Non-classical photon sources are a key component of quantum communication technologies. In contrast to classical light sources, which emit many photons per time interval, they should only emit single photons – but as frequently as possible to enable high data transfer rates. However, these two requirements contradict each other, since a high emission rate also leads to an increased probability of several photons being emitted at the same time. Since the exact times of emission of the individual photons are often unknown, physical processes are used to create correlated photon pairs. If one of the photons is detected, it is highly probable that another photon was generated at the same time, which can be used for quantum communication.
Within the framework of the EU network the TU researchers and their colleagues have now been able to realise a non-classical photon pair source for the first time by coupling cold atoms to a hollow fibre. By strongly spatially confining atoms and light fields to a few micrometres within the fibre, the source could be made so efficient at very low pump power that the maximum possible generation rate was achieved, at which successive photon pairs begin to overlap in time. “Light-Matter Interfaces for Quantum Enhanced Technologies”,
Alexander Bruns, Chia-Yu Hsu, Sergiy Stryzhenko, Enno Giese, Leonid P. Yatsenko, Ite A. Yu, Thomas Halfmann, Thorsten Peters: Ultrabright and narrowband intra-fiber biphoton source at ultralow pump power, Quantum Science and Technology 8, 015002, 2023, https://doi.org/10.1088/2058-9565/ac985c