Researchers have achieved a significant breakthrough in precision timekeeping. To realize their strontium optical lattice clock, this group has achieved an astonishing atomic coherence time of 118 seconds. A multidisciplinary team, under the direction of Kyungtae Kim, made this discovery. It is an impressive advance for the production of highly precise frequency standards, which would have great implications in fundamental physics and global positioning satellites.
To realize the strontium optical lattice clock, we use the collective quantum properties of tens of thousands ultracold atoms. These atoms are suspended in a honeycomb-like arrangement produced by laser beams. The clock flips back and forth between the two different quantum states at an exact frequency. This singular talent allows it to keep time with accuracy that outstrips modern atomic timekeeping devices. The research team realized a stunning atomic instability of only 1.5×10^-18 at one second. This result really underscores just how amazing this performance capability is for the clock.
Innovative Design and Alignment Techniques
To them, this was an opportunity to use cutting-edge methods to maximize the clock’s overall performance. Perhaps the most important one was orienting the optical lattice to align with the direction of gravity. This nonuniformity in alignment introduced a tilted lattice potential, which can be modeled as a staircase of trapping sites. This novel geometry enables better atom trapping and manipulation in the optical lattice.
“We have been pushing the performance of the optical lattice clock,” – Kyungtae Kim
The trapping potential used by the researchers was about five to ten times weaker than that of traditional lattice clocks. This lowering of depth decreases energy barriers between adjacent sites. It does so by enabling better atomic interactions and significantly enhancing stability in measurements.
Kim and his team further looked into the atomic interactions that impact a clock’s performance. They then worked with different physical configurations to make it as effective as possible. These are all critical factors affecting their coherence time and gave them direction to make future improvements.
Understanding Coherence and Performance Limitations
Their in-depth theoretical analysis uncovered several physical processes that can shorten the anticipated coherence time of realistic optical lattice clocks. Specifically, Kim explained that issues at the atomic level—specifically the interaction between neighboring lattice sites—are paramount in capping performance.
“We also identified the atomic interactions that limit performance,” – Kyungtae Kim
The researchers identified two regimes depending on the lattice depth. Inter-site s-wave interactions dominate at shallower depths. Continuing to greater depths, the primary limiting factor becomes s-wave interactions with the spectator atoms produced from lattice photon scattering.
“At shallow lattice depths, inter-site s-wave interactions are dominant, whereas at deep lattice depths, s-wave interactions with spectator atoms generated by lattice photon scattering become the primary limitation,” – Kyungtae Kim
These data and insights will inform the design of follow-on research. Next, they hope to increase coherence time even more and enhance overall clock stability.
Future Directions and Applications
The new precision that was gained with the strontium optical lattice clock paves the way for many more exciting research and application possibilities. Using a lot of atoms to suppress quantum projection noise, Kim and his team hope to increase measurement stability in the frequency domain. The idea is analogous to decreasing statistical uncertainty in coin-tossing. All the while, by increasing their number of trials or atoms, scientists get more solid results.
“To improve frequency measurement stability, we want many atoms to reduce quantum projection noise,” – Kyungtae Kim
The researchers are looking forward to integrating atom interferometry with emerging atomic clock technology. They imagine this coupling within a single, integrated experimental platform, one that could produce revolutionary discoveries. This powerful combination would enable novel measurements in gravimetry and redshift phenomena.
“More importantly, we are now excited about the prospect of combining atom interferometry (for gravimetry) with atomic clocks (for redshift measurements) within the same experimental platform,” – Kyungtae Kim