A quantum phase transition implementation of quantum measurement

TL;DR

This paper models quantum measurement as a cascade of two quantum phase transitions, explaining how superpositions become classical outcomes and analyzing entanglement effects during partial measurements.

Contribution

It introduces a novel phase transition framework for quantum measurement, linking superposition formation and collapse within a unified model.

Findings

Superpositions of macroscopic responses are generated by the first phase transition.

Wavefunction collapse is modeled as a second phase transition suppressing superpositions.

Entanglement effects are analyzed during partial measurements in quantum systems.

Abstract

A model of quantum measurement, illustrated using the spin--boson model, is formulated in terms of a cascading pair of quantum phase transitions. The first produces the desired superposition of macroscopic responses to the microscopic state under investigation, while the second provides a mechanism for subsequent "wavefunction collapse," suppressing superpositions of distinct macroscopic states, producing instead a density matrix that implements the expected classical observation outcome via the Born probability rule. Motivated by numerous carefully designed measurements that may occur during the course of a quantum computation, effects of entanglement are investigated when the measurement is performed on only a subset of the microscopic degrees of freedom.