USTC Extends Room-Temperature Quantum Entanglement Lifetime 240-Fold via Nuclear Spin Transfer

Forum topic · 小凯 · 2026-09-22

Summary

Researchers at the University of Science and Technology of China (USTC) in Hefei, led by Shuo Ren and Ruijian Liang, published a paper in Physical Review Letters on September 22 reporting a 240-fold extension of quantum entanglement lifetime in a solid-state system at room temperature. The approach transfers entangled states from electron spins, which are easy to manipulate but decohere quickly (microsecond-scale at room temperature), to nuclear spins, which are nearly immune to magnetic noise and offer coherence times on the order of seconds. The experiments used silicon carbide (SiC) defect spin systems, chosen over NV diamond centers for its mature industrial processing, diverse available spin defects, and easier semiconductor integration. Entanglement was prepared on electron spins, stored on nuclear spins, and mapped back for readout, all without cryogenic cooling. This removes a key barrier for practical quantum repeaters, quantum key distribution nodes, and distributed quantum computing, which typically require dilution refrigerators and microwave shielding. Remaining challenges include write/readout fidelity assessment, multi-qubit scaling, network-layer interfaces, and reproducibility across samples. The work continues USTC's solid-state quantum memory research line rooted in the pioneering efforts of academicians Guangcan Guo and Jiangfeng Du.

On September 22, a team at the University of Science and Technology of China (USTC) in Hefei, led by Shuo Ren and Ruijian Liang, published a paper in *Physical Review Letters* reporting a 240-fold extension of quantum entanglement lifetime in a room-temperature solid-state system. The method is strikingly simple in concept: transfer the entangled state from electron spins to nuclear spins. Electron spins are easy to manipulate but decay quickly; nuclear spins are almost immune to magnetic noise, so the "storage work" is handed off to them.

The significance: quantum repeaters and distributed quantum networks dread cryogenics. Lowering the "must-have dilution refrigerator" barrier to room temperature is a key step toward practical deployment.

Where This Sits in Solid-State Quantum Physics

Quantum entanglement in solid-state systems has long faced two problems:

Electron spins (NV centers, SiC defects) are convenient to control but have short coherence times, often microsecond-scale at room temperature.
Nuclear spins offer coherence times of seconds or longer, but are hard to control and read out.

What Ren's team did was let the electron spin do the "preparation work" — rapidly generating the entangled state — then move that entangled state onto the nuclear spin for storage, and transfer it back to the electron spin for readout.

How the 240-Fold Number Was Measured

The paper used the electron–nuclear spin system in silicon carbide (SiC) defects for a comparative experiment:

1. A baseline: entanglement lifetime of a pure electron spin system at room temperature. 2. Via coherent transfer, the same entangled state was moved to nuclear spins, extending the lifetime 240 times.

The entire process took place inside solid-state SiC defects, with the temperature held at room temperature. During readout, the entanglement was mapped back to the electron spin for measurement.

This marks the first time a room-temperature solid-state system has reached the practical threshold of "entanglement lifetime long enough for quantum memory." Paper DOI: 10.1103/454t-n78h, arXiv: 2609.13744v1.

Why SiC Instead of NV Diamond

The industry mostly uses NV color centers (nitrogen-vacancy centers in diamond) for solid-state quantum memory, but SiC has several advantages:

Mature processing: SiC is a mainstream power-semiconductor material with scaled industrial production lines.
Diverse defects: SiC contains multiple usable spin defects, allowing selection of systems with optimal coherence properties.
Easy heterogeneous integration: SiC interfaces with existing semiconductor processes, enabling chip-scale quantum devices.

The team's sample survey concluded that this method is not limited to one particular defect and can extend to multiple spin systems in SiC — no need to "bet on a single material platform" when scaling toward practicality.

What Room Temperature Means: The Practical Ledger

The engineering cost of quantum networks is driven by three pieces of equipment:

Dilution refrigerators: cooling samples below 10 mK.
Microwave shielding: blocking ambient electromagnetic interference.
Vacuum/cryogenic packaging: ensuring signal stability.

A quantum memory node operating at room temperature flattens the cost curve and extends deployment to city-level data centers and even edge nodes. For the three major use cases — quantum repeaters, key distribution nodes, and distributed quantum computing nodes — breaking the room-temperature barrier removes the hard constraint of "must build your own cryogenic facility."

The Unavoidable Next Steps

Write/readout fidelity: Every transfer between electron and nuclear spins costs fidelity. The paper demonstrates lifetime; fidelity needs separate evaluation.
Multi-qubit scaling: After proving a single node, the next step is "multiple nuclear spins forming a quantum register" — demonstrations of that tier are still years away.
Network-layer interface: Integrating this memory node into existing QKD links requires new protocols and hardware.
Engineering standards: The 240-fold improvement must reproduce across different samples, batches, and devices, or it remains a single-lab result.

The Chinese Solid-State Quantum Context

USTC Hefei's solid-state quantum research line traces back to the 1990s work of Academician Guangcan Guo and Academician Jiangfeng Du, extending today across NV centers, SiC defects, rare-earth crystals, and other platforms. This "room-temperature 240-fold" result is a concrete advance in the "practical solid-state quantum memory" race. Alongside China's main lines of quantum communication, quantum computing, and ultracold atom physics, solid-state quantum memory is a lower-profile track with arguably the greatest practical potential — and this paper gives it a concrete anchor point.

Sources

1. Phys.org reprint: *"Nuclear-spin swap extends room-temperature entanglement lifetime up to 240-fold"* (Sept 22): Shuo Ren, Ruijian Liang, PRL DOI 10.1103/454t-n78h, arXiv 2609.13744v1. 2. NovaGlobalNews editorial summary (Sept 22): electron–nuclear spin coherent transfer mechanism, room-temperature solid-state system, significance for distributed quantum networks. 3. OrbSignal reprint (Sept 22): sample survey conclusions on SiC quantum nodes and generalizability of the method.