Individual bacteria transported in viscous flows, show complex interactions with flows and bounding surfaces resulting from their complex shape as well as their activity. Understanding these transport dynamics is crucial, as they impact soil contamination, transport in biological conducts or catheters, and constitute thus a serious health thread.

Here we investigate the trajectories of individual E-coli bacteria in confined geometries under flow, using microfluidic model systems in bulk flows as well as close to surfaces using a novel Langrangian 3D tracking method. Combining experimental observations and modeling we elucidate the origin of upstream swimming, lateral drift or persistent transport along corners.

Dispersions of colloidal particles in nematic liquid crystals show new classes of interparticle forces, which are anisotropic, long-range, and several thousand times stronger than van der Waals forces in water-based colloids [1-5]. These forces are responsible for a variety of new self-assembled colloidal microstructures, which cannot be observed in isotropic solvents, such as chains of microspheres and cellular soft solid materials. In this talk, I will present our recent results on the interactions, self-assembly, shape asymmetry, electrophoretic propulsion, bound and metastable states of anisotropic nano and microparticles in nematic liquid crystals [6-10].

References:
1. C Tom, VMSG Tanuku, E Paineau, RK Pujala, ACS Applied Nano Materials 4 (8), 8586 (2021).
2. RK Pujala, HB Bohidar, Journal of Colloid and Interface Science 554, 731-742 (2019).
3. LR Kumbam, et al. Nanoscale 14, 4946-4956 (2022).
4. SN Sangitra, RK Pujala, Soft Matter 19, 5869-5879 (2023).
5. P More, SN Sangitra, HB B, RK Pujala, The Journal of Chemical Physics 157, 214902 (2022).
6. M Rasi, S Archana, RK Pujala, S Dhara, Soft matter 18, 6043-6050 (2022)
7. M Rasi M., RK Pujala, S Paladugu, S Dhara Phys. Rev. E 104 (1), 014706 (2021).
8. DV Sudhakaran, RK Pujala, S Dhara, Advanced Optical Materials 8 (7), 1901585 (2020).
9. M Rasi, RK Pujala, S Dhara, Scientific Reports 9 (1), 1-11 (2019).
10. F Hagemans et al,. Chemistry of Materials 31 (2), 521–531 (2019).

The cooperative binding of molecular agents onto a substrate is pervasive in living systems.

To study whether a system shows cooperativity, one can rely on the fluctuation analysis of quantities such as the number of substrate-bound units and the residence time in an occupancy state.

Here, we present a general-purpose grand canonical Hamiltonian description of a small one-dimensional (1D) lattice gas with nearest-neighbor interactions as a prototypical example of cooperativity-influenced adsorption processes, allowing us to elucidate how the strength of the interaction potential between neighboring bound particles determines the intensity of the fluctuations of the mean occupancy.

Then, we study how said interaction affects the out-of-equilibrium properties of a binding-unbinding process from a substrate, looking into the characteristic relaxation times to the equilibrium state and the dwell times of bound particles.

Finally, we compare the theoretical predictions of our model to data from single molecule experiments on bacterial flagellar motors (BFM). In this way, we find evidence that cooperativity controls the mechano-sensitive dynamical assembly of the torque-generating units, the so-called stators, onto the BFM and estimate the value of the interaction potential.

This work provides a step forward in the understading of the role of cooperativity in the adaptability of small molecular systems such as the bacterial flagellar motor.

The scale at which quantum gravitational effects become manifest, the species scale, has recently been argued to take values parametrically lower than the Planck scale. It is therefore of interest to quantum gravity phenomenology to have a precise definition of how to compute this scale in any EFT that has a UV completion in quantum gravity. Two proposals have been made in the literature, of different conceptual origin; one linked to the size of the smallest black hole that one can describe in an EFT and the other to the scale of higher-derivative corrections to the EFT. Arguably one of the most profound aspects of a theory of quantum gravity is that it should be background independent and that semi-classical spacetime should only "emerge" as a low-energy description. I will demonstrate how this notion of "emergence" unites the two definitions of the species scale.
I will do so by studying small (singular) black hole solutions in string theory and illustrating how higher-derivative corrections obtained from emergence correct these solutions and generate a species scale sized horizon for these black holes.
Based on arXiv:2310.04488.

The quest for efficient spin-photon interfaces is at the core of many proposals in quantum optics. On the one hand, it would allow developing deterministic spin-photon and photon-photon gates for quantum computing, as well as multi-entangled states with N photons, for quantum communications. On the other hand, it would allow implementing interesting fundamental studies on quantum measurement, whereby each photon can be used to « observe » the spin system.

In this seminar, I will briefly review some systems used for spin-photon coupling, and then focus on the recent progress made in C2N, using charged quantum dots in pillar-based cavities. I will show how we can use the same device as a quantum emitter – to emit several photons all entangled with the same spin, or as a quantum receiver – to allow exchanging the quantum information between a confined spin and the incoming photons.


Along the way, I will show how one can play with the polarization degree of freedom in various ways, to encode multi-photon entanglement as well as to extract information on the various processes occurring in our solid-state structures.

Finally, I will discuss some perspectives of our work, for the realization of optimized spin-photon interfaces and their use in various applications.

The addition of heavy right-handed neutrinos to the Standard Model is the simplest way of explaining the existence of neutrino masses. Even when they are too heavy to be produced in experiments, it is still possible to probe their existence since their mixing with the light neutrinos generates deviations from unitarity in the leptonic mixing matrix. These non-unitarity effects can lead to deviations in several low-energy precision observables or to charged lepton flavor violating (cLFV) processes. In this talk, I will review the global fit procedure carried out to extract bounds on heavy neutrino mixing and I will provide the most up-to-date bounds for several heavy neutrino scenarios. These bounds are the strongest for heavy neutrinos above the electroweak scale.

In this seminar, a brief conceptual description about quantum dots and carbon quantum dots (CDots) will be given. After that, an unconventional experimental way of producing Cdots dispersed in a glass matrix will be presented and, finally, the synthesis of magnetic and luminescent nanoparticles for use in the forensic area will be presented.

A common feature of theories of quantum gravity is the presence of light, massive states beyond those described by effective field theory. The species scale gives a measure for the number of such light states and serves as UV cutoff in the gravitational sector of the theory. In the first part of this talk I will discuss the dependence of the species scale on the moduli of the theory and show how, for a large class of examples, it can reliably be computed at any point in moduli space thereby providing new insights into the bulk region of moduli spaces of gravitational theories. Studying the variation of the species scale over the field space I will further argue for a sharp bound on the slope of the species scale. The second part of my talk focuses on asymptotic weak-coupling regions where string theoretic arguments suggest that only certain towers of light states can emerge. By analyzing the universal properties of the density of states in gravitational weak-coupling limits I will provide string-theory-independent evidence for this prediction.

I will show that the supersymmetric deformed CP^1 sigma model -- the supersymmetric generalization of the Fateev-Onofri-Zamolodchikov model -- may be cast in the form of a generalized Gross-Neveu model. The beta function may be easily calculated in this formalism, showing that in the UV the theory flows to the super-Thirring model. I will prove that the latter is equivalent to a sigma model with target space the cylinder by explicitly calculating correlation functions of elementary fields on both sides. (Joint work with A.Pribytok)