“…The term "flashing ratchets" refers to the case of molecules diffusing in a potential with space-time periodic switches and diffusion of size comparable to the period of the potential. Following the setting proposed in [13,14,27,29] (see [20] for another), the molecules are presented by the density n ε (x, t) which evolves by the Fokker-Planck equation ⎧ ⎨ ⎩ n ε,t − εn ε,xx − W y ( x ε , t ε )n ε x = 0 in x ∈ (0, 1) × R, εn ε,x + W y ( x ε , t ε )n ε = 0 at x = 0, 1 and t ∈ R, n ε is ε -periodic in t, n ε > 0, and 1 0 n ε (x, t)dx = 1 for all t ∈ R, (1.1) which is a Floquet eigenproblem that has a unique positive solution (up to multiplication by a constant which explains the unit mass normalization).…”