FBH was a partner in the recently terminated  three-year research project "Error-Proof Bell-State Analyzer (ErBeStA)", which has been funded by the EU. The aim of this demanding project was to realize an analyzer for Bell states. Bell states are a concept from quantum information technology and describe states of quantum entangled particle pairs. An error-free analyzer for Bell states is a key component for optical quantum computers and quantum communication over long distances, e.g. via fiber optic cables. Its realization is be a milestone for all information technologies. High-precision time measurement, tap-proof communication and quantum cloud computing could also benefit from the development of such a component.

The network of seven European research institutions in Denmark, Great Britain, Austria and Germany combined new developments in the field of quantum optics and nanophotonics for this purpose. The strong non-linearities of Rydberg atoms or single quantum emitters coupled to optical micro-sounders were combined with microscopically small optical waveguide devices. Precise control of the light propagation on the scale of the wavelength of the light was the prerequisite for this technological breakthrough.

FBH contributed its expertise in the field of process technology to this highly topical research subject. Optical microresonators and waveguides were produced in the cleanroom using modern lithography and etching processes. By using stepper lithography, structures with smallest dimensions of 400 nm can be produced. For even smaller dimensions, an electron beam lithography system is available that allows structure dimensions of down to 50 nm. The structures generated in a photoresist were then transferred to the optical material using adapted plasma etching processes. For this project, the use of low-damping silicon oxides has been being investigated as an optical material, with which losses can be kept to a minimum. A particular challenge has been to remove the tiny structures from the wafer so that the light guided through the wafer is not attenuated and a sufficiently strong connection between the optical components and the wafer is maintained. The component is mechanically so stable that it can be used not only in laboratory set-ups, but also in commercial assemblies.

The components developed at FBH were extensively optically characterized and tested in close cooperation with the project partners.