Fig. 4: Secular and nonsecular effects.

a Relative modification of the \(\rho _{J_0M_0,J_0 + 2M_0}(t)\) coherence for J₀ = 15 induced by collisional transfers from the coherences \(\rho _{J_1M_1,J_1 + 2M_1}(t)\) with J₁ = 17 (black), J₁ = 19 (red), J₁ = 21 (green), and J₁ = 23 (blue), all normalized to unity at t = 0. This simple modeling (see Supplementary Note 2) of coherence transfers considering only few rotational states around the most populated state of N₂O at 300 K reveals that during the short time evolution of the system, exchanges between coherences are efficient, which slow down the decay of the alignment factor with respect to what would be obtained using the secular approximation that neglects these collisional transfers and only takes the losses into account. b, c Computed real and imaginary parts of the \(\rho _{JM = 0,J + 2M = 0}(t)\) coherences for N₂O in He at 33 amagat, obtained using the nonsecular (full lines) and secular (dashed lines) models.