Australian Researchers Reveal an 11-Qubit Atom Processor: A Quantum Leap in Silicon
The demonstration of a fully controlled 11-qubit atom processor built into a silicon chip by researchers at Silicon Quantum Computing and UNSW Sydney marks a major turning point in the global race towards functional quantum computing. As a significant step towards fault-tolerant quantum processing utilizing the same material that powers contemporary classical computers, the work, which was published in the journal Nature in December 2025, demonstrates a device that achieves industry-leading fidelities.
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The “14|15 Platform”: A Precision Approach
Based on the placements of silicon and phosphorus in the periodic table, the researchers refer to the processor’s use as the “14|15 platform.” Using precision manufacturing, the researchers produced nuclear spin registers by arranging individual phosphorus atoms within a few nanometers of one another. A single, shared electron is connected to these atoms through a hyperfine connection.
Because silicon is compatible with industrial manufacturing and has a tiny footprint, it has become a leading candidate for practical quantum implementation. Even though ion-trap and superconducting processors now have more qubits, silicon-based devices have remarkable coherence times, or how long quantum information stays stable. The coherence periods of the nuclear spins in this processor are several seconds, which is a significant gain over several rival systems.
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Linking the Registers: The Electron Exchange Link
This 11-qubit atom processor‘s connection is its key innovation. Two separate multi-nuclear spin registers make up the processor: a 4P register that houses four nuclei and one electron, and a 5P register that houses five nuclei and one electron. The electron exchange interaction that connects these two registers serves as a quick and effective connection.
Historically, maintaining high-fidelity entanglement over numerous registers has been a challenge for scaling up atom-based processors. To overcome this, the team from Sydney, under the direction of Professor Michelle Simmons, atomically engineered the space between the registers to precisely 13 nanometers. Because of this accuracy, the electrons can be exchange-coupled, allowing for non-local communication throughout the 11-qubit atom processor.
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Breakthrough Performance and Dedication
The CPU has some of the best performance metrics for semiconductor devices ever documented. In order to measure gate fidelities, the researchers used Single-Qubit Randomized Benchmarking (1Q-RB), and the results ranged from 99.10% to 99.99%. Notably, silicon qubits achieved 99.9% two-qubit gate fidelities for the first time.
One of the study’s major accomplishments was the creation of Bell states, which are qubit pairs with maximal entanglement. The researchers set a record for semiconductor devices with local Bell-state fidelities of up to 99.5%. Additionally, even non-local Bell states, which entail entangling qubits across two distinct registers, maintained excellent fidelities, with an average of 97.2%.
In order to illustrate the processor’s “all-to-all” connectedness, the group produced Greenberger–Horne–Zeilinger (GHZ) states. These are multi-qubit, intricate entangled situations. A noteworthy accomplishment for a silicon-based architecture was the researchers’ successful demonstration of true entanglement for up to eight nuclear spins.
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Overcoming the Challenge of Calibration
The calibration of quantum processors usually becomes progressively more complicated as their size rises. 96 electron spin resonance (ESR) frequencies must be characterized for the 11-qubit atom processor. The frequencies within each register, however, shift collectively, the researchers found.
As a result, they were able to develop a scalable calibration technique that required just two measurements, one for each register, to determine the precise locations of all 96 frequencies. For future devices that might contain hundreds or thousands of registers, this linear scalability is crucial.
The Test Setting
At an extreme base temperature of 16 mK, the experiments were carried out in a cryogen-free dilution refrigerator. The principal sensor for reading out the spin states was a single-electron transistor, and a magnetic field of about 1.39 T was provided to sustain the quantum states. The actual gadget was made utilizing hydrogen lithography, a process that enables sub-nanometer accuracy in atom placement.
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Preparing for Error Correction
The team is already moving towards fault-tolerant quantum computing, even though the 11-qubit atom processor is a significant milestone. Quantum error correction, which necessitates qubit stability even in the presence of arbitrary states in “spectator qubits” (those not participating in a particular gate), will be the focus of future research.
Additionally, the researchers want to use atomic engineering to better optimize hyperfine couplings in order to boost gate speeds, which are now constrained in certain qubits. Professor Simmons and her colleagues at Silicon Quantum Computing are using this 11-qubit atom processor as a model for modular, scalable quantum hardware as they continue to enhance the 14|15 platform.
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In simple analogy
To understand, compare the 11-qubit atom processor to a fast telecommunications network that connects two office buildings (the registers). In the past, workers (qubits) could only operate together effectively if they were in the same space. The researchers have made it possible for employees in separate places to work together as though they were seated at the same desk by constructing a precisely designed bridge (the electron exchange link) between the buildings. This has been done without compromising the accuracy or speed of the operation.
