Is the quantum state real – a property of the system it is assigned to? Or does it represent only our (incomplete) knowledge of the system? It is possible that the second alternative – the epistemic character of the quantum state – comes about because quantum mechanics is obtained by some statistical averaging over a “complete” theory of nature. Such models are often called “hidden variable” models, because the true variables describing the system, the ontic state, are not accessible. Recently Pusey, Barrett and Rudolph [1] showed that, assuming the natural assumption of “preparation independence”, epistemic models of the quantum state are in contradiction with the predictions of quantum theory. “Preparation independence” means that independent preparations of systems correspond to a joint distribution (over the ontic states) is the product of individual distributions. Here we adopt a different approach. We show that, assuming both a form of continuity and separability (a weak form of preparation independence), epistemic interpretations of the quantum state are in contradiction with quantum theory. We also discuss some implications of “hidden-variable” models for cryptography. We then describe a simple high-precision experiment optics experiment that tests some of the predictions of continuous and separable epistemic models. The experiment is particularly simple. It involves attenuated coherent states in time bins of dimension up to 80 propagating in optical fibres. Our experimental results are in agreement with the predictions of quantum theory and provide strong constraints on possible epistemic extensions of quantum mechanics. These results are reported in [2]. [1] M. F. Pusey, J. Barrett, and T. Rudolph, On the reality of the quantum state, Nature Physics, 2309, (2012). [2] M. K. Patra, L. Olislager, F. Duport, J. Safioui, S. Pironio and S. Massar, Experimentally probing the reality of the quantum state, submitted (2012)