Figure 2
From: Observation of Time Reversed Light Propagation by an Exchange of Eigenstates
Band structure spanned by the Bloch momentum \(Q\) and the temporal driving \(m\). For a better visibility, only the parts for \(Q\ge 0\) are shown of the otherwise symmetric band structure. For \(\phi =k\pi \), the band gaps close at \(Q=0\) and \(Q=\pi \), which releases the defect to the continuum. Each time the band gap closes, a transition from one band to the other is possible as indicated by the red and brown arrows. The taken path depends on the geometrical relation between the eigenvectors. Changing the band (red curve) inverts the population, and thus starts a time reversal. The right panel depicts the dispersion relation depending on the parameter \(\phi \) of the temporal driving for \(Q=0\).
