Experimental analysis of qudit entangled states using the time-energy degree of freedom

Since the first experimental demonstration of entanglement [1], many applications employing this peculiar quantum feature have emerged. For example, the provable secure communication has been one of the main motivations for the field of quantum communication. In order to achieve high transmission bandwidths for today´s telecommunication networks, entangled systems of increasing complexity become necessary [2]. Higher dimensional, i.e. qudit entangled states, offer a unique possibility in order to pursue this goal. For example, their lower sensitivity to noise allows increasing the security threshold and correspondingly the transmission distance for common quantum cryptography protocols. Similarly, the number of quantum information carriers required for performing any quantum algorithm could be decreased with respect to the qubit case [3].