Find the upcoming seminars below.

TQM seminar #18 : January 26 2023, 2pm (LPTHE library, towers 13-14, 4th floor)

Karim Noui (ICJLab, Orsay)

Topological Invariants and Quantum Gravity

Very naively, quantum gravity would provide a “way” to integrate (using path integral) over all spacetime metrics. Hence, if we integrate on the metrics, finally, the only information that we could extract on the space-time would be its topological properties! This argument is very naive but it illustrates that topology and topological invariants could play a very important role in quantum gravity. This is indeed the case for quantum gravity in 3 (space-time) dimensions where there is, for example, a very beautiful and very deep link between knot invaiants and the physical observables, a link which has been shown by Witten at the end of the 1980s. Quantifying gravity in 4 dimensions is much more involved and to date we do not know a 
solution to this problem. However, we can try to adapt the methods used in dimension 3 to advance in the problem, which is exactly what has been done in some approaches to quantum gravity (loop gravity and spin foam models). Here again, topological invariants play a crucial role… In this talk, I will try to show (through simple examples) the connection between topology and quantum gravity. 

You will then see that the structures which appear are very similar to those that appear in the analysis of the topological phases in condensed matter.

TQM seminar #19 : February 2 2023, 2pm (INSP great hall, towers 22-23, 3rd floor, room 317)

Anne Anthore (C2N Palaiseau & Université Paris Cité)

Noise signatures of Anyon statistics and Andreev scattering in the =1/3 fractional quantum Hall regime

With P. Glidic, O. Maillet, C. Piquard, A. Aassime, A. Cavanna, Y. Jin, U. Gennser, F. Pierre

Anyons are exotic quasiparticles which can carry a fractional charge of an electron and with an exchange statistic inbetween that of fermions and bosons. These properties were revealed using quantum point contacts (QPC) in the fractional quantum Hall regime [1,2].
In this talk, I will report further noise investigation of anyon physics. Sourcing e/3 anyons at a first QPC, noise measured on a downstream “analyzer” QPC reveals different mechanisms. Setting the analyser to allow e/3 tunneling charges, we reproduce the negative cross-correlations previously observed [2], indicative of a non-trivial anyon exchange phase [3]. When 1 e charges tunnel across the analyser, the braid phase is predicted to be trivial. Our observation of negative cross-correlations points on a scattering mechanism akin to Andreev reflection at Normal/Superconductor interfaces, as suggested in [4].
Remarkably, in both cases, electrical conduction through the analyser does not preserve the nature or number of quasiparticles, rendering the beam splitter analogy of a QPC invalid.

[1] L. Saminadayar et al., PRL 79, 2526 (1997)
[2] H. Bartolomei et al., Science 368, 173-177 (2020)
[3] B. Rosenow et al. PRL, 116, 156802 (2016)
[4] C. L. Kane and M. P. A. Fisher, PRB 67, 045307 (2003)

TQM seminar #20 : March 23 2023, 2pm (LPTHE library, towers 13-14, 4th floor)

Marcello Andolina (Collège de France, Paris)


TQM seminar #21 : April 6 2023, 2pm (INSP great hall, towers 22-23, 3rd floor, room 317 ???)

François Dubin (INSP, Sorbonne Université, Paris)


TQM seminar #22 : May 11 2023, 2pm (INSP great hall, towers 22-23, 3rd floor, room 317 ???)

Aurélien Schmitt (LPENS, Ecole Normale Supérieure, Paris)

Klein-Schwinger effect in graphene (provisoire)