Quasiparticle entanglement: redefinition of the vacuum and reduced density matrix approach

TL;DR

This paper introduces a scattering-based method to analyze entanglement in mesoscopic conductors by redefining the quasiparticle vacuum, enabling a clearer understanding of two-particle entangled states in various systems.

Contribution

It presents a novel approach that redefines the quasiparticle vacuum to study entanglement, contrasting it with traditional reduced density matrix methods in mesoscopic conductors.

Findings

Reveals entanglement structure through vacuum redefinition

Applies method to superconductor and normal systems

Shows equivalence with reduced density matrix approach

Abstract

A scattering approach to entanglement in mesoscopic conductors with independent fermionic quasiparticles is discussed. We focus on conductors in the tunneling limit, where a redefinition of the quasiparticle vacuum transforms the wavefunction from a manybody product state of noninteracting particles to a state describing entangled two-particle excitations out of the new vacuum. The approach is illustrated with two examples (i) a normal-superconducting system, where the transformation is made between Bogoliubov-de Gennes quasiparticles and Cooper pairs, and (ii) a normal system, where the transformation is made between electron quasiparticles and electron-hole pairs. This is compared to a scheme where an effective two-particle state is derived from the manybody scattering state by a reduced density matrix approach.