Squarefree numbers in short intervals

We show that there exists $\eta > 0$ such that the interval $[X, X + X^{\frac 15 - \eta}]$ contains a squarefree number for all large $X$. This improves on an earlier result of Filaseta and Trifonov who showed that there is a squarefree number in $[X, X + cX^{\frac 15}\log X]$ for some $c > 0$ and all large $X$. We introduce a new technique to count lattice points near curves, which we use to bound in critical ranges the number of integers in a short interval divisible by a large square. This uses as an input Green and Tao's quantitative version of Leibman's theorem on the equidistribution of polynomial orbits in nilmanifolds.