Evaluating Two-Qubit System Performance

Another quantum computing breakthrough this week - scalable silicon qubits now from a real fab. Diraq + imec report >99% fidelity for all one and two qubit operations across four nominally identical silicon spin qubit unit cells made in an industry 300 mm CMOS flow. (Paper: Nature, “Industry compatible silicon spin qubit unit cells exceeding 99% fidelity” - https://lnkd.in/gQDRMa5u) State prep & measurement hit ~99.9%, with T₁ up to 9.5 s, T* ~40 µs, and Hahn echo T₂ up to ~1.9 ms. Benchmarking used gate set tomography (GST) - a stricter yardstick than RB - and pinpoints the dominant errors as stochastic dephasing from residual ²⁹Si nuclear spins, making isotopic purification the clearest path to ~99.9% class gates. (99.9% SPAM achieved for 3 of 4 devices tested). Why this matters: • CMOS compatibility + reproducibility across multiple devices = credible manufacturing pathway for large arrays. • Fidelities near surface code thresholds suggest tractable error correction overheads if extended to larger tiles. • Noise analysis indicates materials fixes (²⁸Si enrichment) rather than fundamental architectural roadblocks. What’s still hard: • Scaling control: parallel operation, global field schemes, and automation of calibration (today still manual). • Thermal budget with co integrated cryo CMOS control and operation at elevated temps. • Demonstrating error corrected logical qubits in this flow. Q Day lens: Foundry grade, high fidelity silicon qubits tighten timelines toward cryptographically relevant machines. If qubits and control can be tiled at CMOS densities while nudging fidelities to ~99.9%, the path to the millions of physical qubits needed for large scale Shor becomes much more plausible - underscoring the urgency of enterprise PQC migration and crypto agility roadmaps now, not later. Paper is: Nature (Sept 2025), “Industry compatible silicon spin qubit unit cells exceeding 99% fidelity” - https://lnkd.in/gQDRMa5u

Five days to tell you about five things Quantinuum announced last week.  Quantinuum announced so many great things last week, I'm using each day of this week to re-cap. Day 3: Helios Performance By now you've heard that Helios is the "most accurate", "most capable", and "most powerful" quantum computer... and here's why. Helios has: - 98 fully connected qubits. So-called "all-to-all" connectivity continues to prove its power for performing increasingly more complex circuits with less resources.    - 99.92% two-qubit gate fidelity across all-qubit pairs (e.g. we're not just measuring the best 2 or the median... all pairs have this performance!!).   - NVIDIA GPU for doing fast, flexible real-time decoding for error correction - a first-of-a-kind, real-time engine for efficiently doing the operations needed for fault-tolerant operations  - a new programming language, Guppy, which has a Python front-end but high performance under-the-hood code allowing developers to program quantum computers like they do classical computers, and seamlessly combine hybrid compute capabilities — quantum and classical — in a single program. We demonstrated the ability to: - Generate 94 logical qubits with our very efficient Iceberg Error Detection code (https://lnkd.in/gsvFVFja) and globally entangle with performance with better than break-even performance. - Generate 50 logical qubits with a very similar error detection code and used these logical qubits do to a quantum magnetism simulation with 2,500 logical gates at better than break-even performance. - Generate 48 logical qubits with an error correction code, achieving a remarkable 2:1 scaling (only using 2 physical qubits to make 1 error corrected qubit).  Read more about these great achievements with our techncial paper https://lnkd.in/g9bid_2S  and techncial blog https://lnkd.in/gZaN65CY.  

Who has the best quantum processor today? Ask the physics community quietly and many will say: Quantinuum 𝗡𝗼𝘁 IBM Quantum. 𝗡𝗼𝘁 Google. 𝗡𝗼𝘁 IonQ. It’s easy to get caught up in roadmaps, qubit counts or quantum advantage headlines. But the real turning point for the field currently isn’t about scale. It's about fault tolerance - detecting and correcting quantum errors faster than they accumulate. Through that lens, Quantinuum’s H-Series trapped-ion system stands apart. Here’s why: • 𝗥𝗲𝗰𝗼𝗿𝗱-𝗛𝗶𝗴𝗵 𝗚𝗮𝘁𝗲 𝗙𝗶𝗱𝗲𝗹𝗶𝘁𝗶𝗲𝘀: The H-Series delivered a sustained >99.9% two-qubit gate fidelity and >99.99% single-qubit gate fidelity. This is the quality baseline to ensure any QEC code has a chance to work.    • 𝗟𝗼𝗴𝗶𝗰𝗮𝗹 𝗕𝗿𝗲𝗮𝗸-𝗘𝘃𝗲𝗻: They've repeatedly demonstrated logical qubits that are more reliable than the physical hardware they're built from—the first milestone for practical quantum computing.    • 𝗨𝗻𝗶𝘃𝗲𝗿𝘀𝗮𝗹 𝗚𝗮𝘁𝗲 𝗢𝗽𝗲𝗿𝗮𝘁𝗶𝗼𝗻𝘀: Achieved logical gate fidelity an order of magnitude better than physical fidelity on 𝗻𝗼𝗻-𝗖𝗹𝗶𝗳𝗳𝗼𝗿𝗱 𝗴𝗮𝘁𝗲𝘀, which are the hardest operations to perform fault-tolerantly and essential for universal quantum computing.    • ��𝗿𝗰𝗵𝗶𝘁𝗲𝗰𝘁𝘂𝗿𝗮𝗹 𝗔𝗱𝘃𝗮𝗻𝘁𝗮𝗴𝗲: All-to-All Connectivity. The Quantum Charge-Coupled Device (QCCD) system uses ion shuttling to provide full all-to-all qubit connectivity.    • 𝗧𝗵𝗲 𝗤𝗘𝗖 𝗧𝗲𝘀𝘁𝗯𝗲𝗱: This architecture allows them to deploy a diverse range of QEC codes (Steane, Carbon, Tesseract) and test protocols like Single-Shot QEC and Fault-Tolerant Teleportation. It is literally built to explore and accelerate the FTQC roadmap.

IQM Quantum Computers, a global leader in building quantum computers, has demonstrated improvements in two key metrics characterizing the quality of quantum computers. State-of-the-art qubit lifetime on latest IQM test single-qubit device. A record low error rate for two-qubit operations was achieved by demonstrating a CZ gate between two qubits with (99.91 +- 0.02) % fidelity, which was validated by interleaved randomized benchmarking. Achieving high two-qubit gate fidelity is the most fundamental and hardest to achieve characteristic of a quantum processor, essential for generating entangled states between qubits and executing quantum algorithms. https://lnkd.in/e_yiYSmx