Fast Quantum Communication in Linear Networks

TL;DR

This paper demonstrates that high-fidelity, ultra-fast quantum state swaps in linear oscillator networks are achievable using advanced control protocols augmented with path-tracing, surpassing standard methods.

Contribution

It introduces a novel application of path-tracing to find time-optimal control protocols for quantum state transfer in linear networks, revealing solutions standard methods cannot discover.

Findings

Fast state swapping protocols with high fidelity are possible within less than one oscillation period.

Standard gradient search methods fail to find these protocols.

Path-tracing effectively solves complex time-optimal control problems.

Abstract

Here we consider the speed at which quantum information can be transferred between the nodes of a linear network. Because such nodes are linear oscillators, this speed is also important in the cooling and state preparation of mechanical oscillators, as well as frequency conversion. We show that if there is no restriction on the size of the linear coupling between two oscillators, then there exist control protocols that will swap their respective states with high fidelity within a time much less than a single oscillation period. Standard gradient search methods fail to find these fast protocols. We were able to do so by augmenting standard search methods with a path-tracing technique, demonstrating that this technique has remarkable power to solve time-optimal control problems, as well as confirming the highly challenging nature of these problems. As a further demonstration of the power of path-tracing, first introduced by Moore-Tibbets et al. [Phys. Rev. A 86, 062309 (2012)], we apply it to the generation of entanglement in a linear network.