Entanglement is a property of quantum objects in which their state cannot simply be described by the sum of the individual states of their components. One difficulty faced in the study of the fundamental properties of entangled states is that the mathematical complexity of the description increases exponentially with the number of entangled subsystems. Moreover, experimental procedures to reconstruct an entangled state may require an enormous number of measurements, which necessitates a significant amount of resources and time. For instance, the reconstruction of a quantum state with five subsystems requires approximately one thousand measurements, and the reconstruction of a quantum state with ten subsystems requires more than one million measurements. Furthermore, the fragility of a quantum state increases with the number of subsystems, making the complete characterization of these systems practically impossible. Here, we test a novel idea of how to partially characterize a multipartite quantum state with a reduced number of measurements in the laboratory.


We employ an optical setup in which photon pairs are generated using a 325-nm laser to create three- and four-partite states. We find that the number of measurements required scales only linearly with the number of subsystems instead of exponentially, as in the case of a full characterization. Our method is based on the reconstruction of the local states of the subsystems without measuring the correlations between them. Surprisingly, in many cases, it is still possible to determine if the state exhibits genuine multipartite entanglement. We prepare and test quantum states of photons pertaining to different classes of entanglement. We find that this local characterization works not only for the ideal case of pure states but also for states that are moderately mixed because of experimental noise.

We expect that this type of partial characterization will be useful for quantum information applications that use certain entangled states as a resource.

I will discuss the rheology and mechanical properties of wet granular materials, and show why the behavior can be very subtle. Once one understands the mechanical properties, I will show that one can use this knowledge to construct the perfect sandcastle, or to understand why the ancient Egyptians wetted the desert sand with water before sliding heavy stones over it. I will then go on to show some new results on friction at the microscopic scale, between 2 grains. Amonton's famous friction law states that the friction force is proportional to the normal force since both are proportional to the area of contact. However for spherical grains the contact area is not proportional to the normal force, as shown by Hertz long ago. We use new fluorescence technique that allows us to probe the real area of contact between 2 rough surfaces. In our case, we conclude that important deviations from Amonton's law are observed.

Recently, the Cosmological Relaxation idea has been proposed as a new mechanism to generate a naturally small electroweak scale. It exploits the coupling of the Higgs to an axion-like field and a long era in the early universe where the axion unchains a dynamical screening of the Higgs mass. I will present in details the Relaxation idea and its minimal implementations. Moreover I will discuss some extensions of the original models that can postpone any sign of new physics up to a rather large scale, 10^9 GeV, except for two very light and weakly coupled axion-like states.

One of the major environmental issues related to pesticides spraying on cultivated crops is the drift process. Because of the wind, small droplets may drift away from the targeted crop and cause contamination. One way to reduce the drift is to control the spray drop size distribution by reducing the proportion of small drops. In this context, anti-drift additives have been developed, including dilute oil-in-water emulsions. Although being documented, the effects of oil-in-water emulsions on spray drop size distribution are not yet understood. The objective of this thesis is to determine the physical mechanisms at the origin of the changes of the spray drop size distribution for emulsion-based sprays. Spray drops result from the destabilization of a liquid sheet formed at the nozzle exit. With a model experiment, based on the impact of a single tear of liquid on a small target, we investigate the destabilization mechanisms of liquid sheets and compare the results obtained to the drop size distribution of sprays produced with agricultural nozzles. With dilute oil-in-water emulsions, the liquid sheet is destabilized by the nucleation and growth of holes within the sheet that perforate it during its expansion. The physical-chemical parameters of the emulsion, such as the emulsion concentration, the chemical nature of the components and the emulsion drop size distribution, are varied to rationalize their influence on the perforation mechanisms.

As the Higgs boson properties settle, the constraints on the Standard Model extensions tighten. We consider all possible new fermions that can couple to the Higgs, inspecting sets of up to four chiral multiplets. We confront them with direct collider searches, electroweak precision tests, and current knowledge of the Higgs couplings. The focus is on scenarios that may depart from the decoupling limit of very large masses and vanishing mixing, as they offer the best prospects for detection. We identify exotic chiral families that may receive a mass from the Higgs only, still in agreement with the hγγ signal strength. A mixing θ between the Standard Model and non-chiral fermions induces order θ2 deviations in the Higgs couplings. The mixing can be as large as θ∼0.5 in case of custodial protection of the Z couplings or accidental cancellation in the oblique parameters. We also notice some intriguing effects for much smaller values of θ, especially in the lepton sector. Our survey includes a number of unconventional pairs of vector-like and Majorana fermions coupled through the Higgs, that may induce order one corrections to the Higgs radiative couplings. We single out the regions of parameters where hγγ and hgg are unaffected, while the hγZ signal strength is significantly modified, turning a few times larger than in the Standard Model in two cases. The second run of the LHC will effectively test most of these scenarios.

I will discuss the mass reach for electroweakinos at future hadron colliders in several split SUSY scenarios and I will show that collider searches and direct detection experiments have the potential to cover large part of the parameter space. I will then review the zero and finite temperature properties of the QCD axion: despite non-perturbative QCD, axion properties can be extracted at the percent level partially exploiting the foreseen experimental accuracy in case of discovery.