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arXiv:1412.7950

Comment on "Quantum Darwinism, Decoherence, and the Randomness of Quantum Jumps," arXiv:1412.5206

Ruth E. Kastner

Published Dec 19, 2014• 1 citation
arXivHTMLPDF

Abstract

This brief note in response to Wojciech Zurek's article "Quantum Darwinism, classical reality, and the randomness of quantum jumps" (Physics Today, October 2014, page 44) points out extant rebuttals in the literature to some of the author's key claims.
DOI
10.48550/arxiv.1412.7950

Related papers

Classical selection and quantum Darwinism

Ruth E. Kastner

This short letter in response to Wojciech Zurek’s article “Quantum Darwinism, classical reality, and the randomness of quantum jumps” points out extant rebuttals in the literature to some of the author’s key claims.On the first page of his arXiv.org version of the Physics Today article (http://arxiv.org/abs/1412.5206), Zurek states thatdecoherence selects preferred pointer states that survive interaction with the environment. They are localized and effectively classical. They persist while their superpositions decohere. Decoherence marks the border between quantum and classical, alleviating concern about flagrant … manifestations of quantumness in the macroscopic domain.Here we consider emergence of “the classical” starting at a more fundamental pre-decoherence level, tracing the origin of preferred pointer states.However, the idea that preferred pointer states naturally “emerge” from the quantum level has been refuted in the literature, in particular in a paper11. R. E. Kastner, Stud. Hist. Philos. Mod. Phys. 48, 56 (2014), and references therein. https://doi.org/10.1016/j.shpsb.2014.06.004 showing that “classical” pointer states do not emerge unless a key aspect of classicality has been tacitly assumed from the beginning. In other words, the “quantum Darwinism” program is fatally circular.The assumption generating the circularity usually takes the form of a predesignated system that is considered separable from its environment (the same assumption appears in the discussion about information flow in Zurek’s article). The system acquires decohered observable (or stable) states because it is presumed to be distinguishable from a designated set of environmental subsystems, all assumed as having random phases—with respect to each other and the system. The only correlations between the system and the environmental subsystems are assumed to be established via the designated Hamiltonians.However, in the absence of this sort of predesignated partitioning of all degrees of freedom into the system and its surroundings—measurement apparatus, environment, and so forth—where the initial phase of each subsystem is random, the desired decoherence and emergence of pointer states, or einselection, do not follow. The partitioning is inevitably based on what a human observer would be able to identify and measure, such as distinguishable atoms and molecules, so the account is dependent on assuming the classical realm of the observer.The need for this pre-partitioning fatally conflicts with the claim that classicality emerges naturally from the quantum realm: Absent a pre-partitioning of all degrees of freedom into uncorrelated systems of interest, classical pointer states do not emerge. With unitary-only dynamics (lacking nonunitary collapse), the quantum realm does not have any a priori preference for the assumed uncorrelated degrees of freedom. On the contrary, a unitary-only evolution would typically begin with a maximally entangled universal state.As I noted in reference 11. R. E. Kastner, Stud. Hist. Philos. Mod. Phys. 48, 56 (2014), and references therein. https://doi.org/10.1016/j.shpsb.2014.06.004, one can observe the decoherence process experimentally, but that observation does not demonstrate that einselection occurs in a unitary-only dynamics or that classicality emerges in such a dynamics. A key missing ingredient in quantum Darwinism is some real physical randomization process, such as collapse, that could create an observer-independent, physical partitioning at the quantum level. Without such a process, quantum Darwinism contains the same kind of logical circularity as Boltzmann’s H-theorem, which attempted to derive irreversible thermodynamic laws from reversible laws. Boltzmann inadvertently smuggled in irreversibility by assuming molecular chaos; quantum Darwinists smuggle in classicality via their partitioning of the universe into distinguishable systems of interest that interact with mutually randomized environmental subsystems.In his article, Zurek does not address this refutation of quantum Darwinism and repeats the refuted claims and circular assumptions. Similar criticisms of quantum Darwinism’s presumption of classically distinguishable primordial systems, raised by Jasmina Jeknić-Dugić, Miroljub Dugić, and collaborators,2–42. J. Jeknić-Dugić, M. Dugić, A. Francom, Int. J. Theor. Phys. 53, 169 (2014). https://doi.org/10.1007/s10773-013-1794-x3. J. Jeknić-Dugić, M. Dugić, A. Francom, M. Arsenijević, Open Access Libr. J. 1, e501 (2014). https://doi.org/10.4236/oalib.11005014. M. Dugić, J. Jeknić, Int. J. Theor. Phys. 45, 2215 (2006). https://doi.org/10.1007/s10773-006-9186-0 and Chris Fields’s concern about the division of primordial degrees of freedom into a classically distinguishable system and environment55. C. Fields, Phys. Essays 24, 518 (2011). https://doi.org/10.4006/1.3644391 have also not been countered by proponents of quantum Darwinism.I acknowledge and thank Miroljub Dugić for his helpful comments.REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. R. E. Kastner, Stud. Hist. Philos. Mod. Phys. 48, 56 (2014), and references therein. https://doi.org/10.1016/j.shpsb.2014.06.004, Google ScholarCrossref2. J. Jeknić-Dugić, M. Dugić, A. Francom, Int. J. Theor. Phys. 53, 169 (2014). https://doi.org/10.1007/s10773-013-1794-x, Google ScholarCrossref3. J. Jeknić-Dugić, M. Dugić, A. Francom, M. Arsenijević, Open Access Libr. J. 1, e501 (2014). https://doi.org/10.4236/oalib.1100501, Google ScholarCrossref4. M. Dugić, J. Jeknić, Int. J. Theor. Phys. 45, 2215 (2006). https://doi.org/10.1007/s10773-006-9186-0, Google ScholarCrossref5. C. Fields, Phys. Essays 24, 518 (2011). https://doi.org/10.4006/1.3644391, Google ScholarCrossref© 2015 American Institute of Physics.

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In the opening paragraphs of “Quantum Darwinism, classical reality, and the randomness of quantum jumps” (Physics Today, October 2014, page 44), Wojciech Zurek invokes an analogue to Schrödinger’s cat and describes how the environment-driven process of decoherence removes the interferences that would otherwise exist between the live and dead states. He thus explains how the environment effectively “measures” the state of the cat. The article leaves me uncertain whether Zurek judges those comments to be a resolution of the quantum measurement or “Schrödinger’s cat” problem, but some readers might conclude that they indeed offer such a solution. Those readers would be wrong. As Stephen Adler has shown,11. S. L. Adler, Stud. Hist. Philos. Mod. Phys. 34, 135 (2003). https://doi.org/10.1016/S1355-2198(02)00086-2 and as decoherence expert Maximilian Schlosshauer has stated,22. M. Schlosshauer, Rev. Mod. Phys. 76, 1267 (2005). https://doi.org/10.1103/RevModPhys.76.1267 decoherence does not solve the measurement problem because it does not solve the so-called “problem of outcomes.”Decoherence theory shows how interactions with environmental quanta (photons, air molecules, and so forth) convert a quantum system’s superposition state α|s1⟩ + β|s2⟩ into the entangled “measurement state” α|s1⟩|e1⟩ + β|s2⟩|e2⟩, where |e1⟩ and |e2⟩ are orthogonal many-body states of the environment. Thus the environment acts just like a “which-slit” detector in the double-slit experiment with photons. Such a which-slit measurement transforms each photon from its premeasurement superposition over both slits into a measured photon whose single-slit states |s1⟩ and |s2⟩ are entangled with the two orthogonal states |e1⟩ and |e2⟩ of the detector. That removes the interferences from—that is, it decoheres—the photon.At that point, the theory runs into the problem of outcomes: The measurement state is still a superposition, albeit one in which the measured quantum no longer interferes with itself. By what logic does that imply definite (but indeterminate) individual outcomes? In other words, by what logic is Schrödinger’s cat converted into a cat that is either dead or alive rather than one that is both dead and alive? Zurek’s analysis does nothing to resolve that question.REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. S. L. Adler, Stud. Hist. Philos. Mod. Phys. 34, 135 (2003). https://doi.org/10.1016/S1355-2198(02)00086-2, Google ScholarCrossref2. M. Schlosshauer, Rev. Mod. Phys. 76, 1267 (2005). https://doi.org/10.1103/RevModPhys.76.1267, Google ScholarCrossref© 2015 American Institute of Physics.

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This short letter in response to Wojciech Zurek’s article “Quantum Darwinism, classical reality, and the randomness of quantum jumps” points out extant rebuttals in the literature to some of the author’s key claims.On the first page of his arXiv.org version of the Physics Today article (http://arxiv.org/abs/1412.5206), Zurek states thatdecoherence selects preferred pointer states that survive interaction with the environment. They are localized and effectively classical. They persist while their superpositions decohere. Decoherence marks the border between quantum and classical, alleviating concern about flagrant … manifestations of quantumness in the macroscopic domain.Here we consider emergence of “the classical” starting at a more fundamental pre-decoherence level, tracing the origin of preferred pointer states.However, the idea that preferred pointer states naturally “emerge” from the quantum level has been refuted in the literature, in particular in a paper11. R. E. Kastner, Stud. Hist. Philos. Mod. Phys. 48, 56 (2014), and references therein. https://doi.org/10.1016/j.shpsb.2014.06.004 showing that “classical” pointer states do not emerge unless a key aspect of classicality has been tacitly assumed from the beginning. In other words, the “quantum Darwinism” program is fatally circular.The assumption generating the circularity usually takes the form of a predesignated system that is considered separable from its environment (the same assumption appears in the discussion about information flow in Zurek’s article). The system acquires decohered observable (or stable) states because it is presumed to be distinguishable from a designated set of environmental subsystems, all assumed as having random phases—with respect to each other and the system. The only correlations between the system and the environmental subsystems are assumed to be established via the designated Hamiltonians.However, in the absence of this sort of predesignated partitioning of all degrees of freedom into the system and its surroundings—measurement apparatus, environment, and so forth—where the initial phase of each subsystem is random, the desired decoherence and emergence of pointer states, or einselection, do not follow. The partitioning is inevitably based on what a human observer would be able to identify and measure, such as distinguishable atoms and molecules, so the account is dependent on assuming the classical realm of the observer.The need for this pre-partitioning fatally conflicts with the claim that classicality emerges naturally from the quantum realm: Absent a pre-partitioning of all degrees of freedom into uncorrelated systems of interest, classical pointer states do not emerge. With unitary-only dynamics (lacking nonunitary collapse), the quantum realm does not have any a priori preference for the assumed uncorrelated degrees of freedom. On the contrary, a unitary-only evolution would typically begin with a maximally entangled universal state.As I noted in reference 11. R. E. Kastner, Stud. Hist. Philos. Mod. Phys. 48, 56 (2014), and references therein. https://doi.org/10.1016/j.shpsb.2014.06.004, one can observe the decoherence process experimentally, but that observation does not demonstrate that einselection occurs in a unitary-only dynamics or that classicality emerges in such a dynamics. A key missing ingredient in quantum Darwinism is some real physical randomization process, such as collapse, that could create an observer-independent, physical partitioning at the quantum level. Without such a process, quantum Darwinism contains the same kind of logical circularity as Boltzmann’s H-theorem, which attempted to derive irreversible thermodynamic laws from reversible laws. Boltzmann inadvertently smuggled in irreversibility by assuming molecular chaos; quantum Darwinists smuggle in classicality via their partitioning of the universe into distinguishable systems of interest that interact with mutually randomized environmental subsystems.In his article, Zurek does not address this refutation of quantum Darwinism and repeats the refuted claims and circular assumptions. Similar criticisms of quantum Darwinism’s presumption of classically distinguishable primordial systems, raised by Jasmina Jeknić-Dugić, Miroljub Dugić, and collaborators,2–42. J. Jeknić-Dugić, M. Dugić, A. Francom, Int. J. Theor. Phys. 53, 169 (2014). https://doi.org/10.1007/s10773-013-1794-x3. J. Jeknić-Dugić, M. Dugić, A. Francom, M. Arsenijević, Open Access Libr. J. 1, e501 (2014). https://doi.org/10.4236/oalib.11005014. M. Dugić, J. Jeknić, Int. J. Theor. Phys. 45, 2215 (2006). https://doi.org/10.1007/s10773-006-9186-0 and Chris Fields’s concern about the division of primordial degrees of freedom into a classically distinguishable system and environment55. C. Fields, Phys. Essays 24, 518 (2011). https://doi.org/10.4006/1.3644391 have also not been countered by proponents of quantum Darwinism.I acknowledge and thank Miroljub Dugić for his helpful comments.REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. R. E. Kastner, Stud. Hist. Philos. Mod. Phys. 48, 56 (2014), and references therein. https://doi.org/10.1016/j.shpsb.2014.06.004, Google ScholarCrossref2. J. Jeknić-Dugić, M. Dugić, A. Francom, Int. J. Theor. Phys. 53, 169 (2014). https://doi.org/10.1007/s10773-013-1794-x, Google ScholarCrossref3. J. Jeknić-Dugić, M. Dugić, A. Francom, M. Arsenijević, Open Access Libr. J. 1, e501 (2014). https://doi.org/10.4236/oalib.1100501, Google ScholarCrossref4. M. Dugić, J. Jeknić, Int. J. Theor. Phys. 45, 2215 (2006). https://doi.org/10.1007/s10773-006-9186-0, Google ScholarCrossref5. C. Fields, Phys. Essays 24, 518 (2011). https://doi.org/10.4006/1.3644391, Google ScholarCrossref© 2015 American Institute of Physics.
In the opening paragraphs of “Quantum Darwinism, classical reality, and the randomness of quantum jumps” (Physics Today, October 2014, page 44), Wojciech Zurek invokes an analogue to Schrödinger’s cat and describes how the environment-driven process of decoherence removes the interferences that would otherwise exist between the live and dead states. He thus explains how the environment effectively “measures” the state of the cat. The article leaves me uncertain whether Zurek judges those comments to be a resolution of the quantum measurement or “Schrödinger’s cat” problem, but some readers might conclude that they indeed offer such a solution. Those readers would be wrong. As Stephen Adler has shown,11. S. L. Adler, Stud. Hist. Philos. Mod. Phys. 34, 135 (2003). https://doi.org/10.1016/S1355-2198(02)00086-2 and as decoherence expert Maximilian Schlosshauer has stated,22. M. Schlosshauer, Rev. Mod. Phys. 76, 1267 (2005). https://doi.org/10.1103/RevModPhys.76.1267 decoherence does not solve the measurement problem because it does not solve the so-called “problem of outcomes.”Decoherence theory shows how interactions with environmental quanta (photons, air molecules, and so forth) convert a quantum system’s superposition state α|s1⟩ + β|s2⟩ into the entangled “measurement state” α|s1⟩|e1⟩ + β|s2⟩|e2⟩, where |e1⟩ and |e2⟩ are orthogonal many-body states of the environment. Thus the environment acts just like a “which-slit” detector in the double-slit experiment with photons. Such a which-slit measurement transforms each photon from its premeasurement superposition over both slits into a measured photon whose single-slit states |s1⟩ and |s2⟩ are entangled with the two orthogonal states |e1⟩ and |e2⟩ of the detector. That removes the interferences from—that is, it decoheres—the photon.At that point, the theory runs into the problem of outcomes: The measurement state is still a superposition, albeit one in which the measured quantum no longer interferes with itself. By what logic does that imply definite (but indeterminate) individual outcomes? In other words, by what logic is Schrödinger’s cat converted into a cat that is either dead or alive rather than one that is both dead and alive? Zurek’s analysis does nothing to resolve that question.REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. S. L. Adler, Stud. Hist. Philos. Mod. Phys. 34, 135 (2003). https://doi.org/10.1016/S1355-2198(02)00086-2, Google ScholarCrossref2. M. Schlosshauer, Rev. Mod. Phys. 76, 1267 (2005). https://doi.org/10.1103/RevModPhys.76.1267, Google ScholarCrossref© 2015 American Institute of Physics.