High-speed quantum networking by ship

Abstract

Networked entanglement is an essential component for a plethora of quantum computation and communication protocols. Direct transmission of quantum signals over long distances is prevented by fibre attenuation and the no-cloning theorem, motivating the development of quantum repeaters, designed to purify entanglement, extending its range. Quantum repeaters have been demonstrated over short distances, but error-corrected, global repeater networks with high bandwidth require new technology. Here we show that error corrected quantum memories installed in cargo containers and carried by ship can provide a exible connection between local networks, enabling low-latency, high-fidelity quantum communication across global distances at higher bandwidths than previously proposed. With demonstrations of technology with sufficient fidelity to enable topological error-correction, implementation of the quantum memories is within reach, and bandwidth increases with improvements in fabrication. Our approach to quantum networking avoids technological restrictions of repeater deployment, providing an alternate path to a worldwide Quantum Internet.

Figure 1. Physical transport protocol for a transpacific sneakernet using a single ship.

The transpacific connection shows the location of memory stick units both on shore in the U.S. and Japan and in transit aboard a VLCS-class ship. Each cargo container (memorystick) contains the actual memory units as well as any required control, cooling and power infrastructure. Each memory unit (for the specific hardware model of optically connected NV⁻ qubits30) consists of an array of diamond crystals within adjustable single sided cavities which are optically connected to perform individual qubit/qubit interactions.

Figure 2. Properties of the planar code.

The memory unit is a two-dimensional nearest neighbour array of qubits encoded with the topological planar code. (a) Structure of the planar code with the single qubit X_L and Z_L operators. (Gridlines do not represent entanglement bonds.) (b) Logical error rate as a function of physical error rate for different code distances. Simulations confirm that the fault-tolerant threshold of the planar code lies at p ≈ 0.7% under a standard error model. (c) Memory time as a function of N and P_link for a device that has a t = 3.5 μs physical gate time and p = 0.1%. Along the heavy black contour line, an N-qubit memory unit can maintain sufficiently high coherence to achieve the selected P_link after one year of storage time. (d) Per-error correction cycle logical error rate P_L as a function of physical error rate p for different code distances. Numbers in parentheses are total physical qubits per logical qubit at that code distance.