# Quantum Networks

Quantum networks are complex quantum systems where resources such as entanglement, non-locality and randomness can be distributed to both study a wide range of fundamental questions as well as be exploited for future applications. The demonstration of applications requires bringing a wide range of quantum technologies together to make a functional system - quantum system integration. We also look at developing the tools and technologies for certification of these complex quantum systems.

Quantum networks and networking is one of the central themes in our group. Central to these endeavours are the concepts of entanglement, nonlocality and randomness - we see these as a resource and providing the foundations for both diverse quantum applications and fundamental tests. We are working on different types of entanglement and different systems to demonstrate this, not only in the lab but also with the view that, to be useful, it has to survive in the real world. This requires making some compromises, but often, this has also pushed us towards new and exciting directions and opens up opportunities to perform foundational experiments, or on the other end of the spectrum, industrialise quantum technologies.

We are working on multiphoton and multipartite entangled systems, as well as approaches to device-independent and self-testing quantum systems, all addressing the challenges of real-world network deployment. We are also looking into efficient methods for the certification of entanglement in large multipartite and distributed scenarios such as networks, where increasing distances and complexity present significant challenges.

Some key publications are:

- Entanglement swapping between independent and asynchronous integrated photon-pair sources, F. Samara, N. Maring, A. Martin, A. Raja, T. Kippenberg, H. Zbinden and R. T. Thew,
*Quantum Sci. Technol.*x 2058 (2021) - Heralded Distribution of Single-Photon Path Entanglement, P. Caspar, E. Verbanis, E. Oudot, N. Maring, F. Samara, M. Caloz, M. Perrenoud, P. Sekatski, A. Martin, N. Sangouard, H. Zbinden, and R. T. Thew, Phys. Rev. Lett.
**125**, 110506 (2020) - Heralded amplification of path entangled quantum states, F. Monteiro, E. Verbanis, V. Caprara Vivoli, A. Martin, N. Gisin, H. Zbinden and R. Thew, Quantum Science and Technology,
**2**, 024008 (2017). - Demonstration of Einstein-Podolsky-Rosen Steering Using Single-Photon Path Entanglement and Displacement-Based Detection, T. Guerreiro, F. Monteiro, A. Martin, J. Brask, T. Vértesi, B. Korzh, M. Caloz, F. Bussières, V. B. Verma, A. E. Lita, R. P. Mirin, S. W. Nam, F. Marsilli, M. D. Shaw, N. Gisin, N. Brunner, H. Zbinden and R. Thew, Physical Review Letters,
**117**, 070404 (2016) - Resource-Efficient Measurement-Device-Independent Entanglement Witness, E. Verbanis, A. Martin, D. Rosset, C. C. W. Lim, R. Thew and H. Zbinden, Physical Review Letters,
**116**, 190501 (2016)

**Contact:** Rob Thew