In a phone battery, there is always energy that cannot be extracted: it seems glued to the terminals. In the quantum world, this "glued" part is called bound energy. The authors showed that if you connect a helper particle to the battery (it only observes, but doesn't give up its own), bound energy ceases to be dead weight.

The key finding is a hard ceiling for this enhancement. When the battery and the helper are intertwined into a single whole without impurities (physicists say "pure state"), the gain hits exactly the bound energy of the battery. Below (possible, above) never. To avoid guessing with measurements every time, the scientists introduced a "purity index"—a simple guide that tells in advance whether it's worth bothering with the helper.

The most unexpected thing happened when the battery was placed in a shared noisy environment. Usually, noise only interferes. But here, the collective environment created an invisible connection between the battery and the helper, and the gain not only survived but stabilized. In systems with internal interactions, the picture is even more striking: when energy levels shift and rearrange, the available bound energy changes abruptly. The gain begins to depend not only on correlations but also on the energy landscape, just as a harvest depends not only on seeds but also on the field's terrain.