All-Optical Long-Distance Quantum Communication with Gottesman-Kitaev-Preskill qubits

TL;DR

This paper proposes a novel all-optical quantum repeater protocol using Gottesman-Kitaev-Preskill (GKP) qubits, enabling long-distance quantum communication with deterministic Gaussian operations, error correction, and improved efficiency over photonic qubit methods.

Contribution

It introduces a GKP-based quantum repeater scheme utilizing Gaussian operations and post-processing techniques, reducing qubit requirements and enhancing communication rates.

Findings

GKP repeaters achieve comparable secure key rates to photonic qubit methods.

Phase-sensitive amplification reduces Gaussian noise in repeater segments.

Concatenation with higher-level codes boosts communication efficiency.

Abstract

Quantum repeaters are a promising platform for realizing long-distance quantum communication and thus could form the backbone of a secure quantum internet, a scalable quantum network, or a distributed quantum computer. Repeater protocols that encode information in single- or multi-photon states are limited by transmission losses and the cost of implementing entangling gates or Bell measurements. In this work, we consider implementing a quantum repeater protocol using Gottesman-Kitaev-Preskill (GKP) qubits. These qubits are natural elements for quantum repeater protocols, because they allow for deterministic Gaussian entangling operations and Bell measurements, which can be implemented at room temperature. The GKP encoding is also capable of correcting small displacement errors. At the cost of additional Gaussian noise, photon loss can be converted into a random displacement error channel by applying a phase-insensitive amplifier. Here we show that a similar conversion can be achieved in two-way repeater protocols by using phase-sensitive amplification applied in the post-processing of the measurement data, resulting in less overall Gaussian noise per (sufficiently short) repeater segment. We also investigate concatenating the GKP code with higher level qubit codes while leveraging analog syndrome data, post-selection, and path-selection techniques to boost the rate of communication. We compute the secure key rates and find that GKP repeaters can achieve a comparative performance relative to methods based on photonic qubits while using orders-of-magnitude fewer qubits.