Researchers at the International Quantum Academy in Shenzhen reported in Nature Nanotechnology on March 23, 2026, that they had run logical operations on a cluster of phosphorus atoms in silicon. They encoded two logical qubits in the nuclear spins of four atoms with the [[4,2,2]] code and used a fifth spin to perform a logical T gate. The team applied the code’s error checks afterward, in post-processing, instead of during the computation.
A logical qubit is one unit of quantum information spread across several physical qubits so that errors can be detected or corrected. The [[4,2,2]] code can detect an error on any one of its four physical qubits but cannot correct it. Researchers add the T gate to simpler operations to obtain a universal gate set, one able to approximate any quantum computation.
The Shenzhen team works with one of the three routes to silicon spin qubits compared here: phosphorus atoms placed one at a time, quantum dots made in research cleanrooms, and quantum dots made on 300-millimeter wafers in industrial fabs. Groups in all three have published two-qubit gate fidelities above 99%, each in devices with 12 or fewer physical qubits. A gate fidelity of 99% means an average error of about 1% per operation under the benchmark used, and 99.9% an average of about 0.1%.
Spin is a magnetic property of electrons and some atomic nuclei. Researchers use its two basic orientations, up and down, as a qubit’s 0 and 1. A quantum dot is a tiny region of a chip that traps one or a few electrons.
Phosphorus atoms placed one at a time
Phosphorus atoms in silicon are called donors because each can donate an electron. In the donor approach, researchers use a scanning tunneling microscope to strip hydrogen atoms from a silicon surface and expose sites where single phosphorus atoms then embed.
Several phosphorus atoms placed within a few nanometers of each other share a single electron. The nuclear spins of the atoms and the spin of the shared electron act as qubits.
Researchers at Silicon Quantum Computing (SQC), a Sydney company, reported a processor of this kind in a Nature paper on December 17, 2025. The processor has 11 physical qubits in two registers of phosphorus atoms, placed 13 nanometers apart and linked through the exchange interaction of their electrons.
In the paper, the team reported single-qubit and multi-qubit gate fidelities from 99.10% to 99.99%, Bell-state fidelities of up to 99.5%, and entanglement of up to eight nuclear spins. A Bell state is the simplest form of entanglement between two qubits, in which measurements on the pair give correlated results.
The team measured a two-qubit gate fidelity of 99.90% between two nuclear spins in one register by interleaved randomized benchmarking. It reported 99.64% for a gate between the electrons of the two registers. In randomized benchmarking, researchers run long random sequences of gates and track how quickly errors accumulate.
Quantum dots made in research labs
A gate-defined quantum dot confines a single electron beneath metal electrodes patterned on a silicon chip. The electron’s spin serves as the qubit. Voltage pulses on the electrodes control the interaction between neighboring spins.
On January 19, 2022, Nature published two such results. Xiao Xue, Lieven Vandersypen, and colleagues at QuTech in Delft reported single- and two-qubit gate fidelities “all of which are above 99.5%, extracted from gate-set tomography” in their paper. In gate-set tomography, researchers reconstruct each gate’s errors from many sequences of measurements.
Akito Noiri, Seigo Tarucha, and colleagues at RIKEN in Japan reported a two-qubit gate fidelity of 99.5% and a single-qubit gate fidelity of 99.8% the same day. They measured both on a two-qubit device by randomized benchmarking.
In August 2022, Kenta Takeda, Tarucha, and RIKEN colleagues reported in Nature that they had used a code to correct a phase-flip error on any one of three physical qubits. A phase flip is one of the two basic types of qubit error, along with a bit flip.
Quantum dots made in 300-millimeter fabs
In June 2023, Intel released Tunnel Falls to research laboratories and called it a 12-qubit silicon chip. Its qubits are physical qubits, electron spins in quantum dots. Intel said it fabricated the chip on 300-millimeter wafers in its D1 facility, with a “95% yield rate across the wafer” and “over 24,000 quantum dot devices” per wafer.
Diraq, a Sydney company, and imec, a research center in Leuven, Belgium, published a Nature paper on September 24, 2025, about devices that imec made on its 300-millimeter platform. Each device had two physical qubits. The authors characterized the devices with gate-set tomography and reported that “single- and two-qubit control fidelities exceed 99% for all four devices.”
The authors wrote that “residual nuclear spin-carrying isotopes contribute substantially to operational errors.” Silicon-29 atoms have a nuclear spin that disturbs nearby spin qubits. Silicon-28 atoms have none.
Kristiaan De Greve, imec’s program director for quantum computing, said in a joint announcement by Diraq and imec that “higher fidelities can be achieved through even further isotopic enrichment of the silicon-channel layer with 28Si.”
Program milestones
In November 2025, DARPA selected Diraq, SQC, and Quantum Motion, a London company working on silicon spin qubits in metal-oxide-semiconductor structures, among 11 companies for Stage B of its Quantum Benchmarking Initiative. DARPA described Stage B as a yearlong phase of research and development planning.
DARPA designed the initiative to verify whether any approach to quantum computing can reach utility-scale operation by 2033. The SQC authors wrote that “an important requirement for scaling up is the ability to extend high-fidelity entanglement non-locally across several spin registers.”
Update, November 12, 2026: On July 9, Diraq, UNSW Sydney, and imec researchers reported eight physical qubits in a linear array made in imec’s 300-millimeter process, with no gate fidelities for the array. On October 7, DARPA advanced Diraq to Stage C of the Quantum Benchmarking Initiative.
