Long quantum channels for high-quality entanglement transfer

TL;DR

This paper demonstrates that high-quality entanglement transfer over long quantum channels is achievable by tuning the endpoint coupling to an optimal value that scales with channel length, ensuring robust quantum communication.

Contribution

It reveals the optimal coupling scaling law for ballistic quantum channels, enabling high-fidelity entanglement transfer regardless of channel length or initialization.

Findings

Optimal coupling scales as N^{-1/6} for large N

Quantum-state fidelity exceeds 90% for any chain length

High-quality transfer achievable by adjusting channel length to optimal value

Abstract

High-quality quantum-state and entanglement transfer can be achieved in an unmodulated spin bus operating in the ballistic regime, which occurs when the endpoint qubits A and B are coupled to the chain by an exchange interaction $j_0$ comparable with the intrachain exchange. Indeed, the transition amplitude characterizing the transfer quality exhibits a maximum for a finite optimal value $j_0^{opt}(N)$, where $N$ is the channel length. We show that $j_0^{opt}(N)$ scales as $N^{-1/6}$ for large $N$ and that it ensures a high-quality entanglement transfer even in the limit of arbitrarily long channels, almost independently of the channel initialization. For instance, the average quantum-state transmission fidelity exceeds 90% for any chain length. We emphasize that, taking the reverse point of view, should $j_0$ be experimentally constrained, high-quality transfer can still be obtained by adjusting the channel length to its optimal value.