Quantum computer-aided design: digital quantum simulation of quantum processors*

With the increasing size of quantum processors, the sub-modules that constitute the processor will become too large to accurately simulate on a classical computer. Therefore, one would soon have to fabricate and test each new design primitive and parameter choice in time-consuming coordination between design, fabrication, and experimental validation. To circumvent this slow-down, we address the question of how one can design and test the performance of the sub-modules of next-generation quantum devices--by using existing quantum computers. We show how the energy spectra of transmons can be obtained by variational hybrid quantum-classical algorithms that are well-suited for near-term noisy quantum computers. We also numerically demonstrate how single-and two-qubit gates can be realized via Suzuki-Trotter decomposition for digital quantum simulation. Our methods pave a new way towards designing candidate quantum processors when the demands of calculating sub-module properties exceed the capabilities of classical computing resources.