Quantum collision-resistance of non-uniformly distributed functions (QCrypt 2015)
Ehsan Ebrahimi Targhi, Gelo Noel Tabia, Dominique Unruh
[ official ]

We study the quantum query complexity of finding a collision for a function $f$ whose outputs are chosen according to a distribution with min-entropy $k$. We prove that $Ω(2^{k/9})$ quantum queries are necessary to find a collision for function f.