Demonstration of subspace-search variational quantum eigensolver using photonic orbital angular momentum qudits
Abstract
Accurate excited-state energies are essential for interpreting fluorescence and photochemical processes, yet variational quantum eigensolvers (VQEs) on noisy intermediate-scale quantum (NISQ) hardware have largely been confined to ground states. Subspace-search VQE (SSVQE) offers a NISQ-friendly route to excited states without ancilla-based overlap measurements, however it has lacked an experimental demonstration since it requires the coherent preparation and manipulation of multiple orthogonal basis states under a shared variational unitary. Here we realize SSVQE on a photonic platform by encoding orthogonal qudit states in the orbital angular momentum of single photons and optimizing a shared variational circuit. We estimate excited-state energies for a four-dimensional HeH ⁺ molecule and an eight-dimensional Heisenberg chain, thereby demonstrating scalable excited state eigensolving in a high-dimensional Hilbert space. Our results establish photonic qudits as a resource-efficient pathway to excited-state quantum simulation.
Versions
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BibTeX
@article{hu2026demonstration,
title = {{Demonstration of subspace-search variational quantum eigensolver using photonic orbital angular momentum qudits}},
author = {Kang-Min Hu and Myung-Hyun Sohn and Yong-Su Kim and Kwang Jo Lee and Hyun Woo Kim and Hyang-Tag Lim},
journal = {npj Quantum Information},
year = {2026},
month = oct,
doi = {10.1038/s41534-026-01380-2},
url = {https://www.nature.com/articles/s41534-026-01380-2},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Demonstration of subspace-search variational quantum eigensolver using photonic orbital angular momentum qudits
AU - Kang-Min Hu
AU - Myung-Hyun Sohn
AU - Yong-Su Kim
AU - Kwang Jo Lee
AU - Hyun Woo Kim
AU - Hyang-Tag Lim
PY - 2026
DA - 2026/10/07
JO - npj Quantum Information
DO - 10.1038/s41534-026-01380-2
UR - https://www.nature.com/articles/s41534-026-01380-2
AB - Accurate excited-state energies are essential for interpreting fluorescence and photochemical processes, yet variational quantum eigensolvers (VQEs) on noisy intermediate-scale quantum (NISQ) hardware have largely been confined to ground states. Subspace-search VQE (SSVQE) offers a NISQ-friendly route to excited states without ancilla-based overlap measurements, however it has lacked an experimental demonstration since it requires the coherent preparation and manipulation of multiple orthogonal basis states under a shared variational unitary. Here we realize SSVQE on a photonic platform by encoding orthogonal qudit states in the orbital angular momentum of single photons and optimizing a shared variational circuit. We estimate excited-state energies for a four-dimensional HeH ⁺ molecule and an eight-dimensional Heisenberg chain, thereby demonstrating scalable excited state eigensolving in a high-dimensional Hilbert space. Our results establish photonic qudits as a resource-efficient pathway to excited-state quantum simulation.
SN - 2056-6387
ER -