Contextual Subspace Quantum Simulation with Optimized Transpilation on a Trapped-Ion Quantum Computer

We present an experimental demonstration of the contextual subspace variational quantum eigensolver (CS-VQE) on a trapped-ion quantum computer. By combining contextual subspace reduction with an optimized end-to-end transpilation workflow—featuring improved fermion-to-qubit mappings, tailored ansatz Pauli-phase-gadget sequences, and efficient measurement strategies—we achieve accurate ground-state energy estimation for molecular dissociation Hamiltonians. This approach demonstrates how subspace-based quantum algorithms can substantially reduce circuit depth and measurement overhead, enabling realistic quantum simulations within current hardware limits.