Information is physical, for example, encoded in the tiny voltages in our computers. Changing the physical system that we use for encoding information from classical to quantum opens up far greater capabilities, including for example, secure communication and powerful computation. We are interested in bringing these possibilities closer to reality.
Qudit is short for quantum dit. In contrast to the more familiar qubit—quantum bit—which can encode quantum information over two levels, a qudit can encode quantum information over many levels. Think quantum alphabet.
For quantum communication, qudits lead to a higher information capacity and robustness against noise. Qudits also enable more complex simulation of quantum systems and more efficient quantum computation. Most importantly, quantum systems are naturally high-dimensional!
We use the transverse spatial mode—shape—of light as our qudit. In the same way that light comes in many colours, light can also come in different shapes. Combined with quantum phenomena such as entanglement, the shape of photons is an excellent candidate for encoding high-dimensional quantum information.