NIST physicists April Sheffield and Baruch Margulis achieved near-perfect control of a calcium monohydride molecular ion, demonstrating a significant advancement in molecular quantum technologies. Utilizing laser-based techniques originally developed for atomic clocks, the team at the National Institute of Standards and Technology (NIST) in Boulder successfully manipulated the rotational state of the molecule. This control, detailed in a study published in Physical Review Letters, addresses the inherent difficulty in managing molecular complexity—specifically, the numerous states arising from rotation and vibration—and opens pathways for applications in quantum technology, chemical research, and fundamental physics exploration.
Controlling Molecules with Quantum Logic Spectroscopy
NIST physicists achieved near-perfect control—a 99.8% success rate—over a calcium monohydride molecule using a technique called quantum logic spectroscopy. This method, originally developed for atomic clocks, employs a “helper” calcium ion to indirectly manipulate the molecule. Because the calcium monohydride doesn’t readily interact with lasers, the calcium ion acts as an intermediary, signaling changes in the molecule’s rotation with flashes of photons. This advancement opens possibilities for utilizing a broader range of molecules in quantum technologies.
The team’s success stems from controlling the molecule’s rotational state for an extended period—approximately 18 seconds—allowing for numerous measurements before thermal radiation disrupts the state. This sustained control is crucial, providing thousands of opportunities to analyze the molecule. Notably, the molecule itself proved to be a highly sensitive detector of thermal radiation, even surpassing the accuracy of a traditional thermometer within the vacuum chamber, suggesting potential use as microscopic thermometers.
This technique isn’t limited to calcium monohydride, offering a pathway to control a vast array of molecular species for quantum applications. Currently, quantum research primarily utilizes a small subset of charged atoms. By adapting this protocol, scientists envision expanding the possibilities to include diverse molecules, potentially revolutionizing quantum computing, sensors, and even allowing precise control over chemical reactions—though that application remains distant.
Calcium Monohydride as a Test Case
NIST physicists demonstrated near-perfect control over a calcium monohydride molecule—a molecule comprised of calcium and hydrogen with one electron removed—using a “helper” calcium ion. This control was achieved through quantum logic spectroscopy, a technique initially developed for atomic clocks. The team trapped both ions together; the calcium ion responded to lasers while the calcium monohydride did not, allowing researchers to manipulate the molecule’s rotation by observing flashes of photons from the helper calcium ion.
This level of control is significant because molecules are inherently more complex than atoms due to their rotation and vibration. The team achieved a 99.8% success rate in manipulating the calcium monohydride, meaning almost every attempt to change the molecule’s state was successful. Maintaining this state lasted approximately 18 seconds, providing ample time—thousands of opportunities—to measure the molecule before external factors caused a change, as confirmed by observing the calcium ion’s flashes.
Beyond demonstrating control, the experiment revealed calcium monohydride’s sensitivity to thermal radiation, allowing it to function as a highly accurate microscopic thermometer. This capability could prove valuable in improving atomic clocks and potentially measuring specific frequencies of thermal radiation. Furthermore, the techniques used aren’t limited to this specific molecule, suggesting broader applications for controlling a wide variety of molecules in future quantum technologies and chemical research.
Molecules as Quantum Thermometers and Sensors
Molecules, specifically calcium monohydride, can function as microscopic thermometers due to their sensitivity to thermal radiation. During experiments, the molecule provided a more accurate depiction of surrounding thermal radiation than a standard vacuum thermometer. This capability could be beneficial for improving atomic clocks, which are susceptible to thermal fluctuations. Furthermore, a molecule-based thermometer could measure specific frequencies of thermal radiation, offering a level of detail beyond conventional instruments.
The NIST team achieved near-perfect control over the calcium monohydride molecule, reaching a 99.8% success rate in manipulation attempts. This control was demonstrated using a “helper” calcium ion, which acted as an intermediary. Changes in the molecule’s rotation were signaled by flashes of photons from the calcium ion, visible to researchers. Maintaining this controlled rotational state lasted approximately 18 seconds, allowing thousands of measurements before thermal radiation caused a change.
This new level of molecular control isn’t limited to calcium monohydride. The techniques developed are adaptable to a wide range of molecular species, expanding possibilities beyond the limited selection of atoms currently used in quantum technologies. Scientists envision applying this precise control to chemical reactions, potentially opening avenues for new chemical studies, though this remains a long-term goal.
Achieving High-Fidelity Molecular Control
NIST physicists achieved near-perfect control over a calcium monohydride molecule using a “helper” calcium ion and techniques originally developed for atomic clocks. This control is significant because molecules, unlike atoms, rotate and vibrate, possessing many more states—making them difficult to manipulate. The team demonstrated a 99.8% success rate in manipulating the molecule, successfully controlling its state approximately 998 times out of 1,000 attempts, proving the method wasn’t accidental.
The researchers utilized quantum logic spectroscopy, trapping both the calcium helper ion and the charged calcium monohydride molecule together. Because of their equal charge, they repel each other. By cooling the calcium ion with lasers, the team slowed the motion of both ions, allowing for manipulation. The calcium ion “flashes” – releasing photons – indicating changes in the molecule’s rotation, acting as a visual signal of control.
This level of control allows the molecule to maintain its rotational state for approximately 18 seconds, providing thousands of opportunities for measurement. Beyond simply controlling the molecule, the experiment revealed the molecule’s ability to act as a more detailed microscopic thermometer than traditional instruments. The techniques aren’t limited to this specific molecule, offering potential for broad application across various molecular species for quantum technologies and chemical research.
