We ask whether the [[5,1,3]] holographic quantum error-correcting code — previously shown to protect logical correlations under independent physical noise — also protects a quantum battery's extractable work (ergotropy), and whether entangling multiple logical-qubit batteries during charging gives a genuine collective advantage. Part I finds a two-regime result for a single logical qubit: holographic encoding protects ergotropy strongly for noise p<0.36 (z-scores up to +5.8) but the advantage inverts catastrophically above that threshold (z-scores down to −5.0); active syndrome-based recovery removes the threshold entirely. Part II extends the question to N=2–8 entangled logical qubits. Three real methodological errors were caught and corrected en route before a trustworthy answer emerged: optimized entangling coupling gives a real, reproducible ≈2× collective advantage that shrinks monotonically with N, the opposite of the growing scaling predicted in the broader literature — corroborated by an independent ansatz and a symmetry-breaking control. Finally, collective charging's speed advantage is shown not to transfer to noise robustness. Simulation-stage results (exact state-vector and density-matrix simulation); hardware validation proposed as future work.
We ask whether the [[5,1,3]] holographic quantum error-correcting code — previously shown to protect logical correlations under independent physical noise — also protects a quantum battery's extractable work (ergotropy), and whether entangling multiple logical-qubit batteries during charging gives a genuine collective advantage. Part I finds a two-regime result for a single logical qubit: holographic encoding protects ergotropy strongly for noise p<0.36 (z-scores up to +5.8) but the advantage inverts catastrophically above that threshold (z-scores down to −5.0); active syndrome-based recovery removes the threshold entirely. Part II extends the question to N=2–8 entangled logical qubits. Three real methodological errors were caught and corrected en route before a trustworthy answer emerged: optimized entangling coupling gives a real, reproducible ≈2× collective advantage that shrinks monotonically with N, the opposite of the growing scaling predicted in the broader literature — corroborated by an independent ansatz and a symmetry-breaking control. Finally, collective charging's speed advantage is shown not to transfer to noise robustness. Simulation-stage results (exact state-vector and density-matrix simulation); hardware validation proposed as future work.
Abstract Quantum error correction (QEC) protects logical information, whereas a quantum battery is judged by the work it can deliver. We ask when a recovery operation applied during storage may be credited with protecting a battery's ergotropy. The second law bounds the average work of each recovery call from below by the change of nonequilibrium free energy it causes at bath temperature T; as a storage convention we debit the nonnegative part of this change and take the net ergotropy gain left per call as the budget for all further overhead. We apply this ledger to batteries of two to four two-level cells under collective and independent Lindblad noise, testing a coherence-restoring heuristic, the four-qubit [[4,1,2]] amplitude-damping code with two recovery completions, standard channel families, and reset channels. Every state in the code space of the [[4,1,2]] code has zero mean energy and at most half the maximal ergotropy, so a decoder that restores the code space cannot protect a fully charged battery; a completion that leaves the rest of the Hilbert space untouched avoids this bound but still loses ergotropy on a fully charged battery during storage. Unital recoveries cannot raise the ergotropy by more than the energy they supply. For four cells and inputs diagonal in the energy basis, an optimal energy-nonincreasing covariant recovery is attained by a reset channel, whose value we give in closed form and whose gain comes from removing entropy. At 10 mK and 10 GHz the tested recoveries leave at most 3.3×10⁻² energy quanta per call beyond the debit, less than one photon at the cell frequency, so any implementation that dissipates a single quantum per call beyond the debit loses ergotropy.
Charging a quantum battery through a pumped charger can lock a substantial part of its stored energy inside the bipartite correlations that grow between the constituent cells, and this \emph{correlation ergotropy}, being the energy that no local single-cell operation can reach and that only collective operations can recover, is the object of the present study. Following the charging trajectory of two coupled three-level cells, we find that the correlation ergotropy closely tracks the logarithmic negativity, which shows that the locked energy is carried by genuine bipartite entanglement rather than by coherent collective dynamics alone, and that an equal-strength coherent non-entangling drive produces no such locking at all. For a pure two-cell battery we establish an exact, basis-independent closed form in which the locked energy depends only on the sorted eigenvalues of the reduced cell and the cell energy levels, revealing that the locked fraction rises from zero at the separable corners of the Schmidt simplex to unity at the symmetric maximally entangled state and remains invariant under local unitaries. Decoherence and dephasing, which destroy the correlations, do \emph{not} release this energy but erase it, so extraction must be collective and must take place while the correlations persist, while cold damping leaves the effect intact and thermal occupation suppresses it. These results give a resource-theoretic reading of correlations in quantum batteries, sharpen the line between genuine entanglement and coherent collective dynamics, and point to experimentally accessible conditions for correlated-charge and collective-extraction protocols.
This study investigates the performance and ergotropy protection of open collective quantum batteries subject to superradiant decay. By employing a passive spectral detuning strategy within an intermediate cavity, an optimal detuning value (Δ∗) is analytically derived and numerically verified to spectrally isolate the system and protect quantum coherence, achieving up to 1088% ergotropy improvement for single qubits and superextensive collective advantage for N≥3. Our analysis resolves a "non-Markovian paradox," revealing that maximizing ergotropy does not strictly require non-Markovian memory; rather, suppressing environmental memory via detuning optimally preserves coherence, which serves as the fundamental resource. Survival maps across different environments demonstrate that thermal noise dissipates coherence more severely than telegraph noise. Finally, we establish that collective amplification of the effective coupling (geff=gN) inevitably drives large qubit arrays into the ultra-strong coupling regime, providing a quantitative ceiling Nmax on the validity of the Tavis-Cummings description and the current ergotropy protection protocol.
In this work, we investigate the autonomous charging process of a quantum battery coupled to a structured reservoir composed of two qubits, each locally coupled to its own bosonic thermal bath. Moreover, the reservoir interacts with a charger-battery architecture through three configurations: (I) direct coupling between reservoir qubits and battery; (II) collective coupling among the reservoir qubits, charger, and battery; and (III) a collective coupling between the reservoir qubits and charger together with a local charger-battery interaction. However, by using incoherent and coherent initial states, we analyze the stored energy, ergotropy, and charging power of the battery, and derive upper and lower bounds on the extractable work in terms of the free energy of coherence and the correlations exchanged between subsystems. Our results show that global and local coherences, as well as total correlations, act as quantum resources that enhance autonomous charging. Additionally, we demonstrate that the free energy stored in the quantum battery splits into contributions from coherence and correlations, providing numerical evidence that supports the derived ergotropy bounds. Importantly, this work highlights how structured reservoirs enable autonomous and resource-enhanced quantum battery operation.
We present experimental evidence that the [[5,1,3]] perfect quantum error-correcting code produces measurably superior inter-system correlation protection compared to generic Clifford encoders in superconducting quantum hardware. Five main results are reported: (1) hardware validation on IBM Quantum ibm_kingston yields ZZ_holo = +0.46 vs ZZ_rand = +0.025 (p=0.0265); (2) a 9-level capacity curve on ibm_fez confirms |ZZ_holo| = 0.692 vs |ZZ_rand| = 0.084 (t=32.057, p≈0, ratio 8.3×); (3) all-qubit noise experiment confirms amplitude plateau independent of noise level (t=25.265, p≈0); (4) inter-branch conditional correlations C_holo = 0.367 vs C_rand = 0.002 (ratio 172×, p=0.004); (5) Quantum Switch with holographic encoding yields coherence ratio 20× over random encoders (p=0.047). The holographic channel achieves CHSH = 2√2 exactly, confirming standard quantum mechanics. A Leggett-Garg violation K=1.106 > 1 is confirmed from existing hardware data (p=0.0015). All null results are reported with equal prominence. All experiments were pre-registered before data collection.
Quantum batteries utilize nonclassical resources to achieve charging speed and energy storage performances that surpass classical thermodynamic limits. However, the practical realization of quantum batteries is often constrained by the inevitable environment-induced dissipation of both stored ergotropy and coherence. To actively counteract these losses, we propose a dual-channel coherence framework that exploits dark-state protection to stabilize ergotropy. We conduct, for the first time, an investigation of the synergistic interplay between internal charger coherence and reservoir squeezing, the latter acting as a source of external coherence. In the resource-efficient regime where charger and battery sizes are comparable, our study shows that internal charger coherence and reservoir squeezing jointly enhance the transient charging power. Crucially, initial charger coherence is the fundamental resource for maximizing and stabilizing steady-state ergotropy through dark-state protection. Our analysis reveals that these advantages are driven by the buildup of local battery coherence, which emerges from the integration of both internal and external coherence sources. These results offer a robust pathway for high-power, stabilized energy storage in quantum architectures.