The Quantum Communication Systems BMBF junior research group led by Dr. Tobias Heindel seeks to develop completely secure communication systems. The research team was awarded a budget of approximately two million euros by the Federal Ministry of Education and Research in 2018.
The team can now point to its first successes in developing secure data transfer using quantum light sources. Its findings have already been published in a number of renowned journals.
“We are in the process of optimizing and further developing quantum key distribution in such systems,” says Heindel. The research results could be incorporated in future quantum networks, leading to a decisive improvement in performance.
Heindel is awarded this year’s Karl-Scheel-Preis by the German Physics Society Berlin.
If we take the often-quoted secure connection between Alice (sender) and Bob (receiver) as a model, then the research team has been working on both sides of the system. The team addressed the interaction between Alice and Bob in a recently published work in the Nature Partner journal npj Quantum Information.
“We recently examined how Bob has to measure to achieve the most secure possible data rate,” explains Heindel.
The research group developed an experiment which uses single-photon sources for quantum communication. What makes this so interesting is that single photons, unlike laser pulses, can considerably increase the rate of transfer for quantum communication. “Our results have shown that a special two-dimensional filter has to be used for Bob to achieve minimal quantum bit error rates while still being able to use the majority of the single photon signals,” Heindel says by way of explanation.
In addition, the researchers were able to use their method to measure the photon statistics, in other words the temporal distribution of single light quanta within the quantum channel, directly during key generation, thus providing a more effective means to counter eavesdropping. The researchers also plan to test their findings in a telescope connection between buildings at TU Berlin in the near future. “The telescope module we require for this is currently being constructed,” says Timm Kupko, one of the doctoral students in Heindel’s team.
“We have also been working on the sender, Alice as it were. Here, we have been looking at ‘bullseye’ resonators, so called as their structure resembles a dartboard measuring just some micrometers, containing a quantum emitter at their center. Our focus was on optimizing the structures computationally to enable the photons to be directly coupled into those fiber optics which are compatible with internationally used fiber optic networks. These simulated devices deliver a 95 percent photon decoupling efficiency. This has enabled the researchers to demonstrate in their calculations that the majority of photons can be coupled into the fiber optics, without a further optic having to be interposed. “Team member Lucas Rickert is currently creating the first quantum light sources of this type in the clean room at TU Berlin's Center of Nanophotonics," states Heindel.
The junior research group is working closely with the Chair of Optoelectronics and Quantum Devices led by Professor Dr. Stephan Reitzenstein in the development of these quantum devices. The two groups recently jointly published a review discussing the different processes which can be used for scalable production of solid state quantum light sources - in other words the core of Alice. What makes these "deterministic" technologies interesting is that they combine the high performance of quantum light sources with a high utilization of devices. “An essential step if we consider the actual application,” says Heindel.
In the future, the researchers will be strengthening their focus on the processes of quantum communication beyond a direct point-to-point connection and addressing more complex issues than the mere sharing of a secure key between two parties. “We are working together with Freie Universität Berlin, Humboldt Universität zu Berlin and a number of non-university research institutions in Berlin and Brandenburg to develop a Berlin-wide quantum network,” says Heindel focusing on the project’s ambitious plans for the future.
Tobias Heindel is awarded this year’s Karl-Scheel-Preis by the Physics Society Berlin for his outstanding research work in recent years. This prize has been awarded for more than 50 years for outstanding scientific achievement in the years immediately following a doctorate undertaken primarily at research institutions in Berlin or Brandenburg. The prize, worth 5,000 euros, is awarded to Heindel on 26 June 2020 in the Magnus-Haus Berlin.
The junior research group is funded through the “QuSecure project (funding number: 13N14876) as part of the BMBF’s “Photonik Forschung Deutschland” program.