Soft and wet contact arises in a range of phenomena that spans many length and time scales, and includes : landslides, aquaplaning of tires, wear of industrial bearings, ageing of synovial and cartilaginous joints, cell motion in blood vessels or microfluidic devices, and atomic-force or surface-force rheology. Therein, the coupling between boundary elasticity and confined viscous flow leads to a striking zoology of counterintuitive emergent effects. From the canonical situation of a free particle that can simultaneously sediment, slide, and roll in a viscous fluid, and near a soft wall, we study a range of novel inertial-like (despite the low-Reynolds-number flow) features, such as : enhanced sedimentation, elastohydrodynamic bouncing, roll reversal, emergent lift and torque...

Engineering robust solid-state quantum systems is amongst the most pressing challenges to realize scalable quantum photonic circuitry. While several 3D systems (such as diamond or silicon carbide) have been thoroughly studied, solid state emitters in two dimensional (2D) materials are still in their infancy.
In this presentation I will discuss the appeal of an emerging van der Waals crystal – hexagonal boron nitride (hBN). This unique system possesses a large bandgap of ~ 6 eV and can host single defects that can act as ultra-bright quantum light sources. In addition, some of these defects exhibit spin dependent fluorescence that can be initialised and coherently manipulated. On top of that, the hBN crystals can be carefully sculpted into nanoscale photonic resonators to confine and guide light at the nanoscale. It hence has all the vital constituents to become the leading platform for integrated quantum photonics. To this extent, I will highlight the challenges and opportunities in engineering hBN devices and will frame it more broadly in the growing interest with 2D materials nanophotonics.

An analog simulator is a synthetic physical system, which emulates in a controlled way a physical problem. You can get answers about the physical problem by directly performing experiments on the simulator. In the present seminar, I will present the polariton platform and explain how it is relevant for analog simulation of many interesting complex problems.
Cavity polaritons are hybrid exciton-photon quasi-particle emerging from the strong coupling regime between photons confined in an optical cavity and excitons confined in quantum wells. They present physical properties reflecting their mixed nature. From the photon part, they inherit a small effective mass and can be confined in lattices with typical dimensions of the order of a few microns. Their excitonic part endows them with inter-particle interactions resulting in a giant Kerr non linearity. Moreover the system is intrinsically open and out of equilibrium because photons constantly leak out from the cavity. Cavity polaritons have been shown to present fascinating properties such as Bose Einstein condensation at elevated temperature, superfluidity, multistability etc [1].
In the present talk, I will explain how the polariton plateform is particularly suitable to realize analog simulation of open complex systems and explore fundamental physical phenomena.
I will describe a few recent results of our group:
1) How do wave localize in exotic quasi-crystals and how fractality does develop? This physics can be emulated with polariton lattices [2]
2) Polariton condensates are out of equilibrium and their phase dynamics has been predicted to obey the celebrated Kardar Parisi Zhang (KPZ) equation. We have been able to reveal experimentally universal KPZ scaling laws in the first order coherence of a 1D polariton condensate.[3]
3) Polariton lattices are also very interesting for the investigation of topological photonics. In particular, the ability to drive the system with controlled phases opens a new paradigm for non-linear topological photonics. [4]

References :

[1] C. Ciuti & I. Carusotto, Quantum fluids of light, Rev. Mod. Phys. 85, 299 (2013)
[2] V. Goblot et al. Emergence of criticality through a cascade of delocalization transitions in quasiperiodic chains, Nature Physics 16, 832 (2020)
[3] Q. Fontaine et al., Observation of KPZ universal scaling in a one-dimensional polariton condensate, arXiv:2112.09550 (2021)
[4] N. Pernet et al., Topological gap solitons in a 1D non-Hermitian lattice, arXiv:2101.01038 (to appear 2022)

Nanophotonics refers to the unique interactions of light (photonics) and materials at the nanometer scale. Nanometer sized metals (e.g. gold, silver, copper) exhibit extremely high electric field enhancements when excited by laser light, leading to unique opportunities in sensing and therapy in cancer applications. Therapeutically, this interaction can be used to generate heat and mechanical shock waves (nanobubbles) that serve to release drugs, denature proteins, or disrupt cell membranes. We’ve demonstrated these effects can illicit a specific type of cell death that stimulates the body’s immune system to fight cancer in models of breast cancer and melanoma. Diagnostically, these nanomaterials enable a sensing platform using surface enhanced Raman scattering (SERS) that greatly enhances the detection ability of molecules near the particle surface. We are developing implantable devices with SERS sensors to monitor patients at risk for cancer recurrence after treatments.

Quantum is booming, and established quantum platforms (superconducting circuits, trapped ions, Ry atom arrays and photons) are now moving to the realm of industry (IBM, IONQ, PasQal, and PsiQuantum). A key enabler to some of these approaches is a pristine spin-photon interface that allows entangling long-lived matter-based qubits with routable flying qubits in the form of photons. This talk will introduce you to the key concepts and challenges behind quantum computing and contextualize the sustained research efforts to develop the performance of candidate systems such as trapped ions, atomic impurities in solids and quantum dot spins. The talk will then focus on a specific platform: Optically active semiconductor quantum dots (QDs)--which have unparalleled photonic properties, but also modest spin coherence limited by their resident nuclei--and our most recent work on this platform [1]. In a nutshell, we demonstrated that a new generation of lattice-matched QD devices, with vanishing strain, allows dramatic prolongation of the electron spin coherence over conventional QD counterparts. The near two orders of magnitude improvement of electron spin coherence under dynamical decoupling, also attests of a coherence improvement of the electron-nuclear interface as a whole. We envisage this to enable the storage of quantum information in the nuclear spins, a vital resource towards memory-assisted quantum network protocol.

[1] Leon Zaporski et al., Ideal refocusing of an optically active spin qubit under strong hyperfine interactions, arXiv 2206.01223.

Our understanding of the mechanism by which the viscosity of supercooled liquids increases by many orders of magnitude is often described as a major challenge in condensed matter physics [1,2]. It is therefore necessary to discriminate between seemingly incompatible theoretical approaches which provide equally good descriptions of experimental data: a scientific revolution [3]. Much of the perceived incompatibility revolves around whether the glass transition is driven by underlying thermodynamics or is predominantly a dynamical phenomenon. Here we report new results with experiments and simulations which explore previously inaccessible dynamical regimes at the single-particle level [4,5], where we test explicitly the predictions of each approach. We find that the predictions of both thermodynamic and dynamical approaches are upheld and suggest routes out of the scientific revolution of the glass transition.
While the glass transition hard spheres may be somewhat understood, addition of a short-ranged attraction (sticky spheres) results in far-from-equilibrium behavior: aging leads to a change in mechanical properties over time. Remarkably, these “stronger” gels can then undergo spontaneous catastrophic failure with tremendous consequences for the many materials that rely on gelation [6]. We show how this dramatic and counter-intuitive phenomenon may be predicted in a newly-developed experimental system where forces between particles may be resolved [7].

[1] Royall, C. P. & Williams, S. R. “The role of local structure in dynamical arrest”, Phys. Rep. 560 1-75 (2015).
[2] Royall, C. P., Turci, F., Tatsumi, S., Russo, J. & Robinson, J. “The race to the bottom: approaching the ideal glass?”, J. Phys.: Condens. Matter 30 363001 (2018).
[3] Kuhn, T. S. The Structure of Scientific Revolutions Univ. Chicago Press, 1962.
[4] Hallett, J. E., Turci, F and Royall, C. P. “Local structure in deeply supercooled liquids exhibits growing lengthscales and dynamical correlations”, Nature Commun. 9 3272 (2018).
[5] Ortlieb L, Ingebrigtsen TS, Hallett JE, Turci F and Royall CP “Relaxation in supercooled liquids: Cooperatively Re–arranging Regions vs Excitations”, ArXiV 2103.08060 (2021).
[6] Royall CP, Faers MA, Fussell SL and Hallett JE, “Real Space Analysis of Colloidal Gels: Triumphs, Challenges and Future Directions”, J. Phys.: Condens. Matter, 33 453002 (2021).
[7] Dong J, Turci F, Jack RL, Faers MA and Royall CP, “Direct Imaging of Contacts and Forces in Colloidal Gels” J. Chem. Phys. 156 214907 (2022).