Error-mitigated photonic variational quantum eigensolver using a single-photon ququart

Donghwa Lee, Jinil Lee, Seongjin Hong, Hyang Tag Lim, Young Wook Cho, Sang Wook Han, Hyundong Shin, Junaid ur Rehman, Yong Su Kim

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


Variational quantum algorithms, a representative class of modern quantum algorithms, provide practical uses of nearterm quantum processors. The size of the problem that can be encoded and solved on a quantum processor is limited by the dimension of the Hilbert space associated with the processor. One common approach for increasing the system dimension is to utilize a larger number of quantum systems. Here, we adopt an alternative approach to utilize multiple degrees of freedom of individual quantum systems to experimentally resource-efficiently increase theHilbert space.We report experimental implementation of the variational quantum eigensolver (VQE) using four-dimensional photonic quantum states of single photons. The four-dimensional quantum states are implemented by utilizing polarization and path degrees of freedom of a single photon. Our photonic VQE is equipped with a quantum error mitigation protocol that efficiently reduces the effects of Pauli noise in the quantum processing unit.We apply our photonicVQEto estimate the ground state energy of theHe-H+ cation. Simulation and experimental results demonstrate that our experimental resource-efficient photonic VQE can accurately estimate the bond dissociation curve, even in the presence of large noise in the quantum processing unit. We also discuss further possible resource-efficient enhancement of the Hilbert space in photonic quantum processors. Our results propose that photonic systems utilizing multiple degrees of freedom can provide a resource-efficient avenue to implement practical near-term quantum processors.

Original languageEnglish
Pages (from-to)88-96
Number of pages9
Issue number1
Publication statusPublished - 2022 Jan 20

Bibliographical note

Publisher Copyright:
© 2022 Optical Society of America.

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics


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