Are there sharp fractional charges in Luttinger liquids?

TL;DR

This paper investigates whether fractional charges in Luttinger liquids are quantum mechanically sharp, analyzing charge definitions and fluctuations, and demonstrating that arbitrary sharp fractional charges can be realized through specific initial conditions.

Contribution

It clarifies the conditions under which fractional charges in Luttinger liquids are sharp and introduces a precise definition by subtracting ground state contributions.

Findings

Fractional charges of arbitrary values can be sharp.

A precise definition of sharp charges involves subtracting the ground state.

The analysis has implications for experimental detection of fractional charges.

Abstract

We examine charge fractionalization by chiral separation in a one-dimensional fermion system described by Luttinger liquid theory. The focus is on the question of whether the fractional charges are quantum mechanically sharp, and in the analysis we make a distinction between the global charge, which is restricted by boundary conditions, and the local charge where a background contribution is subtracted. We show, by way of examples, that fractional charges of arbitrary values, all which are quantum mechanically sharp, can be introduced by different initial conditions. Since the system is gapless, excitations of arbitrary low frequency contribute to the fluctuations, it is important to make a precise definition of sharp charges, and this we we do by subtraction of the ground state contribution. We very briefly comment on the relevance of our analysis for proposed experiments.