Quantum Entanglement in Large-Scale Systems

A Dark State of 13,000 Entangled Spins Unlocks a Quantum Register Researchers have achieved a major breakthrough in quantum networking by entangling 13,000 nuclear spins within a gallium arsenide (GaAs) quantum dot system, successfully creating a scalable quantum register. This advancement could significantly improve secure quantum communication and long-distance quantum information transfer. Key Breakthrough: 13,000-Spin Quantum Register • Quantum registers are crucial for storing and transferring quantum information over long distances, but scalability and coherence have been major challenges. • The research team developed a quantum register using a network of nuclear spins, demonstrating stable and controllable entanglement across 13,000 qubits. • This marks a significant leap toward practical, large-scale quantum storage and enhances the potential for quantum networks. Why Quantum Dots Matter • Quantum dots are nano-sized semiconductor particles that can trap and control electrons, acting as quantum nodes in a future quantum internet. • They are valuable because they emit single photons, a key requirement for secure quantum communication and quantum computing. • To be truly effective, quantum networks need stable qubits that can interact with photons and store information without significant errors—a challenge that this research addresses. Implications for Quantum Technology • Ultra-Secure Quantum Networks: Scalable quantum registers could enable long-range entanglement, making quantum encryption even more secure. • More Reliable Quantum Computing: Storing information across a large number of nuclear spins enhances quantum memory stability, improving error correction. • Faster Quantum Information Processing: The ability to control thousands of entangled spins could lead to more efficient quantum operations. What’s Next? • Researchers will work on extending coherence times and improving error correction mechanisms to make this technology more practical for real-world quantum applications. • The next phase involves integrating quantum registers with photonic quantum networks, moving closer to a global quantum internet. By unlocking stable, large-scale entanglement within quantum dot systems, this discovery represents a major step toward building ultra-fast, secure quantum networks—bringing the vision of practical quantum communication closer to reality.

PHOTON-INTERFACED SCALABLE QUANTUM NODES LINKING LIGHT AND MATTER The photon‑interfaced ten‑qubit register of trapped ions constitutes a potential advance in the development of scalable quantum network nodes. In this architecture, each ion in a ten‑qubit linear chain is individually entangled with a propagating photon, producing a sequential train of ion–photon Bell pairs with high fidelity. Previous experiments had only achieved this capability for one or two ions, making the extension to a full ten‑qubit register a meaningful step toward practical matter‑to‑light interfaces for distributed quantum information processing. The system operates by dynamically transporting ions into the mode of an optical cavity and driving a cavity‑mediated Raman transition that generates a single photon entangled with the ion’s internal qubit state. This procedure yields a time‑ordered photonic qubit stream in which each photon carries the quantum information of a distinct ion. The significance of this work lies in its direct response to a central challenge in quantum networking: the need to map the quantum state of a multi‑qubit matter register onto a set of photonic qubits that can propagate through optical fiber with low loss. Trapped ions serve as exceptionally coherent stationary qubits, but they cannot be transported between processors. Photons, by contrast, function as low‑loss flying qubits capable of transmitting quantum information over long distances. Ion–photon entanglement is therefore the essential mechanism for linking spatially separated ion‑based processors. Scaling this interface to ten ions establishes a clear path toward high‑rate, multiplexed entanglement distribution. This scaling is particularly relevant in light of recent long‑distance demonstrations in which multiple ions, each entangled with its own photon, were used to increase entanglement distribution rates over fiber links exceeding one hundred kilometers. Generating a rapid sequence of entangled photons—each correlated with a different ion—enables temporal multiplexing, which is indispensable for overcoming fiber loss and improving heralded entanglement rates. The ten‑ion photon‑interfaced register provides precisely the type of multiplexed matter‑to‑light source required for such architectures. Despite its importance, several technical challenges remain. Photon detection probabilities must be increased to support long‑distance networking without excessive repetition rates. Sequential ion shuttling introduces timing overhead and potential motional heating, and cavity alignment and stability become increasingly demanding as the register size grows. Maintaining spectral and temporal indistinguishability across the full photon train is essential for multi‑node entanglement generation and remains an active area of optimization. These challenges, however, represent engineering refinements rather than fundamental limitations. #DOI: https://lnkd.in/e5HRus5e

Breakthrough for the #quantum internet: For the first time a major telco provider has successfully conducted entangled photon experiments - on its own infrastructure. ➡️ 30 kilometers, 17 days, 99 per cent fidelity. Our teams at T-Labs have successfully transmitted entangled photons over a fiber-optic network. Over a distance comparable to travelling from Berlin to Potsdam. The system automatically compensated for changing environmental conditions in the network.   Together with our partner Qunnect we have demonstrated that quantum entanglement works reliably. The goal: a quantum internet that supports applications beyond secure point-to-point networks. Therefore, it is necessary to distribute the types of entangled photons. The so-called qubits, that are used for #QuantumComputing, sensors or memory. Polarization qubits, like the ones used for this test, are highly compatible with many quantum devices. But: they are difficult to stabilize in fibers.   From the lab to the streets of Berlin: This success is a decisive step towards the quantum internet. 🔬 It shows how existing telecommunications infrastructure can support the quantum technologies of tomorrow. This opens the door to new forms of communication.   Why does this matter for people and society?   🗨️ Improved communications: The quantum internet promises faster and more efficient long-distance communications. 🔐 Maximum security: Entanglement can be used in quantum key distribution protocols. Enabling ultra-secure communication links for enterprises and government institutions 💡Technological advancement: high-precision time synchronization for satellite networks and highly accurate sensing in industrial IoT environments will need entanglement.   Developing quantum technologies isn’t just a technical challenge. A #humancentered approach asks how these systems can be built to serve real needs and be part of everyday infrastructure. With 2025 designated as the International Year of Quantum Science and Technology, now is the time to move from research to readiness. Matheus Sena, Marc Geitz, Riccardo Pascotto, Dr. Oliver Holschke, Abdu Mudesir

Under the streets of Manhattan and Brooklyn. Through 60 Hudson, one of the most connected carrier hotels in the world. Real quantum entanglement at scale on 17.6 km of standard telecom fiber. With swapping rates 3+ orders of magnitude beyond prior efforts and fidelity above 99%. This is the full quantum networking stack coming together — hardware, protocol, control, orchestration. Most importantly, we ran this without the shared laser crutch that makes lab experiments unscalable by design. This real-world demo used fully independent quantum sources at each endpoint. With Cisco's quantum software stack handling timing coordination at picosecond precision across three geographically separated nodes using the White Rabbit protocol. Qunnect's room-temperature hardware at the edges. And cryogenic equipment only at the hub for efficiency. Any new nodes could be added to this network without touching the sync infrastructure. And with clean control and data plane separation.   Applying design patterns that scaled the classical internet to quantum networking. I wrote about what this milestone means and how it leads us one step closer to our vision of a quantum data center network, on the Cisco blog today. 🔗 Link in comments. 📸 Photo of Manhattan from the Brooklyn end, by me.

I'm so so thrilled to see our first GothamQ paper formally published in my most favorite journal, PRX Quantum 🎉 (link at the end) I've published many papers as a grad student, postdoc, and now a group lead but this work is so unique to me. To be fully honest, for the first time I feel like we have done something really impactful! On the surface, this is a very simple work! We distributed entanglement in NYC. But in reality this paper is the result of 4 years of nonstop hard work of our physicists, engineers, and software developers. We had to invent and manufacture a new entanglement source that works at room temperature (hence actually useful for qu. networking) but has lots of advantages over all the other alternative options. We had to invent and manufacture the devices that very rapidly and with very low loss monitor the infrastructure for any imperfections. We had to write thousands of lines of codes so both devices work together automatically and without any need for manual optimization. And on top of all that we had to negotiate and build a quantum testbed in one of the world's most busy and chaotic cities. We did all that to prove one thing: Entanglement distribution is ready for prime time, beyond academic and research testbeds. The technology has reached a pivotal point where everything is robust and high quality for practical use cases by a much wider community than just quantum physicists. This shift is not only essential for us to be able to use entanglement for applications we already know of, but also to make it widely available for much more creative people than us to constantly think of use cases for quantum networks and entanglement links. I really hope if you are in this field, you enjoy reading this paper and as always don't hesitate to reach out to me for any questions. Goes without saying, this work is all thanks to our amazing team at Qunnect, and a huge congrats to all the authors Alexander Craddock, Anne Lazenby, Gabriel Bello Portmann, Rourke Sekelsky, Maël Flament https://lnkd.in/eteZNASt