Physicists at the National Institute of Standards and Technology (NIST) have manipulated the quantum rotational state of a single calcium monohydride molecular ion with a 99.8% success rate — roughly 998 successful operations per 1,000 attempts — and held that state for about 18 seconds before ambient thermal radiation disturbed it. The team published the work in Physical Review Letters on Dec. 9, 2025 (DOI: 10.1103/7ypf-91jr).

The numbers matter for anyone building quantum sensors or clocks. Eighteen seconds of rotational coherence gives the researchers thousands of measurement opportunities before the molecule's state changes, and the 99.8% fidelity figure was verified by repeated interrogation of the readout ion, confirming the result was not a statistical fluke. The researchers detected thermal-radiation-driven state changes within roughly 10 milliseconds of occurrence.

The target molecule, CaH+, consists of one calcium atom, one hydrogen atom, and a missing electron that leaves the molecule charged. Unlike a spherical single atom, which looks the same from any angle, CaH+ resembles a lopsided dumbbell. Its asymmetry gives it rotational and vibrational degrees of freedom — and a correspondingly large state space that has historically made molecules far harder to control than atoms.

"To control a particle, we need to pinpoint it in one specific state. A molecule has a large number of states it can be in because of its rotation and vibration," said Dalton Chaffee, lead author on the paper. "This, in essence, is what makes molecules so much harder to control than atoms."

Why the physics changes the buying decision. The technique at the core of the experiment is quantum logic spectroscopy, originally developed to improve the precision and accuracy of trapped aluminum-ion clocks at NIST. The method sidesteps a fundamental measurement problem: CaH+ barely interacts with laser light, so it cannot be laser-cooled or read out directly. The researchers co-trapped a single calcium ion alongside the molecular ion in the same trap. Because both carry equal charge, they repel each other through their shared motion — Dietrich Leibfried likens the coupling to a loaded spring pushing the two particles apart. Lasers cool the calcium ion; through the spring-like coupling, the molecular ion cools as well. The cryogenic environment pays an additional dividend: the molecular state persists 10 times longer than it would at room temperature.

Readout works the same way. A laser pulse flips the molecule's rotational state; the calcium ion senses the change through the shared motion and emits a flash of photons. A second pulse reverses the rotation, and the ion flashes again. That double flash marks two confirmed quantum jumps between molecular states.

"That's quantum mechanics. In our lab, we can see with the camera if our ion is in one quantum state or another, which I find super cool," said NIST postdoctoral fellow Baruch Margulis. "It's captivating to see it with your own eyes."

"It's sort of a peekaboo game, if you wish," Margulis explained. "As soon as thermal radiation drives the molecule to a different state, the flashes of light from the observer ion cease, and we're able to see that almost as it happens, within 10 milliseconds or so."

A thermometer that outperformed the instrument. During the experiment, the molecule delivered a more accurate and detailed picture of the thermal radiation inside the vacuum chamber than the conventional thermometer installed there, according to graduate student April Sheffield, who also co-authored the study. The molecule functions, in effect, as a microscopic quantum thermometer — and unlike a bulk sensor, it can resolve specific frequencies of thermal radiation rather than an aggregate temperature. Leibfried noted that atomic clocks, which suffer from minusculate thermal-radiation fluctuations, are one direct application.

That sensitivity cuts both ways, Leibfried acknowledged. "If you're sensitive to something, it can be a curse, because you would like to not be sensitive, or it can be a blessing. You can use that sensitivity to your advantage."

The protocol is species-agnostic, which is the strategic point. Quantum computing and sensing groups have largely worked with a small set of laser-accessible ions — calcium, barium, aluminum — a narrow slice of the periodic table. Because the quantum logic approach does not depend on the molecule having a convenient optical transition, it can extend to other molecular species. Chaffee's co-authors include Margulis, Sheffield, Julian Schmidt, April Reisenfeld, David R. Leibrandt, Dietrich Leibfried, and Chin-Wen Chou.

"It's not just a one-off, but it's a demonstration of a protocol that can be used for many other molecules," Margulis said. "When you think about a periodic table, it has a finite number of elements. Molecules are more diverse. So, although they are hard to control, there's a huge pool of molecules. If you had perfect control, you could select a candidate based on which technology you're interested in, whether it's quantum sensing, quantum information science, or the search for new physics."

The team cautions that precise control over chemical reactions — the long-term aspiration — remains far off. The nearer-term question for metrology labs and clock developers is whether cryogenic quantum-logic molecular thermometers can be integrated into existing ion-trap platforms to characterize blackbody radiation shifts that currently limit clock systematic budgets.