Chinese Journal of Quantum Electronics ›› 2026, Vol. 43 ›› Issue (1): 120-130.doi: 10.3969/j.issn.1007-5461.2026.01.010

• Quantum Computing • Previous Articles     Next Articles

Application of quantum approximate optimization algorithm in graph coloring

LIU Yutong, LI Zhiqiang *, Yin Jingwei   

  1. College of Information Engineering, Yangzhou University, Yangzhou 225127, China
  • Received:2024-06-19 Revised:2024-09-24 Published:2026-01-28 Online:2026-01-28

Abstract: The graph coloring problem is classified as one of NP-complete problems, and currently there is no known algorithm that can solve such problems in polynomial time in all cases. In response to this issue, we map it to quantum bits and design a quantum circuit in this work based on the quantum approximate optimization algorithm (QAOA). Firstly, we quantize the classical Ising model of the problem using rotation operators and Pauli operators to derive the problem's Hamiltonian. Subsequently, two parameterized unitary transformations are designed based on the mixing Hamiltonian and the problem Hamiltonian, and the expectation value of the problem's Hamiltonian is obtained by alternately applying these two unitary transformations. Specifically, to increase the probability of obtaining the correct solution, the Powell algorithm is used to optimize the parameters during the quantum state evolution to adjust the expectation value. Finally, based on the Hamiltonian, the initial state and the required quantum gates of the algorithm are derived, the quantum circuit is generated, and simulation experiments are conducted using Qiskit quantum framework of IBM. The experimental results show that the proposed approach can obtain the solution of graph coloring problem with high probability in polynomial time, demonstrating a significant exponential speedup.

Key words: quantum computing, quantum approximate optimization algorithm, quantum circuit, Hamiltonian, graph coloring, unitary transformation

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