(color online) Experimental demonstration of spin qubits. (a) SEM image of the silicon CMOS quantum dot for single- and two-qubit operations. The spin states of two qubits are controlled by the magnetic field produced by the ESR transmission line with ac current . A single or double quantum dot can be formed by adjusting the voltages of gates G₁–G₄. G denotes the confinement gate while R denotes the reservoir.^[5] (b) Fidelity of a single qubit formed in the device of panel (a) through randomized benchmarking of Clifford gates. From the decay an average fidelity of 99.6% can be inferred.^[37] (c) Rabi oscillations of individual spin qubit in each quantum dot of panel (a).^[5] (d) Two-spin probabilities as functions of the microwave pulse length on the control qubit (Q₁) after applying a CNOT gate (the inset shows the corresponding Bloch sphere). Black solid lines are the fits based on a CNOT gate considering read-out errors while green dotted lines show the intended maximally entangled states.^[5]