Housing

December 21, 2025, 9:14 AM EST. Researchers from Fudan University and collaborators advance excited-state calculations on near-term quantum computers by analyzing three variants of the Variational Eigensolver (VQE). By embedding orthogonality constraints directly into the cost function, they prevent collapse to the ground state and show each model has a unique property that guarantees a best possible solution. The work surveys state-specific VQE, subspace search VQE, quantum equation of motion VQE, and linear response VQE, highlighting how they cope with complex energy landscapes, symmetry breaking, and degeneracy. Numerical benchmarks on molecular systems assess accuracy, robustness, and scalability, and the authors outline practical directions-improved optimization, flexible trial wavefunctions, and noise mitigation-for reliable excited-state calculations on NISQ devices.