Optimal Design Of Multiqubit Rydberg Quantum Gate Based On Evolutionary Algorithm

Recently,high-fidelity quantum gates serving as the basic units for quantum computation,have become a hot topic by many research teams at home and abroad.Among various physical platforms,neutral Rydberg atoms have a lot of advantages,e.g.long coherence time,strong atom-atom interaction,high scalability,which lead to many frontier applications in the fields of quantum computation,quantum simulation and precision measurement.Accompanied by the rapid development of quantum technology,current quantum computing shows stronger and stronger requirements for a higher gate fidelity as well as a shorter gate operation time.The gate scalability also becomes an important indicator for universal quantum computation at the same time.To solve the above issues,our paper proposes two theoretical schemes: one is about a two-qubit Rydberg controlled phase gate;the other is a three-dimensional multiqubit controlled NOT(or CNOT)gate.These two results can fundamentally put one-step closer to the experimental demonstration of Rydberg quantum gates.The details of our work are shown as follows:1.Two-qubit controlled phase gate based on stimulated Raman adiabatic process.When one atom contains several Rydberg levels nearby,the interspecies resonance dipole-dipole interaction and the intraspecis van der Waals(vd Ws)interaction could coexist in the system.Here we counter-intuitively treat the dipole interaction as one of the two adiabatic pulses(the other adiabatic pulse is an optical pulse)and the vd Ws interaction as the intermediate-state detuning,which constitutes an almost perfect adiabatic passage.By obeying the adiabatic evolution of an absolute dark state,we have achieved an efficient two-qubit controlled phase gate with its fidelity ～ 0.9998 and gate time ～ 80 ns.To our knowledge,fast and high-fidelity quantum gates are essential for realizing universal quantum computing.2.Scalable multiqubit CNOT gates in a three-dimensional(3D)defect-free atomic array.With the rapid development of holographic optical tweezers technology,people are able to carry out precise manipulation of atomic positions in space,which makes the production of3 D multiqubit quantum gates possible.In the present work,we first propose a scheme of 3D spherical multiqubit CNOT gates.Depending on the asymmetric Rydberg blockade mechanism,our model reveals an unprecedented robustness to the 3D atomic position fluctuations.We perform optimization to the spatial position of all control atoms by using evolutionary algorithm.The resulting optimal structures have stronger scalability,which can be used for experimental demonstration of multiqubit quantum computation in the future.