Open shell electronic state calculations on quantum computers: A quantum circuit for the preparation of configuration state functions based on Serber construction
Kenji Sugisaki, Satoru Yamamoto, Shigeaki Nakazawa, Kazuo Toyota, Kazunobu Sato, Daisuke Shiomi, Takeji Takui · Chemical Physics Letters · 2018
• An improved quantum circuit for the preparation of spin symmetry-adapted configuration state function is given. • The quantum circuit contains one-qubit rotations and controlled-NOT operations acting to adjacent two qubits. • The quantum circuit is fully parallelizable. • The depth of the quantum circuit is constant and independent to the number of unpaired electrons. Full configuration interaction (full-CI) calculations can be executed efficiently on quantum computers (QCs) by utilizing a quantum phase estimation algorithm (QPEA). In the QPEA-based full-CI on QCs, the preparation of the initial guess wave functions having large overlap with the full-CI root is crucial. Recently, we proposed a quantum circuit to prepare spin symmetry-adapted configuration state functions (CSFs) toward open shell electronic structure calculations of molecules on QCs. Here, we propose an improved quantum circuit, based on Serber construction of spin eigenfunctions, enabling us to prepare CSFs with much less and easier-to-implement quantum gates than the previously proposed one.