(color online) Experimental demonstration of exchange qubits. (a) False-color SEM image of a device fabricated for both the exchange-only qubit and the resonant exchange qubit.^[60] Triple quantum dots are denoted by small red circles while a bigger quantum dot acting as a charge sensor like a QPC channel is denoted by a big red circle. Voltages applied on and are used to control the charge occupancy of the left and right dots as well as the detuning ε. (b) Schematic diagram of the effects of , on the exchange-only qubit, J_x and J_z on the resonant exchange qubit via Bloch sphere. Two initialization states, |S_l〉 and |S_r〉 are also included. (c) Coherence time T₂ of a resonant exchange qubit^[64] for various orders of CPMG-n pulses. The lower inset demonstrates that each CPMG dynamical decoupling sequence includes rotations around the y axis while the upper inset shows the detuning sequence in the energy level spectrum. The fit denoted by the blue line suggests the coherence time is up to .