Leader: Dr. Andreas Reiserer
A future quantum network [1,2] will consist of quantum processors that are connected by quantum channels, just like conventional computers are wired up to form the Internet. In contrast to classical devices, however, the information that can be encoded in a quantum network grows exponentially with the number of nodes, and entanglement of remote particles gives rise to non-local correlations. Exploring these effects facilitates fundamental tests of quantum theory and the quantum-to-classical transition. In addition, quantum networks will enable applications in precision sensing and in distributed quantum information processing, which will fundamentally enhance computational power and ensure unbreakable encryption over global distances.
Pioneering experiments with atomic ensembles , single trapped atoms [2,4] and solid-state spins  have demonstrated the connection and entanglement of two quantum nodes separated by up to 1.3 km. However, accessing the full potential of quantum networks requires scaling of these prototypes to more network nodes and even larger distances. To this end, a new technology that overcomes the bottlenecks of existing physical systems has to be developed.
The “Quantum Networks Group” will investigate novel quantum systems in this context. The group will focus on individual rare-earth ions in optical resonators, a solid-state platform with exceptional coherence properties  that has unique potential towards this end.
- Kimble: The quantum internet. Nature 453, 1023–1030 (2008).
- Reiserer and Rempe: Cavity-based quantum networks with single atoms and optical photons. Rev. Mod. Phys. 87, 1379–1418 (2015).
- Sangouard et al.: Quantum repeaters based on atomic ensembles and linear optics. Rev. Mod. Phys. 83, 33–80 (2011).
- Duan and Monroe: Quantum networks with trapped ions. Rev. Mod. Phys. 82, 1209–1224 (2010).
- Hensen, Reiserer et al.: Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres. Nature 526, 682–686 (2015).
- Zhong, et al.: Optically addressable nuclear spins in a solid with a six-hour coherence time. Nature 517, 177–180 (2015).