We propose a system of two interacting always-on, exchange-only qubits forwhich CPHASE, CNOT, quantum Fourier transform (QFT) and SWAP operations can beimplemented only in a few electrical pulses in a nanosecond time scale. Eachqubit is built of three quantum dots (TQD) in a triangular geometry with threeelectron spins which are always kept coupled by exchange interactions only. Thequbit states are encoded in a doublet subspace and are fully electricallycontrolled by a voltage applied to gate electrodes. The two qubit quantum gatesare realized by short electrical pulses which change the triangular symmetry ofTQD and switch on exchange interaction between the qubits. We found an optimalconfiguration to implement the $CPHASE$ gate by a single pulse of the order 2.3ns. Using this gate, in combination with single qubit operations, we searchedfor optimal conditions to perform the other gates: CNOT, QFT and SWAP. Ourstudies take into account environment effects and leakage processes as well.The results suggest that the system can be implemented for fault tolerantquantum computations.
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