A copper molecule stores quantum information in its spin, which is like a tiny magnet that can point up or down. But there is always heat around, and the molecule's atoms are constantly jiggling. This jiggling gradually knocks the spin off course, and the information is lost. The question is: which atomic motions cause the most trouble?

Previously, it was thought that slow distortions of the whole molecule were the culprits, as if it were slightly skewing. But calculations with such distortions gave the wrong spin lifetime. Experiments, however, hinted at something else: fast stretches of the bond between the copper atom and neighboring nitrogen atoms matter. The problem was that it is hard to isolate individual motions from a warm, jiggling molecule.

The scientists recorded a short "life" of the molecule at room temperature, measuring how the spin senses the magnetic field every few femtoseconds. Then a computer decomposed this recording into individual vibrations and determined which ones are most strongly coupled to the spin. It turned out that the main culprits are fast stretches of the metal–nitrogen bond, while slow distortions have almost no effect, even though their amplitude is large.

Now, knowing this, one can modify the molecule in advance so that the harmful vibrations are weaker, and the quantum memory lasts longer.