on
Rare-earth ions could enable telecom-ready control of interacting qubits
Quantum technologies are devices and systems that exploit the laws of quantum mechanics and could perform tasks that are difficult or impossible to tackle using their classical counterparts. These technologies process and store information using qubits (i.e., quantum bits), which can exist in a superposition of multiple states simultaneously.
In addition to quantum computers, memories and sensors, quantum scientists have also been trying to develop quantum networks, infrastructure that connects multiple distant quantum devices (i.e., nodes), allowing them to communicate and exchange information.
One approach to creating these networks entails the use of some types of imperfections in crystals (i.e., atomic defects) that can emit single photons. These photons can carry quantum information between distant nodes, but each node must also be able to store and process that information locally.
To develop reliable large-scale quantum networks based on atomic defects, researchers need to be able to distinguish and control several nearby spins to allow basic quantum operations within each node. Spins are intrinsic forms of angular momentum carried by electrons, atomic nuclei and other particles, and they can be used to store information.
Researchers at Princeton University recently demonstrated the precise optical and quantum control of two interacting erbium (Er³⁺) ions and a nearby nuclear spin inside a crystal. Their paper, published in Nature Physics, highlights the potential of Er³⁺ and other rare-earth ions for realizing scalable quantum networks.
"One way to build solid-state quantum network nodes is to use the high density of electron and nuclear spins in a crystal to form a register," Haitong Xu, first author of the paper, told Phys.org.
"Our previous work on spin–photon entanglement demonstrated the potential of our system for long-distance quantum communication, but it did not provide a way to use interactions between electron spins for quantum information processing. The central idea is that rare-earth ions, particularly in our material system, can be distinguished by their optical and spin transition frequencies."
Rare-earth ions open new routes for qubit control
Xu and his colleagues leveraged the fact that individual Er³⁺ ions have slightly different optical and spin transition frequencies to demonstrate the reliable control of two nearby qubits. To perform their experiments, they used two interacting Er³⁺ ions that are only a few nanometers apart and whose electron spins can serve as qubits.
The researchers coherently controlled both the optical transitions and electron spins of the interacting ions using laser pulses. The two ions absorb or emit light with slightly different optical resonance frequencies, allowing the researchers to identify and control them individually.
"Erbium ions implanted in calcium tungstate were coupled to a silicon nanophotonic cavity, and differences in their optical and spin transition frequencies enabled individual control," explained Xu.
"We identified an interacting pair using double electron–electron resonance spectroscopy, then used dynamical-decoupling sequences to turn their magnetic dipolar interaction into a two-qubit gate. The numerical optimal-control method GRASS was used to construct gates between one of the electron spins and a nearby nuclear spin."
In their experiments, the researchers also used a nuclear spin close to the interacting ions as an ancillary qubit. Using their system of interacting qubits as a prototype quantum network node, they were able to perform fundamental operations that underpin quantum computation, called electron-electron gates and electron-nuclear gates.
"We realized two-qubit gates between the electron spins and used them for repeated quantum nondemolition measurements of one spin using the other," said Xu.
"Using numerical optimal control, we also constructed electron–nuclear gates, stored and retrieved qubit information in a nuclear spin with a second-long coherence time, and showed that the nuclear memory survives repeated optical excitation and measurement of the remote electron spin. This capability had not previously been demonstrated for rare-earth ion qubits and is essential for entanglement swapping and distillation."
Real-world applications and next research steps
This study shows that multi-qubit systems based on Er³⁺ ions could be promising for realizing scalable quantum networks. Notably, the ions used by the researchers have optical transitions in the telecommunications band (i.e., around 1.5 micrometers) and would thus be compatible with the existing fiber-optic communication infrastructure.
In the future, the design introduced by the researchers could be scaled up to create larger spin registers, collections of interacting spins that collectively store and process quantum information. In addition, it could pave the way for creating multiplexed quantum repeater nodes, quantum communication devices that can create, store and manage several quantum connections simultaneously, which could enhance long-distance quantum communications.
The system introduced by the researchers was an initial proof of concept, including only two electron spins and one nuclear ancillary qubit. Xu and his co-authors are now planning to use their approach to develop larger spin registers.
"The demonstrated gate fidelities are primarily limited by electron-spin coherence, so one priority is to identify the microscopic source of electron-spin decoherence and reduce its effect," added Xu.
"We also plan to create dense, spatially patterned clusters of erbium ions to demonstrate control of larger spin registers. Combined with our work on telecom-band spin–photon entanglement, these capabilities could enable highly multiplexed quantum repeater nodes. It will be exciting to use such nodes for entanglement swapping and distillation, and eventually for quantum communication using logical qubits."
Written for you by our author Ingrid Fadelli, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.
Publication details
Haitong Xu et al, Coherent control of interacting solid-state spins below the diffraction limit, Nature Physics (2026). DOI: 10.1038/s41567-026-03319-y. On arXiv: DOI: 10.48550/arxiv.2508.09122
Who's behind this story?
Freelance journalist with BSc Psychology and MA International Journalism. Covers AI, robotics, neuroscience, and astrophysics since 2018. Full profile →
BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries. Full profile →
Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →
© 2026 Science X Network
Citation: Rare-earth ions could enable telecom-ready control of interacting qubits (2026, July 29) retrieved 30 July 2026 from https://phys.org/news/2026-07-rare-earth-ions-enable-telecom.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.