Operational Approach towards Non-Gaussian States - One Photon at a Time
Final Report Abstract
Quantum entanglement, one of the key resources for quantum information processing, can be deterministically generated in a scalable manner in continuous variable (CV) systems. However such CV entangled states typically display Gaussian statistics, which limits their use for quantum computing. It is experimentally feasible to overcome this problem by the modeselective subtraction of photons from multimode Gaussian states, thus rendering them non-Gaussian. Furthermore, photon subtraction is known to enhance the entanglement between a pair of modes. In multimode setups, however, the theoretical properties of the resulting non-Gaussian states are still surrounded by open questions. The central aim of this project is to elucidate these properties. As a starting point, we previously derived the general Wigner functions of single-photonadded or -subtracted states. The analytical expression of the Wigner functions provides a series of useful insights, which were use in this project to • Explore the interplay between entanglement and non-Gaussian features: As an important case study, we treat photon subtraction from CV graph states. Photon subtracted in one of the vertices of such a graph state can induce non-Gaussian features that spread through the graph. As a first key result, we showed that non-Gaussianity spreads exactly to the next-to-nearest neighbours (with respect to the graph topology) of the vertex from which the photon was subtracted. Furthermore, we showed that photon subtraction in one vertex can even generate Wigner-negativity in another vertex under the condition that there is Einstein-Podolsky-Rosen steering between the vertices. • Understand the effects of optical losses: We investigated the effect of mode-dependent optical loss on multimode single-photon-subtracted states and showed that losses and photon subtraction generally do not commute. We found that losses acting after photon subtraction alter the modal structure of the subtracted photon. • Guide new experimental developments: The theoretical understanding acquired in the other results was used to design a multimode photon subtraction experiment. We experimentally created Wigner-negativity in a mode-tuneable way and, furthermore, we confirmed the theoretical results on the spread of non-Gaussian features in photonsubtracted graph states. Finally, we also booked significant progress in understanding the multimode states that are generated by the subtraction of multiple photons. Completely general models quickly become intractable, and therefore we resulted to the use of methods from statistical physics. In particular, we applied methods from the study of complex networks to analyse the features of the resulting states. However, at the close of the research fellowship, this part of the project is still unfinished.
Publications
- “Tailoring Non-Gaussian Continuous- Variable Graph States”, Phys. Rev. Lett. 121, 220501 (2018)
M. Walschaers, S. Sarkar, V. Parigi, and N. Treps
(See online at https://doi.org/10.1103/PhysRevLett.121.220501) - “Totally destructive interference for permutation-symmetric many-particle states”, Phys. Rev. A 97, 062116 (2018)
C. Dittel, G. Dufour, M. Walschaers, G. Weihs, A. Buchleitner, and R. Keil
(See online at https://doi.org/10.1103/PhysRevA.97.062116) - “Totally destructive many-particle interference”, Phys. Rev. Lett. 120, 240404 (2018)
C. Dittel, G. Dufour, M. Walschaers, G. Weihs, A. Buchleitner, and R. Keil
(See online at https://doi.org/10.1103/PhysRevLett.120.240404) - “Benchmarking of Gaussian boson sampling using two-point correlators”, Phys. Rev. A 99, 023836 (2019)
D. S. Phillips, M. Walschaers, J. J. Renema, I. A. Walmsley, N. Treps, J. Sperling
(See online at https://doi.org/10.1103/PhysRevA.99.023836) - “Mode-dependent-loss model for multimode photon-subtracted states”, Phys. Rev. A 100, 023828 (2019)
M. Walschaers, Y.-S. Ra, and N. Treps
(See online at https://doi.org/10.1103/PhysRevA.100.023828) - “Signatures of Many-Particle Interference”, J. Phys. B: At. Mol. Opt. Phys. (2019)
M. Walschaers
(See online at https://doi.org/10.1088/1361-6455/ab5c30) - Non-Gaussian quantum states of a multimode light field. Nature Physics
Y.-S. Ra, A. Dufour, M. Walschaers, C. Jacquard, T. Michel, C. Fabre, N. Treps
