No intrinsic decoherence of inflationary cosmological perturbations

Abstract

After a brief summary of decoherence and quantum to classical transition in cosmology we focus on the study of quantum decoherence of cosmological perturbations in inflationary universe, that does not rely on any environment. This is what `intrinsic' in the title refers to -- a closed quantum system. The question is, does its quantum perturbations decohere with an inflationary expansion of the universe. A dominant view which had propagated for a quarter of a century asserts yes, based on the belief that the large squeezing of a quantum state after a duration of inflation renders the system effectively classical. This paper debunks this view by identifying the technical fault-lines in its derivations and revealing the pitfalls in its arguments which drew earlier authors to this wrong conclusion. We use a few simple quantum mechanical models to expound where the fallacy originated: The highly squeezed ellipse quadrature in phase space cannot be simplified to a line, and the Wigner function cannot be replaced by a delta function. These amount to taking only the leading order contributions in seeking the semiclassical limit and ignoring the subdominant contributions where quantum features reside. Doing so violates the bounds of the Wigner function, and its wave functions possess negative eigenvalues. Moreover, the Robertson-Schrodinger uncertainty relation for a pure state is violated. For inflationary cosmological perturbations, in addition to these features, entanglement exists between the created pairs. This uniquely quantum feature cannot be easily argued away. Indeed it could be our best hope to retroduce the quantum nature of cosmological perturbations and the trace of an inflaton field. All this point to the fact that a closed quantum system, even when highly squeezed, evolves unitarily without loss of coherence; quantum cosmological perturbations do not by itself decohere.

arXiv comment55 pages, 5 figures

References in corpus (54)

• Decoherence, the measurement problem, and interpretations of quantum mechanics
• Classical Equations for Quantum Systems
• Open Quantum Systems. An Introduction
• A Spin Entanglement Witness for Quantum Gravity
• Continuous variable quantum information: Gaussian states and beyond
• Semiclassicality and Decoherence of Cosmological Perturbations
• Quantum Decoherence
• Inflation and squeezed quantum states
• Symplectic invariants, entropic measures and correlations of Gaussian states
• Quantum-to-classical transition for fluctuations in the early Universe
• The Quantum Vlasov Equation and its Markov Limit
• Quantum Fluctuations, Decoherence of the Mean Field, and Structure Formation in the Early Universe
• Gravitational Decoherence
• Pointer states for primordial fluctuations in inflationary cosmology
• Quantum Brownian Motion in a Bath of Parametric Oscillators: A model for system-field interactions
• Decoherence during Inflation: the generation of classical inhomogeneities
• Coarse graining and decoherence in quantum field theory
• Quantum Discord of Cosmic Inflation: Can we Show that CMB Anisotropies are of Quantum-Mechanical Origin?
• Emergent/Quantum Gravity: Macro/Micro Structures of Spacetime
• Entropy of a Classical Stochastic Field and Cosmological Perturbation
• An effective field theory during inflation: reduced density matrix and its quantum master equation
• The Entropy of the Gravitational Field
• Entropy of gravitons produced in the early Universe
• Quantum Decoherence During Inflation from Gravitational Nonlinearities
• Coarse-Grained Effective Action and Renormalization Group Theory in Semiclassical Gravity and Cosmology
• Squeezed Vacua and the Quantum Statistics of Cosmological Particle Creation
• Effective noise in stochastic description of inflation
• On the Decoherence of Primordial Fluctuations During Inflation
• Decoherence, discord and the quantum master equation for cosmological perturbations
• Entanglement Entropy of Cosmological Perturbations
• The Noise of Gravitons
• Short distance and initial state effects in inflation: stress tensor and decoherence
• A New Theory of Stochastic Inflation
• Noise and decoherence induced by gravitons
• Quantum Squeezing and Cosmological Entropy Production
• Entropy Production in the Cosmological Amplification of the Vacuum Fluctuations
• Spacetime Quantum Mechanics and the Quantum Mechanics of Spacetime
• Entropy and Uncertainty of Squeezed Quantum Open Systems
• A cosmological open quantum system
• Quantum Superposition of Two Gravitational Cat States
• The Effects of Gravitational Back-Reaction on Cosmological Perturbations
• Decoherence from Isocurvature Perturbations in Inflation
• Decoherence and entropy of primordial fluctuations. I: Formalism and interpretation
• Uncertainty Relation at Finite Temperature
• Decoherence and entropy of primordial fluctuations II. The entropy budget
• Squeezed States and Uncertainty Relation at Finite Temperature
• Uncertainty Relation for a Quantum Open System
• Quantum entanglement and entropy in particle creation
• Gravitational Decoherence: A Thematic Overview
• Quantum Noise of Gravitons and Stochastic Force on Geodesic Separation
• Macroscopic quantum phenomena from the large N perspective
• On the Entropy and the Density Matrix of Cosmological Perturbations
• Cosmological Decoherence from Thermal Gravitons
• Quantum Statistical Field Theory in Gravitation and Cosmology

Cited by in corpus (12)

• Quantum entanglement in cosmology
• Does inflation squeeze cosmological perturbations?
• Real-space quantum-to-classical transition of time dependent background fluctuations
• Entanglement in an expanding toroidal Bose-Einstein condensate
• Graviton physics: Quantum field theory of gravitons, graviton noise and gravitational decoherence -- a concise tutorial
• Quantum Parametric Oscillator Heat Engines in Squeezed Thermal Baths: Foundational Theoretical Issues
• Hot entanglement? -- Parametrically coupled quantum oscillators in two heat baths: instability, squeezing and driving
• Open system dynamics in interacting quantum field theories
• Fluctuations-Induced Quantum Radiation and Reaction from an Atom in a Squeezed Quantum Field
• Entanglement and correlations between local observables in de Sitter spacetime
• Are intrinsic decoherence models physical theories?
• Anharmonic Effects on the Squeezing of Axion Perturbations