Dear Sir or Madam, This letter is addressed to all those who, at some point in their professional lives, have worked at the Institut (formerly Service) de Physique Théorique.   As most of you know, the Institute celebrated its sixtieth anniversary last year. This event brought many of you together. It was an opportunity to measure your attachment to us.   At the same time, our Institute, and theoretical physics in general, is facing many new challenges. Many people today doubt science, not only its usefulness, but also its methods and results. The Covid crisis marked a new stage in this attitude of mistrust, and the research carried out at the Institute is no exception. What's more, funding methods have changed radically, and funds are increasingly allocated on a project basis, focused on priorities that are often far removed from the needs of fundamental research.

A new colleague joins the IPhT!

Carlo Heissenberg graduated with flying colors in 2019 from the Scuola Normale Superiore di Pisa, the Italian twin sister of the Ecole Normale de Paris. His initial research focused on the infrared properties of gravitational theories and higher spin theories from the perspective of asymptotic symmetries, a topic that later found phenomenological applications in the context of gravitational wave studies. It was during his first postdoctoral period at Nordita-Uppsala (2019-2023) that Carlo started working on gravitational wave physics using ideas borrowed from particle physics, such as scattering amplitudes and eikonal exponentiation in particular. He quickly became a leader in the field, publishing several important papers with world-famous physicists such as Gabriele Veneziano.

Antoine Bourget, from the IPhT, will soon be appearing on YouTube with David Elbaz from Irfu, author of a lot o books and  for a round table discussion on YouTube organized by the DCom/CEA digital division. The interview will be done by Marie Treibert, owner of a Youtube channel (La boîte à curiosités.) The YouTube premiere will be held on: Sunday October 27 from 8:00 pm to 9:00 pm. The talk will take the form of an informal round-table discussion about black holes. Antoine Bourget and David Elbaz will share  their complementary approaches. Auditors will be able to follow the program in real time and to ask questions that Antoine and David will answer in the chat. link to the round table If you want to see more about Antoine an David: The Antoine's channel, Scientia Egregia The David Elbaz's show: Have a good listening!

We are delighted to welcome Mrs. Vanessa Bele Bilock at IPhT, in a CNRS administrator position, in anticipation of the departure of Mrs. Justine Dionisi. Justine has told us she would move to the Institute of Space Astrophysics in Orsay, from 1/12/2024. Vanessa holds a licence degree in marketing and communication and is currently studying on the Paris-Saclay campus. You can find her in the room 21. Welcome to Vanessa!

We can see Harold Erbin, post-doc in Theoretical Physics Institute in CEA/Saclay, in a video on the "Phymaths Podcast" channel.

Crédit: Julie Gravier- Evolution between 1829 and 1907 of the spatial distributionof cafes and restaurants in Paris. Analysis of economic activities during a century of urban growth in Paris Evolution between 1829 and 1907 of the spatial distribution of cafes and restaurants in Paris. Researchers Marc Barthelemy (Institut de Physique Théorique and Centre d'Analyse et de Mathématique Sociales, EHESS), and Julie Gravier (Centre de Recherches Historiques and Centre d'Analyse et de Mathématique Sociales, EHESS) have just published in the prestigious journal Nature cities [1] their findings on the analysis of economic activities in a century of urban growth in the city of Paris. Contemporary studies on the dynamics of economic activity in growing cities generally focus on periods of a few years or a few decades.

Jorge FERNANDEZ DE COSSIO DIAZ joined the IPhT on September 2, 2024.

A new article by Roger Balian, Armen Allahverdyan, and Theo M. Nieuwenhuizen!

Olivier Gingras will join the IPhT in early 2025 on a permanent joint position at the IPhT and the QCC, Flatiron, New York. Part of the challenge of this position will be to facilitate interactions and collaborations between the two institutes on the theme of the quantum N-body problem.

Bertrand Eynard, Paolo Gregori, Dimitrios Mitsios and Soufiane Oukassi from the IPhT are among the organisers of the August 2024 session (29 July - 23 August) of the prestigious "Les Houches" International School of Physics. The Les Houches Quantum Geometry School (Mathematical methods for gravity, gauge theories and non-perturbative physics) will bring together leading experts in theoretical physics. It will offer to 50 students from all over the world introductory courses covering topics such as quantum gravity, gauge theories and non-perturbative physics. These courses will focus on the methods of mathematical physics, in particular the theory of random matrices, topological recurrence, resurgence and moduli space. This event is part of the ERC-SyG Project ReNewQuantum.   School website : https://houches24.github.io/

Since the 1980s, many exact results have been discovered in 2d CFT, from critical exponents to correlation functions to complete solutions of certain models. In d>2, there is a wealth of numerical results as well as promising analytic approaches, but comparably fewer exact answers. The aim of this conference is to review the most promising analytic methods and results in CFT in any dimension. In particular we will try to understand to which extent the 2d methods can be extended to d>2, and what is missing to exactly solve d>2 CFTs. Speakers: Fernando Alday Colin Guillarmou Yifei He Gregory Korchemsky Petr Kravchuk Elli Pomoni Ingo Runkel  Hubert Saleur Volker Schomerus Xin Sun Emilio Trevisani Philine van Vliet Registration: The conference is in person only, and limited to 45 participants, who are supposed to attend all the talks. People who would like to participate should fill the registration form no later than June 10th.

An international conference in honour of Philippe Di Francesco's 60th birthday will be held at the IPhT from 24 to 26 June 2024. A distinguished member of the IPhT, Philippe Di Francesco is a mathematical physicist universally known for his work on conformal theories, integrable systems, random matrices, combinatorics and enumerative geometry. Conference website : https://indico.in2p3.fr/event/30593/  

The ESA's Science Programme Committee has just officially adopted the LISA mission [1], thus giving the go-ahead for the construction of instruments and satellites.

The new book written by Marc Barthélémy and Vincent Verbavatz's, "Statistics of Urban populations", has just been published in December 2023 by Oxford University Press.

Researchers at the University of Innsbruck, working with a member of the IPhT, have succeeded in building a node of a quantum communication network and using it to transfer quantum information over a distance of 50 km using standard telecom fibers. The physical platform that has been used was made of a pair of trapped calcium-40 ions, cooled and manipulated by laser to emit single photons. These photons, each of which is entangled with its 'parent' ion, are then converted to telecom wavelengths and sent to 25km-long optical fibres. At last, the ions are manipulated and measured, leaving the two photons separated by 50 km in an entangled state. The theory of this feat had been proposed in 2009. It seemed futuristic at this time, and now represents a step further towards the construction of quantum communication networks. The journal Physics World considers this result, which was published in Physical Review Letters, to be one of the 10 most remarkable of 2023.

Welcome to Anne Capdepon, Deputy Head of Research Support at the IPhT. We are delighted to welcome Anne Capdepon, who joined the Institute on 1 December. She will be in charge of Research Support.

On 7 November 2023, the first images taken by Euclid, an ESA satellite launched on 1 July 2023, were revealed.

The Institute of Theoretical Physics (IPhT), formerly SPhT, is internationally known for the excellence of its scientific research, but has also a very ancient history. Its evolution is inextricably linked to that of the CEA and is almost as old. Its adventure began in 1947 with a small group of physicians passionated for abstraction, and to date more than 500 people have shared the life of the Institute, as well as the many visitors from all over the world. Today, 48 permanent researchers, 25 graduate students and 30 postdoctoral fellows, as well as the support staff, work at IPhT.

Ben Wieder, researcher at the Institut de Physique Théorique, has just been awarded an ERC Starting grant in the field of topological insulators

Michel Gaudin, French mathematical physicist, engineer from the Ecole Polytéchnique (Class 1951) and Ingénieur des Ponts et Chaussées, died on August 4th, 2023, aged ninety-two years old. Gaudin joined the Commissariat à l'Énergie Atomique in 1956, first in the Service de Neutronique Expérimentale, then in the Service de Physique Théorique (later Institut de Physique Théorique, IPhT). He spent his entire career there, with the exception of one year at Stony Brook in 1970.

By establishing an original connection between Feynman integrals and algebraic geometry, a team led by the IPhT has tackled the challenge of computing "scattering amplitudes," which form the basis for the interpretation of particle physics experiments, among other things.

Matt von Hippel went to Stony Brook University for his doctoral studies after obtaining an undergraduate degree at Tufts.  He obtained his PhD in 2014, on N=4 supersymmetric Yang-Mills theory.  His advisor was Michael Douglas.  During his PhD he developed a method to bootstrap perturbative scattering amplitudes in quantum field theories.  He then spent three years as a postdoc at the Perimeter Institute, where he continued working on bootstrapping higher-loop amplitudes in the N=4 theory.  In 2017, he moved to the Niels Bohr Institute in Copenhagen, first as a postdoc and later as an Assistant Professor.  Matt is interested in the broad variety of integral functions that appear in scattering amplitudes.  He seeks to understand them using novel integration methods.  He has already discovered surprising iterative structures in them.

Since 2016 Monica Guica has been working at the Institute of Theoretical Physics in Saclay (CEA/CNRS) in the field of the relation between quantum gravity and conformal quantum theories. In particular, she explores the correspondence between quantum gravity on a spacetime and certain field theories based on the edge of the first spacetime. Using a term used in optics, this correspondence is called "holographic" because all the information contained in a black hole is coded on its surface. This medal rewards her work, in particular that on the integrable deformation of type "J TBar" (J being a current and TBar a component of the tensor-energy impulse) of a two-dimensional field theory invariant by conformal transformations [2]. Congratulations Monica! Links: CNRS' announcement https://arxiv.org/abs/1710.08415 CEA/DRF's announcement

We are glad  to inform  you that  the  27th ITZYKSON CONFERENCE will be held  from Wednesday, the 31st of May in the morning, to Friday the 2nd of June at the Institut de Physique Theorique (IPhT), CEA Universite de Paris-Saclay. This year the ITZYKSON CONFERENCE will be devoted to "Fluctuations far from  Equilibrium". You can find more details on the web-page dedicated to this event: https://indico.in2p3.fr/event/29430/ We hope that the conference will attract the interest of many participants.  We would be grateful if you could register at : https://indico.in2p3.fr/event/29430/registrations/3507/ This will take you a very little time  but it will be of great help to us for practical matters. Best regards, Tomohiro Sasamoto, Laure Sauboy and  Kirone Mallick.

The Nuclear Physics Division of the European Physical Society has awarded Giuliano Giacalone, a former student of IPhT, its PhD prize. This prize is awarded every third year, and the ceremony took place during the EuNPC 2022 conference in Santiago de Compostela, Spain, in October 2022. https://indico.cern.ch/event/1104299/page/26561-npd-2021-phd-prize-winners Giuliano, now a postdoc at the University of Heidelberg, completed his PhD thesis "Observing the shape of nuclei at high-energy colliders" in November 2020 under the supervision of Jean-Yves Ollitrault. His thesis has previously been honoured with an award of the French Physical Society. https://www.sfpnet.fr/accessits-prix-jeunes-chercheurs-euses-2020-de-la-sfp Congratulations!

The retreat of the Institute of Theoretical Physics was held in Autrans (Vercors) from May 23 to 25. The approximately one hundred participants enjoyed the benefits of the altitude and the gorgeous environment surrounding the Escandille congress center, which hosted the event. This intense and joyful retreat provided an opportunity to strengthen the cohesion between members of our laboratory and to discuss among ourselves issues of science and the life of the Institute. The IPhT is characterized by a broad spectrum of research topics. In order to highlight the skills and to pedagogically transmit the knowledge to other non-expert colleagues, 7 scientific presentations of IPhT researchers were organized, complemented by 2 presentations held by external speakers, Professors Luc Blanchet (Institut d'Astrophysique de Paris, long-term visitor at IPhT) and Emil Martinec (University of Chicago).

We are pleased to announce that Ben Wieder will arrive at the IPhT at the end of September 2022 on the position of permanent junior researcher. Benjamin Wieder completed his PhD at the University of Pennsylvania with Charlie Kane in 2016.He was then a postdoc in Andrei Bernevig's group at Princeton University. He is currently a postdoc at MIT, working with T. Senthil among others. He is a theoretical physicist of condensed matter and more specifically of electronic properties in materials with topologically non-trivial band structure. He has worked on the combined aspects of geometry and topology in materials with complex nodal surfaces. He then studied the relationships between energy band connectivity of solids, structural chirality, topology and magnetism. He collaborated with Zahid Hasan's group at Princeton to identify candidate materials with these new properties.

We are pleased to announce that Dalimil Mazáč will join the IPhT as a CEA Permanent Researcher as of August 1, 2023. Dalimil prepared his thesis at the Perimeter Institute under the supervision of Davide Gaiotto, he then did a first postdoc at the SCGP at Stony Brook before joining the IAS at Princeton where he will stay until he will join our Institute. During his thesis, Dalimil wrote a paper on Analytic Bounds and Emergence of AdS2 Physics from the Conformal Bootstrap which raised a lot of interest, as he introduced the notion of analytic functional crucial to obtain rigorous bounds in the conformal bootstrap framework. Even more remarkably, his approach is in fact equivalent to Viazovska's solution of the optimal sphere stacking problem in dimension 8, as Dalimil discovered in later developments.

In the past 10 years, the French community working on maps on surfaces has come together several times per year during the so-called "maps days". The next edition of these maps days will take place at IPhT on Friday 24 June 2022. The scientific program is as follows: see also the webpage   Program: 10h15-11h15 : Nicolas Curien (Université Paris-Saclay), Parking on the infinite binary tree  11h30-12h30 : Fedor Levkovich-Maslyuk (Université Paris-Saclay / CEA), Critical phenomena for dually weighted graphs and spanning forests via matrix models 14h-15h : Zéphyr Salvy (Université Gustave Eiffel), Random planar maps decomposed into blocks: a phase study 15h15-16h15 : David Keating (University of Wisconsin-Madison), k-tilings of the Aztec diamond The talks will take place in person in the Bloch amphitheater.

The chaotic behaviour of classical non-linear systems is an ubiquitous effect which refers to the unpredictability of their complex dynamics, a phenomenon known as the butterfly effect.  In mathematical terms this concept is characterized by the so-called Lyapunov exponent, a quantity which expresses the rate at which trajectories which start from close-by initial conditions (position and velocity), diverge with time. In quantum mechanics it is difficult to find good diagnostics of chaos and this question has been intensively debated since the beginnings of quantum mechanics. Recently, groundbreaking results from high energy physics [1] showed that quantum mechanics imposes a strict bound on the Lyapunov exponent. This novel effect has motivated enormous interest over different fields, leaving, however, several outstanding open questions.

La description microscopique des trous noirs est un défi depuis plus de quarante ans. Il existe aujourd'hui un certain nombre d'approches prometteuses pour résoudre ce problème et l'objectif principal de cette conférence et de ce workshop est de réunir des experts dans ces domaines afin d'identifier les synergies, de s'engager dans une critique constructive et de résoudre les conflits apparents. Une attention particulière sera accordée à la dynamique de la microstructure des trous noirs : comment la matière entrante est brouillée et comment l'information est récupérée. La conférence se tiendra seulement en ligne le lundi 6 juin (jour férié en France) puis en personne à l'IPhT, CEA-Saclay du mardi 7 au vendredi 10 juin. Chaque jour de la conférence sera également retransmis. Inscription sur le site web.

The next colloquium Rencontres de l'IPhT conference will be held in Autrans (Vercors) from 23 to 25 May. It will consist of conferences and lectures concerning both the major fields of research in theoretical physics and supporting activities. The main themes of physics will be: - Mathematical physics: group A - Cosmology, particles and nuclei: group B - Statistical physics - condensed matter: group C Main goals: - To share knowledge on scientific topics and strengthening cohesion within the Institute. - To bring together all of the Institute's collaborators in order to discuss common subjects and activities and to strengthen interactions between members of the different teams, including support. - To unite the teams around a common project. See you soon in Autrans!  

Given a set of deformable polygons with prescribed numbers of sides, in how many inequivalent ways can one glue them edge to edge so as to build a sphere? This mathematical question, which pertains to map combinatorics in random geometry, was partially answered by the mathematician William Tutte in a famous 1962 article "A census of slicings" where he solves the problem in the particular case where all the polygons, except at most two of them, have an even number of sides. In a recent article, Jérémie Bouttier and Emmanuel Guitter (IPhT), in collaboration with the mathematician Grégory Miermont (ENS de Lyon), succeeded, 60 years later, in extending Tutte's formula to the most general case, namely for polygons whose numbers of sides have arbitrary parities. Even though more complex, their general explicit formula is still very elegant and conceals numerous symmetries. It is with no doubt the starting point for new combinatorial discoveries.

Bertrand Duplantier (IPhT) and his collaborators have just obtained an exact expression for the generalized multifractal spectrum, which characterizes the highly singular behavior of the universal fractal curve, here arcuate in a semi-infinite logarithmic spiral, and associated with Schramm-Loewner Evolution (SLE), a   paradigmatic planar stochastic process. The method of passage through Liouville quantum gravity is successfully applied there. The attached file contains a simplified presentation of this mathematical physics result. Developped results

Stéphane Lavignac (IPhT) will be giving a public talk (in French) about « Les neutrinos Les neutrinos, ces particules  mystérieuses qui interrogent les physiciens on Tuesday, March 15th at 7 pm in the framework of the Conférences Université Citoyenne at the Patronage laïque Jules Vallès in Paris. https://www.patronagelaique.eu/event-details/les-neutrinos-ces-particules-mysterieuses-qui-interrogent-les-physiciens-1 You also can find this conference on Youtube: Conferences

  This book Spatial Networks - a complete introduction : From Graph Theory and Statistical Physics to Real-World Applications provides a complete introduction into spatial networks. It offers the mathematical tools needed to characterize these structures and how they evolve in time and presents the most important models of spatial networks. All the theoretical discussions are illustrated on real-world examples.

 The value of the Higgs boson mass and of the neutron electric dipole moment (EDM) have been mysterious for decades. They remain among the deepest open questions in particle physics. Until now they have been treated separately, as they are related to very different symmetries and physical processes. Raffaele Tito D'Agnolo (IPhT Saclay) and Daniele Teresi (CERN) recently proposed a joint solution to the two problems, based on the observation that a single operator in our current theory of Nature has a special sensitivity to both parameters. In their model a Multiverse is populated at early times, as shown in the Figure. It is composed of universes with different values of the fundamental parameters of Nature. A fraction of a second after the birth of these universes, the vast majority of them "crunches" becoming much smaller than an atom.

We will have the pleasure to welcome Cédric Villani at IPhT on Tuesday, March 1st morning. Mathematician, Cédric Villani is a university professor, laureate of the 2010 Fields medal and former director of Institut Henri Poincaré. He is also deputy (MP) for Essonne's 5th constituency in the National Assembly of France.   Here is the program of the meeting :  09:00-09:10 introduction, by Catherine Pépin et François David  09:10-10:00 scientific talk by Cédric Villani 10:00-10:30 break 10:30-11:30 talks by IPhT members : Kirone Mallick, Philippe Brax, Jérémie Bouttier 11:30-12:00 question session, chaired by Bertrand Duplantier  Conference site  The meeting will take place in amphi Bloch and will be streamed online via BBB and on www.youtube.com/c/IPhTTV.

We announce the ExoSup Summer School on unconventional superconductivity,co-organized by Catherine Pépin from IPhT..It will take place at the Institut d'Etudes Scientifiques de Cargèse from June 13 to 25, 2022.

Good news for the IPhT, Mariana Grana has just received the Langevin Prize of the French Society of Physics! Congratulations to Mariana for this well deserved success! Prize citation:

We are pleased to welcome Pierre Fleury, who joins the astrophysics and cosmology group of the IPhT as of February 1st. Pierre Fleury is a specialist of general relativity and gravitational lensing. After a PhD at the Institut d'Astrophysique de Paris in 2015, he successively held postdoctoral positions at the University of Cape Town in South Africa, the Department of Theoretical Physics at the University of Geneva and the Institute of Theoretical Physics at the Universidad Autónoma de Madrid. His research program covers both very formal aspects, such as the study of backreactions in alternative theories of relativity or the study of the concept of emergent gravity, and phenomenological aspects such as the exploration of gravitational lensing effects in a wide variety of contexts. He now joins the IPhT as a permanent CNRS researcher of section 02.  We welcome him !

Pendant des décennies nous avons progressé dans l'étude des lois fondamentales de la nature à travers les collisionneurs des particules. Le Grand Collisionneur de Hadrons (LHC) a eu un impact énorme sur notre connaissance de la physique des particules. Une des conséquences les plus importantes de ce programme expérimental est que la valeur de la masse du boson de Higgs et son origine restent mystérieux.

l’Institut Pascal à l’Université Paris-Saclay organise pendant six semaines avec le concours de plusieurs physiciens dont Philippe Brax de l’IPhT (du 18 octobre au 26 novembre 2021) des exposés  pour le grand public, donnés par des physiciens de renom. Dans ce cadre, Cédric Villani donnera une conférence exceptionnelle le  lundi 22 novembre à 19h30 (Institut Pascal) sur le thème La flèche du temps, du billard moléculaire à la danse des astres. l’accueil du public se fait à partir de 19h. Vous pourrez avoir davantage d’informations via ces liens : https://indico.ijclab.in2p3.fr/event/7119/ Renseignements pratiques et localisation de la conférence Affiche en PDF  

A conference honouring the 60 years anniversary of our former colleague Denis Bernard will take place at the ENS Paris : 45 rue d’Ulm, Salle Dussane - October 14-16, 2021.

Our friend and colleague Hubert Saleur has recently turned 60. A conference celebrating his anniversary and focusing on his numerous contributions to condensed matter physics, low-dimensional quantum field theory, and mathematical physics will take place at the IPhT on September 20-23, 2021.  Participation and talks will be in hybrid mode. On-site participants will have to wear masks inside the Institute building and will have to show a valid immunisation certificate or a valid negative test for SARS-CoV-2 (of less than 72 hours) upon registration on Monday morning. Since the maximum capacity of the Amphi Claude Bloch is restricted to 50 persons, registration is necessary. More details can be found on the webpage of the conference :  http://www.phys.ens.fr/~jacobsen/AMP21.html Organisers: Jesper Jacobsen (ENS Paris), Didina Serban (IPhT Saclay), Nicholas Warner (USC Los Angeles)

The meeting will be held at the Institut de Physique Théorique (IPhT-CEA) in Saclay from Sept 13 to 15 and at the Ecole Normale Supérieure (ENS) in Paris on Sept 16. It will bring together experts in the field of integrable systems and address important open questions in the calculation of correlation functions and wave functions in integrable models, with applications to N=4 Super-Yang-Mills theory, Heisenberg spin chains and 2d relativistic QFTs. Participation will be in person only. Participants will have to wear masks inside the Institute building and will have to show a valid immunisation certificate or a valid negative test for SARS-CoV-2 (of less than 72 hours) upon registration on Monday morning. The maximum capacity of the Amphi Claude Bloch being restricted to 50 persons, registration is necessary and it can be done via the corresponding link on the webpage of the conference: https://indico.in2p3.

Thermalization and out of equilibrium dynamics of many body strongly interacting quantum systems have been the subject of a recent burst of research activities. In particular the dynamics of operator and information spreading (scrambling) as well as its chaotic behavior have been recently investigated starting from models originated in the context of strongly correlated many body systems and have found application to black holes physics. This has been triggered by the appearance of a new class of exactly soluble large N quantum field theories, such as the celebrated Sachdev-Ye-Kitaev model. The aim of this workshop is to review the recent advances in the field and to stimulate further research in this direction which lies at the interface between statistical and condensed matter physics and high-energy/mathematical physics. Due to the current situation, the conference will take place online.

CC BY 3.0 (as fig. 1 from  Event Horizon TelescopeCollaboration, K. Akiyama et al., First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring, Astrophys.J. Lett.875(2019), no. 1, L5,1906.11242 ) More than a century after their theoretical discovery, black holes still hold many mysteries. We have developed new methods to calculate an infinite number of hitherto unknown parameters of any arbitrary black hole, some of which we believe could be observed in current and future experiments. Half of these multipoles are finite, and the other half vanish.  Any ratio of two vanishing moments thus seems to be ill-defined. By embedding black holes in string theory, we develop a novel method to define and calculate such multipole moment ratios unambiguously for any black hole. In this way, we find an infinite number of previously unknown multipole ratios for any Kerr black hole.

  Orazio Scarlatella, former doctoral student at IPhT, is the winner of the 2020 PhD prize "Physics of Waves and Matter" of the Physics Graduate School of the University of Paris-Saclay, in the speciality "Theoretical Physics, Numerics and Modelling". Orazio Scarlatella's thesis work focuses on the dynamics of dissipative quantum many-body systems. These problems are of great richness and complexity because they combine the effects of interactions, quantum fluctuations, and out-of-equilibrium physics. The work of O. Sacarlatella consisted of several new conceptual and methodological developments in this field at the interface between correlated materials and quantum optics, with applications to systems such as arrays of superconducting cavities or ultra cold atoms trapped in optical arrays.

(c) Leo Patrizi Marc Barthelemy and Vincent Verbavatz proposed a new equation to understand the distribution of urban populations in a country and their results are published in the journal Nature (online November 18, 2020) This equation, constructed from data for several countries, accounts for the first time for the temporal variations of urban populations and their organization. This stochastic equation of a new type (with two multiplicative noises, one gaussian and the other of the Levy type) highlights the importance of “interurban migratory shocks”, rare but significant population movements, and makes it possible to understand the hierarchical structure of cities and statistical regularities such as Zipf's law.    More information and the interview with Marc Barthélémy

An IPhT researcher, Nicolas Sangouard, and his partners from the universities of Geneva and Basel have succeeded for the first time in "intriguing" the outputs of two optical fibers sharing a single photon at a distance of 2 km. By this performance, they show how a form of quantum entanglement that is simple to produce can be distributed and detected over long distances. An important step towards the construction of a secure quantum the internet! Quantum entanglement or entanglement refers to a very surprising phenomenon in which two systems form a linked state, with the state of each individual system remaining undefined. Regardless of the distance between them, these systems have correlated physical properties. Without stopping being amazed, physicists have learned to use entanglement and to imagine technological applications that have no classical equivalent.

How do we protect the privacy of a communication if we cannot trust the devices used to communicate? Researchers from IPhT, the University of Basel and ETH Zurich have provided innovative answers to this question, which is at the heart of research in quantum cryptography. Hackers in possession of quantum computers pose a serious threat to some of today's crypto-systems. An interesting solution uses encryption methods based on keys produced by quantum principles. However, current quantum encryption protocols assume that the devices used to communicate are known and trustworthy. Otherwise, a door is opened for eavesdropping. A team of physicists around Nicolas Sangouard from IPhT and the University of Basel, as well as Professor Renato Renner from ETH Zurich, have developed the theoretical bases of a communication protocol that offers ultimate protection of the privacy and can be implemented experimentally.

the IPhT has a new "Adjoint Scientifique" in the person of Gregory Soyez. We wish him all the best in this often difficult job, and thank him in advance for the service he provides to us all! We warmly thank Grégoire Misguich for his unstinting commitment and dedication to the IPhT's management over the past four years. The quality and precision of his work, his availability, his competence and his attentiveness will always be remembered.  A huge thank you Grégoire on behalf of the whole institute!