Physics

Orthogonality

Subspace topology

Mathematics

Domain (mathematical analysis)

Unitarity

Ansatz

Mathematical analysis

Excited state

Geometry

Quantum mechanics

Quantum

Physical Review Research

The authors propose an algorithm, the subspace-search variational quantum eigensolver (SSVQE) that searches a low energy subspace by supplying orthogonal input states to the variational ansatz and relies on the unitarity of transformations to ensure the orthogonality of output states. This work extends the applicable domain of the Variational Quantum Eigensolver to excited states and their related properties.

Subspace-search variational quantum eigensolver for excited states