Breaking barriers in energy-harvesting using quantum physics

Harnessing quantum states that avoid thermalization enables energy harvesters to surpass traditional thermodynamic limits such as Carnot efficiency, report researchers from Japan. The team developed a new approach using a non-thermal Tomonaga-Luttinger liquid to convert waste heat into electricity with higher efficiency than conventional approaches. These findings pave the way for more sustainable low-power electronics and quantum computing.  

Energy harvesters, or devices that capture energy from environmental sources, have the potential to make electronics and industrial processes much more efficient. We are surrounded by waste heat, generated everywhere by computers, smartphones, power plants, and factory equipment. Energy-harvesting technologies offer a way to recycle this lost energy into useful electricity, reducing our reliance on other power sources.

However, conventional energy-harvesting methods are constrained by the laws of thermodynamics. In systems that rely on thermal equilibrium, these laws impose fundamental caps on heat conversion efficiency, which describes the ratio of the generated electrical power and the extracted heat from the waste heat, for example, is known as the Carnot efficiency. Such thermodynamic limits, like the Curzon-Ahlborn efficiency, which is the heat conversion efficiency under the condition for obtaining the maximum electric power, have restricted the amount of useful power that can be extracted from waste heat.

Now, a research team led by Professor Toshimasa Fujisawa from the Department of Physics at Institute of Science Tokyo (Science Tokyo), Japan, in collaboration with Senior Distinguished Researcher Koji Muraki from NTT Basic Research Laboratories, Japan, has found a way to bypass this barrier. In their paper published in Communications Physics on September 30, 2025, the team introduced a novel energy-harvesting technique that uses unique quantum states to achieve efficiencies that go beyond the conventional thermodynamic limits.

Instead of relying on traditional thermal states, the researchers harnessed the properties of a non-thermal Tomonaga-Luttinger (TL) liquid. This is a special type of one-dimensional electron system that, due to its quantum nature, does not thermalize. This means that when heat is introduced, the system holds onto its non-thermal, high-energy state rather than spreading the energy out evenly, as happens in a conventional thermal system.

The research team designed an experiment to demonstrate the potential of this concept. They injected waste heat from a quantum point contact transistor—a device that controls electron flow—into a TL liquid. This non-thermal heat was transported several micrometers to a quantum-dot heat engine, which is a microscopic device that converts heat into electricity through quantum effects. The researchers found that this unconventional heat source produced a significantly higher electrical voltage and achieved higher conversion efficiency, performing much better than a conventional, quasi-thermalized heat source. “These results encourage us to utilize TL liquids as a non-thermal energy resource for new energy-harvesting designs,” says Fujisawa.

Subsequently, the researchers developed a model based on a binary Fermi distribution to provide a description of non-thermal electron states in the proposed system. Using it, they showed that their technique surpasses not only the Carnot efficiency but also the Curzon-Ahlborn efficiency, which describes the efficiency at maximum power output of conventional heat engines.

Overall, this research opens the door to a new generation of energy harvesting, leveraging non-thermal quantum states. “Our findings suggest that waste heat from quantum computers and electronic devices can be converted into usable power via high-performance energy harvesting,” remarks Fujisawa. With any luck, further efforts in this field will make future technologies more powerful and sustainable.

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About Institute of Science Tokyo (Science Tokyo)
Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human wellbeing to create value for and with society.”