In this talk, I will give an overview of recent advances and explicit calculations for the entropy of certain black hole solutions in four-dimensional supergravity theories. Exact results are made available for such black holes thanks to the Quantum Entropy Function formalism and supersymmetric localization, which I will review. Applying this method exhibits some striking connections between the exact entropy of supersymmetric black holes and the mathematics of modular and Jacobi forms. In particular, for the case of 1/4-BPS black holes in the N=4 theory, supergravity organizes the corrections to the area-law (or Bekenstein-Hawking entropy) in a number-theoretic way, and it can be argued that these corrections are related to the ones appearing in the study of mock modular forms.

Monolayers of transition metal dichalcogenides (TMDs) with MoS2 and WSe2 being the prominent examples are actively studied nowadays. These materials demonstrate remarkable optical properties controlled by the robust excitons, Coulomb-correlated electron-hole pairs, with the binding energies on the order of several hundreds millielectronvolts. In semiconductors, Wannier-Mott excitons form a series of 1s, 2s, 2p, … hydrogen-like states. In TMD monolayers the binding energies of the excitonic states strongly differ from the two-dimensional hydrogen atom model.
In my talk, the nonlinear optical and transport effects of excitons in TMD monolayers are discussed.

The enhancement of light-matter interactions when the macroscopic number of quantum emitters in a semiconductor interact resonantly with a cavity mode has led to the observation of spectacular phenomena such as Bose-Einstein condensation at standard cryogenic temperature [1], polariton lasing [2], or light superfluidity [3]. In particular, the properties of the ground state are qualitatively affected in the so-called “ultrastrong” light-matter coupling regime, defined when the collective coupling strength becomes comparable to the bare cavity mode frequency [4]. I will first show that this regime can be achieved in quantum Hall systems with large filling factors [5,6,7], and explain how an interesting ultrastrong coupling regime with low loss can be realized by considering the two-dimensional electron gas embedded in a terahertz photonic band gap material. I will give an example of how this system could be used to observe the dynamical Casimir effect in realistic experimental conditions8. An other interest of quantum Hall systems is the existence of strong correlations due to the quenching of the kinetic energy, leading to exotic electronic phases in the
fractional filling factor regime. I will draw some perspectives on how an interesting interplay between Coulomb and light-matter interactions could be achieved by designing a suitable resonator made of hyperbolic metamaterials. Following the idea of exploring how light-matter coupling in a cavity can modify fermionic properties of condensed matter systems, I will then move to a simple two-band model to study the coherent transport of charges coupled to a cavity mode. In particular, charge current enhancements are predicted in the situation where lower and upper bandwidths are different9. I will conclude by showing how this simple model could be extended to describe incoherent transport in organic semiconductors, drawing a roadmap to enhance the efficiency of light emitting and collecting devices using cavity coupling.



1. Amo, A. et al., Nature Physics 5, 805 (2009)
2. Christopoulos, S. et al., Phys. Rev. Lett. 98, 126405 (2007)
3. Kasprzak, J. et al., Nature 443, 409 (2006)
4. Ciuti, C., Bastard, G. & Carusotto, I., Phys. Rev. B 72, 115303 (2005).
5. Hagenmüller, D., De Liberato, S. & Ciuti, C. Phys. Rev. B 81, 235303 (2010)
6. Scalari, G. et al. Science 335, 1323–1326 (2012)
7. Hagenmüller, D. & Ciuti, C. Phys. Rev. Lett. 109, 267403 (2012).
8. Hagenmüller, D. Phys. Rev. B 93, 235309 (2016)
9. Hagenmüller, D., Schachenmayer, J., Schütz, S., Genes, C. & Pupillo, G. (2017). ArXiv: 1703.00803v2
[quant-ph]. Accepted for publication in Phys. Rev. Lett.

We consider a composite model where both the Higgs and a complex scalar \chi, which is the dark matter (DM) candidate, arise as light pseudo Nambu-Goldstone bosons from a strongly coupled sector with TeV scale confinement. The global symmetry structure is SO(7)/SO(6), and the DM is charged under an exact U(1) \subset SO(6) that ensures its stability. The DM phenomenology depends strongly on whether the \chi shift symmetry is broken or respected by the coupling of the top quark to the strong sector. I will discuss both possibilities in detail, including the interplay with LHC physics. Based on arXiv:1707.07685 and work in progress.

The interaction between the electromagnetic field and matter, either solid state or cold atomic systems, is one of the most fundamental and ubiquitous physical processes. As a transparent or reflective media can be used as tools to generate non-trivial states of light, the latter can be used for the implementation of reversible quantum state mapping between light and matter. As a result of this interplay, the study of light-matter interactions has yielded an amazing variety of quantum information networking applications. In this talk, I will discuss two different light-matter interfaces: ensembles of cold neutral atoms for the controlled transport of single-photon pulses, and excitons-polaritons in solid stated systems for the generation of non-classical states of light.

Due to collective nature of the light-atom interaction, the coupling of atomic ensembles and light modes can be highly efficient. Moreover, due to the large optical density in an atomic cloud, it becomes possible to control the light propagation and storage in such medium. In this work, I will discuss light transport in the dense system of atoms, when the average distance between atoms is comparable with the radiative wavelength and the dipole-dipole interaction plays an important role. The light scattering in such dense atomic configuration is described in terms of microscopic approach based on the standard T-matrix formalism.

A comparable strong light-matter interaction can be also achieved in solid-state systems, in the form of exciton-polaritons. This bosonic quasi-particle can be considered as a hybryd between light and matter and exhibits promising properties for investigating various fascinating physical effects. In this context, I will discuss possible stochastic exciton-photon transformations in bosonic condensates of exciton-polaritons that can lead to the generation of non-classical state of light. The role of the stochastic conversions will be discussed in terms of exciton-photon correlation functions.

Spin waves are the elementary excitations of magnetic materials and may play a key role in future information processing. They can be probed via the magnetic fields they generate, but this requires a technique with high sensitivity and nanometer sensor-sample distances. I will describe how the excellent magnetic-field sensitivity of nitrogen-vacancy spins in diamond can be used to explore spin-wave physics in ferromagnets. We have developed techniques to detect localized spin-wave resonances and thermally excited spin waves, and recently achieved a breakthrough by detecting a spin-wave chemical potential. These results open up exciting possibilities for nanoscale imaging and control of spin transport in mesoscopic spin systems.

Controlling the transmission of electrical current using a quantum point contact constriction paved a way to a large variety of experiments in mesoscopic physics. The increasing interest in heat transfer in such systems fosters questions about possible manipulations of quantum heat modes that do not carry net charge (neutral modes). Here, I will present the transmission of upstream neutral modes through a quantum point contact in fractional hole-conjugate quantum Hall states. Employing two different measurement techniques, we were able to render the relative spatial distribution of these chargeless modes with their charged counterparts. In these states, which were found to harbor more than one downstream charge mode, the upstream neutral modes are found to flow with the inner charge mode - as theoretically predicted. These results unveil a universal upstream heat current structure and open the path for more complex engineering of heat flows and cooling mechanisms in quantum nano-electronic devices.

The response of spatially extended systems to a force leading their dynamics out of equilibrium is strongly affected by the presence of disorder. An archetypal class of systems where this scenario is found is given by extended elastic objects (lines or manifolds) which fluctuate in an heterogeneous medium. Examples range from interfaces in magnetic or ferroic materials, contact lines, charge density waves and vortices in superconductors, to solid membranes in chemical or biological liquids, and fronts in liquid crystals. In this talk I will discuss about two recent research works focusing on this type of system. In a first part I will focus on the so-called creep motion at finite temperature, a regime with highly non-linear, stretched-exponential velocity–force relation. I will introduce an effective model describing the motion of the driven interface at fixed length scale, allowing to recover the creep law, to extend the description of the dynamics from low forces to larger forces, and to characterize the crossover between creep and linear response in finite systems in the very small force regime. In the second part of the talk I will focus on zero-temperature avalanche dynamics at the depinning transition. I will discuss about the amount of energy released in individual avalanches, a question that is relevant not only for these kind of systems, but also for amorphous materials. The scaling of the energy of an avalanche with its size is controlled by a new exponent, recently found in the so far unrelated context of the thermal rounding of the depinning transition. Based on the results of this study I will propose a new numerical method to determine the dynamic exponent at the depinning transition relying on automata-like quasi-static simulations, which are way less costly than simulating real time dynamics.