  Dimension witnesses allow one to test the dimension of an unknown physical
system in a device-independent manner, that is, without placing assumptions
about the functioning of the devices used in the experiment. Here we present
simple and general dimension witnesses for quantum systems of arbitrary Hilbert
space dimension. Our approach is deeply connected to the problem of quantum
state discrimination, hence establishing a strong link between these two
research topics. Finally, our dimension witnesses can distinguish between
classical and quantum systems of the same dimension, making them potentially
useful for quantum information processing.
