MEIGNANT Clément
Supervision : Damian MARKHAM
Cosupervision : GROSSHANS Frédéric
Multipartite communications over quantum networks
The field of quantum networks is currently a major area of investigation in quantum technologies. Research is ongoing at all levels. On the theoretical level, to characterize what a quantum network is and to define appropriate figures of merits. On the implementation level, to define the protocol specifications which should be applied to global networks. On the concrete level, to actually build quantum networks. One of the simplest acts of quantum communication, the distribution of a single bipartite entangled state, has been highly studied as it is a simple problem to characterize, simulate and implement. It is also useful for a prominent quantum network application: the secured distribution of a cryptographic key.
However, the use of quantum networks goes far beyond. A realistic quantum network theory should take into account the multiple simultaneous distributions which will happen over global networks. A complete quantum network theory should take into account the distribution of multipartite entangled states as they are useful for many quantum information applications, such as secret sharing. Thus, the use of quantum networks to their full extent implies the need to study the simultaneous distribution of multipartite states over quantum networks. In this manuscript, we report on several works of progress in the domain. We first study the recycling of previously distributed resources in the asymptotic regime by the use of entanglement combing and quantum state merging. Then, we study and solve the problem of a fundamental network bottleneck by using a particular formalism used across quantum information, the matrix product state formalism. Using this result, we characterize the distribution of quantum states using the tensor network formalism. We also characterize a broad class of classical distribution protocols using this formalism. We use this similarity to compare the distribution of classical correlations over classical networks to the distribution of quantum state over quantum networks. We show the existence of a classical protocol which implies the existence of a quantum one but not the converse. We also build protocols to distribute specific classes of states over quantum networks such as graph states and GHZ states by using the graph state formalism and a bit of graph theory. Finally, we implement the previous protocols in a more realistic setting and participate in the elaboration of multipartite features for a quantum network simulator: QuISP. We also aimed to popularize and disseminate the notions of quantum information to a broad audience. We report on the creation of a video game based on quantum optics, adding to the existing vulgarization ludography. To develop it, we used several mechanisms known in the gamebased learning literature and will test its impact on the broad audience in the next few months. We hope these results will be beneficial to the quantum network theory, for both research and diffusion to the public.
Defence : 12/17/2021  10h  Campus Pierre et Marie Curie, salle Jacques Pitrat (2526/105)
Jury members :
Murao Mio, Professor, University of Tokyo, [Rapporteur]
Dür Wolfgang, Associate Professor, HDR, University of Innsbruck, [Rapporteur]
Grosshans Frédéric, Chargé de recherche au CNRS, HDR, Sorbonne Université
Markham Damian, Chargé de recherche au CNRS, HDR, Sorbonne Université
Perdix Simon, Directeur de recherche, InriaMocqua, Loria
PotopButucaru Maria, Professeure, Sorbonne Université
20192021 Publications

2021
 C. Meignant : “Multipartite communications over quantum networks”, thesis, defence 12/17/2021, supervision Markham, Damian, rapporteurs : GROSSHANS Frédéric (2021)
 C. Meignant, F. Grosshans, D. Markham : “Classicalquantum network coding: a story about tensor”, (2021)
 R. Booth, A. Kissinger, D. Markham, C. Meignant, S. Perdrix : “Outcome determinism in measurementbased quantum computation with qudits”, (2021)

2019
 C. Meignant, D. Markham, F. Grosshans : “Distributing Graph States Over Arbitrary Quantum Networks”, Physical Review A, vol. 100, pp. 052333, (American Physical Society) (2019)
 L. Ostermann, C. Meignant, C. Genes, H. Ritsch : “Super and subradiance of clock atoms in multimode optical waveguides”, New Journal of Physics, vol. 21 (2), pp. 025004, (Institute of Physics: Open Access Journals) (2019)