Extended Data Fig. 5: Decay behaviour as a function of anisotropy.

a, b, Decay behaviour ranging from negative (a) to positive (b) anisotropy, for a fixed wavelength λ = 10.4a. Using Δ ≈ 0 as a reference point, we show how the temporal profile of the decay curve c(t) changes when we introduce positive or negative interactions. Every data point is an average of two measurements at lattice depths 11E_R and 13E_R. In a, from bottom to top: Δ = −0.12 (red), −0.59 (pink), −0.81 (yellow), −1.02 (blue), −1.43 (green) and −1.79 (purple). In b, from bottom to top: Δ = −0.13 (red), 0.08 (purple), 0.35 (pink), 0.55 (orange), 0.78 (yellow), 1.01 (blue), 1.27 (light blue) and 1.58 (green). Regardless of sign, for increasing |Δ| the decay always slows down and the revivals damp more quickly. However, there is a big difference in how this slowdown happens: for increasing positive interactions Δ > 0, the initial rate of decay decreases continuously (b); by contrast, for all negative interactions Δ < 0, the initial rate of decay stays constant (and is ballistic), coinciding with the Δ ≈ 0 case (a). It is only after a critical time t₀ that the decay suddenly starts slowing down (and becomes diffusive) for times t > t₀. This critical time t₀ decreases with increasing negative interaction strength |Δ|.