The relentless pursuit of ever more precise timekeeping has taken a groundbreaking leap forward with recent advancements in optical atomic clocks, thanks to pioneering efforts by a team of physicists at the Massachusetts Institute of Technology (MIT). Atomic clocks underpin much of modern technology: from keeping your smartphone clocks accurate and guiding GPS navigation to facilitating secure online transactions. These clocks harness the exquisite regularity of atomic oscillations—nature’s own ticking—to measure time with astonishing precision. Now, the frontier of temporal accuracy has moved beyond traditional cesium-based clocks towards cutting-edge optical clocks, leveraging atoms that oscillate at staggering frequencies, and MIT researchers have developed a novel quantum technique that significantly sharpens their precision.
Atomic clocks conventionally rely on the microwave frequency oscillations of cesium atoms, which tick roughly 10 billion times per second to keep time. This beat forms the foundation upon which international standards of time are defined. However, cesium’s frequency, while remarkably stable, pales in comparison to certain rare earth atoms, such as ytterbium, which oscillate at optical frequencies—approximately 100 trillion ticks per second. This vast difference presents an opportunity for the next generation of atomic clocks to resolve the passage of time at previously unattainable resolutions. The challenge, however, lies in stabilizing these incredibly fast oscillations and mitigating disturbances known as quantum noise, which fundamentally limit measurement precision.
Quantum noise originates from the intrinsic uncertainty in quantum systems and represents a fundamental limit in sensing and measurement. In atomic clocks, it manifests as unavoidable fluctuations in atomic oscillation frequencies that cloud their otherwise predictable behavior. To overcome this barrier, the MIT team tapped into the bizarre world of quantum mechanics, employing a strategy called quantum entanglement. Entangled atoms behave collectively, sharing information across the ensemble, which allows the redistribution and suppression of noise effects. By creating a correlated state among hundreds of ytterbium atoms using carefully designed laser light within an optical cavity, the researchers have demonstrated enhanced precision that more than doubles the ability to discern the smallest differences in tick frequencies.
A key insight driving these advances stems from realizing that the interaction between the clock laser and the ensemble of entangled atoms can induce a subtle yet exploitable effect known as a “global phase.” Previously dismissed as inconsequential, this global phase encapsulates valuable information about the laser’s frequency deviations relative to the atomic transition. By amplifying this phase through quantum-enhanced spectroscopy techniques, the research team has devised a method that effectively extracts a clearer signal amidst the quantum noise. This approach, dubbed “global phase spectroscopy,” opens the door to optical atomic clocks with unprecedented stability, enabling finer tracking of time intervals.
Central to the researchers’ methodology is the use of a laser that oscillates in synchrony with the atoms’ optical transition frequencies. As photons repeatedly interact with the trapped ytterbium atoms within a high-finesse optical cavity, they facilitate a process of entanglement and disentanglement, a subtle operation that boosts the measurable difference between the clock laser’s frequency and the atoms’ natural oscillations. This technique, inspired by earlier explorations of “time reversal” in quantum systems, magnifies the clock’s sensitivity, effectively doubling precision compared to traditional measurement schemes.
What distinguishes this new technology is not only the amplified precision but also its scalability with atom numbers. The team anticipates that adding more entangled atoms to the system will continuously enhance the clock’s accuracy, suggesting an avenue towards even more reliable and portable timekeeping devices. The prospect of making stable, transportable optical atomic clocks promises transformative applications, from geophysical sensing and earthquake prediction to probing the fabric of the universe itself by testing the constancy of fundamental forces and searching for elusive dark matter signatures.
Previous efforts by the MIT group had demonstrated the feasibility of quantum entanglement to improve atomic clock performance, but these were constrained by the limitations of microwave transitions and laser instability. The transition to optical frequencies, while offering a much faster time base, posed new challenges due to the higher susceptibility to noise and the technical difficulty of stabilizing laser systems at such frequencies. The breakthrough achieved by incorporating the global phase effect bridges this gap, facilitating the successful application of these quantum techniques in the optical domain.
The researchers’ controlled experiments meticulously measured the enhancement in timekeeping precision, showcasing that their entanglement-assisted global phase spectroscopy can resolve differences in clock ticking frequency nearly twice as small as previous methods could manage without this quantum augmentation. This outcome not only validates their theoretical models but also signifies a practical advancement that could influence diverse fields reliant on ultra-precise time measurements.
Looking forward, the team envisions that these quantum-amplified optical clocks could revolutionize scientific and technological endeavours by being deployable beyond the confines of laboratory settings. Portable versions could monitor subtle gravitational variations, contribute to the synchronization of global data networks, or provide new experimental platforms for fundamental physics research. The enhanced ability to measure time at such fine scales could also improve the calibration of space-borne instruments and refine global navigation satellite systems.
Funding from multiple prestigious agencies including the U.S. Office of Naval Research, National Science Foundation, and Department of Energy underpinned this research, highlighting the vital role of sustained investment in quantum science and technology. The collaboration between MIT’s Research Laboratory of Electronics and the MIT-Harvard Center for Ultracold Atoms further underscores the interdisciplinary nature of these advances, combining atomic physics, quantum information science, and optical engineering.
This breakthrough represents a quantum leap in the science and technology of timekeeping, harnessing the strange and powerful principles of quantum mechanics to refine our ability to measure the flow of time itself. As atomic clocks become more precise and portable through global phase spectroscopy, their influence will ripple across fundamental physics, metrology, and emerging quantum technologies, redefining our understanding of time and its role in the universe.
Subject of Research: Precision improvement of optical atomic clocks through quantum amplification and global phase spectroscopy.
Article Title: Quantum-amplified global-phase spectroscopy on an optical clock transition.
Web References: DOI: 10.1038/s41586-025-09578-8
Image Credits: Melanie Gonick, MIT
Keywords: Atomic clocks, Optical clocks, Quantum mechanics, Quantum entanglement, Quantum noise, Quantum dynamics, Quantum computing, Precision measurement, Optical frequency standards, Ytterbium atoms, Timekeeping technology, Quantum-enhanced spectroscopy
