Reaching New Heights in Timekeeping
Every moment you rely on precise timing—whether checking a phone, making a digital payment, or navigating via GPS—you benefit from the extraordinary accuracy of atomic clocks. Today’s standard clocks track cesium atoms, ticking at about 10 billion times per second. But scientists are pushing toward optical atomic clocks that work with even faster natural oscillations in atoms such as ytterbium, potentially reaching 100 trillion ticks per second. A recent breakthrough from MIT researchers promises to dramatically improve the stability of these optical clocks by reducing quantum noise and uncovering a new way in which the clock’s laser interacts with the atoms.
The quantum noise barrier and a new ally
Quantum noise is a fundamental limit in precision measurement arising from quantum mechanics. It blurs the ideal tick of the atoms, making it harder to read the clock’s frequency with highest fidelity. The MIT team has devised a method to suppress this noise and, intriguingly, to exploit a previously overlooked effect: the laser’s influence on the atoms during their interaction. They showed that the laser can imprint a measurable “global phase” onto an ensemble of entangled ytterbium atoms, carrying information about the laser frequency that can be extracted to stabilize the clock further.
Global phase spectroscopy and quantum amplification
The researchers built on prior work that used quantum entanglement to reduce noise in atomic clocks. In earlier experiments, entanglement distributed the clock’s uncertainty across hundreds of ytterbium atoms trapped inside a high-quality optical cavity. Those efforts demonstrated that reducing noise could tighten the clock’s readout, yet laser instability remained a bottleneck. In the new study, the team applied a time-reversal technique to optical clocks. By driving the atoms with a laser near the atoms’ optical transition, they allowed the system to acquire a global phase during the atoms’ interaction, even as the atoms returned to their original states.
Crucially, this global phase becomes a proxy for the laser-atom frequency difference. When the difference is small, quantum noise tends to obscure it; but the team’s approach amplifies the signal relative to the noise. Through a combination of entanglement and the laser-induced global phase, they achieved a doubling of clock precision in their optical setup. The result is a clock that can resolve finer frequency differences without succumbing to the same quantum noise limits as before.
Why this matters for portable, future clocks
The significance of this advance lies not only in a single lab measurement. Optical clocks promise far greater stability than microwave-based clocks, which could yield more accurate navigation, timing for distributed networks, and novel tests of fundamental physics. The MIT findings suggest that the precision gains scale with the number of atoms, meaning larger atomic ensembles could yield even more dramatic improvements. The team envisions transportable, portable optical clocks that can be deployed to diverse locations for field measurements in geophysics, cosmology, and beyond.
What comes next
As researchers continue refining global phase spectroscopy, practical challenges remain: maintaining stable laser systems, expanding entangled atom ensembles, and integrating these clocks into real-world environments. The MIT group argues that their method could lower the barrier to deploying portable optical clocks, enabling applications such as detecting dark matter, testing fundamental forces, and potentially predicting geophysical events like earthquakes with unprecedented precision.
“With these clocks, people are trying to detect dark matter and dark energy, and test whether there really are just four fundamental forces, and even to see if these clocks can predict earthquakes,” notes study author Vladan Vuletić. “Our method can help make these clocks transportable and deployable to where they’re needed.”
The study’s co-authors—León Zaporski, Qi Liu, Gustavo Velez, Matthew Radzihovsky, Zeyang Li, Simone Colombo, and Edwin Pedrozo-Peñafiel—collaborated within the MIT-Harvard Center for Ultracold Atoms and the MIT Research Laboratory of Electronics, underscoring a growing ecosystem of ultracold-atom research driving next-generation timekeeping.
