Robust Quantum Gates With Resonant-Driving–Induced Rydberg-Atom Antiblockade

As basic elements of quantum computing,quantum gates can be used to realize unitary state transformations of quantum systems,playing an indispensable role in quantum simulation,quantum information processing,quantum sensing,and quantum precise measurement.Therefore,realization of quantum gates with high fidelity is of great significance for promoting development of cutting-edge quantum technologies.Compared with other quantum computing platforms,such as superconducting quantum circuits,trapped ions,nuclear magnetic resonance,etc.,Rydberg atoms not only have long coherence time and perfect homogeneity that superconducting qubits do not have,but also is of extraordinary scalability that is inaccessible in systems of trapped ions and nuclear magnetic resonance.Therefore,Rydberg atoms trapped in an array of optical tweezers have become one of potential candidate platforms for quantum computing.In this dissertation,we mainly pay attention to a resonant-driving-induced Rydberg antiblockade regime for proposing quantum gate schemes,improving quantum gate robustness,and analyzing feasibility of the quantum gate schemes.The studies in this dissertation are hopeful to provide valuable theoretical guidance for related experiments,thereby promoting the development of frontier quantum technologies.The dissertation mainly includes the following four sections.First,we propose an unconventional Rydberg antiblockade regime.With an amplitudemodulated field on two Rydberg atoms,the modulation frequency is suitably set to offset the Rydberg interaction and thus to induce the resonant-driving-induced Rydberg antiblockade,based on which an effective Rabi oscillation can be found between the collective ground and excited states of atoms.On this basis,after a Rabi cycle a π phase can be obtained on one of two-atom ground states,so a two-atom control-phase gate can be achieved.Aiming at sensitivity of the Rydberg-antiblockade gates to Rydberg-state decay and deviations in Rydberg interaction,we propose an optimized scheme of quantum gate,and several common problems of Rydberg-antiblockade gates are effectively alleviated.The controlled-phase gate and the controlled-NOT gates realized in this work can be used as universal quantum gates for constructing quantum algorithms.Next,we propose a regime of unselective ground-state blockade of Rydberg atoms,where the evolution of the two-atom system will be blocked when two atoms populate on an identical ground state.Through setting detunings of transitions from two ground states to Rydberg state so as to offset the Rydberg interaction,Rydberg-antiblockade transitions|01(?) (?) |rr(?) (?) |10(?) can be achieved,so this regime can be used to implement a nonadiabatic holonomic quantum SWAP gate.In order to avoid influence of Rydberg-state decay,Doppler dephasing of lasers,and fluctuations in interatomic coupling strength,we optimize parameters to avoid Rydberg excitation of atoms for realizing a dynamical SWAP gate and enhancing robustness of SWAP gate.The SWAP gate realized in this work can improve the efficiency of interconnection between different computing nodes,and can be used to cooperate with universal gates for highly efficient quantum computing.We then propose a regime of Rydberg-antiblockade–based blockade for further enhancing robustness of quantum gates.The control atom is driven by an amplitude-modulated field and the modulation frequency is suitably set to offset the Rydberg interaction so as to achieve Rydberg antiblockade.On this basis,the doubly-excited Rydberg state can be suppressed by enlarging the amplitude of periodic field on the control atom,so robustness of quantum gate against fluctuations of interatomic interactions can be strengthened.By introducing a Landau–Zener–St ¨uckelberg transition on the target qubit,robustness of quantum gate against deviations in gate time and drifts of pulse amplitude can be thereby improved.With experimentally feasible errors in parameters,the fidelity of quantum gate can reach the threshold of quantum surface error-correcting code.This work greatly improves the robustness of Rydberg-antiblockade gate and has potential to promote an experimental verification of Rydberg-antiblockade gates.Finally,we propose a many-body model of Rydberg atoms for implementing robust multiqubit holonomic gates.The dynamics of N control qubits can be equivalent to a two-level transition when the amplitude modulation frequency of periodic field is suitably chosen.Then we can realize(N + 1)-qubit conditional gates based on the regime of Rydberg-antiblockade–based blockade.Within an appropriate parameter range,the operation time of multiqubit gates does not increase with the number of qubits.Besides,N control atoms remain in stable ground states during operations,so the realized multiqubit gates can be effectively protected from systematic errors(including fluctuations in laser parameters and motion dephasing of atoms).The scheme in this work is essentially different from conventional gate schemes based on Rydberg blockade or antiblockade.It can open up an alternative way for the one-step realization of multiqubit gates in the system of trapped Rydberg atoms.