Quantum information theory of the Bell-state quantum eraser

TL;DR

This paper develops a unitary information-theoretic framework to analyze the Bell-state quantum eraser, clarifying the interplay between quantum coherence and classical information in measurement processes.

Contribution

It introduces a novel, unified information-theoretic approach to describe quantum measurements and the dual particle-wave properties in the Bell-state quantum eraser.

Findings

Quantum coherence and classical information are described using quantum-information-theoretic tools.

An equality relates coherence and which-path information based on the chain rule for entropies.

The framework offers simple interpretations of coherence and which-path information in terms of state preparation and determination.

Abstract

Quantum systems can display particle- or wave-like properties, depending on the type of measurement that is performed on them. The Bell-state quantum eraser is an experiment that brings the duality to the forefront, as a single measurement can retroactively be made to measure particle-like or wave-like properties (or anything in between). Here we develop a unitary information-theoretic description of this (and several related) quantum measurement situations that sheds light on the trade-off between the quantum and classical features of the measurement. In particular, we show that both the coherence of the quantum state and the classical information obtained from it can be described using quantum-information-theoretic tools only, and that those two measures satisfy an equality on account of the chain rule for entropies. The coherence information and the which-path information have simple interpretations in terms of state preparation and state determination, and suggest ways to account for the relationship between the classical and the quantum world.