Optical Clock With Integrated Photonics

The Technology

NIST researchers aim to create an optical lattice clock — the most accurate and precise type of clock invented to date — that can be manufactured at scale. Inspired by a record-setting optical lattice clock created at JILA (a joint institute of NIST and the University of Colorado Boulder), the new clock uses atoms of the element strontium to provide a frequency reference to which laser light is tuned.

The JILA clock and its associated hardware occupy several laboratory rooms. To create a scalable, compact device that can be manufactured by the thousands, the NIST team is working to adapt techniques from the microelectronics industry to work with optical light. Specifically, the researchers combined integrated photonics — chip-scale circuits for light — with the emerging science of “metasurface” optics. 

Metasurface optics uses tiny antenna-like structures much narrower than a human hair to miniaturize the lenses, mirrors and waveguides that account for much of the size and power consumption of laboratory clocks. Researchers from NIST and the company Octave Photonics developed small frequency combs to stabilize the laser used to read out the strontium frequency. 

The clock itself was assembled by the company Vector Atomic. The final package was only a few inches on a side, excluding the lasers needed to operate it. The NIST team is now characterizing its performance.

Advantages Over Existing Methods

Today’s optical clocks are large, complex and expensive. The few commercially available versions sell for hundreds of thousands or millions of dollars. 

Meanwhile, chip-scale atomic clocks that use microwave frequencies are much smaller and cheaper, but they are orders of magnitude less accurate and precise than state-of-the-art optical clocks.

A smaller, simpler and cheaper optical clock that can be manufactured at scale could enable high-accuracy optical timekeeping to more readily escape from the lab and be deployed in the field.

Applications

Small, off-the-shelf optical clocks could be used in a variety of important industries. For example, they could be integrated into networks that provide timing for electrical grids, internet data centers, financial markets and other technological infrastructure. Currently, these networks use microwave clocks or rely on GPS timing.

Optical clocks could also serve as exquisite quantum sensors based on the theory of relativity, which predicts that clocks tick slower in higher gravity. While this prediction has been confirmed in experiments, a widely available, affordable optical clock would allow it to be applied for practical purposes.

For example, optical clocks integrated into geodesy infrastructure — the networks of equipment used to measure and monitor Earth’s surface elevation and movement — could enhance current efforts to monitor land subsidence and underground aquifers for groundwater depletion. They could detect tiny movements in Earth’s crust and other geological activity, potentially giving advance warning of earthquakes and volcanic eruptions. Possibly they could even aid in the discovery of underground minerals and hidden tunnels. And if optical clocks someday become cheap and available enough to be integrated into surveying equipment, they could enable surveyors to quickly obtain high-accuracy height measurements.

Compact, widely available optical clocks could also transform navigation. Because precise timing is essential for accurate positioning and navigation, optical clocks aboard planes, ships and vehicles could help enable GPS-free navigation — a long-held goal with profound implications for defense and national security.

Deployed in space, portable optical clocks could even help answer fundamental questions about the universe, including potentially illuminating the nature of dark matter.

Key Papers

Sindhu Jammi, Travis C. Briles and Scott B. Papp. Three-dimensional, multi-wavelength beam formation with integrated metasurface optics for Sr laser cooling. Optics Letters. Published Oct. 17, 2024. DOI: 10.1364/OL.538446

Andrew Ferdinand, Zheng Luo, Sindhu Jammi, Zachary Newman, Grisha Spektor, Okan Koksal, Akash Rakholia, Daniel Sheredy, Parth Patel, Travis Briles, Wenqi Zhu, Martin Machai Boyd, Amit Agrawal and Scott Papp. Laser-cooling 88Sr to microkelvin temperature with an integrated-photonics system. Physical Review Applied. Published March 21, 2025. DOI: 10.1103/PhysRevApplied.23.L031002