Exact Quantum Scars in the Chiral Non-Linear Luttinger Liquid

TL;DR

This paper discovers a set of exact quantum scar states in a non-linear chiral Luttinger liquid, characterized by zero momentum-space entanglement and unique spectral properties, revealing new insights into non-integrable quantum many-body systems.

Contribution

It introduces a systematic method to find exact eigenstates in a non-linear chiral Luttinger liquid, highlighting their unique entanglement features and their role as quantum many-body scars.

Findings

Exact eigenstates exhibit zero momentum-space entanglement.

Some states have logarithmic real-space entanglement, others volume-law.

Level statistics support the scar nature of these states.

Abstract

While the chiral linear Luttinger liquid is integrable via bosonization, its non-linear counterpart does not admit for an analytic solution. In this work, we find a sub-extensive number of exact eigenstates for a large family of density-density interaction terms. These states are embedded in a continuum of strongly-correlated excited states. The real-space entanglement entropy of some exact states scales logarithmically with system size, while that of others has volume-law scaling. We introduce momentum-space entanglement as an unambiguous differentiator between these exact states and the remaining excited states. With regard to momentum space, the exact states behave as bona fide quantum many body scars: they exhibit identically zero momentum-space entanglement, while typical eigenstates behave thermally. We corroborate this finding by a level statistics analysis. Furthermore, we detail the general formalism for systematically finding all interaction terms and associated exact states, and present a number of infinite exact state sequences extending to arbitrarily high energies. Unlike many previous examples of quantum many body scars, the exact states uncovered here do not lie at equidistant energies, and do not follow from a special operator algebra. Instead, they are uniquely enabled by the interplay of Fermi statistics and chirality.