A future quantum network [1,2] will consist of quantum processors that are connected by quantum channels, just as conventional computers are interconnected to form the Internet. Unlike classical devices, however, the information that can be encoded in a quantum network grows exponentially with the number of nodes, and the entanglement of remote particles gives rise to non-local correlations. Exploring these effects not only facilitates fundamental tests of quantum theory, but also paves the way for quantum technologies that outperform their classical counterparts. In particular, quantum networks aim to enable distributed quantum information processing, which will radically improve computational power, unbreakable encryption over global distances, and precision sensing.

In the last decade, first prototypes of elementary quantum networks have been demonstrated [3] and entanglement between remote qubits has been generated via the exchange of photons, achieving rates of <0.1 Hz and fidelities of ~70% over ~30 km of optical fiber [4–6]. To harness the full potential of quantum networks, the challenge now is to scale these prototypes to more network nodes, to larger qubit registers per node, to longer distances and higher fidelities. To this end, new technologies are required to overcome the scaling bottlenecks of the mentioned quantum network prototypes.

For this purpose, we are exploring entirely new material platforms with a high intrinsic scaling potential that is based on their direct compatibility with established technologies. In particular, we are examining quantum network nodes based on spin qubits encoded in erbium dopants in solids, which is the only known system that exhibits coherent transitions at a telecommunication wavelength [7], where loss in optical fibers is minimal. In addition, they exhibit exceptional spin and optical coherence in different host materials [8–11] .

This homepage contains more information about our research, the team and the opportunities offered in our group. In case of further questions, please contact us directly.

Funding is provided by the Technical University of Munich ,by the European Union, by the Cluster of Excellence MCQST and the Munich Quantum Valley, and by the DFG and the BMBF.

References:
[1] H. J. Kimble, The Quantum Internet, Nature 453, 1023 (2008).
[2] S. Wehner, D. Elkouss, and R. Hanson, Quantum Internet: A Vision for the Road Ahead, Science 362, eaam9288 (2018).
[3] A. Reiserer and G. Rempe, Cavity-Based Quantum Networks with Single Atoms and Optical Photons, Rev. Mod. Phys. 87, 1379 (2015).
[4] C. M. Knaut et al., Entanglement of Nanophotonic Quantum Memory Nodes in a Telecom Network, Nature 629, 573 (2024).
[5] T. van Leent et al., Entangling Single Atoms over 33 Km Telecom Fibre, Nature 607, 7917 (2022).
[6] J.-L. Liu et al., Creation of Memory–Memory Entanglement in a Metropolitan Quantum Network, Nature 629, 579 (2024).
[7] A. Reiserer, Colloquium: Cavity-Enhanced Quantum Network Nodes, Rev. Mod. Phys. 94, 041003 (2022).
[8] M. Rančić, M. P. Hedges, R. L. Ahlefeldt, and M. J. Sellars, Coherence Time of over a Second in a Telecom-Compatible Quantum Memory Storage Material, Nature Phys 14, 1 (2018).
[9] B. Merkel, A. Ulanowski, and A. Reiserer, Coherent and Purcell-Enhanced Emission from Erbium Dopants in a Cryogenic High-Q Resonator, Phys. Rev. X 10, 041025 (2020).
[10] A. Gritsch, L. Weiss, J. Früh, S. Rinner, and A. Reiserer, Narrow Optical Transitions in Erbium-Implanted Silicon Waveguides, Phys. Rev. X 12, 041009 (2022).
[11] A. Gritsch, A. Ulanowski, J. Pforr, and A. Reiserer, Optical Single-Shot Readout of Spin Qubits in Silicon, arXiv:2405.05351 (2024).