A breakthrough for long-distance quantum communication
Quantum technologies offer various paths of experimentation and innovation. Merging conceptual and technological expertise, the EU-funded ErBeStA project developed cutting-edge components for optical quantum technologies, expanding the potential of pairs of entangled light particles for quantum communication. ErBeStA’s overall objective was to make a decisive contribution towards realising the grand vision of a ‘quantum internet’. A key component for realising universal optical quantum computers as well as for building efficient quantum repeaters, which are a prerequisite for long-distance quantum communication, is an error-proof optical Bell-state analyser. Building such a device, which can measure the state of a pair of photons in an entangled-state basis, has always been a key challenge for quantum scientists. In particular, it requires an optical non-linearity at the level of single photons, achieved by the strong coupling of light to individual single photon emitters. Within ErBeStA, three different systems of single photon emitters were used: cold atoms, Rydberg superatoms and solid-state quantum emitters. To achieve strong coupling to light fields, nanophotonics was employed.
Crossing the frontiers of nanophotonics
“In the course of the project, we obtained a number of important results in the field of quantum networks and advanced optical circuitry,” states project coordinator Arno Rauschenbeutel from Humboldt University of Berlin. ErBeStA gave rise to the development of novel and improved types of quantum light sources, to novel non-reciprocal optical elements (i.e. elements that treat light differently when propagating forwards or backwards), to novel photon number-resolving photodetectors, and to novel single-photon emitters. All these advancements are paramount for (quantum) optical technologies. On the nanophotonics side, several technologies for the fabrication of nanosized waveguides for enhanced light-matter interactions were developed. Beyond pure scientific interest, these are a crucial component for various novel and innovative applications, such as quantum sensing devices or optical switches that are operated by a single atom. “We are convinced that in the future, these structures will facilitate new opportunities in quantum science and technology,” adds Rauschenbeutel.
Ground-breaking and impactful quantum technology solutions
To advance the field of compact quantum technologies, 3D-printed spectroscopy and laser light-distribution systems together with the world’s first 3D-printed vacuum chamber were developed and implemented. “These printed systems might be a solution for the anticipated widespread use and large impact of quantum technologies for sensing applications. Moreover, they hold the promise of providing a clear pathway for miniaturisation and expanded functionality,” explains Rauschenbeutel. At the conceptual level, ErBeStA made many novel discoveries applicable to future technologies and new research directions. Theoretically studying atomic emitters coupled to a waveguide, the researchers have substantiated the potential of integrated emitter-waveguide systems for the exploration of collective quantum phenomena and the generation of squeezed states for quantum-enhanced metrology. They have also studied light propagation and non-linearities in Rydberg superatoms. There, they could show how the latter can be used to perform photon-sorting operations (i.e. to separate light pulses that contain two photons from those that contain a single photon) and how this will allow for a Bell-state analyser without the need of non-reciprocal elements. Moreover, the team has developed a new approach which uses two-dimensional atomic arrays (so-called ‘quantum mirrors’) to achieve deterministic photon sorting and Bell-state analysis. The conceived schemes currently present the only deterministic methods that can be applied in passive operation, i.e. without prior knowledge of the arrival time of the photons.
Keywords
ErBeStA, bell state analyser, quantum emitters, long-distance quantum communication, nanophotonics, quantum technology
