The interaction between the (2,0) ⊕ ground state and the (1,1) ⊕ ground state generates a visible avoided crossing, in agreement with the experiment. In contrast, using the parameters above, the (2,0) 0 O rst-excited state in Fig. does not develop any avoided crossing with the (1,1) ⊕ ground-state curve. This is in remarkable agreement with the behavior of the experimental curves, suggesting that the valley-orbit coupling in the experimental device is either absent or rather weak.