spin qubit

Imagine trapping a single electron in a tiny pocket of silicon, then using one private property of that electron to hold your quantum information. That property is spin, a built-in magnetic quality that can point in two basic directions you can label 0 and 1. A spin qubit is exactly that: one qubit stored in the spin of a single electron (or sometimes an atomic nucleus) held inside a quantum dot, a nanometer-scale trap patterned into the chip. Because the carrier is just one particle, a spin qubit is extraordinarily small, far tinier than the wiring loops used in some other approaches.

The big practical bet behind spin qubits is manufacturability. They are built in silicon and look, structurally, a lot like the transistors that the chip industry already makes by the billion, so the hope is to borrow mature CMOS fabrication rather than invent it from scratch. Like any qubit, a spin qubit holds a state alpha|0> + beta|1>; you steer it with carefully shaped magnetic or electric pulses, and when you measure you get a single 0 or 1 with probability set by those amplitudes, and the superposition collapses. Two nearby spins can be coupled to entangle them and run two-qubit gates.