Committing light moments to solid quantum memory

Quantum networks form the backbone of a broad variety of pioneering technologies enabled by leveraging the laws of quantum mechanics — from quantum computers and quantum sensors to a quantum internet that provides a level of communication security that is unattainable with current, 'classical' technologies. At the heart of quantum networks lies the exchange of information between different quantum systems. A well-established protocol for such an operation is known as 'quantum teleportation', in which quantum states (not matter itself) are transferred between light and matter systems, such as atoms, ions and crystals. Quantum teleportation experiments have been demonstrated with various combinations of light sources and materials, but doing so on a platform compatible with existing telecommunications infrastructures remains a major challenge. The group of Prof. Xiao-Song Ma at Nanjing University has now taken a major step in addressing this problem. As they write in Physical Review Letters, the researchers have demonstrated quantum teleportation from telecommunication-wavelength light to a solid-state quantum memory. Their experiments vastly exceeded the theoretical limits for classical systems — a clearcut demonstration that this quantum process cannot be replicated by conventional technology. Crucially, their entire system uses components compatible with existing fibre networks, opening the door to large-scale quantum networks.

From storage to distribution

The concept of a quantum internet has been refined continuously over the past two decades, providing blueprints for connecting quantum devices much like today's internet connects computers and storage devices. However, only in recent years have the first practical long-distance quantum networks begun to emerge. Extending these currently small networks to a larger scale requires several further advances, but most importantly compatibility with existing fibre-optic infrastructure.

Large-scale quantum networks need two capabilities: sending quantum information through telecommunications fibres and reliably storing it in quantum memories. Professor Ma's group recently mastered the second capability by demonstrating record-long quantum storage at telecommunications wavelengths [2]. Now they have taken the crucial next step by implementing a quantum teleportation protocol that distributes information between light and solid-state quantum memory.

High-fidelity teleportation

The step from pure storage to teleportation is significant. Crucially, the quantum state itself is never revealed during quantum teleportation. It remains unknown throughout. This is one of the main reasons why quantum teleportation is such a central ingredient in a broad range of quantum technologies. It is all the more essential that the process is executed with high fidelity, to prevent degrading the quantum information — and the experiments, led by Yu-Yang An and Qian He in Ma's group, delivered convincing benchmarks.

They used yttrium orthosilicate (YSO) crystals doped with rare-earth erbium ions. These ions have optical properties ideally suited for existing fibre networks, matching the telecommunications wavelength of around 1.5 μm. By combining this with quantum state generation from an integrated photonic chip based on a silicon nitride microring resonator, the team achieved full quantum state teleportation from telecom photons to an erbium-ion based quantum memory.

The quality of each component enabled them to surpass the 'classical bounds' by more than seven standard deviations. This achievement is significant for two reasons. First, the high fidelity demonstrates that the experiments worked precisely as intended. Second, the researchers firmly established that the same experiment would be impossible using purely classical effects — confirming this is indeed a phenomenon enabled by quantum mechanics. Taken together, this telecom-compatible platform for generating, storing and processing quantum states of light therefore establishes a highly promising approach to large-scale quantum networks and, ultimately, the quantum internet.

References

1. Y.-Y. An, Q. He, W. Xue, M.-H. Jiang, C. Yang, Y.-Q. Lu, S. Zhu & X.-S. Ma. Quantum teleportation from telecom photons to erbium-ion ensembles. Physical Review Letters 135, 010804 (2025).

2. M.-H. Jiang, W. Xue, Q. He, Y.-Y. An, X. Zheng, W.-J. Xu, Y.-B. Xie, Y. Lu, S. Zhu & X.-S. Ma. Quantum storage of entangled photons at telecom wavelengths in a crystal. Nature Communications 14, 6995 (2023).