Researchers from ICGM Université de Montpellier, VSB Technical University of Ostrava, IT4Innovations National Supercomputing Center, and Laboratoire de Chimie Quantique Institut de Chimie have developed a quantum algorithm, StateAveraged OrbitalOptimized VQE (SAOOVQE), to address the electronic structure problem in theoretical chemistry. The SAOOVQE package uses a hybrid quantum-classical approach, offloading some computations to Quantum Processing Units (QPUs) and performing the rest on a classical computer. This method helps to overcome issues such as quantum noise and the lack of large-scale quantum computers. The SAOOVQE can treat degenerate or quasi-degenerate states equally, avoiding numerical optimization problems.
Quantum Algorithm for Electronic States
A team of researchers from ICGM Université de Montpellier, VSB Technical University of Ostrava, IT4Innovations National Supercomputing Center, and Laboratoire de Chimie Quantique Institut de Chimie have developed a quantum algorithm, StateAveraged OrbitalOptimized VQE (SAOOVQE), for the democratic description of ground and excited electronic states. The electronic structure problem is a significant issue in modern theoretical chemistry, and while there are many established methods, it remains a computationally demanding task.
Quantum Processing Units and Quantum Noise
The researchers suggest that offloading some parts of the computation to Quantum Processing Units (QPUs) may offer significant speedup, often referred to as quantum supremacy or quantum advantage. However, this approach presents several problems, most notably naturally occurring quantum decoherence, hereafter denoted as quantum noise, and the lack of large-scale quantum computers. This makes it necessary to focus on Noisy-Intermediate Scale Quantum computers when developing algorithms aspiring to near-term applications.
SAOOVQE Package
The SAOOVQE package aims to answer both these problems with its hybrid quantum-classical conception based on a typical Variational Quantum Eigensolver approach. Only a part of the algorithm utilizes offload to QPUs, and the rest is performed on a classical computer, thus partially avoiding both quantum noise and the lack of quantum bits (qubits). The SAOOVQE has the ability to treat degenerate or quasi-degenerate states on the same footing, thus avoiding known numerical optimization problems arising in state-specific approaches around avoided crossings or conical intersections.
Quantum Chemistry and Real-life Applications
Quantum chemistry is one of the main areas of interest in Quantum Computing. In many real-life applications, there is the necessity of treating both the ground and excited states accurately and in an equal footing. The problem is magnified when the Born-Oppenheimer approximation breaks down due to a strong coupling among degenerate or quasi-degenerate states, most notably the ground and the first excited state.
SAOOVQE Method and Implementation
The State-Averaged Orbital-Optimization Variational Quantum Eigensolver (SAOOVQE) method addresses these problems and provides a way to compute both PES gradients and NACs analytically. Authored by Yalouz et al., there is an exemplary implementation focusing on the pedagogical aspect and relying on matrix-vector multiplications rather than actual measurements, avoiding the utilization of real QC infrastructure.
Features and Getting Started with SAOOVQE
With SAOOVQE, you can obtain potential energy surfaces, circuit or Ansatz gradients, orbital gradients, gradients of potential energy surfaces, and nonadiabatic couplings. For numerical optimization, you can use any of the optimizers supported by Qiskit and the team’s own implementation of Particle Swarm Optimization. The package is prepared with a priority of being very simple to use, and the concise documentation can be found at sa-oo-vqe-qiskit.rtfd.io.
This work/project was publicly funded through ANR, the French National Research Agency under the Investissements d’avenir program with the reference ANR-16-IDEX-0006. This work was also supported by the Ministry of Education, Youth and Sports of the Czech Republic through the e-INFRA CZ ID:90254.
On January 22, 2024, an article titled “State-Averaged Orbital-Optimized VQE: A quantum algorithm for the democratic description of ground and excited electronic states” was published by authors Martin Beseda, Silvie Illésová, Saad Yalouz, and Bruno Senjean. The article was published on arXiv, a repository of electronic preprints approved for publication after moderation, hosted by Cornell University.