Researchers Link Spin Coupling to Differing Energy Efficiencies

An interacting two-qubit system functions as both a quantum battery and a quantum Otto heat engine. The working medium is described by an anisotropic Heisenberg Hamiltonian supplemented by a dipolar interaction, a symmetric spin, orbit interaction, and an external magnetic field. A coherent unitary charging protocol was first analysed within a unified microscopic framework, with resulting energy-storage performance characterised through ergotropy, anti-ergotropy, charging power, storage capacity, and the l1-norm of quantum coherence.

Investigations explored the effects of the dipolar interaction, temperature, and magnetic field on these quantities. Subsequently, the same working medium was employed in a quantum heat engine.

Dipolar interaction boosts work extraction from two-qubit systems beyond established limits

Maximum ergotropy, a measure of extractable work, increased by substantially when dipolar interaction was enhanced within a two-qubit system at Mohammed V University and Ibnou Zohr University. Previously, enhancing one aspect invariably compromised another; this strong improvement surpasses previous limitations where increasing energy storage concurrently reduced operational efficiency. The research establishes a new threshold for simultaneously optimising both energy retention and potential output in quantum devices functioning as batteries and heat engines.

Manipulating microscopic spin interactions offers independent control over these important energetic parameters, paving the way for more flexible quantum technologies capable of efficient energy management and conversion. A fifteen percent increase in charging power accompanied the enhanced ergotropy when scientists and Ibnou Zohr University strengthened dipolar interaction within their two-qubit system.

Storage capacity, representing the total accessible energy range, rose sharply with greater dipolar coupling; anti-ergotropy, measuring unusable internal energy, was carefully characterised during coherent unitary charging where controlled addition of energy occurred to the qubits. However, while enhancing energy retention, maximum work obtainable from an equivalent quantum Otto cycle decreased slightly under stronger interactions demonstrating that optimising one function does not automatically improve another.

Internal cohesion limits power output from advanced energy devices

Building systems that both efficiently store power and effectively deliver it as useful work remains elusive, this work addresses the persistent challenge of optimising energy devices. The findings reveal an inherent tension within this goal: strengthening microscopic interactions responsible for enhanced storage diminishes a device’s ability to perform work during each cycle. This counterintuitive result challenges conventional thinking which assumes improved capacity automatically translates into better performance, raising questions about whether truly universal design principles exist for quantum batteries and heat engines.

Strengthened internal connections hinder performance, meaning enhancing energy storage can simultaneously reduce power output. Understanding these trade-offs is vital as we begin to design more complex quantum systems for future applications; the investigation revealed that boosting interaction between qubits enhances storage capability while reducing work output per cycle. Distinct energetic roles, accumulating power versus converting it to useful activity, respond differently to microscopic adjustments within quantum systems, stressing this point further. Consequently, optimising one function does not guarantee enhancement of the other, highlighting complementary behaviours rather than universal improvements in quantum energy handling.

The research demonstrated that increasing dipolar interactions between two qubits enhanced both maximum ergotropy and storage capacity when functioning as a quantum battery. This suggests a trade-off exists between storing more energy and efficiently delivering it as usable work. The authors characterised how anti-ergotropy, unusable internal energy, changes during charging, providing insight into these competing effects within the system.