This preprint develops a thermodynamic admissibility condition on the persistence of quantum identity in open systems. Standard quantum mechanics allows extremely large spaces of possible system histories, but only a small subset remains experimentally realisable once irreversible entropy production is taken into account. This work formalizes this as an admissibility constraint: any quantum system that preserves a stable, trackable identity over time must satisfy a finite budget on cumulative irreversible dissipation. No new forces, variables, or dynamics are added; the constraint is purely structural and compatible with existing open-systems formalisms. The paper connects this requirement with decoherence, spectrum broadcasting, quantum Darwinism, and the emergence of classical objectivity. It frames identity persistence as a pre-dynamical condition—necessary before predictions about evolution or measurement outcomes are meaningful. This structural account clarifies why only certain histories are physically realisable, how objectivity arises under irreversibility, and how thermodynamic bookkeeping parameters (such as an “identity budget”) implicitly constrain experimental practice. The result provides a unifying, thermodynamically grounded framework linking dissipative quantum processes, system architecture, and long-term identifiability.
This preprint develops a thermodynamic admissibility condition on the persistence of quantum identity in open systems. Standard quantum mechanics allows extremely large spaces of possible system histories, but only a small subset remains experimentally realisable once irreversible entropy production is taken into account. This work formalizes this as an admissibility constraint: any quantum system that preserves a stable, trackable identity over time must satisfy a finite budget on cumulative irreversible dissipation. No new forces, variables, or dynamics are added; the constraint is purely structural and compatible with existing open-systems formalisms. The paper connects this requirement with decoherence, spectrum broadcasting, quantum Darwinism, and the emergence of classical objectivity. It frames identity persistence as a pre-dynamical condition—necessary before predictions about evolution or measurement outcomes are meaningful. This structural account clarifies why only certain histories are physically realisable, how objectivity arises under irreversibility, and how thermodynamic bookkeeping parameters (such as an “identity budget”) implicitly constrain experimental practice. The result provides a unifying, thermodynamically grounded framework linking dissipative quantum processes, system architecture, and long-term identifiability.
This preprint is the third paper in a series on thermodynamic persistence and macroscopic identity. A recently proposed thermodynamic persistence constraint and its empirical test in biological and classical systems suggest that macroscopic identities operating under irreversible dynamics remain admissible only so long as cumulative irreversible dissipation remains finite. The condition does not introduce new dynamical laws or predict lifetimes; it excludes only those histories in which maintaining a coarse-grained identity would require unbounded irreversible entropy production. In this work I examine whether state-of-the-art superconducting qubit platforms are empirically compatible with such a persistence accounting. Using only published device parameters and order-of-magnitude estimates for control and dissipation, I construct an operational diagnostic quantity from independently measurable observables: coherence time, irreversible power dissipation, and device scale. I evaluate this diagnostic in two representative contexts: (i) idle coherence limited by energy relaxation and dephasing, and (ii) driven operation under repeated gate application as characterized by randomized benchmarking and error-per-gate metrics, including logical-level operation in surface-code experiments. Across these regimes, the empirical behavior mirrors that observed in classical and biological systems: coherence time and logical error rates vary primarily through changes in effective dissipation and noise, while the normalized cumulative irreversible burden associated with loss of a qubit’s operational identity remains finite and modest under realistic operating conditions. No violations of the proposed thermodynamic admissibility condition are found within the parameter ranges examined. These results do not establish a thermodynamic bound on quantum coherence or gate fidelities. They do, however, support the empirical viability of treating qubit-level persistence as constrained by cumulative irreversible effects within standard thermodynamic bookkeeping, in continuity with classical and biological systems.
Decoherence and thermodynamic irreversibility are widely regarded as sufficient to explain the emergence of classical behavior from quantum mechanics. Decoherence suppresses interference between branches of the wavefunction, while entropy production provides a direction to macroscopic time. However, neither mechanism alone explains why macroscopic physics exhibits a single, persistent, globally consistent classical history rather than fragmentation into mutually incompatible record sets. In this work, we identify and formalize this unresolved issue as the classicality gap. We show that in finite systems subject to nonzero noise and irreversible record formation, decoherence and entropy production are generically insufficient to stabilize a single coherent macroscopic history. Instead, absent a history-level selection mechanism, redundant records diverge and macroscopic identity becomes ill-defined. We present a general instability result demonstrating this fragmentation tendency and introduce history-level constraint restoration as the minimal structural mechanism capable of preventing it. This mechanism operates without new microdynamics, collapse postulates, or observer dependence. We derive qualitative phase boundaries separating stable and unstable regimes and propose concrete experimental protocols on NISQ-era quantum platforms that can falsify the necessity of history selection. Our results establish that persistent classicality is not guaranteed by decoherence alone, but requires selection acting on histories under irreversible constraints. Keywords: classicality emergence, decoherence limits, record inconsistency, history instability, quantum-to-classical transition, irreversibility, entropy production, information persistence, open quantum systems, foundations of physics
Decoherence theory explains the suppression of interference between branches of a quantum state but does not explain why any particular branch persists as a stable classical history under continued environmental interaction. This unresolved gap lies at the core of the quantum measurement problem. Here we demonstrate that irreversible record formation is a necessary structural condition for the stabilization of quantum histories. Using a minimal open quantum system consisting of a measured qubit coupled to a memory degree of freedom, we show that decoherence alone fails to produce persistent measurement records in the presence of ongoing noise. By contrast, when the memory subsystem is allowed to irreversibly export entropy, stable and distinguishable records emerge robustly. We introduce an operational recordability metric based on the trace-distance distinguishability of conditional memory states and observe a pronounced transition between recordable and non-recordable regimes. These results establish that measurement outcomes do not become classical merely by decohering; they become classical only when they are irreversibly maintained. This mechanism resolves a structural incompleteness in decoherence-based accounts of measurement without invoking wavefunction collapse, observers, or interpretational postulates. Keywords: quantum measurement problem, decoherence, irreversible record formation, open quantum systems, Lindblad dynamics, classical emergence, quantum histories, record stabilization, entropy export, measurement records, trace distance, quantum information, environment-induced decoherence, thermodynamic irreversibility
Redundancy-Limited Emergence of Classical Histories in Quantum Systems This work investigates how classical reality emerges from underlying quantum dynamics, focusing on the role of environmental information, noise, and fundamental entropy limits. In quantum theory, systems evolve into superpositions of many possible outcomes. However, in practice we observe a world with definite, classical histories. A widely accepted explanation is decoherence, in which interactions with the environment suppress interference between different quantum states. More recent developments, particularly in quantum Darwinism, emphasize that classical information becomes objective when it is redundantly recorded across many independent parts of the environment. This paper addresses a key unresolved question: how many distinct classical histories can physically exist? To answer this, we construct a minimal computational model in which a system’s history is encoded into multiple environmental fragments, each subject to noise. By computing how much information about the system can be recovered from subsets of these fragments, we identify a characteristic scale that determines how many fragments are required to reconstruct the system’s history. Our results reveal a simple and robust relationship: the ability to recover classical information depends on the entropy of the noise affecting environmental records. As noise increases, more fragments are required to reconstruct a history, reflecting a loss of distinguishability. This leads to the definition of a “recoverability factor,” which quantifies how efficiently entropy can be converted into usable, classical information. We then connect this information-theoretic result to fundamental bounds from gravitational physics. In particular, existing entropy bounds limit the total amount of information that can pass through a region of spacetime. We show that only a fraction of this entropy—determined by the recoverability factor—can contribute to distinguishable classical histories. This leads to a new principle: the number of classical histories is not limited only by total entropy, but by the efficiency with which that entropy can be encoded, preserved, and accessed. Applying this framework to cosmological entropy estimates, we derive explicit upper bounds on the number of distinguishable classical histories in the observable universe. While this number is extraordinarily large, it is nonetheless finite and strongly constrained by both entropy and noise. These results refine the standard picture of quantum branching. While quantum theory allows a vast number of possible outcomes, only a subset can become physically meaningful in the sense of being stable, redundantly recorded, and accessible to observers. More broadly, this work provides a quantitative bridge between decoherence theory, information theory, and gravitational entropy bounds. It suggests that classical reality is fundamentally constrained not just by physical laws governing entropy, but by the efficiency of information transfer within those constraints.
(This version has been superceeded, see v.3) Contemporary approaches to physical unification typically emphasize dynamical laws, interpretive frameworks, or information-theoretic reconstructions. Less attention is given to the structural constraints that determine which physical descriptions can remain coherent and stable under interaction, scale transition, and aggregation. This paper develops a constraint-first analysis of coherence, arguing that persistence and unification require restrictions on admissible physical continuations that are not reducible to dynamics alone. Within the framework referred to here as Quantum Coherence Theory (QCT), coherence is treated not as a fragile quantum resource but as a structural property governed by interaction geometry and constraint density. On this view, classical behavior emerges when accumulated constraints sufficiently narrow admissible evolution, while quantum behavior re-emerges when constraints are relaxed. The account does not introduce new dynamics, collapse mechanisms, or modifications of quantum formalism, but instead clarifies the conditions under which existing formalisms yield stable, unified descriptions. The resulting constraints distinguish QCT from observer-centric, intrinsic-collapse, and purely descriptive decoherence accounts, while remaining compatible with globally unitary dynamics. Formal analysis in later sections develops operational redundancy conditions, admissibility constraints on joint states, and rigidity-style arguments linking redundant record structure to the stability of classical descriptions. These results do not constitute a complete theory of unification, but they narrow the space of physically admissible descriptions and clarify the structural role of coherence in bridging quantum and classical regimes.
The Born rule assigns probabilities to measurement outcomes under the assumption that a quantum system retains a well-defined identity within a stable coarse-grained description. Experimental studies of open quantum systems, error correction, monitored dynamics, and decoherence report abrupt “avalanche”-like transitions in which probabilistic descriptions of subsystems rapidly fail, even though global unitary evolution is preserved. This work provides a structural interpretation of such transitions by identifying an identity tolerance boundary, denoted Ω, beyond which the thermodynamic identity of a quantum system ceases to be well defined. When cumulative irreversible entanglement or decoherence exceeds this boundary, Born-rule probabilities no longer apply—not due to a failure of quantum mechanics, but because the probabilistic description presupposes a persisting system identity that has been lost. The framework does not introduce new physical laws, collapse mechanisms, or modifications to quantum theory. Rather, it clarifies the domain of applicability of probabilistic descriptions by explicitly separating fine-grained unitary evolution from the persistence of macroscopic or subsystem identity. This perspective unifies observations across decoherence avalanches, error-correction thresholds, and measurement-induced transitions without proposing operational procedures or control mechanisms.