  We propose an experimental method for evaluating the adiabatic condition
during quantum annealing (QA), which will be essential for solving practical
problems. The adiabatic condition consists of the transition matrix element and
the energy gap, and our method simultaneously provides information about these
components without diagonalizing the Hamiltonian. The key idea is to measure
the power spectrum of a time domain signal by adding an oscillating field
during QA, and we can estimate the values of the transition matrix element and
energy gap from the measurement output. Our results provides a powerful
experimental basis for analyzing the performance of QA.
