Quantum measurements without macroscopic superpositions

TL;DR

This paper presents a quantum measurement model where a microscopic object becomes entangled with a macroscopic pointer, leading to decoherence and mixtures of states without requiring macroscopic superpositions, with explicit dynamics analysis.

Contribution

It introduces a model demonstrating how object-pointer entanglement and decoherence occur simultaneously without macroscopic superpositions, with detailed analysis of the dynamics and decoherence times.

Findings

Decoherence time independent of pointer-bath coupling details if coupling is weak.

Decoherence decay can be non-exponential or non-Gaussian.

Decoherence behavior varies with bath spectral properties (Ohmic or super-Ohmic).

Abstract

We study a class of quantum measurement models. A microscopic object is entangled with a macroscopic pointer such that each eigenvalue of the measured object observable is tied up with a specific pointer deflection. Different pointer positions mutually decohere under the influence of a bath. Object-pointer entanglement and decoherence of distinct pointer readouts proceed simultaneously. Mixtures of macroscopically distinct object-pointer states may then arise without intervening macroscopic superpositions. Initially, object and apparatus are statistically independent while the latter has pointer and bath correlated according to a metastable local thermal equilibrium. We obtain explicit results for the object-pointer dynamics with temporal coherence decay in general neither exponential nor Gaussian. The decoherence time does not depend on details of the pointer-bath coupling if it is smaller than the bath correlation time, whereas in the opposite Markov regime the decay depends strongly on whether that coupling is Ohmic or super-Ohmic.