Demonstration of subspace-search variational quantum eigensolver using photonic orbital angular momentum qudits

@misc{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},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.11026},
  eprint = {2610.11026},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.11026},
  note = {CC BY 4.0},
}

TY  - UNPB
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  - 2026/10/08
PB  - arXiv
DO  - 10.48550/arxiv.2610.11026
UR  - https://arxiv.org/abs/2610.11026
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.
ER  -