The identity of a quantum subsystem over time, in the minimal sense in which the question can be given quantities, is what of its origin can still be recovered from it or from whoever inherited it. An earlier paper defined it by the coherent information from a reference maximally entangled with the subsystem at a root time, proved that its heir is unique and that inheriting is the complement of being recorded, and two notes gave the law of its loss to imperfect records and the realization theorem for what two disjoint regions can jointly inherit. This note completes that minimal theory with the two statements that remained: how identity is transformed, and how fast it is lost. Krakauer, Bertschinger, Olbrich, Flack and Ay proposed to measure the individuality of a system by how much of its future is determined by its own past rather than by its environment, decomposing the information its future carries about the past into an organismal and an environmental part. We give a coherent-information analogue of that program for a subsystem in a fixed tensor-product structure, using the same coherent information as the measure of heritage. Four exact statements follow, of which the first and the fourth are, to our knowledge, new in this form. (i) The heritage of a system's future decomposes exactly into an individual part, an environmental part and a non-negative heritage synergy equal to the conditional mutual information of the two pasts given the future, and under closed dynamics the total is fixed by the dimensions: what a system loses in individuality goes into synergy with its environment's past or into environmental determination. (ii) Quantum individuality is monogamous: a past has at most one heir, which has no classical counterpart, where a past can be copied into many futures. (iii) Records and individuality are complementary: the classical information a witness acquires about a basis of the system plus the individuality the system retains is at most log d, a corollary of the uncertainty principle with quantum memory; hence a non-inherited record is bounded by the identity that nobody keeps, and the entropy of the witness does not enter. (iv) The leading short-time loss of individuality is a t^2 log(1/t^2) with a the variance, over the state of the environment, of the fluctuation of the interaction about its mean field on the subsystem; for a maximally mixed environment a is the inverse squared scrambling time of Zanardi, Dallas, Andreadakis and Lloyd, so that the bipartite Gaussian scrambling coefficient underlying their operational mereology is recovered as the maximally-mixed-environment specialization of a state-dependent coefficient, and an environment with vanishing coupling variance has no leading-order loss of individuality, whereas one with non-zero coupling variance does. We relate these to the philosophy-of-physics literature on the individuality of quantum objects, where the question is ordinarily formulated through discernibility and identity conditions rather than through a diachronic quantitative measure of this kind, and state what is not claimed.The identity of a quantum subsystem over time, in the minimal sense in which the question can be given quantities, is what of its origin can still be recovered from it or from whoever inherited it. An earlier paper defined it by the coherent information from a reference maximally entangled with the subsystem at a root time, proved that its heir is unique and that inheriting is the complement of being recorded, and two notes gave the law of its loss to imperfect records and the realization theorem for what two disjoint regions can jointly inherit. This note completes that minimal theory with the two statements that remained: how identity is transformed, and how fast it is lost. Krakauer, Bertschinger, Olbrich, Flack and Ay proposed to measure the individuality of a system by how much of its future is determined by its own past rather than by its environment, decomposing the information its future carries about the past into an organismal and an environmental part. We give a coherent-information analogue of that program for a subsystem in a fixed tensor-product structure, using the same coherent information as the measure of heritage. Four exact statements follow, of which the first and the fourth are, to our knowledge, new in this form. (i) The heritage of a system's future decomposes exactly into an individual part, an environmental part and a non-negative heritage synergy equal to the conditional mutual information of the two pasts given the future, and under closed dynamics the total is fixed by the dimensions: what a system loses in individuality goes into synergy with its environment's past or into environmental determination. (ii) Quantum individuality is monogamous: a past has at most one heir, which has no classical counterpart, where a past can be copied into many futures. (iii) Records and individuality are complementary: the classical information a witness acquires about a basis of the system plus the individuality the system retains is at most log d, a corollary of the uncertainty principle with quantum memory; hence a non-inherited record is bounded by the identity that nobody keeps, and the entropy of the witness does not enter. (iv) The leading short-time loss of individuality is a t^2 log(1/t^2) with a the variance, over the state of the environment, of the fluctuation of the interaction about its mean field on the subsystem; for a maximally mixed environment a is the inverse squared scrambling time of Zanardi, Dallas, Andreadakis and Lloyd, so that the bipartite Gaussian scrambling coefficient underlying their operational mereology is recovered as the maximally-mixed-environment specialization of a state-dependent coefficient, and an environment with vanishing coupling variance has no leading-order loss of individuality, whereas one with non-zero coupling variance does. We relate these to the philosophy-of-physics literature on the individuality of quantum objects, where the question is ordinarily formulated through discernibility and identity conditions rather than through a diachronic quantitative measure of this kind, and state what is not claimed.

Oct 1, 20260 citations

Quantum advantage by designing beneficial dissipation from lossless dynamics

Zeng-Zhao Li, Xiao Xue

Passive loss removes probability from a system and therefore seems unable to improve an unconditional target. This intuition is exact for classical population dynamics under sink-only removal: passive killing obeys a finite-strength monotonicity principle even after optimization over the remaining controls. Here we show that coherent quantum dynamics can violate this classical monotonicity because coherent contributions to the final target can interfere destructively. We derive a trajectory-level criterion that determines when such a detrimental contribution is physically accessible to passive loss and accumulates into a net unconditional benefit. The criterion is encoded in a response operator constructed entirely from the lossless dynamics: its spectrum determines whether weak passive loss can help, while its principal eigenvector identifies the optimal environmental mode. Applying this criterion to vibronically assisted transfer, we identify a beneficial mode formed by coherently combining two individually detrimental local loss directions. The predicted mode remains near-optimal at finite loss, producing an $8.73\%$ enhancement over the independently optimized lossless benchmark, compared with $9.52\%$ under full finite-loss optimization. Our results establish how coherent quantum dynamics can evade classical passive-loss monotonicity and provide a general task-dependent principle for designing beneficial passive environments from lossless dynamics.Passive loss removes probability from a system and therefore seems unable to improve an unconditional target. This intuition is exact for classical population dynamics under sink-only removal: passive killing obeys a finite-strength monotonicity principle even after optimization over the remaining controls. Here we show that coherent quantum dynamics can violate this classical monotonicity because coherent contributions to the final target can interfere destructively. We derive a trajectory-level criterion that determines when such a detrimental contribution is physically accessible to passive loss and accumulates into a net unconditional benefit. The criterion is encoded in a response operator constructed entirely from the lossless dynamics: its spectrum determines whether weak passive loss can help, while its principal eigenvector identifies the optimal environmental mode. Applying this criterion to vibronically assisted transfer, we identify a beneficial mode formed by coherently combining two individually detrimental local loss directions. The predicted mode remains near-optimal at finite loss, producing an $8.73\%$ enhancement over the independently optimized lossless benchmark, compared with $9.52\%$ under full finite-loss optimization. Our results establish how coherent quantum dynamics can evade classical passive-loss monotonicity and provide a general task-dependent principle for designing beneficial passive environments from lossless dynamics.

quant-pharXiv:2610.38183Oct 29, 20260 citations

The Dilemma of Quantum Individuality Beyond Particle Metaphysics

Christian DE RONDE, Raimundo Fernández Mouján

arXiv:2004.07816Synthese Library/Synthese libraryJan 1, 20251 citation

Measurement-induced decoherence and information in double-slit interference

Mackenzie Kincaid, Kyle McLelland, Michael P. Zwolak

The double slit experiment provides a classic example of both interference and the effect of observation in quantum physics. When particles are sent individually through a pair of slits, a wave-like interference pattern develops, but no such interference is found when one observes which "path" the particles take. We present a model of interference, dephasing, and measurement-induced decoherence in a one-dimensional version of the double-slit experiment. Using this model, we demonstrate how the loss of interference in the system is correlated with the information gain by the measuring apparatus/observer. In doing so, we give a modern account of measurement in this paradigmatic example of quantum physics that is accessible to students taking quantum mechanics at the graduate or senior undergraduate levels.The double slit experiment provides a classic example of both interference and the effect of observation in quantum physics. When particles are sent individually through a pair of slits, a wave-like interference pattern develops, but no such interference is found when one observes which "path" the particles take. We present a model of interference, dephasing, and measurement-induced decoherence in a one-dimensional version of the double-slit experiment. Using this model, we demonstrate how the loss of interference in the system is correlated with the information gain by the measuring apparatus/observer. In doing so, we give a modern account of measurement in this paradigmatic example of quantum physics that is accessible to students taking quantum mechanics at the graduate or senior undergraduate levels.

arXiv:1606.09442American Journal of PhysicsJun 22, 201612 citations

Quantum Individuality

Dennis Dieks

Synthese Library/Synthese libraryJan 1, 20234 citations

8.73\%

enhancement over the independently optimized lossless benchmark, compared with

9.52\%

under full finite-loss optimization. Our results establish how coherent quantum dynamics can evade classical passive-loss monotonicity and provide a general task-dependent principle for designing beneficial passive environments from lossless dynamics.