Distributed Quantum Computing across an Optical Network Link (2407.00835v1)

Abstract: Distributed quantum computing (DQC) combines the computing power of multiple networked quantum processing modules, enabling the execution of large quantum circuits without compromising on performance and connectivity. Photonic networks are well-suited as a versatile and reconfigurable interconnect layer for DQC; remote entanglement shared between matter qubits across the network enables all-to-all logical connectivity via quantum gate teleportation (QGT). For a scalable DQC architecture, the QGT implementation must be deterministic and repeatable; until now, there has been no demonstration satisfying these requirements. We experimentally demonstrate the distribution of quantum computations between two photonically interconnected trapped-ion modules. The modules are separated by $\sim$ 2 m, and each contains dedicated network and circuit qubits. By using heralded remote entanglement between the network qubits, we deterministically teleport a controlled-Z gate between two circuit qubits in separate modules, achieving 86% fidelity. We then execute Grover's search algorithm - the first implementation of a distributed quantum algorithm comprising multiple non-local two-qubit gates - and measure a 71% success rate. Furthermore, we implement distributed iSWAP and SWAP circuits, compiled with 2 and 3 instances of QGT, respectively, demonstrating the ability to distribute arbitrary two-qubit operations. As photons can be interfaced with a variety of systems, this technique has applications extending beyond trapped-ion quantum computers, providing a viable pathway towards large-scale quantum computing for a range of physical platforms.

• The paper demonstrates a scalable architecture for distributed quantum computing by linking trapped-ion modules through photonic networks using Quantum Gate Teleportation.
• It experimentally validates non-local CZ gate operations with 86% fidelity and successfully runs Grover’s search algorithm at a 71% success rate.
• The study highlights the potential for enhanced fault tolerance and cross-platform integration, paving the way for a broader quantum computing ecosystem.

Distributed Quantum Computing across an Optical Network Link

The paper "Distributed Quantum Computing across an Optical Network Link" by Main et al. offers a detailed exploration of distributed quantum computing (DQC) enabled through photonically interconnected trapped-ion modules. This paper addresses critical challenges in the field of scalable quantum computing, particularly focusing on the integration and connectivity of multiple quantum processors distributed across physical distances.

Distributed quantum computing represents an architectural shift that effectively leverages multiple interconnected quantum processing units, or modules. These modules, in this implementation, host a modest number of qubits and are linked by a photonic network that supports both classical and quantum communications. Notably, each module within this architecture maintains lower local complexity, yet the network as a whole can tackle larger-scale quantum computations.

A cornerstone of the presented architecture is the use of Quantum Gate Teleportation (QGT), which facilitates non-local quantum gate operations by utilizing remote entanglement and classical communication. QGT is uniquely positioned to circumvent issues of quantum information loss in channels, since the entanglement is established prior to the teleportation of quantum gates, allowing for deterministic outcomes.

In their experimental setup, the authors use trapped-ion technology with modules separated by approximately two meters. They achieve a significant milestone by experimentally demonstrating a controlled-Z (CZ) gate between two circuit qubits in different modules, with a fidelity of 86%. Other prominent circuits, such as the iSWAP and SWAP circuits, are executed using multiple instances of QGT to achieve distributed quantum operations across the modules.

An important aspect of their work involves the execution of Grover’s search algorithm on this distributed quantum system, registering a success rate of 71%. This marks a seminal demonstration of a distributed quantum algorithm necessitating multiple non-local entangling operations, showcasing the practical viability of quantum algorithms in a DQC setup.

The implications of these achievements are multifaceted:

1. Scalability: The demonstrated ability to interconnect and coherently operate distant quantum modules supports the scalability of quantum computing systems. This approach could address physical constraints inherent in monolithic quantum processors by integrating distributed networks into a coherent computational framework.
2. Technological Versatility: Since the photonic network employed in this paper offers compatibility with various quantum systems, there is potential for cross-platform integration. Such compatibility opens pathways toward hybrid quantum networks, utilizing diverse physical qubits (e.g., diamond color centers, superconducting qubits).
3. Fault Tolerance and Practicality: With demonstrated fidelities approaching the threshold for fault-tolerant quantum computation, the paper suggests that increased fidelity in QGT, coupled with advancements in error correction techniques, could significantly enhance practical quantum computing.

For future developments, efforts should focus on improving gate fidelities and entanglement rates further, possibly employing techniques like entanglement purification. Expanding the number of qubits per module and integrating more sophisticated error correction could substantially increase the computational capacity. Moreover, exploring connections with quantum repeaters can facilitate the construction of a quantum internet, thereby broadening the scope of DQC beyond isolated computation to a more global quantum ecosystem.

In conclusion, the paper makes substantive contributions to distributed quantum computing by integrating high-fidelity quantum operations with scalable network architectures, offering a clear step towards a fully connected and practical quantum-computational future.