Quantum Gates and Decoupling in Qubits with Fixed Transverse Coupling

Abstract

Among all the quantum computer candidates, the superconducting system is one of the most convincing platforms due to its strong couplings and scalability. To be more specific, this thesis focuses on the superconducting system, in which the artificial atoms are controlled longitudinally and coupled without any intermediate devices. We propose a superconducting decoupling method in this thesis. Firstly, we state that our algorithm can effectively ‘turn off’ arbitrary couplings. Then, we analyze the errors of our decoupling method and prove that the errors are ignorable when a sequence of decoupling gates are applied on non-nearest-neighboring qubits. We verify the efficiency of our decoupling method using the numerical simulations, which are well-matched with the theoretical predictions. Using 99.6% fidelity isolated CNOT and 99.89% single-qubit gates, we obtain a fidelity of 97.8% with the CNOT implementation in a five-qubit system over 14.84 ns.