Two-qubit silicon quantum processor with operation fidelity exceeding 99% (2111.11937v1)

Abstract: Silicon spin qubits satisfy the necessary criteria for quantum information processing. However, a demonstration of high fidelity state preparation and readout combined with high fidelity single- and two-qubit gates, all of which must be present for quantum error correction, has been lacking. We use a two qubit Si/SiGe quantum processor to demonstrate state preparation and readout with fidelity over 97%, combined with both single- and two-qubit control fidelities exceeding 99%. The operation of the quantum processor is quantitatively characterized using gate set tomography and randomized benchmarking. Our results highlight the potential of silicon spin qubits to become a dominant technology in the development of intermediate-scale quantum processors.

• The paper reports high-fidelity state preparation, measurement, and two-qubit gate operations exceeding 99%, significantly advancing silicon quantum processor benchmarks.
• It employs gate set tomography and randomized benchmarking to precisely quantify single and simultaneous qubit control, achieving fidelities over 99.9% individually.
• The study demonstrates robust Bell state generation and exchange-based two-qubit gate implementation, laying the groundwork for scalable, fault-tolerant quantum computing.

Overview of High-Fidelity Two-Qubit Silicon Quantum Processor

The paper presents notable advancements in the field of silicon quantum computing, specifically focusing on a two-qubit silicon quantum processor. By achieving unprecedented operational fidelities in this domain, the work stands out for its demonstration of high-fidelity state preparation, measurement, and gate operations, which collectively satisfy the DiVincenzo criteria necessary for effective quantum error correction.

Key Findings

1. High Fidelity Achievements: The paper reports state preparation and measurement (SPAM) fidelities exceeding 97% and single and two-qubit gate fidelities exceeding 99%. Notably, the two-qubit controlled-phase (CPHASE) gate operates with a fidelity exceeding 99.8%. These results are significant improvements over previous results in silicon quantum dot systems, where SPAM errors had been higher and gate fidelities lower.
2. Quantum Characterization Techniques: The research employs gate set tomography (GST) and randomized benchmarking (RB) to quantitatively evaluate the quantum processor's performance. These methodologies confirm high fidelity metrics for both single and simultaneous qubit operations, with GST revealing single-qubit control fidelities above 99.9% when assessed individually.
3. Implementation of Bell States and Gate Synthesis: The paper demonstrates Bell state fidelities ranging from 95.4% to 97.5% (without SPAM correction), showcasing coherent quantum entanglement. Additionally, the work synthesizes fundamental two-qubit gates, such as CNOT and SWAP, to illustrate comprehensive control over the quantum system.
4. Resilience and Robustness: The research outlines an exchange-based approach to implementing two-qubit gates under a strong external magnetic field, reducing noise and decoherence effects. The paper underscores the successful integration of the silicon spin qubit processor using isotopically enriched silicon, which significantly enhances coherence times.

Implications and Future Developments

The paper's findings assert silicon spin qubits' potential in developing scalable quantum computing systems. The high-fidelity results attained offer promising perspectives for fault-tolerant quantum computing, aligning closely with the operational requirements for quantum error correction. By leveraging EFT (exchange-based functional transformations) and isotopically purified processing materials, the research surmounts classical challenges associated with quantum coherence and control precision.

As quantum processor complexity escalates, the methodologies validated in this work, such as GST and RB, will be instrumental in quality assurance. These advances also posit a robust foundation for extending qubit arrays, transitioning from two-qubit systems to potentially fault-tolerant architectures. In the immediate future, increasing qubit connectivity, while maintaining the stellar fidelity metrics demonstrated, remains a critical research and development trajectory.

The paper showcases a pathway toward integrating silicon-based quantum devices within the existing semiconductor ecosystem, potentially benefiting from the technological infrastructure and scalable manufacturing techniques used in classical computing.

By achieving operation fidelities comparable to superconducting qubits and surpassing those of trapped ions for specific gate operations, silicon quantum processors emerge as credible contenders in the pursuit of practical and scalable quantum computing solutions.