Hamiltonians for one-way quantum repeaters

TL;DR

This paper introduces Hamiltonian-based models for one-way quantum repeaters that do not require measurements or quantum memories, potentially enhancing long-distance quantum communication with minimal photon signals.

Contribution

It presents two novel methods to construct Hamiltonians for unitary quantum repeaters capable of surpassing fundamental repeaterless key rate bounds.

Findings

Hamiltonian methods can generate effective repeater interactions.

Repeater schemes outperform bounds even with additional coupling loss.

Signals with few photons are sufficient for the proposed schemes.

Abstract

Quantum information degrades over distance due to the unavoidable imperfections of the transmission channels, with loss as the leading factor. This simple fact hinders quantum communication, as it relies on propagating quantum systems. A solution to this issue is to introduce quantum repeaters at regular intervals along a lossy channel, to revive the quantum signal. In this work we study unitary one-way quantum repeaters, which do not need to perform measurements and do not require quantum memories, and are therefore considerably simpler than other schemes. We introduce and analyze two methods to construct Hamiltonians that generate a repeater interaction that can beat the fundamental repeaterless key rate bound even in the presence of an additional coupling loss, with signals that contain only a handful of photons. The natural evolution of this work will be to approximate a repeater interaction by combining simple optical elements.