapter is to expound upon the specic topic of atomic clocks utilizing ion traps and the new challenges engaged presently for the measurement of time with extremely high precision. Today, ion atomic clocks are designed for various systems (that is, the ion-trap-oscillator ensemble) that could offer new opportunities for the design of new ion trapping applications.
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.
Optical clocks enable frequency measurements with a systematicfractionaluncertainty of 10^-18 and lower. These clocks use opticaltransitions ofcold trapped ions in radio-frequency traps or cold ensembles oftrappedneutral atoms as frequency references with long-term stability.There isan increasing demand for commercially available precise clocksfor bigdata, stock exchange, and positioning systems. Further,ultra-precise clockscan be used to test General Relativity, search for new physics,and geodeticmeasurements. Todate, precise clocks are realized mainly inlaboratoryexperiments and require highly trained operators. We aredeveloping chip-basedion traps for portable optical clocks that can be used for field measurements,as well as multi-ion clocks that enable faster precisionmeasurements.In this talk, we will give an update on ion trap technologiesthat willhelp to make the clocks smaller. This includes more compactelectricalconnections and space-saving
Single trapped ions trapped in Paul traps correspond to ideal candidates for realization of extremely accurate optical atomic clocks and practical studies of the light–atom interactions and nonlinear mechanical dynamics. These systems benefit from both, the superb isolation of the ion from surrounding environment and excellent control of its external and internal\ndegrees of freedom, at the same time, which makes them exquisite platforms for experimental studies and applications of light matter interaction at its most fundamental level. The exceptional degree of control of single or few ion's state enabled in past decade number of major advancements in the applications from the fields of experimental quantum information\nprocessing and frequency metrology, including recent realization of scalable Shor's\nalgorithm, fractional uncertainties of the frequency measurements close to 10-18 level, or simulations of complex quantum many-body effects. These results, together with the rapid advancements in the production of low-noise segmented micro-traps, promise prompt access to long-desired regimes of quantum optomechanics and further development and applications\nof optical atomic clocks.
A frequency-stable, broadband laser is presented for experiments on trapped ions. Because the design is based on widely available semiconductor optical amplifier technology, similar lasers can be realized for virtually any wavelength in the near-infrared, and the coherence properties and output power allow for efficient second harmonic generation. No closed-loop frequency stabilization for addressing Doppler- or naturally broadened, dipole-allowed transitions is needed, and the light source can be turned on and off during a measurement cycle with submicrosecond response time. As a case study, a 921.7-nm laser with an output power of 20 mW and a linewidth of 10 GHz is realized, which is then frequency doubled to 460.9 nm for excitation of strontium as the first step in photo-ionization. The excitation efficiency is compared to that achievable with a narrow-linewidth distributed Bragg reflector laser as well as to theory.
Transitions between discrete energy levels in well-isolated atomic systems are highly reproducible and therefore make ideal references for highly accurate frequency standards or clocks. In particular, a single laser-cooled ion confined in a radiofrequency ion trap closely approximates the spectroscopic ideal of a particle at rest in a perturbation-free environment. Narrow optical transitions in such systems are therefore very promising for the realization of optical clocks with accuracy around 2 orders of magnitude higher than current microwave primary standards. In this paper the fundamental aspects, current performance and applications of trapped ion optical clocks are reviewed and the potential for future improvements is considered.