A transformative breakthrough from the University of Chicago’s Pritzker School of Molecular Engineering may change the landscape of quantum networking forever. Led by Assistant Professor Tian Zhong, the research team has engineered a system that could extend the quantum communication range up to a staggering 2,000 kilometers — almost 200 times the previous record. This paradigm-shifting development could finally enable a global quantum internet, connecting distant quantum processors across entire continents.

At the heart of this innovation lies an improvement in quantum coherence times — the duration for which atoms maintain their fragile quantum states when entangled over fiber optic channels. Quantum entanglement is the key to linking spatially separated quantum computers, but decoherence has traditionally limited the effective communication distance. Zhong’s team has achieved a quantum coherence time exceeding 10 milliseconds in erbium atoms embedded within specially crafted quantum materials, a leap from the mere 0.1 milliseconds typical of prior efforts.

This ten-millisecond coherence marks a critical threshold for quantum communication, theoretically enabling quantum links up to 2,000 kilometers — equivalent to connecting quantum devices between Chicago and distant cities like Salt Lake City. In some instances, coherence times extended even further, reaching an impressive 24 milliseconds, which, if realized in practical networks, could allow connections spanning over 4,000 kilometers, from Chicago to Colombia.

Intriguingly, this leap forward did not come from inventing new quantum materials but rather from a revolutionary change in how these materials were manufactured. Traditionally, rare-earth doped crystals — essential for quantum light-matter interfaces — were grown using the Czochralski method, which involves melting raw materials above 2,000 degrees Celsius and cooling them slowly into crystals. Afterward, physical sculpting is used to fashion components from these crystals, a cumbersome and imprecise process.

Instead, the University of Chicago team employed molecular-beam epitaxy (MBE), a technique more akin to 3D printing at the atomic scale. MBE deposits material layer-by-layer, allowing precise control over crystal growth and composition from the ground up. This bottom-up approach produces ultrahigh-purity materials with atomic-level precision, vastly improving the quantum coherence properties of embedded erbium ions critical for long-lived entanglement.

MBE’s application to rare-earth doped crystals is unprecedented in the quantum information domain. Working alongside materials synthesis expert Assistant Professor Shuolong Yang, Zhong’s group adapted MBE to tailor these crystals specifically for quantum networking. The high-quality epitaxial films they created admit a robust spin-photon interface operating at telecom wavelengths, perfectly suited for long-distance fiber transmission compatible with existing infrastructure.

Esteemed experts in photonics and quantum technologies have praised this innovative approach for its scalability and groundbreaking nature. Professor Hugues de Riedmatten of the Institute of Photonic Sciences, a recognized leader in quantum networking, emphasizes that this work demonstrates how precise nanofabrication methods can realize single rare-earth ion qubits with exceptional optical and spin coherence, paving the way for scalable, fiber-compatible quantum devices.

Although the theory and materials science breakthroughs are profound, Zhong and his team acknowledge that practical validation lies ahead. Their next phase involves rigorous laboratory experiments to confirm whether the extended coherence times translate into long-distance quantum communication. This will include linking two qubits housed inside separate dilution refrigerators using spooled fiber lengths simulating up to 1,000 kilometers.

Currently, Zhong’s lab is constructing a third dilution refrigerator to establish a local quantum network capable of simulating future extended quantum internet architectures. These developments represent incremental but essential milestones toward a functional quantum communication network capable of spanning urban centers, states, and ultimately the globe.

The potential implications are immense. A robust quantum internet would revolutionize secure communications by enabling unhackable quantum encryption, advance distributed quantum computing by linking remote quantum processors, and open avenues for quantum-enhanced sensing and metrology over vast distances.

This research fundamentally redefines the material science foundations of quantum networking by combining state-of-the-art nanofabrication with the physics of rare-earth ions. Its success promises to blur geographical boundaries currently limiting quantum technologies, fostering a new era where quantum computers communicate seamlessly from city to city and country to country.

Published in the prestigious journal Nature Communications on November 6, 2025, this work titled “Dual epitaxial telecom spin-photon interfaces with long-lived coherence” marks a significant milestone toward the quantum internet era. Its broad technological ramifications underscore the importance of interdisciplinary collaboration between quantum physics, materials science, and engineering.

In conclusion, the University of Chicago team’s innovative molecular-beam epitaxy fabrication method has unlocked an extraordinary increase in quantum coherence times in telecom-band erbium ions, theoretically extending the quantum communication range by two orders of magnitude. As laboratory tests advance, the dream of connecting quantum computers across continents inches closer to reality, heralding a revolution in secure communication and computational power unparalleled by classical technologies.

Subject of Research: Quantum computing; quantum coherence; rare-earth doped materials; quantum networking; molecular-beam epitaxy.

Article Title: Dual epitaxial telecom spin-photon interfaces with long-lived coherence

News Publication Date: November 6, 2025

Web References:

• Nature Communications Article
• University of Chicago Pritzker School of Molecular Engineering

References:
Gupta et al., “Dual epitaxial telecom spin-photon interfaces with long-lived coherence,” Nature Communications, November 6, 2025, DOI: 10.1038/s41467-025-64780-6

Image Credits: University of Chicago Pritzker School of Molecular Engineering / Jason Smith

Keywords: Quantum computing, Quantum information, Molecular-beam epitaxy, Quantum coherence, Telecommunication wavelength, Rare-earth doped crystals, Quantum internet, Spin-photon interface

Central to quantum communication is the ability to reliably produce and transmit single photons, which serve as quantum carriers of information. These indivisible light quanta are pivotal for protocols such as quantum key distribution, offering theoretically unbreakable encryption. However, the efficiency of single-photon sources interfaced with optical fibers – the backbone of existing communication infrastructure – has been a persistent bottleneck. Conventional approaches involve placing photon emitters like quantum dots or rare-earth element ions outside the fiber, from where emitted photons must be coupled into the fiber. This coupling process is inherently inefficient, resulting in significant transmission loss that compromises communication fidelity over distances.

The innovative solution proposed by Associate Professor Kaoru Sanaka and his team at Tokyo University of Science circumvents this limitation by integrating single photon emitters directly inside the optical fiber itself. Their method selectively excites an individual rare-earth ion embedded within a tapered section of the fiber, enabling photon generation and waveguide transmission to occur simultaneously within the fiber. This closed-loop integration markedly reduces loss and elevates overall system efficiency – a vital advance for building practical quantum networks.

Rare-earth ions, particularly neodymium ions (Nd^3+), were judiciously chosen for this work due to their favorable emission properties across a broad spectral range. Crucially, Nd^3+ emits photons spanning wavelengths compatible with existing telecommunications standards, making these fibers directly adaptable to current fiber-optic infrastructure. The team created these novel light-emitting fibers by uniformly doping silica fibers with Nd^3+ ions before subjecting them to a precision heat-and-pull tapering process. This refined tapering reduces the fiber’s diameter and creates spatially resolvable individual ions within the tapered region, paving the way for selective excitation.

The physical mechanism relies on targeting a single isolated Nd^3+ ion with a pump laser while minimizing excitation of neighboring ions—thereby generating high-purity single photons directly into the fiber’s guided mode. The experimental setup involves collecting photons emitted at one end of the fiber and analyzing their statistical properties using the technique of photon autocorrelation. This approach confirms the hallmark quantum trait of single-photon emission: the anti-bunching effect, wherein photons are emitted one at a time rather than in clumps. This verification is essential, affirming that the device functions as a true single-photon emitter integrated within the fiber.

Importantly, the optical qualities of the Nd^3+ ions—such as emission wavelength and coherence—remain fundamentally unchanged by the tapering process. This preservation assures that the integration technique does not come at the cost of optical performance. Moreover, the team’s results demonstrate a significant increase in photon collection efficiency compared to previous methods where multiple ions were excited simultaneously, leading to a less controlled emission pattern and higher losses. Further efficiency gains are achievable by harvesting photons emitted from both ends of the tapered fiber section.

Operating at room temperature, this technology diverges from many quantum photonic systems that necessitate cumbersome and costly cryogenic cooling. The ability to function efficiently without refrigeration substantially simplifies real-world deployment and reduces associated operational costs. Additionally, since the platform uses commercially available silica fibers doped with rare-earth elements, it offers a cost-effective, scalable, and readily integratable solution for quantum communication networks.

Beyond secure communication, this fiber-embedded single-photon generation technique holds promise for advancing quantum computing architectures. By selectively controlling multiple isolated ions within a single fiber, the system could serve as a scalable quantum processor, enabling multi-qubit operations and sophisticated qubit encoding protocols. Such integrated photonic quantum processors are a key milestone towards practical quantum information processing devices.

Current and future research efforts are expected to focus on fine-tuning the emission wavelengths of single photons and enhancing their coherence properties to optimize system compatibility with various quantum technologies, including spectroscopy and biomedical imaging. These refinements will broaden the utility of this technique beyond communication, opening doors to new quantum applications across scientific disciplines.

The implications of this pioneering work are profound. By demonstrating highly efficient, room-temperature single-photon generation directly inside optical fibers, the researchers have established a practical and scalable platform poised to underpin next-generation quantum networks. This advancement brings us closer to realizing unhackable communication channels and versatile quantum computing systems seamlessly integrated with existing infrastructure.

As quantum information science continues to evolve, innovations like these highlight a transformative path where classical optical technologies and quantum physics converge. The universal adoption of such fiber-coupled quantum light sources will not only elevate data security but also accelerate progress towards a fully quantum-enabled information era, drastically reshaping the technological landscape in the decades to come.

Subject of Research: Not applicable

Article Title: Selective excitation of a single rare-earth ion in an optical fiber

News Publication Date: 22-Sep-2025

References: DOI: 10.1364/OE.570912

Image Credits: Dr. Kaoru Sanaka from Tokyo University of Science, Japan

Keywords

Quantum information science, Information science, Information technology, Quantum information, Computer science, Internet, Physics, Quantum optics, Quantum mechanics, Applied sciences and engineering, Physical sciences, Single photon sources, Quantum computing, Fiber optics

At the forefront of this transformative research are two notable scholars from the Institute of Photonics at the Leibniz University Hannover. They have pioneered a novel approach to entanglement-based quantum key distribution (QKD) using frequency-bin coding. This groundbreaking technique innovatively utilizes various light frequencies, or colors, to encode quantum states, offering a compelling blend of enhanced security and resource efficiency. According to Prof. Dr. Michael Kues, lead researcher and head of the Institute of Photonics, this method could facilitate the future scalability of quantum networks while optimizing resource utilization to connect a more extensive network of users across increased distances. This development is aligned with the university’s key research initiatives focusing on optical technologies and photonic quantum bits.

The application of frequency-bin coding to entanglement-based quantum key distribution yields two primary advantages. The first notable benefit lies in the method’s robustness against noise, particularly against external disturbances stemming from environmental factors like temperature fluctuations and mechanical vibrations that typically plague optical fiber systems. Anahita Khodadad Kashi, a doctoral candidate involved in this research, emphasizes the resilience of the frequency-based approach compared to conventional polarisation methods. The second advantage is the reduction of complexity in the setup and execution of the QKD process, which subsequently leads to a decrease in associated costs. This streamlined approach represents a significant leap forward in making QKD more accessible and practical for broader use.

A key breakthrough in this research involves the successful measurement of the quantum states of light particles using a single detector, a drastic simplification compared to the traditional requirement of four sensitive photon detectors. To achieve the necessary measurements, the researchers employed a method known as frequency-to-time transfer, which effectively maps frequency components to the photons’ arrival time at the detector. Prof. Kues explains that this innovative design has dramatically reduced the expenses associated with standard telecommunications components—from approximately €100,000 down to a mere quarter of that figure. This substantial cost reduction, coupled with an increase in security against potential detector attacks, heralds a new era of viability for quantum key distribution systems.

Aside from its economic and security advantages, the new method also takes advantage of multiple channels simultaneously through a technique dubbed adaptive frequency division multiplexing. This innovation enables an increased key distribution rate without necessitating additional technological infrastructure. Kashi describes how this method allows the performance of the quantum network to adapt dynamically in response to the current load. In the near future, their approach promises a resource-efficient quantum key distribution model, catering to multiple users while facilitating the scalability of quantum networks. As a result, quantum networks have the potential to fortify critical technological infrastructure, particularly in sensitive sectors such as banking and healthcare.

Kues envisions that enhanced research integrating nanophotonics with quantum optics will lead to the development of new methods and components which can generate a diverse array of quantum states for multidimensional coding of quantum information. This breadth of innovation is vital for keeping pace with the rapidly evolving demands of quantum communication technologies. He asserts that the maturation of quantum networks is poised to revolutionize connectivity, raising the standards for communication capacity, distance, and security in the digital landscape. Such advancements will be crucial as society becomes increasingly reliant on secure communication channels amidst an environment marked by escalating data privacy concerns.

Moreover, while promising, the journey towards establishing a quantum internet is still in its early stages. Researchers face the daunting task of overcoming various technical, operational, and economic hurdles that impede the realization of these sophisticated systems. Continued collaboration across interdisciplinary teams—comprising physicists, engineers, and computer scientists—will be essential in addressing these challenges. This collective effort holds the key to unlocking the transformative potential of quantum technology and ensuring the robust security of future digital communications.

To maintain an edge in quantum research, ongoing funding and support remain vital. The current research, backed by TÜV Nord / Alter Technology, the Federal Ministry of Education and Research (BMBF), and the European Research Council (ERC), exemplifies the importance of sustained investment in scientific inquiry. This collaborative approach fosters innovation and propels advancements that could redefine the standards of data security. Moreover, the findings have been shared with the broader scientific community through publication in the journal Light: Science & Applications, ensuring that knowledge continues to flow and inspire further exploration in the field.

Ultimately, the researchers at Leibniz University Hannover are contributing to a formidable quest: the realization of a quantum internet capable of delivering unprecedented levels of security for digital communication. As exploration in quantum technology progresses, the imminent paradigm shift could mark a watershed moment in the landscape of data security globally. Thus, the pursuit of these advanced quantum networks symbolically represents not only a solution to contemporary cybersecurity threats but also a leap towards a future characterized by secure and efficient digital interactions.

As the research landscape evolves, retaining a forward-thinking perspective will be crucial for navigating the complexities of quantum technology. Collaborative ventures and knowledge-sharing will foster the necessary environment for significant breakthroughs. Through sustained commitment and innovative thinking, researchers will continue to shape a safer and more connected future through the full realization of quantum communication capabilities.

Subject of Research: Entanglement-based quantum key distribution using frequency-bin coding
Article Title: Frequency-bin-encoded Entanglement-based Quantum Key Distribution in a Reconfigurable Frequency-multiplexed Network
News Publication Date: 2025
Web References: Light: Science & Applications
References: 10.1038/s41377-024-01696-8
Image Credits: N/A
Keywords: Quantum Information Science, Quantum Key Distribution, Entanglement, Quantum Networking, Photonics