Using the full capabilities of the Quantinuum H1-1 quantum computer, researchers from the Department of Energy’s Oak Ridge National Laboratory not only demonstrated best practices for scientific computing on current quantum systems, but also produced an intriguing scientific result. ORNL team members applied three independent strategies to decrease their project’s computational workload, which reduced their time to solution from months to a few weeks. First, in a technique called qubit tapering, they decreased the number of qubits required to express the problem, reducing the size of the problem itself. Second, they took fewer measurements to solve the problem by measuring groups of terms once rather than measuring each individual term from every group (a process called qubit-wise commutativity). Third, instead of implementing each circuit individually, they found a way to run four circuits in parallel, allowing them to use all 20 qubits in the H1-. By using a quantum computer to model singlet fission — in which absorption of a single photon of light by a molecule produces two excited states — the team confirmed that the linear H4 molecule’s energetic levels match the fission process’s requirements. The linear H4 molecule is, simply, a molecule made of four hydrogen atoms arranged in a linear fashion.
A molecule’s energetic levels are the energies of each quantum state involved in a phenomenon, such as singlet fission, and how they relate and compare with one another.
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