Physicists at the National Institute of Standards and Technology (NIST) have demonstrated a method for controlling a single molecule with near-perfect reliability, using techniques originally developed for atomic clock research.
The work focuses on a charged calcium monohydride molecule, which consists of one calcium atom and one hydrogen atom with an electron removed. Molecules are more complex than atoms because they can rotate and vibrate, creating many possible internal states. This complexity has made them difficult to control precisely in quantum experiments.
To overcome this challenge, the NIST team paired the molecule with a single calcium ion that can be easily manipulated with lasers. The two charged particles were trapped together in an ion trap, where their motions are linked through their mutual electrical repulsion.
The researchers used a technique called quantum logic spectroscopy. Lasers were applied to cool the calcium ion, which in turn cooled the molecule. The team then used lasers to change the rotational state of the molecule. Although the molecule itself does not emit light that can be easily detected, changes in its state affected the calcium ion. When the molecule changed rotation, the calcium ion emitted flashes of light that could be observed with a camera.
By monitoring these flashes, the researchers were able to identify and control the molecule’s rotational state. The molecule remained in a defined state for approximately 18 seconds before thermal radiation caused it to change. During that time, the team could repeatedly confirm the molecule’s state.
According to the researchers, the method achieved a 99.8 percent success rate in controlling the molecule’s quantum state. The experiment also showed that the molecule provided a highly detailed measurement of the surrounding thermal radiation, more precise than the temperature sensor inside the vacuum system.
The technique is not limited to calcium monohydride. NIST researchers state that the same approach can be applied to other molecular species, allowing scientists to select molecules based on specific properties required for different quantum experiments.
The results were published in Physical Review Letters. The work demonstrates a general protocol for molecular control rather than a molecule-specific result.
