Time-optimal universal quantum gates on superconducting circuits

Decoherence is an inevitable problem when targeting to increase the fidelity of quantum gates, and thus is one of the main obstacles for large-scale quantum computation. The longer a gate operation is, the more decoherence-induced gate infidelity will be. Therefore, how to shorten the gate time becomes an urgent problem to be solved. To this end, time-optimal control based on solving the quantum brachistochron equation is a straightforward solution. Here, based on time-optimal control, we propose a scheme to realize universal quantum gates on superconducting qubits, in a two-dimensional square lattice configuration, and the two-qubit gate fidelity can be higher than 99.7%. Meanwhile, we can further accelerate the z-axis gate considerably by adjusting the time-independent detuning. Finally, in order to reduce the influence of the dephasing error, decoherence free subspace is also incorporated in our physical implementation. Therefore, we present a promising fast scheme for large-scale quantum computation.