The SEMPARIS seminar webserver hosts annoucements of all seminars taking place in Paris area, in all topics of physics, mathematics and computer science. It allows registered users to receive a selection of announcements by email on a daily or weekly basis, and offers the possibility to archive PDF or Powerpoint files, making it available to the scientific community. [ More information ]
Upcoming Seminars  [Next 30 ]  
[ scheduler view ] 
Thursday 21 September 2023, 10:00 at IHP, Grisvard (314)  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  The conformal bootstrap equations in any dimension are an infinite set of coupled nonlinear equations in infinitely many variables. According to the lore, the solutions of the full set of equations correspond to physical CFTs. At the same time, the only solutions truly known to exist above two dimensions are mean field theories. In this talk, I will discuss conformal measure spaces, which are objects guaranteed to produce solutions of the conformal bootstrap in any dimension. I will review why hyperbolic manifolds give rise to a particular class of conformal measure spaces, and thus to solutions of the complete set of the conformal bootstrap equations. I will then use the bootstrap equations to prove new bounds on the Laplace spectra of hyperbolic manifolds in two and three dimensions. Finally, I will discuss the similarities and differences between these solutions, and those that are believed to arise in physical CFTs. 
Thursday 21 September 2023, 11:45 at IHP, Grisvard (314)  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  Understanding CalabiYau metrics and hermitian YangMills connections has long been a challenge in mathematics and theoretical physics. These geometric objects play a crucial role in constructing realistic models of particle physics in string theory. However, with no closedform expressions for them, we are unable to compute basic quantities in topdown string models, such as particle masses and couplings. Breakthroughs in machine learning have opened a new path to tackle this problem. After recalling the relationship between these geometric ingredients and 4d effective field theory, I will review recent progress in using machine learning to calculate these metrics and connections numerically. Finally, I will highlight how this newly available geometric data can be used, including studying the spectrum of Laplacetype operators on a CalabiYau in the presence of a background gauge field.  
Attachments: 
Monday 25 September 2023, 10:45 at LPTMC, campus Jussieu, couloir 1213, 5ème, salle 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat 



Abstract:  Landau's Fermi liquid theory provides an effective description of a lowtemperature fermionic system in the form of a dilute gas of quasiparticles confined to the Fermi level. It remarkably applies to systems whose microscopic physics is poorly understood, such as Helium3, and successfully describes their long wavelength collective modes, in particular the phononic ones. However, due to the difficulty of solving exactly the quasiparticle transport equation in the case of arbitrary interactions, Landau's theory is generally used only in the hydrodynamic or collisionless limiting cases. In the case of a twocomponent ultracold Fermi gas in its normal phase, the simplicity of contact interactions has allowed us to go further and describe the entire transition from the hydrodynamic to the collisionless regime. In the weaklyinteracting limit, our results are in excellent quantitative agreement with densitydensity response measurements performed by the Yale group, where the resonance corresponding to the first sound emerges from the Lindhard function of the noninteracting gas. In timeofflight images, which enable tomography of the Fermi liquid, this evolution corresponds to a drastic change in the distribution of quasiparticles on the Fermi sphere. While the density response thus seems to be very well described by Landau's theory, I will show that nonFermi liquid properties appear in the pairing susceptibility, near the superfluid critical temperature. 
Monday 25 September 2023, 14:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTSTA (Séminaire de Physique Statistique, CEA/Saclay)  condmat 


Tuesday 26 September 2023, 10:00 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  This course will give a pedagogical introduction to (quantum) integrability, a topic in mathematical physics with applications ranging from experiments in condensedmatter physics to highenergy theory. The aim is to show some highlights of the field, with a glimpse of the underlying algebraic structures, while keeping technicalities to a minimum. \\ \\ The provisional plan of the course is as follows 
Tuesday 26 September 2023, 11:00 at LPTMS, Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 



Abstract:  In this talk, I will present several results on the Anderson Hamiltonian with white noise potential in dimension 1. This operator formally writes « – Laplacian + white noise ». It arises as the scaling limit of various discrete models and its explicit potential allows for a detailed description of its spectrum. We will discuss localization of its eigenfunctions as well as the behavior of the local statistics of its eigenvalues. Around large energies, we will see that the eigenfunctions are delocalized and follow a universal shape given by the exponential of a Brownian motion plus a drift, a behavior already observed by Rifkind and Virag in tridiagonal matrix models. Based on joint works with Cyril Labbé. 
Tuesday 26 September 2023, 14:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  Gravitational waves with frequencies below 1 nHz are notoriously difficult to detect. In this talk, I will present a new means of probing this regime by using secular drifts in observed pulsar timing parameters. I will show the results of searches for both continuous and stochastic signals in this regime and will discuss what future observations may reveal about the signal recently discovered by pulsar timing collaborations at frequencies above a nanohertz. 
Thursday 28 September 2023, 11:00 at IHES, Amphithéâtre Léon Mochane  MATHIHES (TBA)  math 



Abstract:  In 2010, de CataldoMiglorini used generic flags to compute the perverse filtration on the cohomology of an affine variety with values in a constructible sheaf. In this talk, I shall introduce the BrylinskiRadon transformation, discuss its properties and derive consequences for the perverse filtration. We shall also discuss some arithmetic applications of our results. This is joint work with Ankit Rai. 
Thursday 28 September 2023, 11:00 at LPENS, Salle Dussane, 45 rue d'Ulm  LPENSMDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS)  condmat 



Abstract:  Mechanics has historically played a pivotal role in science by providing the basis for classical physics. Today, with the advent of nanoscale mechanical devices combined with quantum electronic devices, we are witnessing a renaissance in the field of mechanics. After an introductory introduction on the mesoscopic physics of nanomechanical resonators, I will discuss our recent advances on mechanical resonators based on carbon nanotubes. The nanotube in these devices vibrates as a guitar string. Singleelectron tunneling enables coupling the mechanical vibrations to electrons by a large amount. I will show how to use this coupling to create a nonlinear mechanical oscillator approaching the quantum regime, where the resulting quantum energy levels of the mechanical oscillator are no longer evenly spaced [1]. Using mechanical nanotubes hosting multiple quantum dots, we expect that our approach may enable the realization of a mechanical qubit [2] and a quantum simulator of quantum matters featuring strong electronphonon correlations [3,4]. [1] C Samanta, SL De Bonis, CB Møller, R TormoQueralt, W Yang, C Urgell, B Stamenic, B Thibeault, Y Jin, DA Czaplewski, F Pistolesi, A Bachtold, (arXiv:2211.07632) Nature Physics (2023). [2] F. Pistolesi, A. N. Cleland, and A. Bachtold, Phys. Rev. X 11, 031027 (2021) [3] U Bhattacharya, T Grass, A Bachtold, M Lewenstein, F Pistolesi, Nano Lett. 21, 9661 (2021) [4] Lin Zhang, Utso Bhattacharya, Adrian Bachtold, Stefan Forstner, Maciej Lewenstein, Fabio Pistolesi, Tobias Grass, npj Quantum Information 9, 7 (2023) 
Thursday 28 September 2023, 11:00 at IHP, Amphi Darboux (unusual location !)  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 



Abstract:  Coulomb branches have recently been given a rigorous mathematical definition by the work of BravermanFinkelbergNakajima. We will discuss their geometric and categorical structure based on recent work with Harold Williams. The Grothendieck groups of these categories recover previously studied algebras such as double affine Hecke algebras (DAHAs), certain open Richardson varieties in affine flag manifolds, multiplicative Nakajima quiver varieties etc. One of our main results is that these Coulomb categories carry a natural tstructure consisting of what we call Koszulperverse coherent sheaves. The classes of such simple sheaves give a canonical basis of these algebras in a uniform way. These Coulomb categories also carry (conjecturally) a cluster structure. We will survey some of these results as time (and interest) permits. (based on 2306.03023 ) 
Thursday 28 September 2023, 14:00 at LPENS, E244 (24 Rue Lhomond)  LPTENSHE (Séminaire commun LPTENSLPTHE)  hepth 



Abstract:  "Strange metals" exhibit an anomalous temperature dependence of the low temperature resistivity and the measurement of their spectral function via ARPES indicates the breakdown of the conventional quasiparticle picture. In my talk, I will explain how we construct a semiholographic description for such behaviours where we propose an effective theory in which the electron of a twodimensional band hybridizes with a fermionic operator of a critical holographic sector, while also interacting with other bands that preserve quasiparticle characteristics. Besides the scaling dimension $\nu$ of the fermionic operator in the holographic sector, the effective theory has two dimensionless couplings $\alpha$ and $\gamma$ determining the holographic and Fermiliquidtype contributions to the selfenergy respectively. In the case of DC conductivity that irrespective of the choice of the holographic critical sector, there exists a ratio of the effective couplings for which we obtain linearinT resistivity for a wide range of temperatures. This scaling persists to arbitrarily low temperatures when $\nu$ approaches unity in which limit we obtain a marginal Fermi liquid with a specific temperature dependence of the selfenergy. Interestingly, we explain the origin of the linearinT resistivity and strange metallic behavior as a consequence of the emergence of a universal form of the spectral function which is independent of the model parameters when the ratio of the two couplings takes optimal values determined only by the critical exponent. This universal form fits well with photoemission data of copper oxide samples for under/optimal/overdoping with a fixed exponent over a wide range of temperatures. We further obtain a refined Planckian dissipation scenario. 
Thursday 28 September 2023, 17:00 at
CPHT,
Amphitheatre Faure (Ecole Polytechnique) ( Friedmann Colloquium Physics Department Ecole Polytechnique )  SEMEXCEP (Séminaire exceptionel)  hepth 



Abstract:  I will review the progress achieved in theoretical and observational cosmology over the past 40 years and explain how the theoretical predictions for the temperature fluctuations of the Cosmic Microwave Background, made in 1980, have subsequently been fully confirmed in precision measurements for the last 30 years. 
Friday 29 September 2023, 10:00 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  The two parameters of the Standard Model that have the strongest impact on physics at low en ergy are also the most sensitive to the details of the theory at high energies. They are the cos mological constant and the Higgs boson mass. Experimentally they are both associated to energy scales that we can measure. Theoretically they force us to ask questions about physics at higher energies, possibly all the way to the Planck scale. \\ \\ At the moment it is very hard to understand their measured values. The difficulty has the same origin for both parameters and can be traced to the symmetries of fundamental interactions. A prediction based on symmetry gives results that are 120 orders of magnitude too large for the cosmological constant and 34 orders of magnitude too large for the Higgs mass. The course starts with a brief review that makes the meaning of these estimates precise and discusses to what ex tent we have a problem in the theory of fundamental interactions. In the first two lectures I will show that the resolution of this apparent failure of symmetry is guaranteed to teach us something qualitatively new about Nature. \\ \\ I will then discuss theories that can successfully predict the value of the Higgs boson mass, includ ing traditional attempts based on supersymmetry and scale invariance. However, the emphasis will be on modern ideas that involve the evolution of the Universe. I will also review some incom plete, but stimulating proposals based on more radical departures from standard effective field theory arguments. This includes possible UV/IR mixing effects, inspired by string theory, or the role of noninvertible symmetries. The broader aim of this second part of the course is to give a comprehensive overview of all conceptually distinct possibilities that are still viable experimen tally. In the process I will comment on which (very small) subset of these ideas can explain also the value of the cosmological constant. 
Friday 29 September 2023, 11:00 at
CPHT,
Salle de conférences du LLR aile 5 (Ecole Polytechnique) ( Friedmann biseminar CPHTLLR )  SEMEXCEP (Séminaire exceptionel)  hepth 



Abstract:  I will discuss gravitational dark matter production in the Early Universe and how it spoils predictivity of most nonthermal dark matter models. I will give an example of a class of models that are free from such uncertainties known as « stronger coupling freezein » and discuss observational prospects for this framework. 
Friday 29 September 2023, 14:30 at CPHT, Salle de conférences du LLR aile 5 (Ecole Polytechnique)  SEMEXCEP (Séminaire exceptionel)  hepth 



Abstract:  I will consider the case where the potential for the scalar field is either unbounded from below or the second minimum corresponding to the true va cuum has a depth exceeding the height of the potential barrier. In this case, the materialized bubbles dominating the vacuum decay naturally have a thick wall and the thinwall approximation is not applicable. In such a case the main contribution to the action determining the decay probability of the false va cuum comes from the part of the solution for which the potential term in the equation for instantons can be neglected compared to the friction term. I show that the developed approximation exactly reproduces the leading order results for the few known exactly solvable potentials. 
Monday 2 October 2023, 10:30 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  math 



Abstract:  Let G be a simplyconnected complex simple algebraic group and let C be a smooth projective curve of any genus. Then, the moduli space of semistable Gbundles on C admits so called determinant line bundles. E. Verlinde conjectured a remarkable formula to calculate the dimension of the space of generalized theta functions, which is by definition the space of global sections of a determinant line bundle. This space is also identified with the space of conformal blocks arising in Conformal Field Theory, which is by definition the space of coinvariants in integrable highest weight modules of affine KacMoody Lie algebras. Various works notably by TsuchiyaUenoYamada, KumarNarasimhanRamanathan, Faltings, BeauvilleLaszlo, Sorger and Teleman culminated into a proof of the Verlinde formula. The main aim of this talk is to give a basic outline of the proof of this formula derived from the Propogation of Vacua and the Factorization Theorem among others. The proof requires techniques from algebraic geometry, geometric invariant theory, representation theory of affine KacMoody Lie algebras, topology, and Lie algebra cohomology. Some basic knowledge of algebraic geometry and representation theory of semisimple Lie algebras will be helpful; but not required. This lecture should be suitable for any one interested in interaction between algebraic geometry, representation theory, topology and mathematical physics. 
Tuesday 3 October 2023, 10:00 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  The two parameters of the Standard Model that have the strongest impact on physics at low en ergy are also the most sensitive to the details of the theory at high energies. They are the cos mological constant and the Higgs boson mass. Experimentally they are both associated to energy scales that we can measure. Theoretically they force us to ask questions about physics at higher energies, possibly all the way to the Planck scale. \\ \\ At the moment it is very hard to understand their measured values. The difficulty has the same origin for both parameters and can be traced to the symmetries of fundamental interactions. A prediction based on symmetry gives results that are 120 orders of magnitude too large for the cosmological constant and 34 orders of magnitude too large for the Higgs mass. The course starts with a brief review that makes the meaning of these estimates precise and discusses to what ex tent we have a problem in the theory of fundamental interactions. In the first two lectures I will show that the resolution of this apparent failure of symmetry is guaranteed to teach us something qualitatively new about Nature. \\ \\ I will then discuss theories that can successfully predict the value of the Higgs boson mass, includ ing traditional attempts based on supersymmetry and scale invariance. However, the emphasis will be on modern ideas that involve the evolution of the Universe. I will also review some incom plete, but stimulating proposals based on more radical departures from standard effective field theory arguments. This includes possible UV/IR mixing effects, inspired by string theory, or the role of noninvertible symmetries. The broader aim of this second part of the course is to give a comprehensive overview of all conceptually distinct possibilities that are still viable experimen tally. In the process I will comment on which (very small) subset of these ideas can explain also the value of the cosmological constant. 
Tuesday 3 October 2023, 11:00 at LPTMS, Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 


Tuesday 3 October 2023, 14:00 at IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  The presence of nearby complex conformal field theories (CCFTs) hidden in the complex plane of the tuning parameter was recently proposed as an elegant explanation for the ubiquity of "weakly firstorder" transitions in condensed matter and highenergy systems. Recently, we have numerically confirmed the presence of such a CCFT in a loop model which derives from a hightemperature formulation of the O(n) model. Surprisingly, we found that the CCFT only survives until n=12.34, beyond which the transfer matrix acquires a gap. In this talk, I will discuss ongoing work in trying to explain this loss of complex conformality at large n, using a mapping to a hard hexagon model for n going to infinity. I will also discuss the connection between the original O(n) model and its loop version and the consequences for CCFTs in these models. 
Wednesday 4 October 2023, 11:00 at LKB, Amphi 25 – Sorbonne université – 4 place Jussieu – 75005 Paris  SEMLKB (Séminaire du Laboratoire Kastler Brossel)  quantph 



Abstract:  I will discuss how irradiation of certain quantum materials with coherent electromagnetic radiation at TeraHertz and midinfrared frequencies can induce transient high temperature states that have striking similarities with equilibrium superconductors. These phases are observed at base temperatures as high as room temperature, underscoring the ability to impress coherence with light. This talk will also cover our search for new experimental methods that enable the characterization of these transient phases, to measure optical, structural, electrical and magnetic properties at very fast speeds. (https://qcmd.mpsd.mpg.de) 
Wednesday 4 October 2023, 12:45 at LPENS, Seminar room, 3 rue d’Ulm, College de France  FORUMENS (Forum de Physique Statistique @ ENS)  condmat.statmech 



Abstract:  For gapped topological systems, there exist several approaches to construct higherdimensional models by combining lower dimensional ones (e.g. coupled wires or decorated domain wall constructions). In this talk, we will propose a generalization of this approach to gapless systems. We construct a class of solvable models for 2+1D quantum critical points by attaching 1+1D conformal field theories (CFTs) to fluctuating domain walls. Our local Hamiltonian attaches gapless spin chains to the domain walls of a triangular lattice Ising antiferromagnet. The macroscopic degeneracy between antiferromagnetic configurations is only split by the Casimir energy of each decorating CFT, which is usually thought to be a universal function of the central charge $E_{Cas} =  (\pi c)/(3 L)$. Remarkably, we found several examples of 1D Hamiltonians realizing CFTs for which the Casimir energy is positive (i.e. $c<0$ in the last formula, making it favorable for domain walls to condense into a single selfavoiding random walk (or "snake") visiting every site of the 2D lattice. Since the snake is macroscopically long, the CFT living on it has a vanishing gap, and the resulting 2+1D theory is thus gapless. We obtain predictions for critical exponents and for entanglement by combining results about 1+1D CFTs and about the statistical fluctuations of the snake (which are described by the $O(n=0)$ fullypacked loop model). We show that the area law for entanglement is restored for the 2D state (despite the log term for the entanglement of the 1+1D CFTs) but that it is nonlocal in nature. Finally, we provide a verification of our predictions based on Monte Carlo calculations. 
Thursday 5 October 2023, 14:00 at LPTMC, Jussieu, towers 1213, 5th floor, LPTMC seminar room  SEMEXCEP (Séminaire exceptionel)  condmat 



Abstract:  The spinstatistics relation is a pillar of our description of the world. In this seminar, I will show that it is possible to introduce a measurable spin also for the quasiparticles of the quantum Hall effect, and that this spin satisfies a spinstatistics relation. I will discuss this idea in several explicit cases (including the case of Laughlin's quasielectron) and lay down a sketch of the proof. [1,2] Finally, I will conclude the seminar discussing the entanglement properties of FQHE wavefunctions using a BisognanoWichmann Hamiltonian (see Ref. [3] for a recent experiment in the noninteracting case). References: [1] Nardin, Ardonne, LM, Spinstatistics relation for quantum Hall states, https://arxiv.org/abs/2211.07788 [2] Nardin, LM, Laughlin's quasielectron is a nonlocal composite fermion, https://arxiv.org/abs/2306.13972 [3] Redon, Liu, Bouhiron, Mittal, Fabre, Lopes, Nascimbene, Realizing the entanglement Hamiltonian of a topological quantum Hall system, https://arxiv.org/abs/2307.06251 
Thursday 5 October 2023, 14:00 at IJCLAB, Salle A018 (IJCLab)  NUCTHEO (Séminaire de physique nucléaire théorique)  nuclth 



Abstract:  CERN experiment  PUMA  is going to form antiprotonic atoms of unstable nuclei. The purpose is to detect $\pi$mesonic decays of such atoms and extract the neutron excess at nuclear surfaces  
Attachments: 
Monday 9 October 2023, 14:00 at IHES, Bâtiment Alix et Marwan Lahoud  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  We discuss general properties of perturbative RG flows in AdS with a focus on the treatment of boundary conditions and infrared divergences. In contrast with flatspace boundary QFT, general covariance in AdS implies the absence of independent boundary flows. We illustrate how boundary correlation functions remain conformally covariant even if the bulk QFT has a scale. We apply our general discussion to the RG flow between consecutive unitary diagonal minimal models which is triggered by the φ(1,3) operator. For these theories we conjecture a flow diagram whose form is significantly simpler than that in flatspace boundary QFT. 
Monday 9 October 2023, 14:00 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  I will explain why positive representations of fundamental groups of surfaces satisfy a "collar lemma" similar to the classical collar lemma for hyperbolic geometry, and have associated positive crossratios. As a consequence, I will deduce that positive representations form closed subsets of the representation variety. I will spend some time recalling what a positive representation is, what the associated crossratios are, and explain the main new object that we shall use and that we call "photons". This is joint work with Jonas Beyrer, Olivier Guichard, Beatrice Pozzetti and Anna Wienhard. 
Monday 9 October 2023, 16:00 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  Quantum representations are families of finitedimensional representations of mapping class groups satisfying strong compatibility conditions. One of the most wellknown (the socalled SO(3)TQFT) depends on a parameter q which is a root of unity of order 2r (r odd). These representations preserve a Hermitian form: recently, with B. Deroin, we explained how to compute its signature (among other things). More recently, I observed that this computation is related to the trace field of the 2bridge knot K(r,s) where q=exp(iπs/r). During the talk, I will explain this relation and the objects involved in it. 
Tuesday 10 October 2023, 11:00 at LPTMS, Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 


Wednesday 11 October 2023, 10:00 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  The two parameters of the Standard Model that have the strongest impact on physics at low en ergy are also the most sensitive to the details of the theory at high energies. They are the cos mological constant and the Higgs boson mass. Experimentally they are both associated to energy scales that we can measure. Theoretically they force us to ask questions about physics at higher energies, possibly all the way to the Planck scale. \\ \\ At the moment it is very hard to understand their measured values. The difficulty has the same origin for both parameters and can be traced to the symmetries of fundamental interactions. A prediction based on symmetry gives results that are 120 orders of magnitude too large for the cosmological constant and 34 orders of magnitude too large for the Higgs mass. The course starts with a brief review that makes the meaning of these estimates precise and discusses to what ex tent we have a problem in the theory of fundamental interactions. In the first two lectures I will show that the resolution of this apparent failure of symmetry is guaranteed to teach us something qualitatively new about Nature. \\ \\ I will then discuss theories that can successfully predict the value of the Higgs boson mass, includ ing traditional attempts based on supersymmetry and scale invariance. However, the emphasis will be on modern ideas that involve the evolution of the Universe. I will also review some incom plete, but stimulating proposals based on more radical departures from standard effective field theory arguments. This includes possible UV/IR mixing effects, inspired by string theory, or the role of noninvertible symmetries. The broader aim of this second part of the course is to give a comprehensive overview of all conceptually distinct possibilities that are still viable experimen tally. In the process I will comment on which (very small) subset of these ideas can explain also the value of the cosmological constant. 
Wednesday 11 October 2023, 13:30 at DPTPHYSENS, ConfIV (E244)  Dépt de Physique de l'ENS  24 rue Lhomond 75005 PARIS  COLLOQUIUMENS (Colloquium of the Physics Department of ENS)  physics 



Abstract:  One of the first model systems we encounter in quantum mechanics class is a mass on a spring. However, in practice, it is not easy to observe a massive mechanical object exhibiting the quantum properties of a harmonic oscillator, such as zeropoint fluctuations, energy quantization, or quantum superpositions. Nevertheless, in recent years, it has become possible to control and the measure the quantum states of the motion of macroscopic mechanical objects. I will present our recent experiments on creating “Schrödinger cat” states in a bulk acoustic wave resonator by coupling it to a superconducting circuit, and how we can observe the quantum ground state of a several hundred microgram mechanical mode using light. I will also discuss the applications of these systems in quantum information, quantum sensing, and explorations of fundamental physics. 
Thursday 12 October 2023, 14:00 at LPTMC, Jussieu, towers 1213, 5th floor, LPTMC seminar room  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat 



Abstract:  TBA 

[ English version ] 