Researchers use quantum computer to model singlet fission in H4 molecule

Researchers from the Department of Energy’s Oak Ridge National Laboratory made significant progress in scientific computing using the advanced capabilities of the Quantinuum H1-1 quantum computer. They investigated singlet fission, a process where a molecule absorbs a single photon of light and produces two excited states. The team focused on the linear H4 molecule composed of four hydrogen atoms aligned in a linear structure, finding that its energetic levels match the requirements for singlet fission. This discovery could have valuable implications in developing more efficient solar panels.

Singlet fission has the potential to surpass the theoretical maximum efficiency of conventional solar cells, which is around 33%. By identifying materials that exhibit singlet fission properties, researchers aim to break this efficiency limit. However, it has been challenging to find materials that fulfill the specific energetic requirement for singlet fission.

To tackle this complexity, the ORNL team employed a quantum solver called PDS, based on the Peeters-Devreese-Soldatov approach and developed at the Pacific Northwest National Laboratory. This quantum computing approach offered high accuracy with a manageable computational cost, enabling the accurate calculation of the quantum states involved in the singlet fission phenomenon.

The team’s groundbreaking work, utilizing the capabilities of a quantum computer, was published in The Journal of Physical Chemistry Letters, demonstrating the potential of quantum computing in advancing scientific research.

The Quantum Computational Science group at Oak Ridge National Laboratory (ORNL) achieved significant advantages using the PDS quantum solver compared to classical strategies for determining material’s energetic properties. PDS offered higher accuracy than density functional theory and lower computational demands than coupled cluster theory. Leveraging the power of quantum computers, PDS proved well-suited for studying singlet fission due to its ability to handle double electronic excitations, a challenging task for classical algorithms.

The team accessed the H1-1 quantum computer, provided by Quantinuum, through the Quantum Computing User Program at the Oak Ridge Leadership Computing Facility. Quantum computing with qubits enables exponential processing power for certain equations based in quantum mechanics, but it also poses challenges due to high error rates. To overcome this, the team developed measurement optimization techniques to reduce the computational workload and achieve reliable results.

The ORNL team successfully applied qubit tapering, reduced the number of measurements, and ran multiple circuits in parallel, significantly decreasing the computation time from months to weeks. Although quantum computing is still limited by the current state of the technology, this project demonstrated the potential of quantum computers to address real-world scientific problems.

While the approaches they used have been previously published, they are not widely adopted. The ORNL team emphasizes the importance of adopting these techniques to maximize quantum resources and minimize errors in simulations. Looking ahead, the group is exploring other scientific problems that can benefit from quantum computing techniques demonstrated in this project.

Source: Oak Ridge National Laboratory

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