Subspace variational quantum simulator on superconducting qubit system*

Quantum simulation is one of the key applications of quantum computing, which accelerates research and development in the fields such as chemistry and material science. The recent development of noisy intermediate-scale quantum (NISQ) devices urges the exploration of applications without the necessity of quantum error correction. Here, we propose an efficient method to simulate quantum dynamics driven by a static Hamiltonian on NISQ devices, named subspace variational quantum simulator (SVQS). SVQS employs the subspace-search variational eigensolver (SSVQE) to find a low-lying subspace and extends it to simulate dynamics within the subspace with lower overhead compared to the existing schemes. We successfully simulate the time evolution of a quantum state in a hydrogen molecule with the subspace process fidelity from 0.90 to 0.99 using superconducting qubits.