Eight-qubit Operation Achieved in 300mm SiMOS Device, Demonstrating 41s Ramsey Times and 1.31ms Coherence
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Silicon spin qubits represent a leading technology for future quantum computers, offering both control and the potential for large-scale manufacturing, but building systems with many qubits remains a significant challenge. Andreas Nickl, Nard Dumoulin Stuyck, Paul Steinacker, and colleagues at the University of New South Wales now demonstrate a crucial step forward, successfully operating and coherently controlling an array of eight silicon spin qubits. Fabricated using a standard 300mm CMOS process, this achievement extends operational scalability beyond previous two-qubit limitations and establishes coherence times sufficient for complex computations, with Ramsey dephasing times reaching 41 seconds and Hahn-echo coherence times up to 1. 31 milliseconds.
The team also demonstrates high-fidelity readout of the central qubits and performs a two-qubit gate operation, paving the way for larger, more powerful silicon-based quantum processors. Silicon spin qubits are a promising platform for quantum computing, offering high coherence, controllability, and compatibility with established manufacturing processes. Recent advances have focused on scaling these systems beyond a few qubits, and researchers have now demonstrated a pathway towards dense, two-dimensional arrays of qubits fabricated using standard complementary metal-oxide-semiconductor (CMOS) technology. This work centres on a novel qubit architecture based on silicon nanowires, which exhibit strong spin-orbit interaction and enable all-electrical control of qubit states. By carefully controlling the geometry and doping profiles of these nanowires, the team achieved strong qubit confinement and minimised unwanted interactions, leading to improved coherence times and gate fidelities. These findings represent a significant step towards realising large-scale, fault-tolerant quantum computers based on silicon technology, paving the way for practical quantum computation.
Silicon Quantum Dot Chain Fabrication and Control This research focuses on a silicon-based quantum dot array, specifically an eight-dot chain, with the goal of creating and controlling qubits within these dots and demonstrating coherent control and readout. The device is fabricated using lithography and etching techniques to define the quantum dots and control gates. Key features include the use of silicon, a mature semiconductor technology that promises scalability, and a linear chain arrangement that allows for exploring interactions between neighboring qubits. Control gates regulate the potential barriers between dots, enabling electron transport and qubit manipulation, while single-electron transistors are used to read out the charge state of the quantum dots, providing a means to measure the qubit state. A cascaded readout technique, where the state of one qubit influences the readout of another, further improves measurement fidelity. Experiments involved sequentially loading electrons into the quantum dots to define the desired charge state and create the qubits. Researchers demonstrated the ability to isolate and control individual double quantum dots, essential for creating well-defined qubits, and mapped out the regions of stable electron occupancy using charge stability diagrams. Rabi-chevron measurements confirmed the ability to drive transitions between qubit states using microwave pulses. Calibration of the cascaded readout technique showed improved signal-to-noise ratios and increased measurement fidelity. Furthermore, the team demonstrated control over the exchange interaction between neighboring qubits, crucial for implementing two-qubit gates, and observed that the qubits are sensitive to external magnetic fields, allowing for tuning of their Larmor frequencies and implementation of quantum gates. These results demonstrate precise electron control, qubit isolation and stability, coherent control, and the potential for scalable quantum computation.
Eight Silicon Qubits Demonstrate Long Coherence Times Scientists have achieved a significant breakthrough in silicon spin qubit technology by successfully tuning and coherently controlling an eight-qubit linear array. Fabricated using a 300mm CMOS-compatible process, this work demonstrates operational scalability beyond previously limited two-qubit systems.
The team meticulously tuned all eight qubits, configured as four double dot pairs, and characterised their coherence properties across the entire array. Experiments revealed remarkably long Ramsey dephasing times exceeding 41 microseconds and Hahn-echo coherence times reaching 1. 31 milliseconds for each qubit. A cascaded charge-sensing architecture was implemented for the central four qubits, enabling simultaneous, high-fidelity readout of the entire multi-qubit array. This innovative readout scheme allows for efficient measurement of qubit states across the extended linear chain. Furthermore, the team demonstrated a two-qubit gate operation between adjacent qubits with low phase noise, confirming the ability to perform quantum operations within the array. These results demonstrate that silicon spin qubit arrays can be scaled to medium-sized arrays of eight qubits while maintaining system coherence. Measurements confirm the viability of the materials, gate stack engineering, and fabrication uniformity required for scaling quantum devices.
The team successfully implemented a method for initialising pairwise spin parity states and utilised Pauli spin blockade to read the qubit pairs’ spin parity state with high fidelity. This work establishes a crucial step towards building practical, large-scale quantum computers based on silicon spin qubits, leveraging the advantages of CMOS compatibility and long coherence times.
Eight Qubit Control in Silicon CMOS This research demonstrates a significant step towards scalable silicon spin qubit computing through the successful fabrication and control of an eight-qubit array. Researchers achieved coherent control of all eight qubits, arranged as four double dot pairs, fabricated using a standard 300mm CMOS-compatible process. The qubits exhibited Ramsey dephasing times exceeding 41 microseconds and Hahn-echo coherence times reaching 1. 31 milliseconds, demonstrating coherence maintained beyond the two-qubit level previously achieved in similar CMOS-based devices. Importantly, the team implemented a cascaded charge readout protocol, enabling simultaneous, high-fidelity measurements across the entire multi-qubit array. Furthermore, the researchers demonstrated a two-qubit gate operation between adjacent qubits with low phase noise, confirming the potential for interconnected qubit manipulation. These results demonstrate the viability of scaling silicon spin qubit systems beyond the limitations of previous two-qubit devices. While acknowledging challenges in precisely controlling electron exchange due to the device layout and electron distribution, the team successfully loaded sufficient electrons to enable qubit operation. The observed qubit characteristics, including coherence times and Rabi frequencies, are comparable to, and in some cases exceed, those reported from devices fabricated in academic settings. This achievement establishes operational scalability beyond the two-qubit regime and paves the way for exploring medium-sized silicon spin qubit arrays, bringing practical quantum computation closer to reality. 👉 More information 🗞 Eight-Qubit Operation of a 300 mm SiMOS Foundry-Fabricated Device 🧠 ArXiv: https://arxiv.org/abs/2512.10174 Tags: