This paper proposes a diagnosis-first reading layer for approximate quantum error correction (AQEC) and entanglement wedge reconstruction (EWR) in the language of Okada Theory. It does not attempt to replace AQEC or EWR theorems, nor does it claim a full recovery theorem. Instead, it separates four roles inside a recovery reading: the designated dominant route, retained history, competitor route, and the first visible handle. On that basis, it introduces a diagnostic ratio that classifies recovery windows as clean, mixed, or contaminated. The paper includes worked toy calibrations on both the AQEC side and the EWR side, showing that contamination can become visible before the designated signed handle fully disappears. In this sense, the note is positioned as a worked diagnostic bridge: it exports an early-warning grammar on top of imported recovery theorems and recovery observables, and it argues that the same bridge grammar can be computed in both decoder-facing and wedge-facing settings.
This paper proposes a diagnosis-first reading layer for approximate quantum error correction (AQEC) and entanglement wedge reconstruction (EWR) in the language of Okada Theory. It does not attempt to replace AQEC or EWR theorems, nor does it claim a full recovery theorem. Instead, it separates four roles inside a recovery reading: the designated dominant route, retained history, competitor route, and the first visible handle. On that basis, it introduces a diagnostic ratio that classifies recovery windows as clean, mixed, or contaminated. The paper includes worked toy calibrations on both the AQEC side and the EWR side, showing that contamination can become visible before the designated signed handle fully disappears. In this sense, the note is positioned as a worked diagnostic bridge: it exports an early-warning grammar on top of imported recovery theorems and recovery observables, and it argues that the same bridge grammar can be computed in both decoder-facing and wedge-facing settings.
This paper proposes a diagnosis-first reading layer for branch competition in quantum extremal surface (QES) and island analyses. It does not attempt to replace the island formula, the QES prescription, or existing Page-curve and entanglement-wedge results with a new universal theorem. Instead, it isolates a narrower operational question: when does a candidate island signal amount only to a false onset, and when has the branch competition entered a genuine onset regime in which the designated reading is no longer clean? In the language of Okada Theory, the paper separates four roles inside branch competition: the currently designated branch, retained branch history, competitor branch pressure, and the first visible handle. On that basis it introduces a local diagnostic ratio together with a clean/mixed/contaminated classification, and it includes a worked toy calibration showing a false-onset window in which a geometric cue becomes positive before the competitor branch has genuinely taken over. The note is deliberately local in scope: it is a branch-competition diagnostic note, not a full replica-wormhole or island theorem.
Universal recovery -- the existence of a single recovery map that corrects an entire family of error channels -- is a central feature of quantum error correction (QEC). In exact QEC, linearity guarantees that a code correcting a given error set also corrects every channel whose Kraus operators lie in its linear span, and that a single recovery map suffices for all such channels. Approximate quantum error correction (AQEC), which relaxes perfect recovery to recovery with controlled error, has traditionally lacked this structure. In a recent paper (arXiv:2607.22995), we developed a theory of approximate quantum error correction showing that a restricted form of linearity persists in the approximate setting, yielding uniform AQEC guarantees for the family of channels controlled by a given error set.
In this work, we complete the picture by establishing the second half of universal recovery in the approximate setting: a single recovery map can simultaneously correct every channel controlled by a given error set. The error-set theory we proposed quantifies approximate correctability through two parameters: the environment-leakage distance, governing worst-case performance, and the Knill--Laflamme Hellinger distance, governing average-case performance. We show here that both quantities also control universal decoding. We further study the Petz map naturally associated with an error set as an explicit universal recovery, and obtain uniform average- and worst-case guarantees across the entire family of channels.
This paper develops an engineering-facing diagnostic bridge between the recoverability-based theory of structural irreversibility and practical evaluation in quantum error correction and monitored quantum platforms. The central problem addressed in this work is that structural recoverability, threshold-like margins, false-collapse, and Recoverability Index–type diagnostics provide useful theoretical distinctions, but they do not by themselves specify how experimentalists or engineers should organize platform-level data, compare regimes, or report recoverability-relevant behavior. The paper therefore introduces a proxy map from structural quantities to engineering diagnostics. Generalized recoverability is associated with recovery performance, decoder-assisted restoration, logical-state fidelity, and related reconstruction-sensitive quantities. Threshold-like margins are associated with entropy-like, noise-sensitive, or transition-localizing proxies. False-collapse is associated with mismatch windows in which collapse-like or transition-like indicators become strong while recovery-sensitive records still indicate residual recoverability. The paper also proposes a minimal diagnostic architecture for QEC and monitored platforms. This architecture consists of four layers: an appearance-sensitive proxy, a recoverability-sensitive proxy, a threshold-like locator, and a window-based reporting layer. Together, these layers support regime classification, early-warning detection, false-collapse-like mismatch identification, finite-window reporting, and cross-regime comparison. A QEC-oriented realization is presented to show how syndrome histories, logical-failure markers, logical recovery performance, entropy-like proxies, false-collapse window frequencies, and RI-like summaries can be organized into a coherent diagnostic workflow. The goal is not to replace detailed decoder analysis or hardware-specific benchmarking, but to provide a bridge-level language for deciding what should be logged, estimated, compared, and reported when studying the approach to effective irreversibility in error-managed quantum systems. This work should be read as an engineering and experimental companion to the broader recoverability program. Its contribution is to make structural irreversibility operationally legible by mapping theoretical quantities to measurable, computable, and reportable diagnostics in contemporary quantum platforms.
This work establishes the Black-Hole Information Sector Connection of Return Theory (RT) in finite-dimensional quantum hosts. It applies RT’s typed observational roles—observer, host stage, validation reference, representation reference, access, record, and reconstruction—to black-hole information problems while retaining the supplied quantum dynamics. The central result is a three-level conditional classifier that locates an apparent conflict at its first failed level: host-state feasibility, same-run record and access compatibility, or equivalence between reconstructed images. In the Hayden–Preskill host, an old black hole is maximally entangled with early radiation, a one-qubit diary is scrambled by a fixed Haar unitary, and recovery is evaluated through two access channels on the same dynamics: emitted radiation R alone and the combined system ER. Classical diary content is assessed by exact binary minimax error, while coherent recovery is assessed separately by Petz entanglement fidelity. Across 36 fixed unitaries with total coherent register sizes of 8, 10, and 12 qubits, ER reaches both declared recovery thresholds after two emitted qubits in every run, whereas R reaches them only after complete emission. In the selected 12-qubit realization at k = 2, adding access to E changes the minimax error from 0.472087 to 0.031872 and the Petz fidelity from 0.252652 to 0.948306, with the unitary dynamics held fixed. The AMPS audit is evaluated under two explicit factorization declarations. With independent tensor factors E, b, and b̃, simultaneous exact Bell targets for Eb and bb̃ define an empty marginal-feasibility set. The conflict is therefore classified at the host-state level. When b̃ is instead declared as a logical algebra encoded in E by a [[4,1,2]] quantum error-correcting code, one consistent joint state exists and the issue moves to access, records, and reconstruction. Within the encoded realization, the disjoint logical-Z representatives Z₁Z₃ and Z₂Z₄ generate exact, order-independent records against a stable external validation reference and satisfy the declared RT operational-objectivity conditions on the binary logical-codeword ensemble. These objective classical records reduce logical coherence, while persistent coherent extraction transfers full logical fidelity to the first output and leaves only Bell fidelity 1/4 for a later E-only output. The calculation therefore distinguishes redundant objective records of commuting classical content from reconstruction of the complete logical quantum state. The finite connection further includes five modules: a sequential evaporation host that instantiates the RT Time role and distinguishes monotone admitted-record histories from observer accesses that lose records; an exact independent-factor Bell-fidelity frontier with symmetric optimum 3/4; a graded early-radiation-entanglement sweep that moves the ER and R recovery thresholds in opposite directions; a three-qutrit code whose two-share recoverability coexists with record redundancy one; and typing witnesses showing how verdicts change when minimax admission, joint realization, records, occupied order, or certified validation are replaced by inequivalent proxies. The resulting sector connection shows how factorization, observer-supported access, reference stability, record admission, and reconstruction jointly determine the consistent observational reading of a supplied black-hole information model. It provides formal statements, executable finite-dimensional witnesses, independent numerical verification, machine-readable results, complete source code, and cryptographic checksums.
We develop a theory of approximate quantum error correction (QEC) based on the error-set model, complemented by general methods for code construction. Exact QEC has a powerful error-set structure: by the Knill-Laflamme conditions, a code correcting a given error set automatically protects against every channel whose Kraus operators lie in their linear span. This linearity gives rise to code distance, the equivalence between erasures and general errors, and a theory of asymptotically good codes. A longstanding view has been that these features do not extend to AQEC, leaving the theory essentially channel-by-channel. We show instead that, although full Knill--Laflamme linearity fails, a restricted form survives and suffices to extend all three structural features to the approximate setting. Specifically, a common error-set criterion governs families of channels whose Kraus operators are linear combinations of a given error set and whose coefficient matrices satisfy a spectral constraint. Using the Bény-Oreshkov worst-case and Petz average-case frameworks, we derive uniform fidelity guarantees for these families in terms of two new code parameters--the \emph{environment-leakage distance}, controlling worst-case performance, and the \emph{Knill-Laflamme Hellinger distance}, characterizing the average-case performance of Petz recovery.
To demonstrate the scope of this model, we develop partition-based constructions across diverse quantum systems and geometries, placing exact and approximate correction on equal footing. These constructions lead to a metric--error alignment hierarchy for Hilbert spaces, metrics, and error families, which in turn characterizes the resulting recovery guarantees. They yield the first known asymptotically good code families for fermionic systems, one-dimensional Rydberg-blockaded systems, and deletion errors, and extend to other physical platforms.
This paper is the seventh in a sequence developing an interpretive framework that redescribes physical reality as a causally consistent history of information updates rather than as a collection of objects independently existing within spacetime. Two prior results set up its question. The third paper (Uchida, 2026c) characterized public finality—recoverability of a committed fact by many mutually independent accessors, non-disturbingly and repeatably—as a broadcast redundancy: an effectively classical pointer value proliferated across many disjoint environmental fragments, approximately in the form of spectrum broadcast structure. The fourth paper (Uchida, 2026d) read the evaporating black hole as the regime in which a committed interior record crosses, at the Page time, from hidden to recoverable encoding, reconstructible from the radiation through entanglement-wedge reconstruction; and the parent framework (Uchida, 2026a, §10) had flagged holographic quantum error correction as a place its language of protected, redundantly encoded, locally recoverable records might find content. The present paper makes that content precise as a structure theory of recoverable records, kept separate from any claim of new physics or any suggestion that the framework derives the underlying results. The central claim is conditional and structural. The framework does not claim that every recoverable piece of information is a code, that the universe is literally a quantum error-correcting code, or that AdS/CFT describes our universe. It claims that when information qualifies as an erasure-recoverable record because an encoding preserves a logical degree of freedom—or a logical operator algebra—against a specified family of physical erasures, then that recoverability is formalized as an exact or approximate quantum error-correcting structure, in which each correctable erasure leaves an authorized complementary region supporting a recovery map. That formalization is itself an established mathematical classification; the paper's interpretive contribution is to read the series' recoverable record through it, and to set it against a second, distinct architecture. Broadcast redundancy makes the same effectively classical value legible from many disjoint fragments; erasure-correcting redundancy protects noncommuting logical quantum information by keeping each correctable erased region ignorant of—approximately private with respect to—the protected logical content, while suitable remaining regions recover it. The formal engine of this distinction is the duality between correctability and privacy (the information–disturbance tradeoff), not the no-cloning theorem; no-cloning, with the access structure of quantum secret sharing, survives as the reason independently usable recovery regions for arbitrary unknown logical quantum information must overlap. Three commitments keep the reading honest. First, it separates three senses of "record"—protected logical quantum information, a committed classical record, and a publicly final record—and insists that recovery or decoding restores access to logical quantum information but does not, by itself, commit a classical value; commitment additionally requires measurement, pointer imprinting, decoherence, and stabilization (Uchida, 2026f), and public finality a still later broadcast. Second, holographic quantum error correction is offered as the sharpest worked model of the distinction, with exactly solvable tensor-network toy codes (exact within the model) kept distinct from realistic semiclassical holographic reconstruction beyond those limits (generally treated as approximate), and both from the further question of state-dependence. Third, code-recoverability does not by itself imply public finality: protected quantum information can be recoverable from authorized regions while remaining non-public. The framework relabels code structure as the architecture of recoverability and derives none of it, making no independent empirical prediction. Its disciplined thesis is that codes protect recovery; broadcasts create publicity—different architectures that a single physical history may nonetheless realize in sequence.