Over the last decades, the concept of topology and the associated topological materials have been at the center of the attention in condensed matter physics giving rise to a nobel prize in 2016.
Recently, theoretical articles have define a new class of artificial topological materials made of multiterminal Josephson Junctions (JJs) [1,2]. For these materials, the topology arises from their bandstructure in function of the phases φ of the junctions, instead of the wave vector k for conventional topological materials. Such a difference can be interesting to tailor and control exotic quantum states as Majorana bound states, or Weyl sinularities which are fundamental in the emergence of future quantum computer.
Here we are presenting the realization of a two- and three-terminal Josephson interferometer based on proximity effect and fully controlled by phase coherence [3,4]. The three terminal device in particular shows a non trivial phase-tunable switch from a regime where the normal metal spectrum has a gap in the density of states to a gapless regime which characterize a protected topological phase transition in full agreement with recent predictions [5,6]. It represents the first essential step towards phase-engineering of an artificial topological material hosting Majorana bound states.
 T.Yokoyama andY.V. Nazarov, Phys. Rev. B 92, 155437 (2015).
 R.-P. Riwar, M. Houzet, J. S. Meyer, and Y. V. Nazarov, Nature Commun. 7 11167 (2016).
 S. D’Ambrosio, M. Meissner, C. Blanc, A. Ronzani, and F. Giazotto, Appl. Phys. Lett. 107, 113110 (2015).
 S. D’Ambrosio, E. Strambini, F. Vischi, F. S. Bergeret, Y.V. Nazarov, and F. Giazotto, Nature Nanotechnol. 11 1055 (2016).
 C. Padurariu, T. Jonckheere, J. Rech, R. Mélin, D. Feinberg, T.Martin, and Yu. V. Nazarov, Phys. Rev. B 92, 205409 (2015).
 F. Vischi, M. Carrega, E. Strambini, S. D’Ambrosio, F. S. Bergeret, Yu. V. Nazarov, and F. Giazotto, Phys. Rev. B 95, 054504 (2017)