Sometimes scientific breakthroughs are born from unexpected turns. A group led by Oscar Dahlsten, an associate professor in the Department of Physics at City University of Hong Kong, set out to prove a theoretical limit, but instead discovered a quantum solution. The work was published in the journal Physical Review Letters.
Energy from natural sources is often accompanied by entropy - a measure of chaos and randomness. Because of this, it is difficult to convert into predictable power for charging batteries and running electronics.
The study shows that a feature of quantum theory known as the non-uniqueness of the decomposition of mixed states can provide deterministic energy harvesting. In simple terms, energy is transferred from a source to a storage device without an accompanying transfer of entropy.
The key idea: a quantum storage device can be charged in several ways corresponding to different intermediate states of superposition - a state in which the system appears to be in several variants at once. If the source causes one of these transitions in the storage device, the final state will with certainty turn out to be charged. This points to a possible mechanism for predictable energy transfer without the transfer of entropy.
"At first we wanted to show that such a protocol might be impossible. To our surprise, the effort led to a quantum solution that provides exactly the deterministic energy transfer we were looking for," Dahlsten said.
The proposed theoretical framework describes the conversion of ambient energy into useful power with minimal losses. In the future, this could reduce the losses of conventional AC-to-DC rectifiers and power Internet of Things devices, wearable electronics, smart city sensors and 6G equipment from ambient sources.
For now this is theoretical work, not finished devices. Nevertheless, the authors see in it a possible path toward future low-power technologies.