Experimental Investigation Of High-fidelity Quantum Logic Gates On Solid-state Spin Qubits

As a new choice of information processing,quantum computation is able to solve several intractable problems in classical computation such as factoring,utilizing the principles of quantum mechanics.To realize realistic scalable quantum computation,it is required to realize fault-tolerant quantum computation via error correction,which sets a threshold for the fidelity of quantum logic gates.The fault-tolerant threshold is generally stringent.Taking the surface code as an example,quantum gate fidelity up to above 0.99 is generally believed to be required to reach the threshold.On the other hand,the fidelity of logic gates on a quantum system is susceptible to noises.A great challenge for quantum computation is to realize high-fidelity quantum logic gates under noises.We experimentally investigate approaches to suppress noises and to realize high-fidelity quantum logic gates on electron and nuclear spin qubits of nitrogen-vacancy centers in diamond,which is an important candidate for quantum computation.Single-qubit gate fidelity up to 0.99995 and two-qubit gate fidelity of 0.992 are achieved,which not only reach the fault-tolerant threshold for surface code,but also stand for the state-of-art gate fidelity in solid-state spin systems to the best of our knowledge.This thesis is mainly to introduce the results of our researches on high-fidelity quantum logic gates based on the system of nitrogen-vacancy centers in diamond.The following work is related.1.Experimental demonstration and realization of dynamically corrected gates.Via dynamically corrected gates,we realize the suppression of noise during quantum logic gates up to the 6th order,and prolong the coherence time available for logic gates to T_1?-limit for the first time.2.Experimental realization of fault-tolerant universal quantum logic gates.Meth-ods and techniques such as a new composite pulse,optimal control,and wavefor-m calibration are developed to achieve quantum gate fidelity reaching the fault-tolerant threshold.Single-qubit gate fidelity up to 0.99995 and two-qubit gate fidelity of 0.992 are achieved at room temperature under ambient conditions with a nitrogen-vacancy center in diamond.3.Experimental realization of time-optimal universal quantum logic gates.We ap-ply the quantum brachistochrone equation to the system of nitrogen-vacancy cen-ters in diamond,and realize universal quantum logic gates in the time-optimal way for the first time.The fidelity of the realized quantum gates is up to 0.99,and the gate time is remarkably shorter than that with conventional methods.