As a Co-Sponsor of the Norman F. Ramsey Prize 2019 Menlo Systems congratulates Dr. Jun Ye. In this interview Jun Ye talks about the most precise time measurement-techniques of the world, how they could change our communication technologies and even our horizons in quantum mechanics.

Dr. Jun Ye was awarded with the Norman F. Ramsey Prize in Atomic, Molecular and Optical Physics 2019 by the American Physical Society. Jun Ye leads the research group „Amo Physics and Precision Measurement at JILA, NIST and the University of Colorado Boulder. He was recognized with the prize for his ground-breaking contributions to precision measurements and the quantum control of atomic and molecular systems, including atomic clocks. As a Co-Sponsor of the Ramsey Prize Menlo Systems warmly congratulates Dr. Jun Ye. With science journalist Thorsten Naeser Jun Ye talked about his research, his aims and his visions as well.

Congratulations on winning the Norman F. Ramsey Prize 2019. A main part of your work deals with the development of world-leading experimental atomic clocks that tick at optical frequencies? What is your imagination of time?

Jun Ye: Time is a fundamental concept and operating mechanism for human civilization, ranging from philosophical explorations, biological and society functions, and scientific and technological advances. My interest in time is mostly driven from the latter aspect. We are aiming to push the scientific frontier of how to measure and use time in the most precise and meaningful way. For example, the measurement precision we are now achieving for time can already benefit advanced communication networks and monitoring of geological activities. A new suite of technologies emerges as a natural consequence of this exciting scientific endeavor, which provides new technical capabilities that impact our society. The scientific exploration itself enables us to ponder big problems in the modern framework of fundamental physics and tests our imaginations for harnessing quantum science for the next economic revolution.

Your research on very precise optical atomic clocks are based on laser technology. Can you explain in a few words, how these chronometers work in comparison to the chronometers we use?

Jun Ye: Our atomic clock is based on the use of an ultrastable laser to probe the transition frequency between two specific energy levels in Sr atoms. The laser is an optical oscillator whose phase noise is sufficiently small to allow for a very long interrogation period for the quantum coherence of an atom. This laser development is itself a huge technological advance. The atoms are confined in specially designed optical traps called optical lattices. In our latest development of the Sr optical lattice clock, the atomic motional degrees of freedom are fully quantized in all three spatial directions, such that our measurement is no longer limited by thermal averaging, and the longest coherence time has been obtained.

What is the difference to the conventional Cesium atoms when designing the most precise clocks of the world?

Jun Ye: The difference between a conventional Cs clock and our Sr clock is that we use an atomic transition whose frequency is located in the visible spectrum, rather than the microwave transition used in the Cs clock. Because of the use of an optical frequency, the quality factor of the transition, namely the product of the oscillation frequency and the coherence time, is many orders of magnitude higher. This has allowed us to easily achieve a much better measurement precision for the clock frequency. At this time, both the measurement precision and the total uncertainty are two orders of magnitude better than the performance level for a traditional Cs clock.

How can you precisely measure the optical frequencies, which are necessary for the clocks?

Jun Ye: An optical frequency is difficult to measure using conventional radio frequency electronics. Fortunately a revolutionary technology that emerged two decades ago, namely optical frequency comb, provides a phase coherent connection between an optical frequency oscillator and a radio frequency one. Prof Ted Hänsch and Prof Jan Hall were awarded the Nobel Prize in physics in 2005 for this development. Our laboratory participated in the work of developing optical frequency combs from the early epoch. After nearly 20 years, modern optical frequency combs (such as a Menlo comb) are now so robust that we can operate our Sr clocks with 95% up time when our systems are tuned up.

How precise can a clock at least get from a technological point of view?

Jun Ye: Within the next few orders of magnitude of the clock performance I don’t see a fundamental limit yet on its precision. On the measurement precision, we have by now comfortably entered the 19th digit level, and the accuracy we are at the low 18th. In the next decade or two of development, I can see the clock measurement precision advance by another factor of 10 or more. Along with such high measurement precision, we can find issues impeding clock accuracy at a much shorter time, thus enabling further improvement of the clock accuracy as well. The clock precision and accuracy have always advanced together in locked steps.

Your work contributes to a better understanding of the quantum world and light-matter interactions? What perspectives does your insights offer to the measurement sciences?

Jun Ye: Clearly quantum physics provides a rich recipe for the continued advance of the measurement frontier involving light and matter. We are witnessing the important advantages that quantum systems provide. As we continue to increase the number of particles to improve the measurement precision, we must face the consequence of their interactions. Understanding them would not only secure a guarantee for the measurement accuracy in the world of quantum many-body physics, but also provide new opportunities to surpass the traditional quantum limit set by single particle physics.

How will the always growing knowledge of quantum phenomena and especially light-matter interactions change the world in, let’s say, 20 years?

Jun Ye: I am hoping that in 20 years we might be able to shed light to some of the fundamental aspects of physics, including connections between gravity and quantum mechanics. And I hope that a network of satellites in space with optical clocks on board will provide an ultimate time service for our global society and become a new “telescope” for discoveries.

Author: Thorsten Naeser

Image credit: J. Burrus/NIST

Ramsey Prize: https://www.aps.org/programs/honors/prizes/ramsey.cfm