Scaling up quantum computers requires adding and interconnecting more qubits, but previous attempts often reduced connection quality, or fidelity. A new study published in Nature describes a processor that overcomes this challenge. Developed by Silicon Quantum Computing, the processor uses silicon—commonly employed in classical computers—combined with phosphorus atoms to link 11 qubits.

14/15 Quantum Platform

The new processor design employs precisely placed phosphorus atoms in isotopically purified silicon-28, organized into two multi-nuclear spin registers—one with four phosphorus atoms and the other with five. Each register shares an electron spin, and the registers are linked via electron exchange interaction, enabling non-local connectivity across all 11 qubits.

Figure 1. Single-Qubit Properties of the 11-Qubit Processor

Because of the silicon and phosphorus arrangement in the periodic table, the system is called the “14|15 platform.” This 11-qubit silicon atom processor is the largest of its kind, representing a significant milestone in quantum computing. Figure 1. Single-Qubit Properties of the 11-Qubit Processor

“We controlled the 11 qubits by managing multiple microwave frequencies, using techniques that manipulate electron and nuclear spins at different resonance frequencies,” the study authors explained.

Scaling Made Smooth

The standout feature of the new design is its ability to maintain exceptionally high fidelity while scaling. While superconducting, ion-trap, and neutral-atom processors have previously reached hundreds of qubits, they face platform-specific challenges such as manufacturing, control-system miniaturization, and materials engineering [1]. The 14|15 platform, however, demonstrates a path toward scalable, fault-tolerant quantum computing using practical silicon technology, achieving fidelities exceeding 99%.

“Even as we increase the number of connected qubits, we have maintained—and in some cases improved—physical-level benchmarks, with two-qubit gate fidelities reaching 99.9% for the first time in silicon qubits,” the study authors report.

The team reported that every nuclear-spin pair in the 11-qubit system was successfully entangled, with Bell-state fidelities ranging from 91.4% to 99.5% within each register and 87.0% to 97.0% between registers. Entanglement was maintained across up to eight nuclear spins.

Quantum Computing Implications

The team is optimistic about the future of the 14|15 platform. “Our research represents a milestone in moving from experimental quantum devices to practical, modular, and scalable systems,” they said. “We have shown that reliable, large-scale quantum systems can be built using atomically engineered silicon, precisely integrating qubits and their control elements with subnanometer accuracy using just two types of atoms—phosphorus and silicon. This demonstrates technical mastery and lays crucial groundwork for the future of quantum computing.”

Next steps include benchmarking with arbitrary spectator qubit states, optimizing control pulses, engineering registers for stronger hyperfine couplings, and further scaling up qubit numbers. The ultimate aim is to leverage such technologies to accelerate the development of powerful quantum devices for real-world applications.

References:

1. https://phys.org/news/2025-12-silicon-atom-processor-links-qubits.html

Cite this article:

Janani R (2025), Silicon Processor Connects 11 Qubits with Over 99% Fidelity, AnaTechMaz, pp.440