(QCxQC) Mekena Metcalf: Resource Efficient Chemistry on QCs with the VQE and The Double Unitary ...
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Full talk title: Resource Efficient Chemistry on Quantum Computers with the Variational Quantum Eigensolver and The Double Unitary Coupled-Cluster Approach
Authors: Mekena Metcalf, Nicholas Bauman, Karol Kowalski and Wade De Jong
Abstract: Applications of quantum simulation algorithms to obtain electronic energies of molecules on NISQ devices require careful consideration of resources for describing complex inter-electron correlation effects. In modeling of these problems, a big challenge is posed by the fact that the number of qubits scales linearly with the size of molecular basis, which significantly limits basis set size and the number of correlated electrons included in quantum simulations of chemical processes. To address this issue and enable more realistic simulations on near-term quantum computers, several algorithms have been proposed to effectively downfold correlation effects into the reduced-size orbital space, commonly referred to as the active space. Using downfolding techniques based on double unitary coupled-cluster (DUCC) Ansatz we demonstrate that dynamic correlation can be captured by small-size active spaces and by properly constructed active-space effective Hamiltonians. Combining the downfolding pre-processing technique with the Variational Quantum Eigensolver, we solve for the ground-state energy in the DUCC reduced active space and compare results to the configuration-interaction for $\text{Li}_2$, $\text{H}_2$ and $\text{BeH}_2$ using RHF and natural orbitals.