Published online by Cambridge University Press: 13 March 2018
We show that there is an irrational rotation $Tx=x+\unicode[STIX]{x1D6FC}$ on the circle
$\mathbb{T}$ and a continuous
$\unicode[STIX]{x1D711}:\mathbb{T}\rightarrow \mathbb{R}$ such that for each (continuous) uniquely ergodic flow
${\mathcal{S}}=(S_{t})_{t\in \mathbb{R}}$ acting on a compact metric space
$Y$, the automorphism
$T_{\unicode[STIX]{x1D711},{\mathcal{S}}}$ acting on
$(X\times Y,\unicode[STIX]{x1D707}\otimes \unicode[STIX]{x1D708})$ by the formula
$T_{\unicode[STIX]{x1D711},{\mathcal{S}}}(x,y)=(Tx,S_{\unicode[STIX]{x1D711}(x)}(y))$, where
$\unicode[STIX]{x1D707}$ stands for the Lebesgue measure on
$\mathbb{T}$ and
$\unicode[STIX]{x1D708}$ denotes the unique
${\mathcal{S}}$-invariant measure, has the property of asymptotically orthogonal powers. This gives a class of relatively weakly mixing extensions of irrational rotations for which Sarnak’s conjecture on the Möbius disjointness holds for all uniquely ergodic models of
$T_{\unicode[STIX]{x1D711},{\mathcal{S}}}$. Moreover, we obtain a class of ‘random’ ergodic sequences
$(c_{n})\subset \mathbb{Z}$ such that if
$\boldsymbol{\unicode[STIX]{x1D707}}$ denotes the Möbius function, then
$$\begin{eqnarray}\lim _{N\rightarrow \infty }\frac{1}{N}\mathop{\sum }_{n\leq N}g(S_{c_{n}}y)\boldsymbol{\unicode[STIX]{x1D707}}(n)=0\end{eqnarray}$$
${\mathcal{S}}$, all
$g\in C(Y)$ and
$y\in Y$.