Communication at the quantum speed limit along a spin chain

TL;DR

This paper demonstrates that optimal control of an external magnetic field can significantly accelerate quantum information transfer along a spin chain, reaching the theoretical maximum speed and revealing fundamental physical limits.

Contribution

It introduces a method to drastically increase the propagation rate of quantum excitations in spin chains using optimal control, approaching the physical speed limit.

Findings

Propagation rate increased by two orders of magnitude

Achieved the theoretical maximum propagation speed

Excitation propagates as a dispersed wave at maximum speed

Abstract

Spin chains have long been considered as candidates for quantum channels to facilitate quantum communication. We consider the transfer of a single excitation along a spin-1/2 chain governed by Heisenberg-type interactions. We build on the work of Balachandran and Gong [1], and show that by applying optimal control to an external parabolic magnetic field, one can drastically increase the propagation rate by two orders of magnitude. In particular, we show that the theoretical maximum propagation rate can be reached, where the propagation of the excitation takes the form of a dispersed wave. We conclude that optimal control is not only a useful tool for experimental application, but also for theoretical enquiry into the physical limits and dynamics of many-body quantum systems.