The pursuit of scalable quantum computation faces significant hurdles, prompting researchers to explore methods beyond building ever-larger single processors. Johannes Knörzer, from ETH Zürich, Xiaoyu Liu and Jordi Tura of Universiteit Leiden, along with Benjamin F. Schiffer and colleagues, address this challenge by reviewing the rapidly developing field of distributed quantum information processing. This approach connects multiple smaller quantum devices, effectively increasing computational power and enabling access to more complex problems. Their work highlights how distributing quantum processing not only expands qubit numbers, but also unlocks qualitatively new capabilities, such as performing joint measurements on multiple quantum states, and clarifies the trade-offs between different communication methods, ultimately paving the way for practical, scalable quantum computers.
Distributed Quantum Processing and Multi-copy Access
Distributed quantum information processing seeks to overcome the scalability limitations of individual quantum devices by connecting multiple processing units via classical and quantum communication. This approach expands the capabilities of existing devices, allowing access to larger, more complex problems and enabling the development of novel algorithmic techniques. Beyond simply increasing the number of qubits, this interconnection unlocks qualitatively new possibilities, such as performing joint measurements on multiple copies of high-dimensional quantum states. Understanding the difference between single-copy and multi-copy access to quantum information is crucial, as it impacts the fundamental limits of distributed quantum computation and communication.
This work investigates how entanglement-based quantum repeaters can efficiently distribute high-dimensional quantum states, specifically qudits with a dimension greater than two. The research demonstrates that distributing high-dimensional entanglement differs significantly from distributing single-qubit entanglement, requiring careful design of the entanglement generation and swapping protocols. The team explores heralded entanglement generation, where successful entanglement creation is signalled by a detection event, to mitigate the effects of noise and signal loss during distribution. The results show that combining heralded entanglement generation with entanglement swapping significantly improves the fidelity and rate of high-dimensional entanglement distribution, even with substantial signal loss. This achievement represents a crucial step towards realising practical distributed quantum information processing systems capable of tackling complex computational problems and securing long-distance quantum communication.
Authors and Contributors to Quantum Research
Distributed Quantum Processing and Resource Access
This work details significant advances in distributed quantum information processing, a field poised to overcome the scalability limitations of single quantum devices. Researchers have demonstrated the potential of interconnecting multiple processing nodes via both classical and quantum communication, enabling access to larger, more complex problems and novel algorithmic techniques. The study highlights a crucial distinction between single-copy and multi-copy access to quantum information, revealing how this impacts task complexity and identifies problems best suited for distributed resources. Interactions between light and matter underpin fundamental processes enabling quantum state transfer and remote entanglement generation between spatially separated nodes.
Recent progress in implementing these concepts on various physical platforms is detailed, showcasing the growing maturity of the field. Researchers are actively exploring protocols and physical realisations, with a focus on high-level principles and design considerations. The study outlines a theoretical framework for modelling and understanding the generation, transfer, and manipulation of quantum information in distributed systems, encompassing both classical and quantum communication channels. This research represents a crucial step toward scaling quantum technologies beyond the limits of individual devices, enabling complex computations and unlocking new possibilities in quantum science and technology.
Distributed Quantum Computing Extends Computational Frontiers
This review demonstrates the potential of distributed quantum information processing to overcome limitations inherent in single quantum devices. By interconnecting multiple quantum processors, researchers extend computational capabilities and enable new approaches to quantum algorithms and measurements. Recent advances have brought practical realisation of distributed quantum computing closer, with key capabilities demonstrated in both laboratory-scale systems and metropolitan-scale networks. While significant progress has been made, challenges remain in building robust quantum repeaters to extend the range of quantum communication, given the fundamental limitations on amplifying quantum signals. Future research will likely focus on improving these repeaters and developing more sophisticated protocols for coordinating quantum operations across multiple nodes.