Distributed Quantum Computing in Silicon (2406.01704v1)

Abstract: Commercially impactful quantum algorithms such as quantum chemistry and Shor's algorithm require a number of qubits and gates far beyond the capacity of any existing quantum processor. Distributed architectures, which scale horizontally by networking modules, provide a route to commercial utility and will eventually surpass the capability of any single quantum computing module. Such processors consume remote entanglement distributed between modules to realize distributed quantum logic. Networked quantum computers will therefore require the capability to rapidly distribute high fidelity entanglement between modules. Here we present preliminary demonstrations of some key distributed quantum computing protocols on silicon T centres in isotopically-enriched silicon. We demonstrate the distribution of entanglement between modules and consume it to apply a teleported gate sequence, establishing a proof-of-concept for T centres as a distributed quantum computing and networking platform.

• The paper demonstrates remote entanglement between silicon-based T center modules, providing a key proof-of-concept for distributed quantum systems.
• It implements a teleported CNOT gate sequence using distributed entanglement to enable scalable quantum operations.
• The study rigorously characterizes T centers, achieving high entanglement fidelity projections and setting benchmarks for future silicon quantum networks.

Distributed Quantum Computing in Silicon

The paper "Distributed Quantum Computing in Silicon," authored by Photonic Inc., presents significant advancements in the realization of distributed quantum computing using silicon-based T centers. The research focuses on the demonstration of key distributed quantum computing protocols, leveraging the reliable properties of silicon photonics and T centers to achieve remote entanglement between modules.

Summary of Contributions

The paper begins by addressing the essential challenge in quantum information science: executing commercially impactful quantum algorithms such as Shor's algorithm and quantum chemistry simulations, which demand a number of qubits and gates far exceeding the capacity of existing monolithic quantum processors. To overcome this, the researchers propose a networked, modular quantum architecture that horizontally scales by distributing entanglement across quantum computing modules.

Key Achievements:

1. Demonstration of Remote Entanglement: The paper provides preliminary demonstrations showcasing the successful distribution of entanglement between two T center modules. This represents a critical proof-of-concept for T centers facilitating fault-tolerant distributed quantum computing and networking.
2. Implementation of Teleported Gate Sequence: Utilizing the distributed entanglement, the authors demonstrate a teleported Controlled-NOT (CNOT) gate sequence. This teleported gate execution is foundational for scalable distributed quantum computing.
3. Characterization and Feasibility of T Centers: Detailed characterization of T centers in silicon is provided, including state initialization, single-shot nuclear spin readout, nuclear spin control, and coherence time measurements. These findings underscore the viability of T centers as qubit platforms for modular quantum processors.
4. High Entanglement Fidelity Projections: The paper projects achievable rates and fidelities for T center distributed entanglement, estimating a fidelity of 0.999 with low distribution rates or 0.998 at a rate of roughly 200 kHz. These projections are based on established parameters and anticipated improvements in integrated photonics and material quality.

Technical Insights

Phases of Quantum Technology Development:

The paper posits three phases of quantum technology:

• Phase 1 Quantum (NISQ): Characterized by noisy, intermediate-scale quantum hardware without quantum error correction (QEC).
• Phase 2 Quantum: Introduction of single-module QEC protocols but limited by the finite scale of individual quantum modules.
• Phase 3 Quantum: Era of quantum supercomputers featuring networked, modular architectures enabling horizontal scaling through distributed fault-tolerant gates.

Experimental Setup:

The researchers outlined a robust experimental setup including silicon photonic chips cooled to 1.5 K, embedded with T centers within optical cavities. This setup ensures compatibility with commercial low-loss components and facilitates high-rate, high-fidelity remote entanglement distribution.

Performance Metrics:

The paper emphasizes a detailed analysis of metrics such as Purcell-enhanced lifetimes, optical linewidths, entanglement distribution rates, and coherence times for both electron and nuclear spins. Notably, the authors report the longest observed spin coherence times in a commercial setting to date.

Implications and Future Directions

The implications of this research are manifold, having both practical and theoretical significance. Practically, the successful demonstration of distributed entanglement lays the groundwork for scalable quantum computing networks. Theoretically, this work supports the broader vision of quantum supercomputers capable of outpacing classical computation in specific, high-impact applications.

Looking forward, several key developments are anticipated:

• Material Improvements: Enhanced material quality, reduced system noise, and higher fidelity operations are expected as the T center technology matures.
• Integration with Telecommunications Infrastructure: Given that T centers operate in the telecom O-band, there is potential for seamless integration with existing fiber-optic networks, paving the way for globally distributed quantum networks.
• Optimization of Quantum Network Protocols: Further optimization of entanglement distribution protocols and quantum error correction codes tailored for networked quantum architectures will be crucial.

Conclusion

This paper from Photonic Inc. marks significant progress in the domain of distributed quantum computing, leveraging the unique advantages of silicon-based T centers to establish a pathway towards scalable, fault-tolerant quantum networks. The promising results set a strong foundation for future research and development, with the potential to transform both commercial and academic landscapes in quantum information technology.