Dr. Y. Ismail
BSc (Physics, Chemistry), BSc (Hons) (Physics), MSc (Physics), PhD (Physics)
Quantum communication exploits some of the fundamental features of the quantum world, namely, the superposition principle and the Heisenberg uncertainty relation. One of the most advanced quantum information related technology at present is Quantum Key Distribution (QKD) which is a process that involves transmitting a secret key between two individuals. Aimed at secure data transfer for longer periods of time. The most vital characteristic of such a method is that the secrecy of the generated key is guaranteed by the laws of nature.
The key distribution process is achieved by the use of quantum carriers in the form of single photons which can be encoded making use of phase by means of states carrying orbital angular momentum or through polarisation. This process comprises of two channels, a quantum channel for the encoding and a classical channel for the post processing. The quantum channel can be chosen to either be an optical fibre or free-space whilst the classical channel is an internet connection. The choice of the quantum channel dictates the type of encoding used the key distribution process.
Although states carrying orbital angular momentum expands infinite state space, they suffer from severe breakdown of the phase when propagating through the atmosphere. Its if for this reason, that it is appropriate to use polarisation for the encoding when considering a free-space channel.
The key distribution process can be exploited by making using entanglement since it offers greater security to the system. One method of obtaining entanglement, using single photons, lies in the successful implementation of a second-order nonlinear process which is referred to as spontaneous parametric down conversion (SPDC).
Free-space QKD systems introduces its own challenges which are due to turbulence within the atmosphere.The development of these systems however, is of importance for the advancement of ground to ground communication in areas where an optical fibre network is non-existent.
Quantum Research Group
H-Block, Room H3-100
School of Physics
University of KwaZulu-Natal
Tel: +27 31 260 2809