Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Highly charged ions


Multiply-ionized atoms for clocks, qubits, and constants

The world is mostly neutral. That is, most of the atoms in our environment are electrically neutral. The number of electrons in the outer parts of atoms equals the number of protons at the centers of atoms. As one or more electrons are plucked away from the atoms, the remaining electrons feel a much stronger positive pull from the nucleus.

Why Can't Neodymium Be More like Tin?

The best highly charged ions seem to be atoms such as Nd, Pr, and Sm that can be ionized to have the same number of electrons as four successive elements -- Ag, Cd, In, and Sn -- in another part of the periodic table.

Credit: Adapted from Los Alamos figure

This enhanced pull, causing the atoms to shrink in size, ensures that those electrons are less vulnerable to the distractions of their environment, making them potentially valuable for next-generation atomic clocks, for quantum information schemes (where the loss of quantum coherence in qubits is a paramount danger), and for experiments trying to detect slight variations in the fine structure constant, the parameter that sets the overall strength of the electromagnetic force.

A new theoretical study conducted by JQI adjunct fellow Marianna Safronova and her colleagues from groups around the world (1) provides the best yet study of how highly charged ions could be used for atomic timekeeping and for processing quantum information. They identify 10 such ions---for instance, samarium-14+ and neodymium-10+---along with estimates of ion properties experimenters need to know before beginning their work, things such as the expected lifetimes and internal energy levels for the excited states of the ions.


Charged-up atoms are hard to produce and control. At one of the facilities dedicated to this purpose, the Electron Beam Ion Trap (EBIT) at the Lawrence Livermore National Lab, a beam of electrons intercepts a beam of atoms, ionizing the atoms at they go. In this way charge states all the way up to +92 (fully ionized uranium atoms) have been achieved. The trick is to store such charged ions and to cool them to low temperatures. In the kind of atomic environments typical of atomic clocks or quantum computers, low temperature means small ion motion, which makes for better spectroscopy.

Spectroscopy, the measurement of the energy of atomic transitions, is all important for the applications mentioned above---clocks, quantum computing, and testing the constants of nature. Currently the world's time standard is pegged to a particular microwave transition in cesium-133 atoms.. Even higher precision and better clocks will result from the use of transitions in the optical range.

One problem of working with highly charged ions is that the gaps in the energy levels are too great. This is because when you ionize an atom, its energy levels get further apart. The light emanating from transitions in these ions is at too great a frequency, often in the ultraviolet part of the electromagnetic spectrum. Precision control and manipulation of ions needed for clocks and quantum information is harder or presently impossible to do in that UV or even x-ray energy regime. So in choosing ion candidates, it is important to search for transitions in the optical or near-optical range.

Another criterion is that the ions should be able to attain semi-stable excited states. A third criterion is that the characteristic transition is not between the states from the same electronic configuration. Such transitions do not have enhanced sensitivity to the study whether the fine structure constant is changing over time.. A fourth criterion is that the final ionic state should not be a radioactive substance, thus reducing handling problems.

Safronova and her colleagues, using these criteria and a state-of-the-art methods that they developed to study atoms arrived at their list of ten worthy ion species. They publish their results in the 18 July 2014 issue of Physical Review Letters (2).

Not the least part of their achievement is the authors' specification of the frequencies to be expected from the critical transitions in the candidate ions. It's hard enough to calculate the transition energies of un-ionized atoms, but even harder with these particular highly charged ions. They calculated the frequencies for their select ions and then compared (where appropriate) with the values observed in the lab. The difference, generally less than 1%, should reassure experimenters that Safronova and her colleagues can accurately predict properties of ions where no experimental data are available. .


The use of highly charged ions might result in more accurate clocks since the atoms will be more immune from interference from nearby electric or magnetic fields. But aren't atomic clocks already good? They are. In January 2014, physicists at NIST-Boulder announced the creation of an atomic clock that sets records for accuracy and stability, at the 6 parts-per-10^-18 level. This clock uses strontium atoms, and the observed transition is reported to an astounding degree of explicitness. The energy corresponds to a wave with a frequency of 429,228,004,229, 870.0(1.1) Hz.

If, however, we could go just a bit further, to the level of 10^-19, then important physics tests might be possible, including the chance to determine whether the fine structure constant (denoted by the Greek letter alpha), is changing in time or space. Astronomical data has been interpreted by some to suggest that alpha is changing at a small level. At the finer level of precision offered by highly charged ions, terrestrial tests of alpha's constancy could be carried out.

Other potential uses for atomic clocks emerge in areas where high precision is critical: geodesy, hydrology, navigation, and even the deep tracking of spacecraft. Safronova singles out the potential for quantum computing: "The highly charge ions we recommend," she said, "present a completely unexplored resource for quantum information owing to their unique atomic properties and their potential for reducing the sensitivity to troubling decoherence effects."


(1) Safronova is an adjunct fellow of the Joint Quantum Institute (NIST/University of Maryland) and is also a professor at the University of Delaware. Her colleagues hail from Delaware, the University of New South Wales, the University of Nevada, the University of Notre Dame, the Petersburg Nuclear Physics Institute, and the St. Petersburg Electrotechnical University.

(2) "Highly charged ions for atomic clocks, quantum information, and search for alpha variation," M.S. Safronova, V.A. Dzuba, V.V. Flambaum, U.I. Safronova, S.G. Porsev, and M.G. Kozlov, Phys. Rev. Lett. 113, 030801 – Published 16 July 2014. DOI:

Marianna Safronova,

Press contact at JQI: Phillip F. Schewe,, 301-405-0989.

Phillip F. Schewe | Eurek Alert!

Further reports about: JQI Quantum clock electrons ions levels sensitivity structure transition

More articles from Physics and Astronomy:

nachricht Engineering team images tiny quasicrystals as they form
18.08.2017 | Cornell University

nachricht Astrophysicists explain the mysterious behavior of cosmic rays
18.08.2017 | Moscow Institute of Physics and Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>



Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

Latest News

Nagoya physicists resolve long-standing mystery of structure-less transition

21.08.2017 | Materials Sciences

Chronic stress induces fatal organ dysfunctions via a new neural circuit

21.08.2017 | Health and Medicine

Scientists from the MSU studied new liquid-crystalline photochrom

21.08.2017 | Materials Sciences

More VideoLinks >>>