Solving the electronic structure for molecules and materials is one of the most promising application area of quantum computers. However, since the current quantum computers have limited qubit number and two-qubit gate fidelities, it becomes crucial to develop new algorithms to reduce the amount of quantum resources required to simulate electronic systems. In this work, we use a seniority-zero wave fuction ansatz: the unitary pair coupled cluster wave function, to study potential energy surfaces for small molecules. The seniority-zero nature of this ansatz allows us to treat electrons pairs only, which could be condensed to bosons. This reduces the number of required qubits by a factor of 2 and avoids dealing with antisymmetry of single electrons. Orbital optimization techniques and perturbation theory based on this ansatz is also developed simply by performing more measurements, without increasing the depth of the quantum computer. We performed simulations of these methods on ion trapped quantum computers, and mitigated errors by various error correction techniques. The results show excellent agreement with exact predictions.

Seniority-zero error corrected quantum chemistry simulations on ion-trapped quantum computers

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ACS Fall 2022

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