Quantum Communication with Higher Alphabets

The proposed project promises novel insights in the future technology of quantum information. The field of quantum information, including quantum computing, communication and cryptography, has attracted the attention of the scientific community and the interest of industry due to the development of experimental means to not only implement the quantum bits (or q-bits), but also compute and measure them. The very heart of the field lies in the study of the fundamental information carried by a quantum system. The prototypical case is the single q-bit. In contrast to the classical bit of information, which can only be in a state `1` or `0`, the q-bit is a quantum superposition of both states and may therefore carry more information. The quantum character of the q-bits makes them suitable for quantum communication and quantum cryptography. Recently, it has been shown that the use of other levels than two (multidimensional states or q-Nits) improves the security and efficiency in quantum cryptography. Altogether, the study of the quantity of information carried by this q-Nits brings new insights into the formal definition of the information in a quantum system. The main experiment proposed in the project is a proof-of-principle of a quantum cryptography system with a higher dimensional alphabet. We will investigate the possibilities of multidimensional states based on the entangled orbital angular momentum state of light and their applications for the future technologies of quantum information. So far, most experiments in this field were performed with bidimensional states (q-bits). The potential of innovation of the proposed project is focused on the emerging technology of quantum information. A high impact on other fundamental issues of quantum experiments, like the quantum description of light, is expected.