RT info:eu-repo/semantics/article T1 Finding eigenvectors with a quantum variational algorithm A1 García Escartín, Juan Carlos K1 Computación cuántica K1 Fotónica K1 Quantum algorithms K1 Variational algorithms K1 Hybrid quantum algorithms K1 Eigenvectors K1 Quantum principal component analysis K1 SWAP test K1 2210.23 Teoría Cuántica K1 1203 Ciencia de Los Ordenadores K1 2209 Óptica AB This paper presents a hybrid variational quantum algorithm that finds a random eigen-vector of a unitary matrix with a known quantum circuit. The algorithm is based on theSWAP test on trial states generated by a parametrized quantum circuit. The eigenvec-tor is described by a compact set of classical parameters that can be used to reproducethe found approximation to the eigenstate on demand. This variational eigenvectorfinder can be adapted to solve the generalized eigenvalue problem, to find the eigen-vectors of normal matrices and to perform quantum principal component analysis onunknown input mixed states. These algorithms can all be run with low-depth quantumcircuits, suitable for an efficient implementation on noisy intermediate-scale quantumcomputers and, with some restrictions, on linear optical systems. In full-scale quan-tum computers, where there might be optimization problems due to barren plateausin larger systems, the proposed algorithms can be used as a primitive to boost knownquantum algorithms. Limitations and potential applications are discussed. PB Springer YR 2024 FD 2024 LK https://uvadoc.uva.es/handle/10324/75146 UL https://uvadoc.uva.es/handle/10324/75146 LA eng NO Quantum Information Processing, 2024, vol. 23, n. 7 NO Producción Científica DS UVaDOC RD 10-abr-2025