In quantum chemistry, it is important to estimate an energy gap between a ground state and an excited state of molecular Hamiltonians. In previous researches, it was necessary to measure the energy of the ground state and that of the excited state separately, and the energy gap was estimated from the subtraction between them. Here, we show a novel scheme to estimate such an energy gap in a more direct manner. We use a concept of a Ramsey type measurement in the quantum annealing (QA) for such a direct estimation of the energy gap. In our scheme, the measured signal oscillates with a frequency of the energy gap. To study the performance of our scheme, we perform numerical simulations. The results show our scheme is robust against non-adiabatic transitions between the ground state and first excited state. Our scheme paves the way for the practical application of QA in quantum chemistry.

在量子化学中，重要的是估计分子哈密顿量的基态和激发态之间的能隙。在以前的研究中，有必要分别测量基态和激发态的能量，并且根据它们之间的相减来估算能隙。在这里，我们展示了一种新颖的方案，可以更直接的方式估算这种能隙。我们在量子退火（QA）中使用Ramsey类型测量的概念来直接估计能隙。在我们的方案中，被测信号以能隙的频率振荡。为了研究我们方案的性能，我们进行了数值模拟。结果表明，我们的方案对基态和第一激发态之间的非绝热跃迁具有鲁棒性。