Adversary Lower Bound for the k-sum Problem
  We prove a tight quantum query lower bound $\Omega(n^{k/(k+1)})$ for the problem of deciding whether there exist $k$ numbers among $n$ that sum up to a prescribed number, provided that the alphabet size is sufficiently large.   This is an extended and simplified version of an earlier preprint of one of the authors arXiv:1204.5074. 
Aleksandrs Belovs and Robert Spalek
quant-ph cs.CC