Synthesizing Three-body Interactions With Superconducting Qubits

Quantum simulation is an efficient way to solve many-body problems of complex quantum systems.There are two strategies in quantum simulation,one is digital quantum simulation based on quantum gates,and the other is analog quantum simulation which uses a controllable quantum system to mimic the Hamiltonian of the targe one,Analog quantum simulation is more attainable in the near future because of its higher tolerance level of errors.However,the scope of application of analog quantum simulation is limited by the form of Hamiltonian that can be physically achieved in the controllable quantum system.Superconducting qubits have been one of the most popular platforms in performing quan-tum simulation tasks,due to the flexibility and scalability of superconducting circuits.The first half of this thesis introduces in detail the construction of experimental superconducting qubit platforms,including the chip design of superconducting qubits and the construction of measure-ment and control systems.However,in a superconducting multiqubit device,the physical form of couplings between qubits is either an electric(capacitor)or magnetic field(inductor),and the associated quadratic field energy determines that only two-body interaction in the Hamiltonian can be directly realized.Interactions containing three or more qubits,which are common in real quantum systems,remain challenging to be experimentally realized.To address the problem,we demonstrate two schemes of synthesizing three-body interac-tion with superconducting qubits in this thesis.One of them is based on Floquet engineering.In a three-qubit system with pairwise two-qubit coupling,the interaction between two qubits can be dynamically turned off and further the three-body interaction of spin chirality can be created by periodically modulating the resonant frequencies of the qubits.The three-body interaction is characterized by the chiral flows of the excitations in the three-qubit circular loop.Another scheme is based on quantum transition induced by two-photon absorption.One of the super-conducting qubits with a cascade three-level generates a time-frequency correlated photon pair,which simultaneously excites two noninteracting qubits.The strong coupling regime of this process enables the synthesis of a three-body interaction Hamiltonian,which allows the gener-ation of the tripartite Greenberger-Horne-Zeilinger(GHZ)state in a single step with a fidelity as high as 95%.These two schemes of generating three-body interactions extend the interaction types that we can achieve in superconducting qubits,which may play a key role in quantum simulation tasks.