Spin Qubit

A spin qubit encodes information in the spin orientation of a single electron or atomic nucleus, confined to a tiny region of a semiconductor (most often silicon) called a quantum dot. Because the fabrication process borrows heavily from the existing semiconductor industry, spin qubits are physically small, roughly a thousand times smaller than a superconducting transmon, which makes this modality attractive for eventually packing large qubit counts onto a single chip using tooling the chip industry already has. The tradeoff has historically been control: reading out and coupling spin qubits with high fidelity took longer to solve than for superconducting or trapped-ion qubits, though progress from groups including Intel, Diraq, and HRL Laboratories (acquired by IBM in 2026 specifically for its silicon spin-qubit engineering) has been closing that gap. Coherence times for isotopically purified silicon spin qubits can exceed those of superconducting qubits by orders of magnitude.