Optical atomic clocks are among the most accurate measuring instruments of our time. They are not only used for precise time measurement, but also in satellite navigation and fundamental physics. Researchers at the Physikalisch-Technische Bundesanstalt (PTB) and Leibniz Universität Hannover (LUH) have now for the first time experimentally realised a method for accelerating measurements with atomic clocks that was previously only described theoretically. Their results, which were obtained as part of the Cluster of Excellence QuantumFrontiers and the Collaborative Research Centre DQ-mat, have now been published in the journal Physical Review Letters.
The most accurate atomic clocks currently available use various charged atoms (ions) as clocks. These are trapped in ion traps using electric fields, cooled with laser light and then their reference transition is compared to a highly stable laser. The more ions that can be trapped and the longer they are scanned, the faster the clock reaches a certain resolution. Up to now, however, most ion clocks have only used one ion, as inhomogeneous fields make it difficult to control several ions.
A team led by Lennart Pelzer from PTB has now succeeded in making a larger chain of calcium ions less sensitive to the effects of electric and magnetic fields. To do this, they used a quantum mechanical trick called "continuous dynamical decoupling". In doing so, they couple several atomic levels in the calcium ion by radiating special radio frequency fields. In this way, they were able to interrogate several ions for much longer and thus achieve a low measurement uncertainty much more quickly. Using this method, the researchers were able to transform calcium, an atomic species that was previously less suitable due to its sensitivity to electric and magnetic fields, into a good frequency reference. Calcium is an attractive clock candidate because it can be controlled with comparatively simple laser systems and scaling techniques are being developed for the control of many ions for quantum computing. The technique could now be used in a combined aluminium-calcium clock to improve the overall system. Similar tricks could also be of interest for other clock systems.
Original publication
Multi-ion frequency reference using dynamical decoupling
Lennart Pelzer, Kai Dietze, Víctor José Martínez-Lahuerta, Ludwig Krinner, Johannes Kramer, Fabian Dawel, Nicolas C. H. Spethmann, Klemens Hammerer, and Piet O. Schmidt
Phys. Rev. Lett. 133, 033203
DOI: https://doi.org/10.1103/PhysRevLett.133.033203
