1. Multilevel variational spectroscopy using a programmable quantum simulator
- Author
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Zhikun Han, Chufan Lyu, Yuxuan Zhou, Jiahao Yuan, Ji Chu, Wuerkaixi Nuerbolati, Hao Jia, Lifu Nie, Weiwei Wei, Zusheng Yang, Libo Zhang, Ziyan Zhang, Chang-Kang Hu, Ling Hu, Jian Li, Dian Tan, Abolfazl Bayat, Song Liu, Fei Yan, and Dapeng Yu
- Subjects
Physics ,QC1-999 - Abstract
Energy spectroscopy is a powerful tool with diverse applications across various disciplines. Variational quantum-classical algorithms based on programmable digital quantum simulators have emerged as promising approaches for conducting spectroscopy on various models using a single device, despite facing significant quantum and classical resource overheads. Here, we experimentally demonstrate multilevel variational spectroscopy for fundamental many-body Hamiltonians using a superconducting digital quantum simulator. By exploiting symmetries and the subspace search method, we achieve full spectroscopy for a four-qubit Heisenberg spin chain, yielding an average energy deviation as small as 0.13 from the theoretical values, assuming unity coupling strength. Our method, when extended to eight-qubit Heisenberg and transverse-field Ising Hamiltonians, successfully determines the three lowest-energy levels. In achieving the above, we introduce a circuit-agnostic compilation method that enhances the robustness of our simulator against signal crosstalk. Our study highlights the combination of the subspace search method and symmetry-assisted resource efficiency in variational quantum algorithms and lays the foundation for practical spectroscopy on near-term quantum simulators, with potential applications in quantum chemistry and condensed matter physics.
- Published
- 2024
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