Efficient Charging of Nuclear Quantum Batteries via Chain-STIRAP: A Five-State Ladder System with XFEL Pulses

Abstract We propose an efficient scheme for charging a quantum battery based on a five-state ladder-type nuclear system using the chain-STIRAP technique. Four time-delayed X-ray free-electron laser pulses interact with an accelerated nuclear beam, where the relativistic Doppler effect compensates the frequency mismatch between gamma-ray transitions and laser photons. Using 168Er as a realistic example, we demonstrate complete population transfer from |1⟩ to |5⟩ without populating interme-diate states. In addition to population dynamics, we calculate the stored energy and ergotropy as key performance metrics for quantum battery applications. A three-state system is also analyzed for comparison. Our results show that the final ergotropy reaches 99% of the stored energy for the five-state system, compared to 95% for the three-state case. The charging efficiency exceeds 0.98 under optimal pulse conditions, while the required peak laser intensity is about 1026 W/cm2, considerably lower than conventional π-pulse or STIRAP protocols. This work establishes chain-STIRAP as a viable tool for high-density energy storage in nuclear quantum batteries.