Physicists are developing a new way to define temperature using the principles of quantum mechanics, potentially eliminating the need for traditional calibration methods that rely on a chain of commercially certified sensors. The breakthrough, presented at the American Physical Society Global Physics Summit, involves a device leveraging the behavior of ultra-cooled rubidium atoms to establish an absolute standard for the kelvin scale.
The Problem with Current Temperature Standards
Currently, temperature measurements—whether in Celsius, Fahrenheit, or the physicist’s standard kelvin—ultimately trace back to calibrations performed by national standards institutions like the National Institute of Standards and Technology (NIST). This process, while effective, is inherently indirect. Every sensor relies on another sensor’s calibration, creating a dependency that introduces potential error. Zero kelvin represents the theoretical absolute coldest temperature, but verifying a single kelvin’s accuracy remains a complex task.
How the Quantum Device Works
The new device sidesteps this issue by directly linking temperature to a fundamental quantum property. Researchers trap rubidium atoms and manipulate them with lasers and electromagnetic fields, chilling them to roughly 0.0000017 of room temperature (half a millikelvin). At this extreme cold, the outermost electrons become incredibly sensitive to even minute temperature fluctuations.
When exposed to heat, these electrons “jump” into different quantum states. The key is that these jumps follow well-defined mathematical rules, meaning temperature can be determined directly from the frequency of these electron transitions.
“Every rubidium atom in the world is exactly the same, and they will behave in exactly the same way in the same environment. I can rebuild the device on the other side of the world, and it will be exactly the same,” says Noah Schlossberger of NIST, highlighting the device’s potential for universality.
Implications and Future Development
The International Bureau of Weights and Measures already defines the kelvin based on quantum constants. However, even NIST uses conventional sensors for actual calibration. This new device offers a fully quantum-based verification method. Its greatest advantage is the inherent reproducibility: since all rubidium atoms behave identically under the same conditions, the device could, in theory, be replicated anywhere with identical results.
This level of precision is crucial for high-precision technology like atomic clocks, which operate optimally at ultra-low temperatures.
While still a prototype—currently bulky and taking months to build—the team is working to refine the design, improve detection accuracy, and make it more practical for real-world applications. The long-term goal is a self-calibrating temperature standard that eliminates reliance on external verification, fundamentally redefining how we measure heat itself.
