Quantum Networking with Multi-Qubit Devices

Check out the latest from MIT EQuS and Lincoln Laboratory published in @NaturePhysics! In this work, we demonstrate a quantum interconnect using a waveguide to connect two superconducting, multi-qubit modules located in separate microwave packages. We emit and absorb microwave photons on demand and in a chosen direction between these modules using quantum entanglement and quantum interference. To optimize the emission and absorption protocol, we use a reinforcement learning algorithm to shape the photon for maximal absorption efficiency, exceeding 60% in both directions. By halting the emission process halfway through its duration, we generate remote entanglement between modules in the form of a four-qubit W state with concurrence exceeding 60%. This quantum network architecture enables all-to-all connectivity between non-local processors for modular, distributed, and extensible quantum computation. Read the full paper here: https://lnkd.in/eN4MagvU (paywall), view-only link https://rdcu.be/eeuBF, or arXiv https://lnkd.in/ez3Xz7KT. See also the related MIT News article: https://lnkd.in/e_4pv8cs. Congratulations Aziza Almanakly, Beatriz Yankelevich, and all co-authors with the MIT EQuS Group and MIT Lincoln Laboratory! Massachusetts Institute of Technology, MIT Center for Quantum Engineering, MIT EECS, MIT Department of Physics, MIT School of Engineering, MIT School of Science, Research Laboratory of Electronics at MIT, MIT Lincoln Laboratory, MIT xPRO, Will Oliver

IBM Successfully Links Two Quantum Chips to Operate as a Single Device Key Insights: • IBM has achieved a significant milestone by linking two quantum chips to function as a single, cohesive system, enabling them to perform calculations beyond the capability of either chip independently. • This accomplishment supports IBM’s modular approach to building scalable quantum computers, a strategy aimed at overcoming the limitations of single-chip architectures. • The linked chips demonstrated successful cooperation, marking a step closer to larger and more powerful quantum systems capable of addressing complex real-world problems. The Modular Quantum Computing Approach: • IBM employs superconducting quantum chips, manufactured using processes similar to traditional semiconductor technology, allowing scalability and integration with existing hardware infrastructure. • Modular quantum systems involve linking smaller quantum processors, rather than relying on a single massive chip, reducing fabrication challenges and improving scalability. • This architecture allows multiple chips to share quantum information seamlessly, paving the way for constructing larger quantum systems without exponentially increasing hardware complexity. Addressing Key Challenges in Quantum Computing: • Scalability: Connecting multiple chips is a critical step toward scaling quantum computers to thousands or even millions of qubits. • Error Reduction: Larger quantum systems increase susceptibility to errors. Modular architectures provide pathways for better error management and correction across linked processors. • Coherence Across Chips: Maintaining the delicate quantum states across separate chips is technically challenging, and IBM’s success suggests progress in solving this issue. Implications of IBM’s Achievement: • Enhanced Computational Power: Linked quantum chips unlock the potential for more complex simulations and problem-solving capabilities. • Practical Quantum Applications: Industries like pharmaceuticals, cryptography, and materials science may soon benefit from more robust and scalable quantum computing solutions. • Competitive Advantage: IBM’s progress underscores its leadership in modular quantum computing, positioning it strongly in the competitive quantum technology landscape. Future Outlook: IBM’s successful demonstration of inter-chip quantum communication validates the modular quantum computing strategy as a viable path to scaling up systems. Future advancements will likely focus on enhancing chip-to-chip communication fidelity, increasing the number of interconnected chips, and reducing overall error rates. This breakthrough brings us one step closer to practical, large-scale quantum computing systems capable of solving problems previously deemed unsolvable by classical computers.

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

Is this the "Attention Is All You Need" moment for Quantum Computing? Oxford University scientists in Nature have demonstrated the first working example of a distributed quantum computing (DQC) architecture. It consists of two modules, two meters apart, which "act as a single, fully connected universal quantum processor." This architecture "provides a scalable approach to fault-tolerant quantum computing". Like how the famous "Attention Is All You Need" paper from Google scientists introduced the Transformer architecture as an alternative to classical neural networks, this paper introduces Quantum gate teleportation (QGT) as an alternative to the direct transfer of quantum information across quantum channels. The benefit? Lossless communication. But not only communication: computation also. This is the first execution of a distributed quantum algorithm (Grover’s search algorithm) comprising several non-local two-qubit gates. The paper contains many pointers to the future, which I am sure will be pored over by other labs, startups and VCs. I am excited to follow developments in: - Quantum repeaters to increase the distance between modules - Removal of channel noise through entanglement purification - Scaling up the number of qubits in the architecture Amid all the AI developments, this may be the most important innovation happening in computing now. https://lnkd.in/e8qwh9zp

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.

Quantum computers have the potential to solve complex problems that are beyond the capabilities of classical supercomputers. Current methods ("point-to-point" ) involve complex intermediary circuits, which introduce noise and loss. To overcome these challenges, Massachusetts Institute of Technology researchers have developed a new interconnect device that supports scalable, "all-to-all" communication. This allows all superconducting quantum processors in a network to communicate directly with each other. Key Takeaways: 💻 The new device supports scalable, "all-to-all" communication among quantum processors. ⚛️ Demonstrates remote entanglement, a key step toward developing a powerful, distributed network of quantum processors. ⚡ The interconnect can send photons at different frequencies, times, and in two propagation directions, enhancing network flexibility and throughput. 📈 Achieved over 60% photon absorption efficiency using a reinforcement learning algorithm. 🪴 This technology could be expanded to other kinds of quantum computers and larger quantum internet systems, essential for scalable quantum networks Read more at https://lnkd.in/efj23u6t Research from Aziza Almanakly , Beatriz Yankelevich, Max Hays, Bharath Kannan, Reouven Assouly, Alex Greene, Michael Gingras, Bethany Niedzielski Huffman, Hannah Stickler, Mollie Schwartz, Kyle Serniak, Joel I-Jan Wang, Terry P. Orlando, Simon Gustavsson, Jeffrey A. Grover, and Will Oliver in the MIT Lincoln Laboratory MIT Department of Physics Massachusetts Institute of Technology