Our lab focuses on quantum computation using the technology of single and entangled photon sources based on spontaneous parametric down-conversion in bulk non-linear crystals. We use single photons and their various degrees of freedom to investigate the diverse aspects of quantum computation.
Current investigations centre on the study of qudits — higher-dimensional quantum systems — leading into higher-dimensional quantum computing based on novel spatial degrees of freedom of a single photon. Rather than increasing the number of qubits (which becomes difficult beyond a certain point due to decoherence), we explore changing the base of the computation by using higher-dimensional units.
The quantum information and computation community is collectively working towards systems with large numbers of qubits in coherent superposition. As the exponential advantage of quantum computers scales as 2n where n is the number of qubits, more qubits means more speed-up — but it becomes increasingly difficult to increase n beyond a certain point due to the onset of decoherence.
An alternative approach is to change the base: instead of two-dimensional qubits, one can use higher-dimensional qudits where the "2" is replaced by 3, 4, 5 and so on. For a smaller n, one can then envisage a similar speed-up. In our lab, we are exploring a qudit architecture based on the spatial degree of freedom of a single photon.
