Study Of Optimal Control Theory Based On NV Center System In Diamond

Quantum computation is an important aspect of quantum information processing.As the platform for realizing quantum computation,quantum computer should fulfil the requirements about initialization,control,coherence time,readout and scalability.For its optical property,NV center system is one of the promising candidate for quantum computer.There are two factors affecting our control in NV center system:the decoherence resulting from environment,and the control error.For the hybrid system consisting of NV center and nuclear spins,the decoherence is more obvious:For the small magnetic moment,the nuclear spins are difficult to be driven by control field;The needed control time for nuclear spins can be comparable with the coherence time of NV center.We should realize control on the hybrid system and keep the coherence of NV center.On the other hand,utilizing the quantum holonomy,holonomic quantum computation can suppress certain types of control error.And the non-adiabatic holonomic quantum computation(NHQC),combing the geometric feature and speed,is more applicable.To utilize NHQC in NV system,we should search the NHQC scheme with more feasibility,and with the robustness against other types of error(such like the thermal noise of NV center and the control amplitude error).Quantum optimal control theory(QOCT),which combines quantum mechanics and numerical optimization,has many applications in NV system.In this paper,we use QOCT solve the two mentioned problems.As discussed below:·Combing with average Hamiltonian theory,we develop the QOCT method in the hybrid system consisting of NV center and weak coupling 13C,and we demonstrate the method in experiments.The proposed scheme can realize the objective evolu-tion,and suppress the quantum noise resulting form bath evolution.In experiments,we realize the control-phase gates,iSWAP(?)gate in hybrid 3-qubit system.In the control process,the NV coherence time is extended to 1.08 ms,which is about 5 times of the NV T2 time.And we we prepare an entanglement state on the two nuclear spins with a fidelity of 73%.·We proposed a general optimization method,which can search the NHQC scheme automatically,and be robust against the noise with quasi-static property.We com-pare this method with the former NHQC scheme in NV system in numerical simula-tion,and demonstrate the advantages.To demonstrate the generality of this method,we search NHQC scheme in qubits system with ZZ coupling.