Talks

CondMat for Dummies: Symmetric mass generation

Origin of mass is a fundamental question in physics. In the Standard Model of particle physics, it is known that elementary particles become massive due to the Higgs mechanism. A prominent feature of the Higgs mechanism is the involvement of spontaneous symmetry breaking (SSB). In this talk, I will explore another mass generation mechanism for fermions that does not require symmetry breaking, simply called the symmetric mass generation (SMG). I will firstly give a definition of SMG. Then I will discuss the consequences/applications of SMG in two different contexts: (1) an example of interaction reduced classification of symmetry protected topological (SPT) phases: from Z to Z_8 classification of Kitaev chain, which would be of interests to the condensed matter community; (2) lattice regularization of chiral fermions, i.e. how to get rid of the fermion doubler in the Nielsen-Ninomiya fermion doubling theorem, which would be of interests to the high energy community.

ATOM24

ATOM24

Nuclear spins in semiconductor quantum dots: a many-body quantum system with interesting physics and prospective applications in quantum technologies

Epitaxial semiconductor quantum dots (QDs) have long been investigated in the context of quantum physics and quantum information processing (QIP). The solid-state nature of the quantum dots poses many challenges. One such challenge comes from the magnetic moments of the atomic nuclei that make up the crystal lattice of a QD. The dense 3D lattice of the nuclear spins often acts as a source of magnetic noise, limiting quantum coherence of the electron and photon qubits. However, introduction of a new generation of low-strain optically-active GaAs/AlGaAs QDs has shifted the paradigm with recent efforts focused on harnessing nuclear spin magnetism as a testbed for fundamental quantum physics and QIP applications. The advances of the past few years include demonstrations of electron [1] and nuclear [2] spin qubits in a semiconductor quantum dot, as well as reversible transfer of quantum states between electron and nuclear spins [3], offering a pathway to implementation of a solid-state quantum memory. I will discuss recent advanced both in fundamental physics and prospective applications of QD nuclear spins in QIP. Recent findings include an experimental answer to the long-standing dilemma of nuclear spin diffusion in a central-spin model [4]; ferromagnetic ordering of nuclear spin ensembles, with record-high polarisations exceeding 95% [5]; nondemolition measurement of the central electron spin through entanglement with a nuclear spin ensemble [6], which allows for single-shot qubit readout with fidelities exceeding 99.85%. Moreover, we show how strain-engineering of semiconductor lattice can be used to turn the nuclear spin ensemble into an efficient quantum memory, which can store coherent states for very long times, exceeding 100 ms. [1] L. Zaporski et al., Nature Nano 18, 257 (2023) [2] E. A. Chekhovich et al., Nature Nano 15, 999 (2020) [3] M. Appel, et al., arXiv:2404.19680 (2024) [4] P. Millington-Hotze, et al., Nature Comm. 14, 2677 (2023) [5] P. Millington-Hotze, et al., Nature Comm. 15, 985 (2024) [6] H. Dyte et al., Phys. Rev. Lett. 132, 160804 (2024)

ATOM24

ATOM24

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ATOM24

ATOM24

Of emergent genealogical demixing and organizational entropy in developing living systems

Spatiotemporal organization of individuals, for instance within growing bacterial colonies, is a key determinant of intraspecific interactions and colony-scale heterogeneities [1]. Many species are surface associated, yet how they distribute genealogically, i.e., how daughter cells distribute in relation to their mother cells, specifically during the early stages of biofilm formation, remains unknown. Recently, by analyzing expanding colonies using a custom-built label-free algorithm [2], we tracked bacterial growth, revealing distinct self-similar genealogical enclaves that intermix over time. While biological activity determines the intermixing dynamics, emergent topological defects at the interfaces shape the finger-like morphology of interfacial domains. Interestingly, the Shannon entropy of cell arrangements reduce over time with faster-dividing cells possessing higher spatial affinity to genealogical relatives, at the cost of a well-mixed, entropically favorable state. A coarse-grained lattice model confirmed these observations, further revealing that the genealogical enclaves emerged due to an interplay of division-mediated dispersal, stochasticity of division events, and cell-cell interactions. These results uncover so-far hidden emergent self-organizing features arising due to entropic suppression, which modulate intraspecific genealogical distances within growing colonies. The spatio-genealogical proximity to kith and kin offers an intrinsic feature of early developmental stages that depends on the local conditions [3,4], with functional relevance not just for bacterial colonies but also for developing consortia and tissues. References [1] J. Dhar, A. Thai, A. Ghoshal, L. Giomi, & A. Sengupta, Nature Physics 18, 2022 [2] G. Rani & A. Sengupta, Biophysical Reports 4, 2024 [3] R. Riedel, G. Rani & A. Sengupta, arXiv preprint, 2024 [4] G. Rani, R. Riedel & A. Sengupta, in preparation Short Bio Prof. Anupam Sengupta is an FNR-ATTRACT Fellow and head of the Physics of Living Matter Group at the University of Luxembourg. He holds a Dual Degree in Mechanical Engineering from the Indian Institute of Technology, Bombay (India), with specialization in Thermal and Fluids Engineering. After a short stint in industry, Anupam joined the Max Planck Institute for Dynamics and Self-Organization, Göttingen (Germany), where in 2013, he received a Ph.D. with summa cum laude in condensed matter physics for his work on liquid crystal microfluidics. Between 2014 and 2017, Anupam was a Human Frontier Cross-Disciplinary Fellow, first at the Massachusetts Institute of Technology (USA) and then at the ETH Zurich (Switzerland), working on a range of problems on the physical ecology of microorganisms. Since 2018, Anupam is based in Luxembourg where his multi-disciplinary team combines material physics, microbiology, mathematical modelling and machine learning to understand microbial response and adaptation to different dynamic settings, from marine and freshwater ecosystems to the human gut and cancer environments. Currently, Anupam is a member of the Institute for Advanced Studies at the University of Luxembourg, and among other roles, serves as the Director of the Undergraduate Physics Studies of the University of Luxembourg.

Phase transitions in confluent epithelia

In spite of the absence of gaps and interstitial structures, confluent layers of epithelial cells are able to migrate collectively and remove excess cells by extrusion. While in common with foams and other passive confluent fluids, both these phenomena crucially rely on the active remodelling of the cellular network, via topological transformations known as T1 and T2 processes. Using a combination of active hydrodynamics and Renormalization Group methods, I will show that both collective migration and cell extrusion can be thought as continuum phase transitions, with the former being in the same universality class of the Kosterlitz-Thouless transition and the latter reminiscent of sublimation in solids.

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IMPRS Seminar

IMPRS Seminar

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