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Organisation/Company Université de Strasbourg Department Institut de Science et d'Ingénierie Supramoléculaires (ISIS) Research Field Physics » Solid state physics Researcher Profile Recognised Researcher (R2) Positions Postdoc Positions Country France Application Deadline 31 Dec 2025 - 23:55 (Europe/Paris) Type of Contract Temporary Job Status Full-time Offer Starting Date 1 Mar 2026 Is the job funded through the EU Research Framework Programme? Not funded by a EU programme Is the Job related to staff position within a Research Infrastructure? No

Quantum mechanics tells us that empty space is not void but is characterized by vacuum fluctuations of quantum fields, including the electromagnetic field. While vacuum fluctuations in free space are often negligible in condensed matter systems, the situation changes radically when collective excitations are considered inside electromagnetic or optical cavities, that significantly enhance interactions between the quantized modes of the electromagnetic field and charged matter particles. This can alter their properties and can induce novel material phases. Researchers currently aim to leverage the so-called ‘ultra-strong light-matter coupling regime’ to modify molecular structures, enhance electron-phonon couplings, and facilitate the emergence of new electronic phases.

In traditional condensed matter physics, the integer and fractional quantum Hall effects, both discovered in the early 1980s, are well-known —yet endlessly fascinating— electronic phases. They appear when a two-dimensional gas of electrons lies in a very strong transverse magnetic field. In these systems the electrons organize themselves in an insulating state in the bulk of the material, but they conduct the electric current along the one-dimensional edges of the sample. Moreover, the edge current is chiral (i.e. uni-directional) and it is quantized, a fundamental phenomenon known as ‘topological protection’ that has found many applications from metrology to photonics. Many more topological phases of matter have since been discovered, like topological insulators and superconductors and many others.

So far there are very few experimental results on topological phases in a cavity. Very recently, a team at ETH Zürich has claimed to have observed deviations from the quantized value of the edge current in an integer quantum Hall effect coupled to a cavity, in the case of not-too- strong magnetic fields (corresponding to the case where the electrons occupy many ‘Landau levels’). In contrast, experiments by the same group at higher magnetic field (corresponding to the case where only a few of the lowest ‘Landau levels’ are occupied) have concluded that there is no modification of the quantized Hall conductance.

On the theory side, the topic is also in its infancy. An argument put forward by Cristiano Ciuti is that the destruction of quantization is due to long-range electron hopping mediated by the cavity. This idea has several drawbacks, including the fact that it makes no distinction between the cases of few and many occupied Landau levels, and that long-range hopping of massive particles would violate basic principles of physics like impossibility of faster-than-light propagation. Another very recent preprint has used the ‘Chern-Simons theory’ of electrons in a single Landau level and has concluded that there should be no effect at all. While this is in agreement with the experiment at high magnetic field, it does not explain the observations in higher Landau levels. A handful of other recent works have focused on electrons in the lowest Landau level coupled to a cavity, but they also do not explain the experimental observations.

With this project, we want to reach a detailed theoretical understanding of the integer quantum Hall effect in a cavity mode, from the point of view of the edge modes of the sample.

E-mail j.dubail@unistra.fr

Research Field Physics » Quantum mechanics Education Level PhD or equivalent

Skills/Qualifications

• Advanced knowledge of theoretical physics is required. Experience with field theory methods for quantum one-dimensional systems, e.g. conformal field theory or Luttinger liquid theory is expected.

Good programming skills in python, julia or C++ are required.