Initializing an unmodulated spin chain to operate as a high quality quantum data-bus

TL;DR

This paper investigates how the initial state of spin chains affects their ability to transmit quantum information and entanglement, revealing differences between free-fermionic and interacting models and identifying optimal initialization strategies.

Contribution

It provides the first analysis showing that state and entanglement transmission maxima occur at different points depending on interactions and initializations.

Findings

Non-interacting systems' entanglement can be improved by initialization.

In the XX model, ferromagnetic initial states eliminate destructive effects.

Interacting systems can enhance transmission through proper initialization.

Abstract

We study the quality of state and entanglement transmission through quantum channels described by spin chains varying both the system parameters and the initial state of the channel. We consider a vast class of one-dimensional many-body models which contains some of the most relevant experimental realizations of quantum data-buses. In particular, we consider spin-1/2 XY and XXZ model with open boundary conditions. Our results show a significant difference between free-fermionic (non-interacting) systems (XY) and interacting ones (XXZ), where in the former case initialization can be exploited for improving the entanglement distribution, while in the latter case it also determines the quality of state transmission. In fact, we find that in non interacting systems the exchange with fermions in the initial state of the chain always has a destructive effect, and we prove that it can be completely removed in the isotropic XX model by initializing the chain in a ferromagnetic state. On the other hand, in interacting systems constructive effects can arise by scattering between hopping fermions and a proper initialization procedure. Remarkably our results are the first example in which state and entanglement transmission show maxima at different points as the interactions and initializations of spin chain channels are varied.