  Photons with a twisted phase front can carry a discrete, in principle
unbounded amount of orbital angular momentum (OAM). The large state space
allows for complex types of entanglement, interesting both for quantum
communication and for fundamental tests of quantum theory. However, the
distribution of such entangled states over large distances was thought to be
infeasible due to influence of atmospheric turbulence, indicating a serious
limitation on their usefulness. Here we show that it is possible to distribute
quantum entanglement encoded in OAM over a turbulent intra-city link of 3
kilometers. We confirm quantum entanglement of the first two higher-order
levels (with OAM=$\pm 1 \hbar$ and $\pm 2 \hbar$). They correspond to four new
quantum channels orthogonal to all that have been used in long-distance quantum
experiments so far. Therefore a promising application would be quantum
communication with a large alphabet. We also demonstrate that our link allows
access to up to 11 quantum channels of OAM. The restrictive factors towards
higher numbers are technical limitations that can be circumvented with readily
available technologies.
