Manipulating energy and spin currents in nonequilibrium systems of interacting qubits

TL;DR

This paper investigates how to control energy and spin currents in nonequilibrium qubit chains by manipulating boundary conditions, revealing symmetries that simplify steady-state correlations and enable current switching.

Contribution

It introduces a symmetry-based framework for understanding and controlling currents in interacting qubit chains under nonequilibrium conditions.

Findings

Symmetries restrict steady-state density matrices and correlations.

Boundary conditions can switch off spin or energy currents.

Certain correlations vanish due to symmetry constraints.

Abstract

We consider generic interacting chain of qubits, which are coupled at the edges to baths of fixed polarizations. We can determine the nonequilibrium steady states, described by the fixed point of the Lindblad Master Equation. Under rather general assumptions about local pumping and interactions, symmetries of the reduced density matrix are revealed. The symmetries drastically restrict the form of the steady density matrices in such a way that an exponentially large subset of one--point and many--point correlation functions are found to vanish. As an example we show how in a Heisenberg spin chain a suitable choice of the baths can completely switch off either the spin or the energy current, or both of them, despite the presence of large boundary gradients.