We describe a quantum PAC learning algorithm for DNF formulae under the uniform distribution with a query complexity of
O~(s3/ε+s2/ε2), where
s is the size of DNF formula and
ε is the PAC error accuracy. If
s and
1/ε are comparable, this gives a modest improvement over a previously known classical query complexity of
O~(ns2/ε2). We also show a lower bound of
Ω(slogn/n) on the query complexity of any quantum PAC algorithm for learning a DNF of size
s with
n inputs under the uniform distribution.
We generalize the notion of probably approximately correct (PAC) learning from an example oracle to a notion of efficient learning on a quantum computer using a quantum example oracle. This quantum example oracle is a natural extension of the traditional PAC example oracle, and it immediately follows that all PAC-learnable function classes are learnable in the quantum model. Furthermore, we obtain positive quantum learning results for classes that are not known to be PAC learnable. Specifically, we show that disjunctive normal form (DNF) is efficiently learnable with respect to the uniform distribution by a quantum algorithm using a quantum example oracle. While it was already known that DNF is uniform-learnable using a membership oracle, we prove that a quantum example oracle with respect to uniform is less powerful than a membership oracle.