Quantum physicists have harnessed a peculiar phenomenon known as entanglement to enhance the accuracy of optical atomic clocks, which measure time through the inherent ‘ticking’ of atoms.
Picture entering a room filled with various grandfather clocks, each ticking at unique intervals.
Researchers from the University of Colorado Boulder and the National Institute of Standards and Technology (NIST) have effectively recreated that experimental space at the atomic and electronic level. Their innovation could lead to the development of advanced optical atomic clocks, devices that gauge time by monitoring the natural “ticking” of atoms.
The new clock design utilizes dozens of strontium atoms arranged in a lattice configuration. To boost its effectiveness, the team induced a type of ethereal interaction, termed quantum entanglement, between groups of atoms—essentially merging four distinct types of clocks into one timekeeping device.
This isn’t just an average timepiece: The researchers demonstrated that, under specific conditions, their clock could surpass a precision benchmark known as the “standard quantum limit,” which physicist Adam Kaufman refers to as the “Holy Grail” of optical atomic clocks.
“We can subdivide the same duration into increasingly smaller intervals,” explained Kaufman, the study’s lead author and a researcher at JILA, a collaborative institute between CU Boulder and NIST. “This enhancement could enable more accurate timekeeping.”
The advancements made by the team could lead to the creation of novel quantum technologies, including sensors capable of detecting subtle environmental changes, such as variations in Earth’s gravity due to altitude.
Kaufman and his team, including Alec Cao, a graduate student at JILA and the study’s primary author, published their research findings on October 9 in the journal Nature.
Lassoing atoms
This research marks a significant leap forward for optical atomic clocks, which serve more functions than merely keeping time.
To construct such a device, scientists typically begin by collecting and cooling a cloud of atoms to near absolute zero. They then target those atoms with a carefully calibrated laser. If the laser’s frequency is correctly adjusted, the electrons surrounding those atoms will jump from a lower to a higher energy state and back, much like the pendulum of a grandfather clock moving back and forth—only these atomic clocks “tick” more than a trillion times each second.
These clocks are extraordinarily precise. The latest optical atomic clocks at JILA, for instance, can detect slight gravitational changes if raised by just a tiny fraction of a millimeter.
“Optical clocks have become a vital tool in numerous facets of quantum physics because they enable precise control over individual atoms—both in their location and their energy states,” Kaufman noted.
However, these clocks face a significant limitation: Quantum mechanics dictates that even atomic-scale particles can behave unpredictably, establishing a theoretical ceiling on clock precision.
Entanglement, however, may provide a means to overcome this limitation.
Fluffy orbits
Kaufman clarified that when two particles become entangled, knowing something about one automatically informs you about the other. In practice, entangled atoms in a clock operate more like a single atom than distinct entities, making their behavior more predictable.
In this study, the researchers created this quantum linkage by moving their strontium atoms such that their electrons orbited far from their nuclei—almost as if they were composed of a cotton candy-like structure.
“It’s like a fluffy orbit,” Kaufman described. “This fluffiness enables the electrons from two nearby atoms to interact strongly with one another.”
These paired atoms also “tick” faster than those functioning independently.
The team investigated clocks that combined single atoms with entangled groups of two, four, and eight atoms—essentially integrating four clocks ticking at four different rates into one device.
They observed that, under certain conditions, the entangled atoms exhibited significantly less uncertainty in their ticking compared to traditional optical atomic clocks.
“This indicates we can reach the same precision levels in less time,” he stated.
Exquisite control
The team recognizes that further work is necessary. Currently, their clock can operate effectively for only about 3 milliseconds. Beyond that threshold, the entanglement among atoms begins to diminish, leading to chaotic atomic ticking.
Nonetheless, Kaufman is optimistic about the device’s potential. His team’s method for entangling atoms may lay the groundwork for what physicists refer to as “multi-qubit gates”—fundamental operations essential for computations in future quantum computers, which may eventually outperform classical computers for specific tasks.
“The challenge now is: Can we produce new clock designs with specific attributes, made possible by the extraordinary control we have over these systems?” Kaufman pondered.
