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Selected Publications

G. Sorelli, M. Gessner, M. Walschaers, and N. Treps, Quantum limits for resolving Gaussian sources, Phys. Rev. Research 4, L032022 (2022).
 M. Walschaers, NonGaussian Quantum States and Where to Find Them, PRX Quantum 2, 030204 (2021).

M. Walschaers, V. Parigi, and N. Treps, Practical Framework for Conditional NonGaussian Quantum State Preparation, PRX Quantum 1, 020305 (2020)
 M. Walschaers, C. Fabre, V. Parigi, and N. Treps, Entanglement and Wigner function negativity of multimode nonGaussian states, Phys. Rev. Lett. 119, 183601 (2017).
Bio
Current work
NonGaussian quantum correlations
In continuous variable systems, quantum correlations have been studied in great detail for Gaussian states. Many of the Gaussian techniques can be applied to also detect certain instances of quantum correlations in nonGaussian states. However, nonGaussian states provide much more structure than what can be captured in a covariance matrix. In our group, we try to understand quantum correlations in nonGaussian states exactly where Gaussian techniques fail. This notably leads us to investigate quantum states with entanglement that survives in every mode basis or under every Gaussian unitary transformations.
Techniques used: (Quantum) Fisher information, Wigner functions, stellar representation, convex analysis, neural networks, …
Quantum computational advantages
In some recent work, we showed that any boson sampling setup can be strongly simulated by one of several coherent state samplers. This allows us to study the resources needed for reaching a quantum computational advantage all on the level of the state. Understanding the hardness of boson sampling problems thus boils down to understanding for which quantum states it is computationally hard to sample from the Husimi Qfunction. We use this approach to study the physical resources that are required to reach a quantum computational advantage with bosonic systems.
Techniques used: NonGaussian entanglement, coherent state sampling, stellar representation, Markov chain, …
Quantum(inspired) parameter estimation
[Under construction]
Previous work
PhD work
Mattia Walschaers got his PhD from the universities of Freiburg (Germany) and Leuven (Belgium) for a cotutelle project, supervised by Andreas Buchleitner and Mark Fannes. His work initially focused on the role of quantum effects in photosynthesis, where he developed analytically solvable toy models to better understand the role of disorder in coherent transport of photosynthetic excitons. Later on, his attention shifted to dynamical features of manyparticle systems and he spent a big part of the final years of his PhD project working on manyparticle interference a phenomenon which induced by indistinguishability of quantum particles. This ultimately led to the development of an experimentally implementable statistical benchmark for boson sampling.
The resulting dissertation was published as a book in the Springer Theses series, and it was also one of the four nominees for the SAMOP dissertation prize of the German Physical Society.
Postdoc
From 2016 until 2019, Mattia was a postdoctoral researcher in multimode quantum optics group of the Laboratoire Kastler Brossel, where his research interests shifted to continuousvariable quantum optics and quantum information. During his postdoc, most of his attention is devoted to understanding multimode photon addition and subtraction. Between May 2018 and October 2019, Mattia was funded by a research fellowship from the German Research Foundation (DFG).
Full Bibliography
Research Articles

M. Walschaers, V. Parigi, and N. Treps, Practical Framework for Conditional NonGaussian Quantum State Preparation, PRX Quantum 1, 020305 (2020)
 D. Barral, M. Walschaers, K. Bencheikh, V. Parigi, J. A. Levenson, N. Treps, and N. Belabas, Quantum state engineering in arrays of nonlinear waveguides, Phys. Rev. A 102, 043706 (2020).

D. Barral, M. Walschaers, K. Bencheikh, V. Parigi, J. A. Levenson, N. Treps, and N. Belabas, Versatile Photonic Entanglement Synthesizer in the Spatial Domain, Phys. Rev. Applied 14, 044025 (2020).

F. Flamini, M. Walschaers, N. Spagnolo, N. Wiebe, A. Buchleitner, F. Sciarrino, Validating multiphoton quantum interference with finite data, Quantum Sci. Technol.5 045005 (2020)

M. Walschaers and N. Treps, Remote generation of Wignernegativity through EinsteinPodolskyRosen steering, Phys. Rev. Lett. 124, 150501 (2020).
 Y.S. Ra, A. Dufour, M. Walschaers, C. Jacquard, T. Michel, C. Fabre, N. Treps, NonGaussian quantum states of a multimode light field, Nat. Phys. 16, 144–147(2020).
Reviews
 M. Walschaers, Signatures of manyparticle interference, J. Phys. B: At. Mol. Opt. Phys. 53 043001 (2020).
Research articles

U. Chabaud, G. Roeland, M. Walschaers, F. Grosshans, V. Parigi, D. Markham, N. Treps, Certification of nonGaussian states with operational measurements, arXiv:2011.04320
 P. Boucher, A. Goetschy, G. Sorelli, M. Walschaers, N. Treps, Full characterization of the transmission properties of a multiplane light converter, arXiv:2005.11982
Research Articles
 M. Walschaers, Y.S. Ra, N. Treps, ModeDependent Loss Model for Multimode PhotonSubtracted States, Phys. Rev. A 100, 023828 (2019).
 D. S. Phillips, M. Walschaers, J. J. Renema, I. A. Walmsley, N. Treps, J. Sperling, Benchmarking of Gaussian boson sampling using twopoint correlators, Phys. Rev. A 99, 023836 (2019).
Research articles
 T. Giordani, F. Flamini, M. Pompili, N. Viggianiello, N. Spagnolo, A. Crespi, R. Osellame, N. Wiebe, M. Walschaers, A. Buchleitner, and F. Sciarrino, Experimental statistical signature of manybody quantum interference, Nat. Photonics 12, 173178 (2018).
 C. Dittel, G. Dufour, M. Walschaers, G. Weihs, A. Buchleitner, and R. Keil, Totally destructive manyparticle interference, Phys. Rev. Lett. 120, 240404 (2018).
 C. Dittel, G. Dufour, M. Walschaers, G. Weihs, A. Buchleitner, and R. Keil, Totally destructive interference for permutationsymmetric manyparticle states, Phys. Rev. A 97, 062116 (2018).
 V. N. Shatokhin, M. Walschaers, F. Schlawin, and A. Buchleitner, Coherence turned on by incoherent light, New J. Phys. 20, 113040 (2018).
 M. Walschaers, S. Sarkar, V. Parigi, and N. Treps, Tailoring NonGaussian ContinuousVariable Graph States, Phys. Rev. Lett. 121, 220501 (2018).
Books
Research articles
 M. Walschaers, A. Buchleitner, and M. Fannes, On optimal currents of indistinguishable particles, New J. Phys. 19, 023025 (2017).
 M. Walschaers, R. Mulet, and A. Buchleitner, Scattering Theory of Efficient Quantum Transport across Finite Networks, J. Phys. B: At. Mol. Opt. Phys. 50, 224003 (2017).
 M. Walschaers, C. Fabre, V. Parigi, and N. Treps, Entanglement and Wigner function negativity of multimode nonGaussian states, Phys. Rev. Lett. 119, 183601 (2017).
 M. Walschaers, C. Fabre, V. Parigi, and N. Treps, Statistical signatures of multimode singlephoton added and subtracted states of light, Phys. Rev. A 96, 053835 (2017).
Research articles
 M. Walschaers, J. Kuipers, J.D. Urbina, K. Mayer, M. C. Tichy, K. Richter, and A. Buchleitner, Statistical Benchmark for BosonSampling, New J. Phys. 18, 032001 (2016).
This article was featured in an associated perspective.  M. Walschaers, J. Kuipers, and A. Buchleitner, From ManyParticle Interference to Correlation Spectroscopy, Phys. Rev. A 94(R), 020104 (2016).
Review articles
 M. Walschaers, F. Schlawin, T. Wellens, and A. Buchleitner, Quantum Transport on Disordered and Noisy Networks: An Interplay of Structural Complexity and Uncertainty, Annu. Rev. Condens. Matter Phys. 7, 223 { 248 (2016).
Research articles
 T. Zech, M. Walschaers, T. Scholak, R. Mulet, T. Wellens, and A. Buchleitner, Quantum transport in biological functional units: Noise, disorder, structure, Fluct. Noise Lett. 12, 1340007 (2013).
 M. Walschaers, J. FernandezdeCossio Diaz, R. Mulet, and A. Buchleitner, Optimally Designed Quantum Transport across Disordered Networks, Phys. Rev. Lett. 111, 180601 (2013).
 M. Walschaers, R. Mulet, T. Wellens, and A. Buchleitner, Statistical theory of designed quantum transport across disordered networks, Phys. Rev. E 91, 042137 (2015).