Quantum Theory: Concepts and Methods

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Quantum Theory: Concepts and Methods is a 1993 quantum physics textbook by Israeli physicist Asher Peres.

Contents

Contents

In his preface, Peres summarized his goals as follows:

The purpose of this book is to clarify the conceptual meaning of quantum theory, and to explain some of the mathematical methods that it utilizes. This text is not concerned with specialized topics such as atomic structure, or strong or weak interactions, but with the very foundations of the theory. This is not, however, a book on the philosophy of science. The approach is pragmatic and strictly instrumentalist. This attitude will undoubtedly antagonize some readers, but it has its own logic: quantum phenomena do not occur in a Hilbert space, they occur in a laboratory. [lower-alpha 1]

The book is divided into three parts. The first, "Gathering the Tools", introduces quantum mechanics as a theory of "preparations" and "tests", and it develops the mathematical formalism of Hilbert spaces, concluding with the spectral theory used to understand the quantum mechanics of continuous-valued observables. Part II, "Cryptodeterminism and Quantum Inseparability", focuses on Bell's theorem and other demonstrations that quantum mechanics is incompatible with local hidden-variable theories. (Within its substantial discussion of the failure of hidden variable theories, the book includes a FORTRAN program for testing whether a list of vectors forms a Kochen–Specker configuration. [lower-alpha 2] ) Part III, "Quantum Dynamics and Information", covers the role of spacetime symmetry in quantum physics, the relation of quantum information to thermodynamics, semiclassical approximation methods, quantum chaos, and the treatment of measurement in quantum mechanics.

To generate the figures in his chapter on quantum chaos, including plots in phase space of chaotic motion, Peres wrote PostScript code that executed simulations in the printer itself. [lower-alpha 3]

The book develops the methodology of mathematically representing quantum measurements by POVMs, [4] [5] and it provided the first pedagogical treatment of how to use a POVM for quantum key distribution. [6] Peres downplayed the importance of the uncertainty principle; that specific term only appears once in his index, and its entry points to that same page in the index. [7] The text itself does discuss the uncertainty principle, pointing out how an oversimplified "derivation" of it breaks down, and posing as a homework problem the task of finding three quantum-physics textbooks with a demonstrably incorrect uncertainty relation. [8]

Reception

Physicist Leslie E. Ballentine gave the textbook a positive review, declaring it a good introduction to quantum foundations and ongoing research therein. [9] John C. Baez also gave the book a positive assessment, calling it "clear-headed" and finding that it contained "a lot of gems that I hadn't seen", such as the Wigner–Araki–Yanase theorem. [10] Michael Nielsen wrote of the textbook, "Revelation! Suddenly, all the key results of 30 years of work (several of those results due to Asher) were distilled into beautiful and simple explanations." [11] Nielsen and Isaac Chuang said in their own influential textbook that Peres' was "superb", providing "an extremely clear exposition of elementary quantum mechanics" as well as an "extensive discussion of the Bell inequalities and related results". [12] Jochen Rau's introductory textbook on quantum physics described Peres' work as "an excellent place to start" learning about Bell inequalities and related topics like Gleason's theorem. [13]

N. David Mermin wrote that Peres had bridged the "textual gap" between conceptually-oriented books, aimed at understanding what quantum physics implies about the nature of the world, and more practical books intended to teach how to apply quantum mechanics. Mermin found the book praiseworthy, noting that he had "only a few complaints". He wrote:

Peres is careless in discriminating among the various kinds of assumptions one needs to prove the impossibility of a no-hidden-variables theory that reproduces the statistical predictions of quantum mechanics. I would guess that this is because even though he is a master practitioner of this particular art form, deep in his heart he is so firmly convinced that hidden variables cannot capture the essence of quantum mechanics, that he is simply not interested in precisely what you need to assume to prove that they cannot. [4]

Mermin called the book "a treasure trove of novel perspectives on quantum mechanics" and said that Peres' choice of topics is "a catalogue of common omissions" from other approaches. [4]

Meinhard E. Mayer declared that he would "recommend it to anyone teaching or studying quantum mechanics", finding Part II the most interesting of the book. While he noted some disappointment with Peres' selection of topics to include in the chapter on measurement, he reserved most of his negativity for the publisher, saying (as Ballentine also did [9] ) that they had priced the book beyond the reach of graduate students:

Such pricing practices are not justified when one considers that many publishers provide very little copyediting or typesetting any more, as is obvious from the "TeX"-ish look of most books published recently, this one included. [14]

Mermin, Mayer and Baez noted that Peres briefly dismissed the many-worlds interpretation of quantum mechanics. [4] [10] [14] Peres argued that all varieties of many-worlds interpretations merely shifted the arbitrariness or vagueness of the wavefunction collapse idea to the question of when "worlds" can be regarded as separate, and that no objective criterion for that separation can actually be formulated. [lower-alpha 4] Moreover, Peres dismissed "spontaneous collapse" models like Ghirardi–Rimini–Weber theory in the same brief section, designating them "mutations" of quantum mechanics. [4] In a review that praised the book's thoroughness, Tony Sudbery noted that Peres disparaged the idea that human consciousness plays a special role in quantum mechanics. [15]

Manuel Bächtold analyzed Peres' textbook from a standpoint of philosophical pragmatism. [16] John Conway and Simon Kochen used a Kochen–Specker configuration from the book in order to prove their free will theorem. [17] Peres' insistence in his textbook that the classical analogue of a quantum state is a Liouville density function was influential in the development of QBism. [18]

John Watrous places Peres' textbook among the "indispensable references", along with Nielsen and Chuang's Quantum Computation and Quantum Information and Mark Wilde's Quantum Information Theory. [19] In their obituary for Peres, William Wootters, Charles Bennett and coauthors call Quantum Theory: Concepts and Methods the "modern successor" to John von Neumann's 1955 Mathematical Foundations of Quantum Mechanics. [7]

Editions

Notes

  1. Preface, p. xi. The last remark is often quoted, [1] for example by Brukner and Zeilinger [2] and by Czartowski and Życzkowski. [3]
  2. Section 7-5, "Appendix: Computer test for Kochen–Specker contradiction", p. 209
  3. Section 11-7, "Appendix: PostScript code for a map", p. 370
  4. Section 12-1, "The ambivalent observer", p. 374

Related Research Articles

The Copenhagen interpretation is a collection of views about the meaning of quantum mechanics, principally attributed to Niels Bohr and Werner Heisenberg. It is one of the oldest of numerous proposed interpretations of quantum mechanics, as features of it date to the development of quantum mechanics during 1925–1927, and it remains one of the most commonly taught.

<span class="mw-page-title-main">Many-worlds interpretation</span> Interpretation of quantum mechanics that denies the collapse of the wavefunction

The many-worlds interpretation (MWI) is an interpretation of quantum mechanics that asserts that the universal wavefunction is objectively real, and that there is no wave function collapse. This implies that all possible outcomes of quantum measurements are physically realized in some "world" or universe. In contrast to some other interpretations, such as the Copenhagen interpretation, the evolution of reality as a whole in MWI is rigidly deterministic and local. Many-worlds is also called the relative state formulation or the Everett interpretation, after physicist Hugh Everett, who first proposed it in 1957. Bryce DeWitt popularized the formulation and named it many-worlds in the 1970s.

In quantum mechanics, counterfactual definiteness (CFD) is the ability to speak "meaningfully" of the definiteness of the results of measurements that have not been performed. The term "counterfactual definiteness" is used in discussions of physics calculations, especially those related to the phenomenon called quantum entanglement and those related to the Bell inequalities. In such discussions "meaningfully" means the ability to treat these unmeasured results on an equal footing with measured results in statistical calculations. It is this aspect of counterfactual definiteness that is of direct relevance to physics and mathematical models of physical systems and not philosophical concerns regarding the meaning of unmeasured results.

An interpretation of quantum mechanics is an attempt to explain how the mathematical theory of quantum mechanics might correspond to experienced reality. Although quantum mechanics has held up to rigorous and extremely precise tests in an extraordinarily broad range of experiments, there exist a number of contending schools of thought over their interpretation. These views on interpretation differ on such fundamental questions as whether quantum mechanics is deterministic or stochastic, which elements of quantum mechanics can be considered real, and what the nature of measurement is, among other matters.

Bell's theorem is a term encompassing a number of closely related results in physics, all of which determine that quantum mechanics is incompatible with local hidden-variable theories given some basic assumptions about the nature of measurement. "Local" here refers to the principle of locality, the idea that a particle can only be influenced by its immediate surroundings, and that interactions mediated by physical fields can only occur at speeds no greater than the speed of light. "Hidden variables" are hypothetical properties possessed by quantum particles, properties that are undetectable but still affect the outcome of experiments. In the words of physicist John Stewart Bell, for whom this family of results is named, "If [a hidden-variable theory] is local it will not agree with quantum mechanics, and if it agrees with quantum mechanics it will not be local."

Wigner's friend is a thought experiment in theoretical quantum physics, first conceived by the physicist Eugene Wigner in 1961, and further developed by David Deutsch in 1985. The scenario involves an indirect observation of a quantum measurement: An observer observes another observer who performs a quantum measurement on a physical system. The two observers then formulate a statement about the physical system's state after the measurement according to the laws of quantum theory. However, in most of the interpretations of quantum mechanics, the resulting statements of the two observers contradict each other. This reflects a seeming incompatibility of two laws in quantum theory: the deterministic and continuous time evolution of the state of a closed system and the nondeterministic, discontinuous collapse of the state of a system upon measurement. Wigner's friend is therefore directly linked to the measurement problem in quantum mechanics with its famous Schrödinger's cat paradox.

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<span class="mw-page-title-main">Asher Peres</span> Israeli physicist

Asher Peres was an Israeli physicist. He is well known for his work relating quantum mechanics and information theory. He helped to develop the Peres–Horodecki criterion for quantum entanglement, as well as the concept of quantum teleportation, and collaborated with others on quantum information and special relativity. He also introduced the Peres metric and researched the Hamilton–Jacobi–Einstein equation in general relativity. With Mario Feingold, he published work in quantum chaos that is known to mathematicians as the Feingold–Peres conjecture and to physicists as the Feingold–Peres theory.

The free will theorem of John H. Conway and Simon B. Kochen states that if we have a free will in the sense that our choices are not a function of the past, then, subject to certain assumptions, so must some elementary particles. Conway and Kochen's paper was published in Foundations of Physics in 2006. In 2009, the authors published a stronger version of the theorem in the Notices of the American Mathematical Society. Later, in 2017, Kochen elaborated some details.

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<span class="mw-page-title-main">N. David Mermin</span> American physicist

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<span class="mw-page-title-main">Quantum Bayesianism</span> Interpretation of quantum mechanics

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The PBR theorem is a no-go theorem in quantum foundations due to Matthew Pusey, Jonathan Barrett, and Terry Rudolph in 2012. It has particular significance for how one may interpret the nature of the quantum state.

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<i>Quantum Computation and Quantum Information</i> Textbook by scientists Michael Nielsen and Isaac Chuang

Quantum Computation and Quantum Information is a textbook about quantum information science written by Michael Nielsen and Isaac Chuang, regarded as a standard text on the subject. It is informally known as "Mike and Ike", after the candies of that name. The book assumes minimal prior experience with quantum mechanics and with computer science, aiming instead to be a self-contained introduction to the relevant features of both. The focus of the text is on theory, rather than the experimental implementations of quantum computers, which are discussed more briefly.

Quantum foundations is a discipline of science that seeks to understand the most counter-intuitive aspects of quantum theory, reformulate it and even propose new generalizations thereof. Contrary to other physical theories, such as general relativity, the defining axioms of quantum theory are quite ad hoc, with no obvious physical intuition. While they lead to the right experimental predictions, they do not come with a mental picture of the world where they fit.

In quantum information theory and quantum optics, the Schrödinger–HJW theorem is a result about the realization of a mixed state of a quantum system as an ensemble of pure quantum states and the relation between the corresponding purifications of the density operators. The theorem is named after physicists and mathematicians Erwin Schrödinger, Lane P. Hughston, Richard Jozsa and William Wootters. The result was also found independently by Nicolas Gisin, and by Nicolas Hadjisavvas building upon work by Ed Jaynes, while a significant part of it was likewise independently discovered by N. David Mermin. Thanks to its complicated history, it is also known by various other names such as the GHJW theorem, the HJW theorem, and the purification theorem.

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