11-Qubit Atom Processor in Silicon revealed by UNSW and SQC
Australian Researchers Unveil 11-Qubit Atom Processor: Silicon Quantum Leap
The demonstration of a fully controlled 11-qubit atom processor on a silicon device by Silicon Quantum Computing and UNSW Sydney researchers is a turning moment in the global race to functional quantum computing. The December 2025 Nature publication shows a device with industry-leading fidelities, a step towards fault-tolerant quantum processing using the same material as classical computers.
Precision Approach to the “14|15 Platform”
Based on silicon and phosphorus' periodic table positions, the researchers call the CPU the “14|15 platform.” Researchers made nuclear spin registers by arranging phosphorus atoms within nanometres using precision manufacturing. One hyperfine connection links these atoms to a common electron.
Due to its compatibility with industrial manufacture and small footprint, silicon is a top choice for quantum implementation. Silicon-based devices have long coherence times, even if ion-trap and superconducting computers have more qubits. This processor's nuclear spin coherence periods are many seconds, a major advantage over rival devices.
The Electron Exchange Link Links Registers The 11-qubit atom processor's link is its main breakthrough. A 4P register holds four nuclei and one electron, and a 5P register holds five nuclei and one electron. The electron exchange interaction between these registers is fast and effective.
Scaling up atom-based processors has been difficult due to maintaining high-fidelity entanglement spanning several registers. Professor Michelle Simmons' Sydney team atomically tailored the distance between the registers to 13 nanometres to overcome this. This accuracy allows electron exchange-coupling and non-local communication in the 11-qubit atom processor.
Outstanding Work and Dedication
CPU performance is among the best in semiconductor devices. The researchers measured gate fidelities using Single-Qubit Randomised Benchmarking (1Q-RB) and found 99.10% to 99.99%. For the first time, silicon qubits had 99.9% two-qubit gate fidelities.
It created Bell states, qubit pairs with maximal entanglement, as a notable achievement. The researchers set a record for semiconductor devices with 99.5% local Bell-state fidelities. Even non-local Bell states, which entangle qubits in two registers, have 97.2% fidelities.
Greenberger–Horne–Zeilinger (GHZ) states showed the processor's “all-to-all” connectivity. These complex circumstances include several qubits. The researchers demonstrated full entanglement for up to eight nuclear spins using a silicon-based architecture.
Overcoming Calibration Challenge
Quantum processor calibration becomes increasingly challenging as they get larger. Characterise 96 ESR frequencies for the 11-qubit atom processor. Researchers noticed that register frequencies shift collectively.
They developed a scalable calibration method that required only two tests, one for each register, to locate all 96 frequencies. Linear scalability is essential for future devices with hundreds or thousands of registers.
The Test Environment
The trials were done in a cryogen-free dilution refrigerator at 16 mK. A single-electron transistor read spin states, and a 1.39 T magnetic field sustained quantum states. The device was built using hydrogen lithography, which allows sub-nanometer atom placement.
Prepare for Error Correction
The 11-qubit atom processor is a milestone, but the team is already working towards fault-tolerant quantum computing. Quantum error correction requires qubit stability even in “spectator qubits” (those not participating in a gate). Future research will focus on this.
The researchers also intend to optimise hyperfine couplings using atomic engineering to increase gate speeds in qubits that are currently limited. While improving the 14|15 platform, Professor Simmons and her Silicon Quantum Computing colleagues are modelling modular, scalable quantum hardware using this 11-qubit atom processor.
Simple analogy
To explain, compare the 11-qubit atom processor to a rapid telecommunications network connecting two office buildings (registers). Before, qubits could only work together in the same space. By developing a precise electron exchange link across buildings, the researchers allowed personnel in different locations to work together as if they were at the same desk. This was done without affecting accuracy or speed.
