Fluctuation-free Quantum Battery Charging Enabled by Bell-like Entangled and Separable Charger States

The implication of entanglement in quantum battery charging remains poorly understood. In addition, intrinsic quantum randomness poses a fundamental challenge to charging uniformity across distinct trials. To address these issues, we study a three-qubit system within a cascaded collision frame, with two qubits acting as the charger and the third serving as the battery. After each collision, an adaptive measurement is performed on the charger, yielding four conditional post-measurement battery states with identical expected stored energy. For arbitrary fixed charger states, we derive analytical expressions for the recurrence relation of stored energy. We find that stored-energy fluctuations depend on whether the dynamics relies on the battery phase ${\gamma }_n$. For two Bell-like families of entangled states, together with their computational basis states termed Bell-like separable states, the dynamics is ${\gamma }_n$-independent and fluctuations vanish, whereas for other entangled and separable states, fluctuations emerge. These insights establish a paradigm for engineering charger states to design uniform-charging quantum-battery architectures despite inherent quantum randomness.