Fig. 5: One-way excitation transfer process.

a Excitation transfer process when an excitation is initially injected into the leftmost resonator A₁. b Excitation transfer process when an excitation is initially injected into the rightmost resonator A_M. The nearest-neighbor couplings J₁ and J₂ are governed by the scheme of tangent modulation with the modulation amplitude λ = 1, the free parameter \(\xi =\frac{\pi }{2}+0.4\), and the total evolution time τ = 135. The inset in (b) shows the finial excitation population for the initial rightmost excitation and it is obvious that there is almost no output from the leftmost resonator A₁.