From Quantum B\"acklund Transforms to Topological Quantum Field Theory

TL;DR

This paper develops a quantum analogue of B"acklund transformations for the quantised Ablowitz-Ladik chain, linking integrable systems, quantum algebra, and topological quantum field theory through the construction of Q-operators and fusion matrices.

Contribution

It introduces a quantum B"acklund transform for the q-boson model and connects it to 2D TQFT fusion matrices, providing a novel link between integrable systems and topological quantum field theory.

Findings

Derived quantum B"acklund transformations for the q-boson model.

Constructed two related Q-operators and established their relations.

Linked multi-B"acklund transforms to fusion matrices of a 2D TQFT.

Abstract

We derive the quantum analogue of a B\"acklund transformation for the quantised Ablowitz-Ladik chain, a space discretisation of the nonlinear Schr\"odinger equation. The quantisation of the Ablowitz-Ladik chain leads to the $q$-boson model. Using a previous construction of Baxter's Q-operator for this model by the author, a set of functional relations is obtained which matches the relations of a one-variable classical B\"acklund transform to all orders in $\hbar $. We construct also a second Q-operator and show that it is closely related to the inverse of the first. The multi-B\"acklund transforms generated from the Q-operator define the fusion matrices of a 2D TQFT and we derive a linear system for the solution to the quantum B\"acklund relations in terms of the TQFT fusion coefficients.