Fig. 2. QRM energy spectrum and SUSY.

a Theoretical energy gaps between the ground state and the first two excited states as a function of r in Eq. (2). b Experimentally measured energy gaps. At r = 0, the system is supersymmetric with a unique bosonic ground state and degenerate first and second excited states for the bosonic and the fermionic modes. As r → 1, the Hamiltonian approaches the other supersymmetric point, but the unique ground state disappears and the lowest bosonic and fermionic states become degenerate, which indicates a spontaneous SUSY breaking. c, d The resonant signals probed by a weak pulse for energy gaps at r = 0 and r = 0.3, respectively. The solid blue curves are the theoretical results and the red dots are the measured data, which are fitted by multiple Gaussian functions as the dashed orange curves to extract the peak locations.