Researchers at the University of Oulu in Finland have identified a fundamental limit that prevents quantum batteries from delivering energy and power with perfect stability at the same time.
The study found that increasing the charging power of a quantum battery can also increase fluctuations in its output, making maximum power alone an insufficient measure of performance.
Quantum batteries store and transfer energy using quantum systems rather than the chemical reactions employed by conventional batteries. They are being investigated as potential power sources for quantum processors and other quantum technologies, although their development remains at the theoretical and proof-of-principle stage.
The research establishes fundamental limits on fluctuations in both the energy delivered by a quantum battery and the rate at which it is delivered.
Brij Mohan, postdoctoral researcher at the University of Oulu in Finland and first author of the study, said: “A quantum battery ideally should not only be fast and powerful but also needs to charge or deliver energy in a reliable and stable manner at the same time. Our work shows that quantum mechanics places fundamental limits on the reliabilities of quantum batteries.”
The researchers used noise-to-signal ratios to compare fluctuations in work and power with their average values. Lower ratios represent more consistent and reliable operation.
They found that a quantum-mechanical uncertainty relation prevents fluctuations in delivered energy and power from both being made arbitrarily small simultaneously. The effect arises because work and power are represented by non-commuting operators in closed quantum batteries, similar to the relationship between position and momentum in quantum mechanics.
The University of Oulu team compared three approaches to charging batteries containing multiple quantum cells. Under parallel charging, each cell operates independently. Collective charging involves all the cells acting together, while hybrid charging allows groups of cells to interact.
Collective charging can exploit quantum entanglement to increase power as more cells are added. The study found, however, that stronger collective interaction also produces greater power fluctuations and therefore reduces reliability.
Parallel charging provided greater stability but did not deliver the same increase in power. An intermediate hybrid arrangement offered the best compromise between output and consistent energy delivery.
Tanmoy Pandit of VTT Technical Research Centre of Finland said: “Our results show that there is a meaningful way to balance power enhancement and the reliability of work and power. Intermediate-range interactions based charging scheme can provide a useful compromise between high power and stable operation.”
The researchers obtained similar results from quantum batteries modelled using transverse Ising-like many-body interactions, indicating the trade-off was not confined to the simplest theoretical system.
Manabendra Nath Bera of the Indian Institute of Science Education and Research Mohali said: “The reliability limits connect quantum fluctuations with many-body quantum physics in a direct way. They provide useful charging strategies that are practically advantageous.”
Maciej Lewenstein of the Institute of Photonic Sciences in Spain said: “Quantum batteries offer a fascinating link between quantum information, thermodynamics, and many-body physics. Understanding their fluctuations is essential if these systems are eventually to become useful technological resources.”
The study, Fundamental Limitations on the Reliabilities of Power and Work in Quantum Batteries, was published in PRX Quantum. Contributors also came from VTT and QMill in Finland, IISER Mohali in India, Leibniz University Hannover and TU Berlin in Germany, and ICFO in Spain.
Future research will examine reliability limits under more realistic conditions, including environmental noise, energy dissipation, open-system dynamics and experimentally relevant quantum platforms.
