Advances in Atomic and Optical Clocks: Pushing the Boundaries of Precision Timing

Dear Colleagues,

This Special Issue invites submissions on optical clocks, frequency combs, time and frequency synchronization, and optical transmission techniques, particularly those that focus on advances in optical clock technologies and scientific explorations for ground and space.

Atomic microwave clocks, including microwave time and frequency transfer techniques, have revolutionized timekeeping and space navigation. Due to their inherently higher transition frequencies, optical clocks are at least an order of magnitude better in terms of performance compared to the microwave standard. Optical clocks have begun to be considered in practical and portable applications, not just in laboratory settings.

Paper submissions are solicited, covering the basics and advances in optical clocks, including optical lattice clocks, trapped ion optical clocks, and nuclear clocks. Studies on the atomic species used for optical and nuclear clocks, such as strontium, ytterbium, aluminum, calcium, rubidium, iodine, methane, thorium, etc., are of relevant interest. Recent progress in the development, evaluation, and application of high-performance clocks, which continue to drive the frontiers of precision measurement in both fundamental science and applied metrology, are of relevance to this Special Issue. Optics-based time and frequency transfer methods are of significant interest to ensure the synchronization between distant optical clocks.

The contribution of optical clocks to UTC has already begun, and it will increase in the future; this is a requirement to progress towards a redefinition of seconds based on one or several species. These optical devices could potentially improve the stability and accuracy of TAI. Furthermore, optical-clock-driven timescales will be implemented in some laboratories, enhancing the metrological quality of local representations of UTC. Improvements in the reliability and frequent availability of optical clock signals is of relevance for the above-mentioned practical applications.

The key aspects of optical clocks, such as clock laser stabilization methods, vacuum and thermal control advances, compact and portable frequency combs, innovative approaches to improving accuracy, quantitative characterizations of perturbation factors, fractional frequency instability (Allan deviation), long-term performance, low-frequency drift, time deviation, reproducibility, compactness, portability, robustness, reliability, accurate time and frequency transfer, etc., are of relevance to this Special Issue.

Emerging applications of optical lattice/ion/nuclear atomic clocks, such as the search for new physics, gravitational wave detection, and relativistic geodesy, are particularly encouraged.

Dr. Thejesh N. Bandi
Dr. Judah Levine
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Time and Space is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• optical clocks
• UTC
• redefinition of time
• optical cavity
• frequency combs
• long-term stability
• optical time and frequency transfer