Quantum correlation functions and the classical limit

Abstract

We study the transition from the full quantum mechanical description of physical systems to an approximate classical stochastic one. Our main tool is the identification of the closed-time-path (CTP) generating functional of Schwinger and Keldysh with the decoherence functional of the consistent histories approach. Given a degree of coarse-graining in which interferences are negligible, we can explicitly write a generating functional for the effective stochastic process in terms of the CTP generating functional. This construction gives particularly simple results for Gaussian processes. The formalism is applied to simple quantum systems, quantum Brownian motion, quantum fields in curved spacetime. Perturbation theory is also explained. We conclude with a discussion on the problem of backreaction of quantum fields in spacetime geometry.

30 pages, latex; minor changes, added some explanations and refeences

References in corpus (6)

• Stochastic semiclassical gravity
• Decoherent Histories and the Emergent Classicality of Local Densities
• Classical Dynamics of the Quantum Harmonic Chain
• Fluctuations of Energy Density and Validity of Semiclassical Gravity
• Histories quantisation of parameterised systems: I. Development of a general algorithm
• Quantum theory without Hilbert spaces

Cited by in corpus (10)

• Probing a Gravitational Cat State
• Can Spacetime be a Condensate?
• Uniformly Accelerated Charge in a Quantum Field: From Radiation Reaction to Unruh Effect
• Quantum Field Theory based Quantum Information: Measurements and Correlations
• Quantum processes on phase space
• Decoherence in Quantum Gravity: Issues and Critiques
• Comments on the adiabatic theorem
• Gravity, Quantum Fields and Quantum Information: Problems with classical channel and stochastic theories
• Principal Component Analysis of Quantum Correlation
• Phase Space Representations and Perturbation Theory for Continuous-time Histories