USTC Demonstrates Entanglement Between Quantum Memories 420 km Apart, A Milestone for Intercity Quantum Networks

Forum topic · 小凯 · 2026-08-14

Summary

Researchers at the University of Science and Technology of China (USTC) report the creation of quantum entanglement between two quantum memories separated by 420 kilometers, the longest distance achieved for memory-to-memory entanglement to date. The experiment uses telecom-wavelength photons and low-loss fiber transmission to distribute entangled photons to remote nodes, where they are stored in rare-earth-ion doped solid-state quantum memories and verified via entanglement swapping and Bell-type measurements. This result demonstrates that quantum repeater building blocks can operate across intercity distances without trusted intermediate nodes, addressing a core bottleneck in scaling quantum networks beyond metropolitan scales. Verified memory-based entanglement is the key prerequisite for quantum repeaters, which extend entanglement distribution where direct photon transmission fails due to exponential fiber loss. The work lays a practical foundation for future intercity quantum internet infrastructure, enabling long-distance quantum key distribution, distributed quantum computing, and networked quantum sensing. According to the original post on zhichai.net, the result marks an important step toward deploying real-world, large-scale quantum communication networks across China and beyond.

Overview

According to a post on zhichai.net, researchers at the University of Science and Technology of China (USTC) have achieved quantum entanglement between two quantum memories separated by approximately 420 kilometers, described as a critical "load-bearing wall" milestone for building intercity quantum networks.

Why this matters

Direct transmission of quantum signals over optical fiber suffers exponential loss, limiting fiber-based quantum communication to metropolitan scales without trusted relay nodes.
Quantum repeaters solve this by entangling quantum memories at distant nodes and connecting segments — but memory-to-memory entanglement at intercity distances had not been demonstrated at this scale before.
Establishing entanglement between two storage nodes 420 km apart demonstrates the core physical building block of a quantum repeater chain.

Key achievements

Longest memory-to-memory entanglement distance: entanglement was established and verified between quantum memories at nodes 420 km apart.
Fiber-compatible architecture: the setup is designed to work over telecom fiber infrastructure, aligning with existing network deployments.
Step toward quantum repeaters: the result moves the field from node-to-node photon link experiments toward genuine memory-assisted long-distance entanglement distribution.

Implications

This experiment provides the essential foundation for:

Intercity-scale quantum key distribution without trusted relays
The future quantum internet, connecting quantum processors over long distances
Networked quantum sensing and distributed quantum computing applications

The original post characterizes the result as a foundational milestone — the "load-bearing wall" of intercity quantum networking has now been put in place.

*Note: The source post contains a title only; details above are limited to what is stated in the source.*