Quantum Computer Simulates Excited States of Molecule

One of the most promising and practical applications of quantum computing is quantum chemistry, in which the properties of molecules and materials are calculated from first principles. Compared with classical computers, quantum devices are expected to eventually perform quantum chemistry calculations more quickly and accurately, and they are also expected to handle much larger molecules. This quantum speedup could lead to the design and discovery of new pharmaceuticals, materials, and industrial catalysts. Fortunately, the pace of progress has exceeded expectations. In the last few years, researchers have used various quantum devices comprised of a few quantum bits (or “qubits”) to compute the ground-state energies of molecules, such as H2 and BeH2 [2–6]. Another important frontier is the simulation of excited states, which are fundamental to understanding a molecule’s absorption and emission of light as well as its chemical reactivity. James Colless of the University of California, Berkeley, and co-workers have advanced towards this goal by simulating the excited states of the hydrogen molecue H2 on a two-qubit processor (Fig. 1).