Experimental Realization of a Nonreciprocal Quantum Battery
Quantum batteries promise faster and more efficient energy storage and extraction by harnessing quantum mechanics, serving as essential building blocks for future quantum devices. A key practical requirement-unidirectional energy flow during charging-is straightforward in classical batteries via potential difference, yet remains a major challenge in the quantum regime due to the inherent reciprocity of coherent coupling. Here, we realize the first backflow-free, nonreciprocal quantum battery in the few-quantum regime, implemented in a highly controlled trapped-ion system via a qubit-reservoir engineering technique. By subtly tailoring quantum interference between coherent and dissipative couplings of two laser-cooled motional modes, we achieve strictly unidirectional energy flow from the charger to the battery. We observe maximum charging power at an exceptional point and demonstrate a complete charge-discharge cycle with unitary work extraction. This work establishes the foundation for directional energy transfer and storage in micro- and nanoscale quantum devices, with broad implications for nonreciprocal energy harvesting, precision metrology, information processing, and quantum thermodynamics.