Initiés en septembre 2019, les Ateliers du LKB se veulent être un espace de rencontre et de débat entre physiciens, philosophes, sociologues et historiens.
Séminaire de réflexion sur la recherche en physique quantique, les Ateliers visent à présenter la diversité des questionnements que peuvent soulever les activités menées au laboratoire.
Trois axes thématiques, en particulier, sont privilégiés : épistémologie, fondements théoriques et étude des pratiques de recherche.

Ateliers à venir


2023/10/05 - 2PM : Andrea DI BIAGIO (IQOQI Vienna)

Title : Relative facts in relational quantum mechanics

Location: Sorbonne Université – LKB – Room  210 –  Tour 13/23 – 2e – Campus Jussieu – Paris 5e

Meeting at 2pm, arriving at 1:45pm you can have a tea (or coffee) with us!

Abstract: to be announced…

2023/11/16 - 2PM : Bruno MANSOULIÉ (CEA)

Title : La naturalité en physique—vrai ou fausse amie ?

Location: Sorbonne Université – LKB – Room  210 –  Tour 13/23 – 2e – Campus Jussieu – Paris 5e

Meeting at 2pm, arriving at 1:45pm you can have a tea (or coffee) with us!

Abstract: to be announced…

Ateliers passés


Carla ALMEIDA (UFABC, Brazil)
7 septembre 2023, 14h 

Shaping a concept – a historical view of the public perception of black holes

Location: Sorbonne Université – LKB – Room 210 – Tour 13/23 – 2e – Campus Jussieu – Paris 5e


Abstract: A cosmic drain, a galactic vacuum cleaner, a planet eater, a portal to another universe, a black hole in space. One of the best ways to explain an intricate theory to the general audience is through analogies, and they were heavily used to spread the word about the most intriguing astrophysical concept of the second half of the 20th century. But when and why black holes became these black holes? We will explore these questions from a historical perspective, trying to understand how black holes were shaped in people’s minds and the influences they had over future scientific endeavors.



Thomas RYCKMAN (Stanford University)
27 mars 2023, 14h

Niels Bohr: Transcendental Physicist

Location: Sorbonne Université – LKB – Room 210 – Tour 13/23 – 2e – Campus Jussieu – Paris 5e


Abstract: Bohr’s understanding of quantum theory, not to be confused with the ‘Copenhagen Interpretation’, stemmed from his attempt to address “the problem of how objectivity may be retained during the growth of experience beyond the events of daily life.”A defining trait of transcendental philosophy regards objectivity as not given (a perspective-free picture of reality) but a problem requiring solution. Neither a philosopher nor adherent of any philosophical school, Bohr’s transcendental solution to the problem of objective description in quantum theory locates it within « conditions of the possibility of unambiguous communication » of experimental setups and results of measurement. In this regard, Bohr is a precursor of contemporary interpretations of the quantum state, according to which the meaning of the quantum state consists in information to better inform expectations of those employing it.

Marco Túlio QUINTINO (Lip6, Sorbonne Université)
27 mars 2023, 14h

Parallel, sequential, and non-causal strategies for transforming unitary operations and discriminating quantum channel via a higher-order approach

Location: Sorbonne Université – LKB – Room 210 – Tour 13/23 – 2e – Campus Jussieu – Paris 5e


Abstract: Higher-order quantum operations is a paradigm where operations, such as quantum channels and unitary gates, play the role of a quantum states and are viewed as objects which may be subjected to transformations. In this talk, we show how the framework of higher-order quantum operations provide powerful mathematical methods to tackle several problems in quantum information. We will conduct our talk following two motivating and recurring examples, the problem of designing quantum circuits for inverting an arbitrary unitary operation and how to computationally tackle different strategies for discriminating quantum operations. In the end of the talk, we will also discuss the constraints imposed by causality and how strategies without a definite causal order may be used as a resource in quantum information processing.

This talk will cover results from various papers, such as:

Karim THÉBAULT (University of Bristol)
20 janvier 2023, 14h

Modelling Open Systems in Quantum Physics and Cosmology

James Ladyman & Karim Thebault (University of Bristol)

Location: Sorbonne Université – LKB – Room 210 – Tour 13/23 – 2e – Campus Jussieu – Paris 5e


Abstract: None of the systems that we find in nature are in reality ‘closed systems’. Rather, they are all sub-systems of the universe. When we talk of ‘closed systems’ in physics we are describing systems that can be effectively modelled as closed since their exogenous interactions with the rest of the universe are not important for the relevant purposes, on the relevant scale. The characteristic feature of such models is conservation of a relevant quantity on the relevant time scale. For example, conservation of heat in closed thermodynamics systems, conservation of matter in closed chemical systems, and conservation of coherence in closed quantum systems.

Conversely, when we talk about ‘open systems’ in physics, we are not making the trivial claim that a system is coupled to the environment. Since gravitational interactions are unscreenable, technically all systems are so coupled. When we talk of ‘open systems’ in physics we are describing systems that can be effectively modelled as open since their exogenous interactions with the rest of the universe are important for the relevant purposes, on the relevant scale. The characteristic feature of such models is failure of conservation of a relevant quantity on the relevant time scale.

Under this way of thinking about open systems, we do not preclude the possibility of modelling a system as open such that the failure of conservation of the relevant quantity is combined with autonomous dynamics in which there are well-posed equations of motion for the system degrees of freedom alone. How should we interpret such autonomous open system models? Should they always be taken to implicitly represent the system in question as part of a larger, closed system? And what would it mean for us to model the universe as an autonomous open system? In this talk we will offer a framework for thinking about these questions drawing upon recent work on open quantum systems due to to Cuffaro and Hartmann (2021) and on autonomous non-conservative cosmology due to Sloan (2021).


Cuffaro, Michael E., and Stephan Hartmann. « The open systems view.” 2021, https://arxiv.org/abs/2112.11095

Sloan, David. « New action for cosmology. » Physical Review D 103.4 (2021): 043524. https://arxiv.org/abs/2010.07329

Patrice CAMATI (Institut Néel – Grenoble)
17 novembre 2022, 14h

Can we extend the notions of work and heat to the quantum realm?

Location: Sorbonne Université – LKB – Room 210 – Tour 13/23 – 2e – Campus Jussieu – Paris 5e


Abstract: The emergent field of Quantum Thermodynamics extends thermodynamic concepts to small quantum systems. A number of important results have been obtained in the past decades, e.g., quantum fluctuation relations and thermodynamic uncertainty relations, among others. Many of the results consider a system coupled to a heat reservoir and/or driven by a time-dependent Hamiltonian to define the widely accepted notions of work and heat. Apart from such settings, there is currently no consensus on how work and heat should be defined. How can heat be defined without resorting to the coupling with a heat reservoir? For strongly coupled quantum systems, how should we handle the non-negligible coupling energy? Can notions of work and heat be defined for two interacting qubits? A number of proposals have been made and this endeavor is still an open problem, comprising an active research area in the field. I will review the accepted notion of work and heat and discuss a few proposals put forth recently. In particular, I will present and discuss some consequences of a general energetic framework we have been developing. In this talk, we will discuss the conceptual hurdles of extending thermodynamic concepts to non-thermodynamic settings.
Alastair ABBOTT (Inria)
13 octobre 2022, 14h

Causal indefiniteness from quantum control of processes

Location: Sorbonne Université – LKB – Room 210 – Tour 13/23 – 2e – Campus Jussieu – Paris 5e


Abstract: Causality is often treated as a classical notion but there have been growing calls for a fundamentally quantum notion of causal structure, motivated e.g. by the quest to develop a theory of quantum gravity or to explain various nonclassical features of quantum mechanics. This has led to the development of an abstract framework in which causally indefinite processes can be formulated, for example by superposing quantum processes with different causal orders. However, interpreting many of these processes is difficult.

In this talk I will give an overview of indefinite causal order in quantum mechanics and some of the recent efforts to understand it within quantum information theory. I will focus, in particular, on the question of which causally indefinite processes can be given physical interpretations. On one hand, information theoretic principles may allow certain types of causal indefiniteness to be ruled out as non-physical; while on the other hand, certain processes can be interpreted concretely as generalisations of quantum circuits with quantum control. This interpretation moreover raises questions about the physical limits of computation and whether causal indefiniteness can be exploited


9 juin 2022, 14h

Fragility and strength of non-classicality for quantum networks

Location : Campus Pierre & Marie Curie – Place Jussieu – Tour 13/23 salle 210  – 75005 Paris
There are probably as many notions of non-classicality as there are people who will attend this talk (or read this post). In quantum information, we are in the privileged position (or not, according to taste) of having, in recent years, developed some pretty formal mathematical frameworks for what we mean by non-classicality.
In this talk I will present some of these, how they are used to prove quantum behaviour, how this can translate to quantum advantage for certain information processing tasks in networks, and their fragility and what we can try to do about it.
31 mars 2022, 14h

Quantum superposition of thermodynamic evolutions with opposing time’s arrows?

Location : Campus Pierre & Marie Curie – Place Jussieu –  Tour 13/23 salle 210 – 75005 Paris

Microscopic physical laws are time-symmetric, hence, a priori there exists no preferential temporal direction. However, the second law of thermodynamics allows one to associate the « forward » temporal direction to a positive variation of the total entropy produced in a thermodynamic process, and a negative variation with its « time-reversal » counterpart.

This definition of a temporal axis is normally considered to apply in both classical and quantum contexts. Yet, quantum physics admits also superpositions between forward and time-reversal processes, whereby the thermodynamic arrow of time becomes quantum-mechanically undefined. In this work, we demonstrate that a definite thermodynamic time’s arrow can be restored by a quantum measurement of entropy production, which effectively projects such superpositions onto the forward (time-reversal) time-direction when large positive (negative) values are measured. Remarkably, for small values (of the order of plus or minus one), the amplitudes of forward and time-reversal processes can interfere, giving rise to entropy-production distributions featuring a more or less reversible process than either of the two components individually, or any classical mixture thereof.

10 mars 2022, 14h

Why decoherence does not solve the measurement problem?

Location :Campus Pierre & Marie Curie – Place Jussieu – Tower 44-54 – Room 105 – 75005 Paris and on Zoom

The measurement problem is often considered an inconsistency inside the quantum formalism. Even though it is now generally agreed that it is not the case, decoherence has sometimes been viewed as a possible solution. I will show that it is indeed not the case and will present what decoherence actually brings and which the problems we are left with are. I will then propose a possible solution to the measurement problem taking the role of the observer into account.
– 2016 “The Measurement Problem: Decoherence and Convivial Solipsism”, Found. Phys., 46: pp 635

-667. https://arxiv.org/abs/1505.05029
– 2017 “Delayed Choice, Complementarity, Entanglement and Measurement”, Physics Essays, 30, 3.

– 2020 “Non Locality versus Modified Realism: Convivial Solipsism”, Found. Phys. Vol. 50, pp. 1-26,


– 2020 « L’observateur, un défi pour la physique quantique« ; Pour la Science N°509, Mars 2020.

– 2021 “Is the Past Determined?”, Found. Phys. Vol. 51, 57, https://rdcu.be/cj3a7, https://arxiv.org/abs/2009.02588

10 février 2022, 14h

Weak value : a property of a single pre and post-sele
cted system

Location : zoom

Weak value of a quantum variable was introduced by Aharonov, Albert and Vaidman in 1988 as an outcome of a standard quantum measurement with weakened coupling performed on an ensemble of pre and postselected  systems. A common interpretation of the weak value is a conditional expectation value (there are even claims that it is not necessarily a quantum concept). I will argue that it has a deeper meaning as a robust property of a single pre and postselected system. Experimental demonstrations supporting this claim will be reported and some controversies about weak values will be discussed.  An application of a new paradigm of the past of a quantum particle as the weak value of a projection for a novel alignment method will be reported.

13 janvier 2022, 14h

Philosophysics: A case study of a successful interplay between physics and philosophy for the establishment of quantum foundations in Vienna

Location : Jussieu Tour 13/23 salle 210, inscription obligatoire sous couvert d’avoir le pass sanitaire à jour ou via Zoom
Si vous souhaitez vous lancer dans la discussion, consultez le papier de Flavio ici

The field of Foundations of Quantum Mechanics (FQM) suffered varying fortunes in its history. This field of research is quite unconventional within physics, for it often addresses questions that lie at the border of philosophical investigation. In this talk I will elucidate a case study which aims to show that in Vienna –where in recent years FQM has become one of the main research fields within physics– it was a particularly strong connection between physics and philosophy that paved the way for the establishment of the prolific field of FQM there. This could lead to draw general conclusions about the value of a structured interaction between philosophers and physicists concerned with the foundational aspects of this discipline.

Vincent Bontems and Christian de Ronde 
21 octobre 2021

You can’t always get what you want. (A simondonian interpretation of quantum entanglement)

En présentiel : Amphithéâtre Charpak sur le campus Pierre-et-Marie Curie à Jussieu, le 21 octobre 2021 à 17H30 et en distanciel
The understanding of QM is obscured by a twofold “epistemological obstacle” (Bachelard 1938) that has taken quite different and apparently opposed forms in the interpretation of the theory: substantialism and instrumentalism. While substantialism is the ontological assumption that reality is entirely composed of individuals with permanent unity and identity (Bontems & de Ronde 2011), instrumentalism is the anti-realist assumption that science is just a procedure to make predictions about measurement outcomes (‘clicks’ in detectors). Instead of searching for new concepts that would explain what QM is really talking about, the Bohrian ‘solution’ that prevailed was, on the contrary, to subvert realism by retaining classical substantialist concepts as fictions embedded in paradoxical story-tellings illustrating experimental procedures with essential gaps bridged by irrepresentable notions such as ‘quantum particles’ and ‘quantum jumps’.
One of the kernel notions of QM is entanglement, originally designed by Einstein as a « spooky action at a distance » to demonstrate the inconsistency of ‘quantum jumps’ in a substantialist framework. Even though entanglement, considered as a spooky philosophical notion, was completely erased from physics for half a century, during the 1990s it was included –due to its pragmatic possibilities– once again within the still orthodox contemporary Borhian narrative. After recalling the conceptual bases of a Simondonian interpretation of QM (Bontems & de Ronde 2019) – the hypothesis of preindividuality and the postulate of a realism of relations – we discuss the inconsistencies present in the orthodox definition of entanglement.
Our claim is that the Bohrian narrative is biased by the fact that it presupposes the existence of individuated particules, while Simondon’s realism of relations shifts the focus on preindividuality and the processes of individuation that may (or may not) generate such individuals. This allows us to sketch a realist but non-substantialist understanding of entanglement that leaves behind both the mere instrumentalist reference to measurement outcomes and substantialism: “You can’t always get what you want… but why did you want particles in the first place?”


Giacomo Mauro D’Ariano



No purification ontology, no quantum paradoxes

It is almost universally believed that in quantum theory the two following statements hold: 1) all transformations are achieved by a unitary interaction followed by a von Neumann measurement; 2) all mixed states are marginals of pure entangled states. I name this doctrine the dogma of purification ontology. The source of the dogma is the original von Neumann axiomatisation of the theory, which largely relies on the Schroedinger equation as a postulate, which holds in a nonrelativistic context, and whose operator version holds only in free quantum field theory, but no longer in the interacting theory. In the present paper I prove that both ontologies of unitarity and state purity are unfalsifiable, even in principle, and therefore axiomatically spurious. I propose instead a minimal four-postulate axiomatisation:

1) associate a Hilbert space HA to each system A;

2) compose two systems by the tensor product rule HAB = HAxHB;

3) associate a transformation from system A to B to a quantum operation, i.e. to a completely positive trace-non-increasing map between the trace-class operators of A and B;

4) (Born rule) evaluate all joint probabilities through that of a special type of quantum operation: the state preparation. I then conclude that quantum paradoxes-such as the Schroedinger-cat’s, and, most relevantly, the information paradox-are originated only by the dogma of purification ontology, and they are no longer paradoxes of the theory in the minimal formulation. For the same reason, most interpretations of the theory (e.g. many-world, relational, Darwinism, transactional, von Neumann-Wigner, time-symmetric, …) interpret the same dogma, not the strict theory stripped of the spurious postulates.

Fabien Grégis



Approches fréquentistes et bayésiennes dans l’analyse des incertitudes de mesure : principes conceptuels et enjeux épistémologiques

«Plusieurs siècles après les débuts de la théorie mathématique des erreurs, il n’y a pas encore aujourd’hui de consensus parfaitement clair quant au calcul et à l’interprétation des incertitudes de mesure. Ma présentation visera à exposer les fondements conceptuels et épistémologiques d’un débat récent sur les fondements statistiques de l’analyse d’incertitude en métrologie. Confrontés à un problème concret, touchant au traitement probabiliste des erreurs systématiques, métrologues et statisticiens ont saisi l’opportunité d’un regain général d’intérêt envers les statistiques bayésiennes pour proposer une nouvelle conception de l’incertitude de mesure qui remet en question la tradition fréquentiste, jusque là dominante durant le 20e siècle. Je chercherai à expliquer d’une part les raisons pour lesquelles les métrologues en sont venus à proposer une alternative bayésienne, et à décrire d’autre part l’entremêlement des enjeux à la fois pratiques et épistémologiques de ce tournant, qui engage en particulier une réflexion sur la subjectivité de l’activité de mesure et amène à reconsidérer l’interprétation du concept d’incertitude de mesure dans les sciences expérimentales.»




On the persistent reality of the observer’s perception

« The discussion about the quantum mechanical thought experiment « Wigner’s friend » has recently gained renewed intensity. The original thought experiment involved the « observation of an observer », in which the friend not only observes a physical system, but is simultaneously the object of another observation by Wigner. Recent theoretical results and experimental tests of extended Wigner-friend scenarios suggest that treating observational knowledge of other agents as if it were one’s own can be problematic in quantum mechanics. In short, « facts are only relative to observers ». In my talk, I will review these findings before arguing that a single agent’s knowledge over time can have even more counterintuitive consequences: when making predictions about one’s observations at two different points in time, it may be untenable in quantum mechanics to treat a single agent’s knowledge acquired in the past as if it were still present.»


Antoine Tilloy


Les modifications non-linéaires de la mécanique quantique

Les postulats de la mécanique quantique sont étranges : ils disent à la fois ce qu’est la dynamique du monde, avec l’équation de Schrödinger, et ce que l’on peut en observer, avec le postulat de la mesure. A priori, dans une théorie plus standard, le second postulat devrait être une conséquence mathématique du premier, et non une hypothèse indépendante. Si la décohérence permet de comprendre pourquoi les deux postulats n’entrent pas en conflit en pratique, elle ne permet pas de réduire le second au premier : c’est le problème de la mesure. Vers la fin des années 1980, des théoriciens ont cherché à réduire cette bizarrerie à l’aide de petites modifications non-linéaires et stochastiques de l’équation de Schrödinger. Au prix d’infinitésimales déviations au prédictions usuelles, ces dernières permettent de réduire le postulat de la mesure à la dynamique de la fonction d’onde. Dans cette approche, l’effondrement de la fonction d’onde est objectif, et prédit par la dynamique. Mon objectif sera de présenter l’idée générale de ces modifications, d’expliquer leurs contraintes théoriques et leurs conséquences expérimentales. J’essaierai de mettre en avant un point contre-intuitif et je crois peu connu : le contenu empirique de ces modifications reste reproductible par une dynamique purement linéaire, et en ce sens elles ne changent pas tant les prédictions de la théorie quantique au sens large que celle de son instanciation actuelle où le Hamiltonien est celui du Modèle Standard.

Pierre Verschueren


Jeunes-Turcs et Mandarins : le doctorat ès sciences physiques et les transformations du métier de physicien (1945-1968)

Le visage des sciences physiques change profondément après 1944 : elles sont les premières disciplines confrontées à la massification exponentielle du système d’enseignement supérieur et de recherche, ce qui se traduit par une recomposition des rapports entre leurs acteurs et leurs institutions, ainsi que par une transformation de ce qui fait leur métier. En prenant comme point d’observation les doctorats ès sciences physiques soutenus devant la faculté des sciences de Paris, en particulier la composition des jurys et le contenu des rapports, il s’agit d’étudier la transformation des normes qui structurent et conditionnent l’entrée dans les carrières de l’enseignement supérieur et de la recherche ; l’hypothèse discutée est que s’opère alors un basculement, la sortie d’un monde professionnel tourné vers l’idéal du savant et l’entrée dans un autre monde, organisé autour de l’idéal du chercheur.

Vincent Ardourel


Les idéalisations infinies en mécanique statistique

Nous nous intéresserons ici au problème des idéalisations infinies en mécanique statistique, un problème discuté en philosophie des sciences depuis quelques années. Ce problème apparaît avec le recours indispensable à certaines hypothèses que l’on sait pourtant fausses dans le but d’expliquer certains phénomènes physiques. Les débats se concentrent principalement autour de la limite thermodynamique. Il est en effet généralement admis que celle-ci est nécessaire pour expliquer les phénomènes de transitions de phase en physique statistique. J’expliciterai en quoi cela est un problème pour la réduction de la thermodynamique à la physique statistique et quelles sont les tentatives proposées pour résoudre ce problème.

Michel Bitbol
(ENS – Archives Husserl)


La physique quantique à la première personne du singulier du temps présent

Le QBism (Quantum Bayesianism) repose sur une interprétation subjectiviste des probabilités. Mais, au-delà de cette simple option interprétative, le QBism opère un changement sans précédent du sens et du statut de la théorie physique. Dans le QBism, les symboles de la théorie, comme par exemple  l’état quantique, ne font plus du tout référence à d’hypothétiques microsystèmes. Ils dénotent un instrument de calcul des probabilités de résultats expérimentaux, valant pour chaque agent particulier. Ici, l’agent est à la fois l’origine (i) de l’évaluation probabiliste et (ii) de l’intervention qui suscite les résultats dont il estime les probabilités.
On développera à partir de là l’idée d’une physique en première personne, d’une physique valant pour le physicien qui cherche à prédire les phénomènes qu’il co-produit par son action. Et on l’opposera à une physique en troisième personne, une physique visant à décrire des objets et des processus se produisant d’eux-mêmes, indépendamment des physiciens qui les étudient. Une bonne raison d’opter pour une physique en première personne est l’immense simplification que cela occasionne dans l’élucidation des « paradoxes » quantiques.

Vincent Bontems


De quoi l’innovation est-elle le nom ?

Le mot « innovation » a envahi les discours au point de devenir l’horizon contemporain des activités de recherche. Il désigne désormais l’objectif prioritaire, sinon exclusif, du travail des chercheurs. Mais à quoi correspond-il ? En revenant à ses origines politiques lointaines, puis aux disciplines (sociologie et économie) qui en ont élaboré un usage réglé, et enfin à l’évolution des différents modèles de la « chaîne de l’innovation », on esquissera une généalogie du terme. Celle-ci ne révélera pas nécessairement la vérité du concept mais éclairera les enjeux actuels.

Alexei Grinbaum


Quantum Foundations in the XXI Century

What’s new since Bell inequalities? Are we still debating the interpretations of quantum mechanics? Can one teach physics today without using Popescu-Rohrlich boxes? I’ll describe several new research directions, including postquantum correlations, quantum contextuality, and indefinite causal orders.