Optical atomic clocks hold the promise of enhancing timekeeping and positioning in everyday devices by a factor of one thousand. Yet their large size and complex design have kept them confined to advanced laboratories. Researchers at Purdue University, USA, and Chalmers University of Technology, Sweden, have now devised a method using on-chip microcombs to dramatically reduce the size of these p by Robert Schreiber
Berlin, Germany (SPX) Feb 24, 2025
Optical atomic clocks hold the promise of enhancing timekeeping and positioning in everyday devices by a factor of one thousand. Yet their large size and complex design have kept them confined to advanced laboratories. Researchers at Purdue University, USA, and Chalmers University of Technology, Sweden, have now devised a method using on-chip microcombs to dramatically reduce the size of these precision systems, potentially transforming navigation, autonomous vehicles, and geospatial monitoring.
More than 400 atomic clocks around the globe ensure that mobile phones, computers, and GPS devices deliver accurate time and location data. Whether mechanical, atomic, or those embedded in smartwatches, every clock depends on an oscillator to produce a steady frequency and a counter to tally its cycles. In atomic clocks, the measured oscillations stem from atoms transitioning between two precise energy states.
Conventional atomic clocks typically employ microwave frequencies to stimulate these atomic oscillations. In recent years, scientists have explored the use of lasers to induce optical oscillations. Much like a finely marked ruler, optical atomic clocks can divide a second into exceedingly small intervals, yielding time and position measurements that are thousands of times more precise.
Prof. Minghao Qi from Purdue University, co-author of a study recently published in Nature Photonics, says, "Today's atomic clocks enable GPS systems with a positional accuracy of a few meters. With an optical atomic clock, you may achieve a precision of just a few centimeters. This improves the autonomy of vehicles, and all electronic systems based on positioning. An optical atomic clock can also detect minimal changes in latitude on the Earth's surface and can be used for monitoring, for example, volcanic activity."
Despite their superior accuracy, today's optical atomic clocks remain bulky and depend on intricate laboratory setups with specialized laser configurations and optical components, limiting their use in satellites, remote research stations, or drones. The new development by Purdue University and Chalmers University of Technology overcomes these limitations by substantially miniaturizing the clock system.
Microcombs shrink system footprint
At the heart of this breakthrough are tiny, chip-based devices known as microcombs, as detailed in a recent Nature Photonics article. Resembling the evenly spaced teeth of a comb, these devices generate a broad spectrum of uniform light frequencies.Minghao Qi explains, "This allows one of the comb frequencies to be locked to a laser frequency that is in turn locked to the atomic clock oscillation," emphasizing the crucial role of microcombs in synchronizing the system.
Although optical atomic clocks operate at oscillation frequencies in the hundreds of THz-a range far beyond the direct counting capabilities of electronic circuits-the researchers' microcomb chips effectively bridge this gap, allowing the overall system to be significantly downsized.
Overcoming self reference challenges
Achieving the necessary "self-reference" for system stability while precisely aligning microcomb frequencies with those of the atomic clock has posed a major challenge. Kaiyi Wu, the leading author of the study at Purdue University, states, "It turns out that one microcomb is not sufficient, and we managed to solve the problem by pairing two microcombs, whose comb spacings, i.e. frequency interval between adjacent teeth, are close but with a small offset, e.g. 20 GHz. This 20 GHz offset frequency will serve as the clock signal that is electronically detectable. In this way, we could get the system to transfer the exact time signal from an atomic clock to a more accessible radio frequency, "
Integrated photonics offers compact clock solutions
The system also incorporates integrated photonics, replacing cumbersome laser optics with compact, chip-based components. Dr. Kaiyi Wu notes, "Photonic integration technology makes it possible to integrate the optical components of optical atomic clocks, such as frequency combs, atomic sources and lasers, on tiny photonic chips in micrometer to millimeter sizes, significantly reducing the size and weight of the system," which marks a significant step toward practical, portable atomic clocks.This advancement paves the way for the mass production of optical atomic clocks, potentially making them more affordable and widely accessible for diverse scientific and commercial applications. Although the complete system requires additional elements-such as modulators, detectors, and optical amplifiers-this study lays the groundwork for integrating all necessary components onto a single chip.
Victor Torres Company expresses optimism about the future, stating, "We hope that future advances in materials and manufacturing techniques can further streamline the technology, bringing us closer to a world where ultra-precise timekeeping is a standard feature in our mobile phones and computers," underscoring the transformative potential of this innovation.
Study Background and Details:
The research, titled "Vernier microcombs for integrated optical atomic clocks," was published in Nature Photonics. The collaborative team included Kaiyi Wu, Nathan P. O'Malley, Saleha Fatema, Cong Wang, Marcello Girardi, Mohammed S. Alshaykh, Zhichao Ye, Daniel E. Leaird, Minghao Qi, Victor Torres-Company and Andrew M. Weiner. At the time of the study, the researchers were active at Purdue University, USA; Chalmers University of Technology, Sweden and King Saud University, Saudi Arabia.Research Report:Vernier microcombs for integrated optical atomic clocks
Related Links
Chalmers University of Technology
GPS Applications, Technology and Suppliers