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| Autori principali: | , , , |
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| Natura: | Preprint |
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2026
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| Accesso online: | https://arxiv.org/abs/2602.20881 |
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| _version_ | 1866913131581669376 |
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| author | Carolan, Eoin Keenan, Nathan Cenedese, Gabriele Benenti, Giuliano |
| author_facet | Carolan, Eoin Keenan, Nathan Cenedese, Gabriele Benenti, Giuliano |
| contents | We present and benchmark a type of variational quantum eigensolver (VQE), which we denote $σ$-VQE. It is designed to target mid-spectrum eigenstates and prepare quantum many-body scar states. The approach leverages the fact that noisy intermediate-scale quantum devices are limited in their ability to generate generic highly entangled states. This modified VQE pairs a low-depth circuit with an energy-selective objective that explicitly penalizes energy variance around a chosen target energy. The cost function exploits the limited expressibility of the shallow circuit as atypical low-entanglement eigenstates such as scar states are preferentially selected. We validate this mechanism across two complementary families of models that contain many-body scar states: the Shiraishi-Mori embedding approach and a matrix product state parent Hamiltonian construction. We define an unbiased estimation scheme for the nonlinear cost function that is compatible with qubit-wise commuting grouping and bitstring reuse. A proof-of-principle demonstration using a small-system instance was performed on IBM Fez (Heron r2 QPU). These results motivate its use as a practical algorithm for detecting quantum many-body scars and variationally generating states with appreciable scar state overlap. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2602_20881 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | $σ$-VQE: Excited-state preparation of quantum many-body scars with shallow circuits Carolan, Eoin Keenan, Nathan Cenedese, Gabriele Benenti, Giuliano Quantum Physics We present and benchmark a type of variational quantum eigensolver (VQE), which we denote $σ$-VQE. It is designed to target mid-spectrum eigenstates and prepare quantum many-body scar states. The approach leverages the fact that noisy intermediate-scale quantum devices are limited in their ability to generate generic highly entangled states. This modified VQE pairs a low-depth circuit with an energy-selective objective that explicitly penalizes energy variance around a chosen target energy. The cost function exploits the limited expressibility of the shallow circuit as atypical low-entanglement eigenstates such as scar states are preferentially selected. We validate this mechanism across two complementary families of models that contain many-body scar states: the Shiraishi-Mori embedding approach and a matrix product state parent Hamiltonian construction. We define an unbiased estimation scheme for the nonlinear cost function that is compatible with qubit-wise commuting grouping and bitstring reuse. A proof-of-principle demonstration using a small-system instance was performed on IBM Fez (Heron r2 QPU). These results motivate its use as a practical algorithm for detecting quantum many-body scars and variationally generating states with appreciable scar state overlap. |
| title | $σ$-VQE: Excited-state preparation of quantum many-body scars with shallow circuits |
| topic | Quantum Physics |
| url | https://arxiv.org/abs/2602.20881 |