Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physica Scripta

The Transition Point Between Classical and Quantum Mechanical Systems Deterministically Defined

Terence William Barrett

Published Apr 1, 1987• 1 citation
Publisher

Abstract

From a deterministic point of view of quantum theory the Schrodinger equation, considered as an equation of motion, is defined within an area of instability formed by two potential minima.This view can be related to the renormalization group theory of critical phenomena, and the location of two nontrivial fixed points can be defined with respect to those two potential minima.The renormalization group theory parameter: d, the dimensionality of space, defines the transition between classical and quantum theory.For a system in which d 2 4, classical mechanics applies, and for d < 4, quantum mechanics applies.Whereas the classical potential defining an equation of motion has one potential minimum (at the Gaussian fixed point), the quantum potential defining an equation of motion has two potential minima (at the nontrivial fixed points).An analogy exists between systems based on wave mechanics and those based on lattice systems.The underlying dynamics of that potential, the minimization of which results in an equation formally equivalent to the Schrodinger equation, can, in this formal analogy, be identified with the underlying dynamics of the exchange energy at the vertex of a lattice.There is thus a mathematical global similarity underlying the behavior of these two distinct theoretical frameworks which describes both.The principal and angular momentum quantum numbers of electron systems in this analogy are equivalent to the dimensionality of space, d, and the dimensionality of spin space, n, in the general theory of critical phenomena.The general theory describes the phase transitions of electron (wave mechanical) systems, and also a "Mendeleev's table" based on the d and n parameters constructed for those electron systems, in analogy with such a table for lattice systems.

DOI
10.1088/0031-8949/35/4/001

Related papers

Quantum entanglement

Eduardo Fradkin

Classical and quantum criticality In most cases the phases of quantum field theories, in particular those of interest in condensed matter physics, can be described in terms of the behavior of local observables, such as order parameters or currents that transform properly under the symmetries of the theory. Quantum and thermal phase transitions are characterized by the behavior of these observables as a function of temperature and of the coupling constants of the theory. The phase transitions themselves, quantum or thermal, are classified into universality classes, which are represented by the critical exponents which specify the scaling laws of the expectation values of the observables. Historically, the development of this approach to critical behavior goes back to the Landau theory of critical behavior. It acquired its most complete form with the development of the renormalization group (RG) in the late 1960s and early 1970s. It is the centerpiece of Wilson’s approach to quantum field theory, in which all local quantum field theories are defined by the scaling regime of a physical system near a continuous phase transition. From this point of view there is no fundamental difference between classical (or thermal) phase transitions, which are described by the theory of classical critical behavior, and quantum phase transitions. For example, the expectation value of a local order parameter M as the thermal phase transition is approached from below behaves as M ~ (Tc − T) β . Here T c is the critical temperature and β is a critical exponent that depends on the universality class of the thermal phase transition and on the dimensionality of space. While quantum mechanics can play a key role in the existence of the ordered phase, e.g. superfluidity and superconductivity are macroscopic manifestations of essentially quantum-mechanical phenomena, the thermal transition itself is governed entirely by classical statistical mechanics, and quantum mechanics plays a role in setting the value of non-universal quantities such as the critical temperature, etc. On the other hand, in the case of a quantum phase transition, the order parameter M has a similar scaling behavior as a function of the coupling constant, M~(gc−g)β˜, where g is the coupling constant, g c is the critical coupling constant, and β˜ is a critical exponent that depends on the universality class of the quantum phase transition. Here we assume that M has a non-vanishing expectation value only for g < g c .

Cambridge University Press eBooks•Feb 28, 2013•0 citations

The Quantum Mechanical Density Operator And Its Time Evolution: Quantum Dynamics Using The Quantum Liouville Equation

Abraham Nitzan

The starting point of the classical description of motion is the Newton equations that yield a phase space trajectory (rN (t), pN (t)) for a given initial condition (rN (0), pN (0)). Alternatively one may describe classical motion in the framework of the Liouville equation (Section (1.2.2)) that describes the time evolution of the phase space probability density f (rN , pN ; t). For a closed system fully described in terms of a well specified initial condition, the two descriptions are completely equivalent. Probabilistic treatment becomes essential in reduced descriptions that focus on parts of an overall system, as was demonstrated in Sections 5.1–5.3 for equilibrium systems, and in Chapters 7 and 8 that focus on the time evolution of classical systems that interact with their thermal environments. This chapter deals with the analogous quantum mechanical problem. Within the limitations imposed by its nature as expressed, for example, by Heisenbergtype uncertainty principles, the Schrödinger equation is deterministic. Obviously it describes a deterministic evolution of the quantum mechanical wavefunction. The analog of the phase space probability density f (rN , pN ; t) is now the quantum mechanical density operator (often referred to as the “density matrix”), whose time evolution is determined by the quantum Liouville equation. Again, when the system is fully described in terms of a well specified initial wavefunction, the two descriptions are equivalent. The density operator formalism can, however, be carried over to situations where the initial state of the system is not well characterized and/or a reduced description of part of the overall system is desired. Such situations are considered later in this chapter.

Oxford University Press eBooks•Apr 6, 2006•1 citation

Quantum mechanical motion of classical particles

V. D. Rusov, Konstantin Alexandrovich Lukin

The Schrödinger equation for the particle wave function introduced via its action was derived from Newton equation for a point-like particle moving under effect of both potential force and fluctuation-dissipative environment, provided considering only stable motion of the particle. The model considered assumes existence of wave function as a physical field rather than just a mathematical abstraction.

Journal of Physics Conference Series•May 10, 2012•0 citations

Coherent and dissipative wave packet dynamics in cyclic model systems with four equivalent potential minima

O. Brackhagen, Oliver Kühn, Jörn Manz +2 more

The dynamics of cyclic systems with four equivalent potential minima is studied here from two different points of view. The solution of the time-dependent Schrödinger equation provides insight into the coherent wave packet motion. The resulting reaction mechanism involves relocalization between opposite, not neighboring potential minima. The inclusion of an environment within a density matrix description leads to dissipation and therefore to a transition from coherent to incoherent dynamics. The theoretical considerations are applied to a simple model of the cyclic motion of a proton in a molecular framework.

The Journal of Chemical Physics•Jun 15, 1994•11 citations

From Qubit to Qubit: A Graduate Course in Quantum Mechanics

Jeremy Levy

This textbook is drawn from notes for a two-semester graduate course in quantum mechanics. It begins with the most constrained quantum system, and recovers the rest of the subject by relaxing those constraints one at a time. The starting point is a single qubit, the smallest nontrivial Hilbert space with the strongest possible restriction on its dynamics, made concrete by a Bloch cube whose six faces are the cardinal states of a spin-1/2 system. Tensor products admit many qubits; lattices give them a place to live; time evolution sets them in motion; the continuum limit produces wavefunctions; three-dimensional angular momentum, the hydrogen atom, and perturbation theory follow; Lorentz invariance promotes the lattice of spinors to the Dirac equation; and the renormalization group asks how theories at different scales relate. Each chapter loosens one feature of the qubit while keeping the others fixed, so that the standard apparatus of graduate quantum mechanics arrives as a sequence of controlled generalizations rather than as separate topics. Discrete-to-continuous transitions recur at four scales: in Hilbert-space dimension, in real space, in time, and in coupling. The book closes by reimposing one of the original constraints, returning to a two-level system that is now a logical qubit protected by quantum error correction, with the fault-tolerance threshold appearing as an unstable RG fixed point and supplying the reason a logical qubit, independent of its underlying hardware, can exist at all.

quant-pharXiv:2605.01585•May 5, 2026•0 citations

Phase Transitions and Critical Phenomena in Quantum Systems

N. Boccara

Abstract From the point of view of phase transitions and critical phenomena quantum systems do not differ from classical systems. Such concepts as order parameters, self‐consistent approximations and critical exponents are reviewed for both types of systems and their similarities are stressed with the help of group theoretical considerations.

Berichte der Bunsengesellschaft für physikalische Chemie•Mar 1, 1972•1 citation
From a deterministic point of view of quantum theory the Schrodinger equation, considered as an equation of motion, is defined within an area of instability formed by two potential minima.This view can be related to the renormalization group theory of critical phenomena, and the location of two nontrivial fixed points can be defined with respect to those two potential minima.The renormalization group theory parameter: d, the dimensionality of space, defines the transition between classical and quantum theory.For a system in which d 2 4, classical mechanics applies, and for d < 4, quantum mechanics applies.Whereas the classical potential defining an equation of motion has one potential minimum (at the Gaussian fixed point), the quantum potential defining an equation of motion has two potential minima (at the nontrivial fixed points).An analogy exists between systems based on wave mechanics and those based on lattice systems.The underlying dynamics of that potential, the minimization of which results in an equation formally equivalent to the Schrodinger equation, can, in this formal analogy, be identified with the underlying dynamics of the exchange energy at the vertex of a lattice.There is thus a mathematical global similarity underlying the behavior of these two distinct theoretical frameworks which describes both.The principal and angular momentum quantum numbers of electron systems in this analogy are equivalent to the dimensionality of space, d, and the dimensionality of spin space, n, in the general theory of critical phenomena.The general theory describes the phase transitions of electron (wave mechanical) systems, and also a "Mendeleev's table" based on the d and n parameters constructed for those electron systems, in analogy with such a table for lattice systems.
Classical and quantum criticality In most cases the phases of quantum field theories, in particular those of interest in condensed matter physics, can be described in terms of the behavior of local observables, such as order parameters or currents that transform properly under the symmetries of the theory. Quantum and thermal phase transitions are characterized by the behavior of these observables as a function of temperature and of the coupling constants of the theory. The phase transitions themselves, quantum or thermal, are classified into universality classes, which are represented by the critical exponents which specify the scaling laws of the expectation values of the observables. Historically, the development of this approach to critical behavior goes back to the Landau theory of critical behavior. It acquired its most complete form with the development of the renormalization group (RG) in the late 1960s and early 1970s. It is the centerpiece of Wilson’s approach to quantum field theory, in which all local quantum field theories are defined by the scaling regime of a physical system near a continuous phase transition. From this point of view there is no fundamental difference between classical (or thermal) phase transitions, which are described by the theory of classical critical behavior, and quantum phase transitions. For example, the expectation value of a local order parameter M as the thermal phase transition is approached from below behaves as M ~ (Tc − T) β . Here T c is the critical temperature and β is a critical exponent that depends on the universality class of the thermal phase transition and on the dimensionality of space. While quantum mechanics can play a key role in the existence of the ordered phase, e.g. superfluidity and superconductivity are macroscopic manifestations of essentially quantum-mechanical phenomena, the thermal transition itself is governed entirely by classical statistical mechanics, and quantum mechanics plays a role in setting the value of non-universal quantities such as the critical temperature, etc. On the other hand, in the case of a quantum phase transition, the order parameter M has a similar scaling behavior as a function of the coupling constant, M~(gc−g)β˜, where g is the coupling constant, g c is the critical coupling constant, and β˜ is a critical exponent that depends on the universality class of the quantum phase transition. Here we assume that M has a non-vanishing expectation value only for g < g c .
The starting point of the classical description of motion is the Newton equations that yield a phase space trajectory (rN (t), pN (t)) for a given initial condition (rN (0), pN (0)). Alternatively one may describe classical motion in the framework of the Liouville equation (Section (1.2.2)) that describes the time evolution of the phase space probability density f (rN , pN ; t). For a closed system fully described in terms of a well specified initial condition, the two descriptions are completely equivalent. Probabilistic treatment becomes essential in reduced descriptions that focus on parts of an overall system, as was demonstrated in Sections 5.1–5.3 for equilibrium systems, and in Chapters 7 and 8 that focus on the time evolution of classical systems that interact with their thermal environments. This chapter deals with the analogous quantum mechanical problem. Within the limitations imposed by its nature as expressed, for example, by Heisenbergtype uncertainty principles, the Schrödinger equation is deterministic. Obviously it describes a deterministic evolution of the quantum mechanical wavefunction. The analog of the phase space probability density f (rN , pN ; t) is now the quantum mechanical density operator (often referred to as the “density matrix”), whose time evolution is determined by the quantum Liouville equation. Again, when the system is fully described in terms of a well specified initial wavefunction, the two descriptions are equivalent. The density operator formalism can, however, be carried over to situations where the initial state of the system is not well characterized and/or a reduced description of part of the overall system is desired. Such situations are considered later in this chapter.
The dynamics of cyclic systems with four equivalent potential minima is studied here from two different points of view. The solution of the time-dependent Schrödinger equation provides insight into the coherent wave packet motion. The resulting reaction mechanism involves relocalization between opposite, not neighboring potential minima. The inclusion of an environment within a density matrix description leads to dissipation and therefore to a transition from coherent to incoherent dynamics. The theoretical considerations are applied to a simple model of the cyclic motion of a proton in a molecular framework.
This textbook is drawn from notes for a two-semester graduate course in quantum mechanics. It begins with the most constrained quantum system, and recovers the rest of the subject by relaxing those constraints one at a time. The starting point is a single qubit, the smallest nontrivial Hilbert space with the strongest possible restriction on its dynamics, made concrete by a Bloch cube whose six faces are the cardinal states of a spin-1/2 system. Tensor products admit many qubits; lattices give them a place to live; time evolution sets them in motion; the continuum limit produces wavefunctions; three-dimensional angular momentum, the hydrogen atom, and perturbation theory follow; Lorentz invariance promotes the lattice of spinors to the Dirac equation; and the renormalization group asks how theories at different scales relate. Each chapter loosens one feature of the qubit while keeping the others fixed, so that the standard apparatus of graduate quantum mechanics arrives as a sequence of controlled generalizations rather than as separate topics. Discrete-to-continuous transitions recur at four scales: in Hilbert-space dimension, in real space, in time, and in coupling. The book closes by reimposing one of the original constraints, returning to a two-level system that is now a logical qubit protected by quantum error correction, with the fault-tolerance threshold appearing as an unstable RG fixed point and supplying the reason a logical qubit, independent of its underlying hardware, can exist at all.