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Information Theoretic Foundations for Physics

Conference Date: 
Lundi, Mai 11, 2015 (All day) to Vendredi, Mai 15, 2015 (All day)
Scientific Areas: 
Mathematical Physics
Quantum Foundations
Quantum Gravity
Quantum Information

 

In the last few decades, there has been a growing consensus that information theory is of fundamental importance for theoretical physics. The information paradigm has yielded successes in many different areas of the foundations of physics, including the development and application of quantum information theory, Jacobson’s thermodynamic derivation of the Einstein equations, the black-hole information paradox, Jaynes’ maximum entropy principle, or operational approaches to the foundations of quantum mechanics. These novel approaches are obviously motivated by the development of modern computer science and information technology, continuing the linkage of science and technology that once also linked the steam engine to the development of thermodynamics.

Parallel to this fruitful development, there is a growing number of physicists who endorse the general attitude that fundamental physics may need new foundations or at least a new perspective. Despite amazing recent successes, there remains the profound challenge that experiments have not confirmed many of the recent theoretical ideas: the universe seems simpler than our ideas of unification predicted. Information-theoretic approaches can provide a starting point, which is exceptionally careful in the assumptions that it makes, and broad in its applicability, since it does not rely on specific laws of motion or formal properties of underlying theories.  As such it can complement other research activities in the field.  For instance, information-theoretic operational approaches may also help in developing a missing "operational sense" and a conceptual scheme for already existing approaches to quantum gravity.

Triggered by quantum information theory, information-theoretic approaches to fundamental physics are currently experiencing an exceptional growth, with a flourishing of new results and an increasing amount of scientists joining the general research direction. We want to boost this process by organizing a conference that is able to bring together researchers from different fields of theoretical physics, in order to discuss information-theoretic approaches and their potential for innovations in the foundations of physics, ideally building an international community of researchers that are aware of this new direction and pursue it in fruitful collaborations. The aim of the conference is to provide an overview and discussion over existing ideas and approaches, promoting the exchange and cross-fertilization of ideas, developing a common language for different communities involved, and enabling collaborative work in a relaxed atmosphere.

In order to foster this process, the schedule will be restricted to five talks a day, together with a substantial amount of time reserved for free discussions and collaboration.  There will also be organized discussion sessions which will allow people from different fields to engage in the cross-community common topic discourse.  The organized sessions will be subject to a more structured time plan to have more people speak out.

Registration for this conference is now closed.

Sponsorship for this conference has been provided by:

  • Howard Barnum, University of New Mexico
  • Cédric Bény, Institute for Theoretical Physics, University of Hannover
  • Dorje Brody, Brunel University London
  • Časlav Brukner, Institute for Quantum Optics & Quantum Information Vienna
  • Ariel Caticha, University at Albany
  • Giulio Chiribella, Institute for Interdisciplinary Information Sciences
  • Gemma De las Cuevas, Max Planck Institute
  • Felix Finster, Regensburg University
  • Doreen Fraser, University of Waterloo
  • Steve Giddings, University of California, Santa Barbara
  • Lucien Hardy, Perimeter Institute
  • David Jennings, Imperial College London
  • Achim Kempf, University of Waterloo
  • Tim Koslowski, University of New Brunswick
  • Lluis Masanes, University of Bristol
  • Rob Myers, Perimeter Institute
  • Robert Oeckl, Universidad Nacional Autónoma de México
  • Jonathan Oppenheim, University College London
  • Ruediger Schack, University of London
  • Lee Smolin, Perimeter Institute
  • Robert Spekkens, Perimeter Institute
  • Daniel Terno, Macquarie University
  • Gerard 't Hooft, Utrecht University
  • Erik Verlinde, University of Amsterdam
  • Javier Alvarez, UNAM
  • Howard Barnum, University of New Mexico
  • Cédric Bény, Institute for Theoretical Physics, University of Hannover
  • Daniel Brod, Perimeter Institute
  • Časlav Brukner, Institute for Quantum Optics & Quantum Information Vienna
  • Ariel Caticha, University at Albany
  • Giulio Chiribella, Institute for Interdisciplinary Information Sciences
  • Dorje Brody, Brunel University London
  • Gemma De las Cuevas, Max Planck Institute
  • Felix Finster, Regensburg University
  • Doreen Fraser, University of Waterloo
  • Antonia Frassino, Perimeter Institute
  • Henrique Gomes, Perimeter Institute
  • Carlos Gonzalez-Gullen, University of Ottawa
  • Matthew Graydon, Perimeter Institute
  • Lucien Hardy, Perimeter Institute
  • Philipp Hoehn, Perimeter Institute
  • David Jennings, Imperial College London
  • Achim Kempf, University of Waterloo
  • Tim Koslowski, University of New Brunswick
  • Ryszard Kostecki, Perimeter Institute
  • Marius Krumm, Heidelberg University
  • Matthew Leifer, Perimeter Institute
  • Lluis Masanes, University of Bristol
  • Markus Mueller, Heidelberg University
  • Rob Myers, Perimeter Institute
  • Robert Oeckl, Universidad Nacional Autónoma de México
  • Jonathan Oppenheim, University College London
  • Matthew Pusey, Perimeter Institute
  • Daniel Ranard, Perimeter Institute
  • Katja Reid, Perimeter Institute
  • Aldo Riello, Perimeter Institute
  • Ruediger Schack, University of London
  • John Selby, Imperial College London
  • Lee Smolin, Perimeter Institute
  • Robert Spekkens, Perimeter Institute
  • Barak Shoshany, Perimeter Institute
  • Daniel Terno, Macquarie University
  • Gerard 't Hooft, Utrecht University
  • Cozmin UdudecInvenia Technical Computing
  • Erik Verlinde, University of Amsterdam
  • Steven Weinstein, University of Waterloo
  • Elie Wolfe, Perimeter Institute

Monday, May 11, 2015

Time

Event

Location

8:30 – 9:00am

Registration

Reception

9:00 – 9:15am

Welcome and Opening Remarks

Bob Room

9:15 – 10:05am

Caslav Brukner,
Institute for Quantum Optics and Quantum Information Vienna
Indefinite causal order in quantum mechanics

Bob Room

10:05 – 10:55am

Ruediger Schack, University of London
Agency, causal structure and locality in Qbism

Bob Room

10:55 – 11:15am

Coffee Break

Bistro – 1st Floor

11:15 – 12:05pm

Giulio Chiribella,
Institute for Interdisciplinary Information Sciences
Towards an information-theoretic foundation of (quantum) thermodynamics  

Bob Room

12:05 – 12:55pm

Jonathan Oppenheim, University College
The second laws of quantum thermodynamics

Bob Room

12:55 – 2:15pm

Lunch

Bistro – 2nd Floor

2:15 – 3:05pm

Howard Barnum, University of New Mexico
Entropy, majorization, and thermodynamics in general
probabilistic theories.

Bob Room

3:05 – 3:55pm

David Jennings, Imperial College London
Limitations of statistical mechanics for quantum thermodynamics.

Bob Room

3:55 – 4:10pm

Coffee Break

Bistro – 1st Floor

4:10 – 5:10pm

Organized Discussion Session:
Information theory and thermodynamics

Bob Room

5:10pm onwards

Open Discussion Space

Bob Room

 

Tuesday, May 12, 2015

Time

Event

Location

9:00 – 9:50am

Philipp Hoehn, Perimeter Institute
Information and the architecture of quantum theory

Bob Room

9:50 – 10:40am

Markus Mueller, Heidelberg University
Quantum theory and spacetime: allies, not enemies

Bob Room

10:40 – 11:00am

Coffee Break

Bistro – 1st Floor

11:00 – 11:50am

Lucien Hardy, Perimeter Institute
Bringing General Relativity into the Operational Probabilistic Framework

Bob Room

11:50 – 12:40pm

Robert Spekkens, Perimeter Institute
Nonclassicality as the failure of noncontextuality

Bob Room

12:40 – 2:00pm

Lunch Break

Bistro – 2nd Floor

2:00 – 2:50pm

Lee Smolin, Perimeter Institute
Quantum mechanics from first principles

Bob Room

2:50 – 3:40pm

Daniel Terno, Macquarie University
How far can you stretch classical mechanics?

Bob Room

3:40 – 3:50pm

Conference Photo

TBA

3:50 – 4:10pm

Coffee Break

Bistro – 1st Floor

4:10 – 4:50pm

Organized Discussion Session:
Information theoretic axiomatisations of quantum theory

Bob Room

4:50pm onwards

Open Discussion Space

Bob Room

 

Wednesday, May 13, 2015

Time

Event

Location

9:00 – 9:50am

Tim Koslowski, University of New Brunswick
Physical records and emergence of information in the gravitationally dominated universe

Bob Room

9:50 – 10:40am

Robert Myers, Perimeter Institute
Scanning the Horizon:  Information, Holography and Gravity

Bob Room

10:40 – 11:00am

Coffee Break

Bistro – 1st Floor

11:00 – 11:50am

Achim Kempf, University of Waterloo
What if nature is bandlimited by a Planck scale cutoff?

Bob Room

11:50 – 12:40pm

Steve Giddings, University of California, Santa Barbara
Remote talk by teleconference
Quantum information and the algebraic
structure of quantum gravity

Bob Room

12:40 – 2:00pm

Lunch Break

Bistro – 2nd Floor

2:00 – 3:30pm

Erik Verlinde, University of Amsterdam
Colloquium
String Theory, Entropic Gravity and the Dark Universe

Theater

3:30 – 4:00pm

Coffee Break

Bistro – 1st Floor

4:00 – 5:00pm

Open Discussion Space

Bob Room

6:00pm onwards

Banquet

Bistro – 2nd Floor

 

Thursday, May 14, 2015

Time

Event

Location

9:00 – 9:50am

Ryszard Kostecki, Perimeter Institute
Quantum information geometric foundations: beyond
the spectral paradigm

Bob Room

9:50 – 10:40am

Ariel Caticha, University at Albany
Entropic Dynamics:
from Entropy and Information Geometry to Quantum Mechanics

Bob Room

10:40 – 11:00am

Coffee Break

Bistro – 1st Floor

11:00 – 11:50am

Cedric Beny, University of Hannover
Tangent field theory

Bob Room

11:50 – 12:40pm

Gemma De las Cuevas, Max Planck Institute
What discrete states have a continuum limit?

Bob Room

12:40 – 2:00pm

Lunch Break

Bistro – 2nd Floor

2:00 – 3:30pm

Gerard ‘t Hooft, Utrecht University
Colloquium
The CA interpretation of quantum mechanics

Theater

3:30 – 4:00pm

Coffee Break

Bistro – 1st Floor

4:00 – 5:00pm

Organized Discussion Session:
Emergence of space-time

Bob Room

5:00pm onwards

Open Discussion Space

Bob Room

 

Friday, May 15, 2015

Time

Event

Location

9:00 – 9:50am

Felix Finster, Regensburg University
Causal fermion systems from an information theoretic perspective 

Bob Room

9:50 – 10:40am

Robert Oeckl,
Universidad Nacional Autónoma de México
Towards new foundations of quantum theory from first principles and from quantum field theory

Bob Room

10:40 – 11:00am

Coffee Break

Bistro – 1st Floor

11:00 – 11:50am

Lluis Masanes, University of Bristol
A derivation (and quantification) of the third law of thermodynamics

Bob Room

11:50 – 12:40pm

Dorje Brody, Brunel University London
Communication without transmission

Bob Room

12:40 – 2:00pm

Lunch Break

Bistro – 2nd Floor

2:00 – 2:50pm

Doreen Fraser, University of Waterloo
Theories of heat as inspiration for electrodynamics:  
From Kelvin to QFT

Bob Room

2:50 – 3:05pm

Coffee Break

Bistro – 1st Floor

3:05 – 4:05pm

Organized Discussion Session:
Prospects and limitations of information theoretic approaches

Bob Room

4:05pm onwards

Open Discussion Space

Bob Room

 

 

Howard Barnum, University of New Mexico

Entropy, majorization, and thermodynamics in general probabilistic theories.

Much progress has recently been made on the fine-grained thermodynamics and statistical mechanics of microscopic physical systems, by conceiving of thermodynamics as a resource theory: one which governs which transitions between states are possible using specified "thermodynamic" (e.g. adiabatic or isothermal) means.  In this talk we lay some groundwork for investigating thermodynamics in generalized probabilistic theories.  We describe simple, but fairly strong, postulates: unique spectrality,  projectivity, and symmetry of transition probabilities, that imply that a system has a well-behaved convex analogue of the spectrum, and show that the spectrum of a state majorizes the outcome probabilities of any fine-grained measurement, allowing the operationally defined measurement entropy (and Schur-concave analogues) to be calculated from the spectrum.  These are implied by, but probably weaker than, Axioms 1 (weak  spectrality) and 2 (strong symmetry) of a recent characterization of Jordan-algebraic and quantum systems by Barnum, Mueller, and Ududec.   It is an open question whether  theories beyond the Jordan-algebraic ones satisfy them.  We describe how part of von Neumann's argument that spectral entropy is a good candidate for thermodynamic entropy generalizes to systems satisfying our postulates, and discuss whether its assumptions  are reasonable there, suggesting that the extendibility of certain processes to  reversible ones is crucial.  We will discuss further postulates and results that might suffice to obtain, in this more general setting, a thermodynamical resource theory  similar to the one that is emerging for quantum theory.
 
(Joint work with Jon Barrett, Marius Krumm, Matt Leifer, Markus Mueller.)

 

Cedric Beny, Institute for Theoretical Physics, University of Hannover

Tangent field theory

The modern understanding of quantum field theory underlines its effective nature: it describes only those properties of a system relevant above a certain scale. A detailed understanding of the nature of the neglected information is essential for a full application of quantum information-theoretic tools to continuum theories.
 
I will present an operationally motivated method for deriving an effective field theory from any microscopic description of a state.  The approach is based on dimensional reduction relative to a quantum distinguishability metric. It relies on a microscopic description of experimental limitations, such as a finite spatial resolution. In this picture, the emergent field observables represent cotangent vectors on the manifold of states, and are not necessarily endowed with the full semantic of standard quantum observables.
 
Dorje Brody, Brunel University London
 
Communication without transmission 
 
It is sometimes envisaged that the behaviour of elementary particles can be characterised by the information content it carries, and that exchange of energy and momentum, or more generally the change of state through interactions, can likewise be characterised in terms of its information content. But exchange of information occurs only in the context of a (typically noisy) communication channel, which traditionally requires a transmitter and a receiver; whereas particles evidently are not equipped with such devices. In view of this a new concept in communication theory is put forward whereby signal processing is carried out in the absence of a transmitter; hence mathematical machineries in communication theory serves as new powerful tools for describing a wide range of observed phenomena. In the quantum context, this leads to a tentative—and perhaps speculative—idea that the dynamical evolution of the state of a quantum particle is such that the particle itself acts as if it were a "signal processor", trying to identify the stable configuration that it should settle, and adjusts its own state accordingly. It will be shown that the mathematical scheme of such a hypothesis works well for a broad class of noise structures having stationary and independent increments. (The talk will be based on work carried out in collaboration with L. P. Hughston.)
 
Caslav Brukner, Institute for Quantum Optics and Quantum Information Vienna
 
Indefinite causal order in quantum mechanics
 
One of the most deeply rooted concepts in science is causality: the idea that events in the present are caused by events in the past and, in turn, act as causes for what happens in the future. If an event A is a cause of an effect B, then B cannot be a cause of A.
Recently  we proposed a framework that assumes that operations in local laboratories are described by quantum mechanics, but where no reference is made to any global causal relations between these operations. The central notion of the formalism is “process” which is a generalization of the causal notion of “quantum state”. The framework allows for processes in which two operations are neither causally ordered nor in a probabilistic mixture of definite causal orders, i.e. one cannot say that A is before or after B. However a physical interpretation of such correlations was lacking. I will show that the “superposition of quantum circuits” – in which the gate ordering is not fixed but controlled by a quantum system – is an example of a process with indefinite causal order. This process provides a reduction in query complexity of certain computational problems and can be realized by placing the laboratories in the gravitational field of a massive object in a spatial superposition.
 
Ariel Caticha, University at Albany 
 
Entropic Dynamics: from Entropy and Information Geometry to Quantum Mechanics
 
Our subject is Entropic Dynamics, a framework that emphasizes the deep connections between the laws of physics and information. In attempting to understand quantum theory it is quite natural to assume that it reflects laws of physics that operate at some deeper level and the goal is to discover what these underlying laws might be. 
In contrast, in the entropic view no fundamental underlying dynamics is invoked. Quantum theory is an application of entropic methods of inference and the goal is to make the best possible predictions on the basis of some limited information represented by appropriate constraints. It is through the choice of microstates and of these constraints that the “physics” is introduced.
In Entropic Dynamics a relational notion of entropic time is introduced as a book-keeping device to keep track of changes. We show that a non-dissipative entropic dynamics naturally leads to generic forms of Hamiltonian dynamics, and notions of information geometry naturally lead to those specific Hamiltonians (that is, those that include the correct quantum potential) that describes quantum mechanics.
 
Giulio Chiribella, Institute for Interdisciplinary Information Sciences
 
Towards an information-theoretic foundation of (quantum) thermodynamics  
 
In the classical world of Newton and Laplace, fundamental physics and thermodynamics do not blend well: the former puts forward a picture of nature where states are pure and processes are fundamentally reversible, while the latter deals with scenarios where states are mixed and processes are irreversible.  Many attempts have been made at reconciling the two paradigms, but ultimately the source of all troubles remains: if every particle possesses a definite position and a definite velocity, why should experimental data depend on the expectations of agents who have only partial information?   Quantum theory offers a way out. Thanks to entanglement, a system and its environment can be  jointly in a pure state, while the system alone is in a mixed state.  Similarly, the evolution of system and environment can be jointly reversible, but locally irreversible.  At the level of axioms, these facts are captured by the Purification Principle [1], from which the whole of quantum theory was derived in Ref. [2].  
 
In this talk I will report on a new research programme, aimed at establishing the Purification Principle as the conceptual foundation for thermodynamics.  I will start from the idea that thermodynamical transformations can be mapped into transformations that degrade entanglement. This will lead to a duality between entanglement and thermodynamics, which will be used to define measures of entanglement/entropy and to explore operational tasks like information erasure. At this level, thermodynamical requirements lead directly to requirements on the particular type of Purifications allowed by the theory: for example, forbidding the existence of Entropy Sinks (systems that can absorb entropy from the environment without increasing their internal entropy) is equivalent to imposing the existence of Symmetric Purifications (purifications in which the environment is a mirror image of the system). I will conclude by giving a glimpse on quantitative measures of entanglement/entropy. By adding a requirement about the existence of sharp measurements, I will show that Purification leads directly the an operational version of the spectral theorem, allowing one to define a zoo of well-behaved entropies. 
 
[1] G. Chiribella, G. M. D’Ariano, and P. Perinotti, Probabilistic Theories with Purification, Phys. Rev. A 81, 062348 (2010)
[2] G. Chiribella, G. M. D’Ariano, and P. Perinotti, Informational Derivation of Quantum Theory, Phys. Rev. A 84, 012311 (2011)
 
Gemma De las Cuevas, Max Planck Institute
 
What discrete states have a continuum limit?
 
Renormalization to low energies is widely used in condensed matter theory to reveal the low energy degrees of freedom of a system, or in high energy physics to cure divergence problems. Here we ask which states can be seen as the result of such a renormalization procedure, that is, which states can “renormalized to high energies". Intuitively, the continuum limit is the limit of this "renormalization" procedure. We consider three definitions of continuum limit and characterise which states satisfy either one in the context of Matrix Product States. 
 
Joint work with N. Schuch, D. Perez-Garcia and I. Cirac.
 
Felix Finster, Regensburg University
 
Causal fermion systems from an information theoretic perspective
 
The theory of causal fermion systems is an approach to describe fundamental physics. It gives quantum mechanics, general relativity and quantum field theory as limiting cases and is therefore a candidate for a unified physical theory. Instead of introducing physical objects on a preexisting space-time manifold, the general concept is to derive space-time as well as all the objects therein as secondary objects from the structures of an underlying causal fermion system. The dynamics of the system is described by the causal action principle.
 
I will give a non-technical introduction, with an emphasis on conceptual issues related to information theory.
 
Doreen Fraser, University of Waterloo
 
Theories of heat as inspiration for electrodynamics:  From Kelvin to QFT
 
Perhaps the first use of the mathematical theory of heat to develop another theory was Thomson’s use of Fourier’s equations to formulate equations for electrostatics in the 1840s. After extracting a lesson from this historical case, I will fast forward more than a century to examine the relationship between classical statistical mechanics and QFT that is induced by analytic continuation. While there is no doubt that this mathematical relationship has been heuristically useful in guiding developments in both statistical mechanics and QFT, this is a case in which the physical interpretation of the mathematics does not carry over from one theory to the other. 
 
Steve Giddings, University of California, Santa Barbara
 
Quantum information and the algebraic structure of quantum gravity
 
Lucien Hardy, Perimeter Institute
 
Bringing General Relativity into the Operational Probabilistic Framework
 
I will discuss my work (in progress) to formulate General Relativity as an operational theory which includes probabilities and also agency (knob settings).  The first step is to find a way to discuss operational elements of GR. For this I adapt an approach due to Westman and Sonego.  I assert that all directly observable quantities correspond to coincidences in the values of scalar fields.  Next we need to include agency.  Usually GR is regarded as a theory in which a solution is simply stated for all space and time (the Block Universe view).  Here, instead, we find a way to treat agents as making choices.  Finally, we need to incorporate probabilities.  For this purpose we take a compositional point of view.  We associate a generalized state with regions of the space consisting of coincidences in the values of scalars.  We then show how to combine these generalized states to make probabilistic predictions using the duotensor machinery developed previously. 
 
Philipp Hoehn, Perimeter Institute
 
Information and the architecture of quantum theory
 
I will argue that, apart from their ever growing number of applications to physics, information theoretic concepts also offer a novel perspective on the physical content and architecture of quantum theory and spacetime. As a concrete example, I will discuss how one can derive and understand the formalism of qubit quantum theory by focusing only on what an observer can say about a system and imposing a few simple rules on the observer’s acquisition of information.
 
David Jennings, Imperial College London
 
Limitations of statistical mechanics for quantum thermodynamics.
 
How should we describe the thermodynamics of extreme quantum regimes, where features such as coherence and entanglement dominate?
 
I will discuss possible limitations of a traditional statistical mechanics approach, and then describe work that applies modern techniques from the theory of quantum information to the foundations of thermodynamics. In particular I discuss recent progress in quantum resource theories and argue that to properly encapsulate the thermodynamic structure of quantum coherence and entanglement we must make use of concepts beyond free energies.
 
Achim Kempf, University of Waterloo
 
What if nature is bandlimited by a Planck scale cutoff?
 
Tim Koslowski, University of New Brunswick
 
Physical records and emergence of information in the gravitationally dominated universe
 
The second law of thermodynamics appears to be a universal law of physics. This universality suggests that entropy and with it information theory is part of the foundations of physics.
 
In this talk I take the opposite (probably more conservative) approach: I assume that the dynamics of relational degrees of freedom form the foundation of physics. Physical information is an emergent phenomenon. This approach has an interesting consequence: Typical (initial) data for a gravitationally dominated universe leads to the spontaneous emergence of a gravitational arrow of time for the universe as a whole. This primary gravitational arrow of time generates secondary thermodynamic arrows of time in sufficiently isolated subsystems of the universe, which coincide with the gravitational arrow of time. This coincidence explains the universality of the second law of thermodynamics. 
 
I conclude the talk with a speculation about the emergence of quantum information: I assume (1) that the purpose of a physical law is the prediction of future properties of the universe based on the knowledge of records and (2) that gravity generates physical records (as in the classical part of the talk). This suggests a scenario in which stable quantum information is spontaneously generated.
 
Collaborators for the classical part of the talk where Julian Barbour and Flavio Mercati
 
Ryszard Kostecki, Perimeter Institute
 
Quantum information geometric foundations: beyond the spectral paradigm
 
In the last decade there were proposed several new information theoretic frameworks (in particular, symmetric monoidal categories and "operational" convex sets), allowing for an axiomatic derivation of finite dimensional quantum mechanics as a specific case of a larger universe of information processing theories. Parallel to this, there was an influential development of quantum versions of bayesianism and causality, and relationships between quantum information and space-time structure. In the face of structural problems encountered when moving beyond finite dimensional quantum mechanics, as well as the lack of a mathematically and predictively sound nonperturbative framework for quantum field theories, a question appears: which of the existing structural assumptions of quantum information theory should be relaxed, and how?
 
In this talk I will present a new approach to the information theoretic foundations of a "general" quantum theory (i.e., beyond quantum mechanics), that is a specific answer to the above question, with a hope to reconstruct both emergent space-times and emergent QFTs. Its mathematical setting is based on using quantum information geometry and integration over noncomutative algebras as structural and conceptual replacements of spectral theory and probability theory, respectively. This corresponds to a paradigmatic change: considering expectation values as more fundamental than eigenvalues. We construct a nonlinear generalisation of quantum kinematics using quantum relative entropies and spaces of states over W*-algebras. Unitary evolution is generalised to nonlinear hamiltonian flows, while Bayes' and Lueders' rules are generalised to constrained relative entropy maximisations. Combined together, they provide a framework for nonlinear causal inference (information dynamics), that is a generalisation and replacement of completely positive maps. As a result, we construct a large class of information processing theories, containing Hilbert space based QM and probability theory as two special cases. On the conceptual level, we propose a new approach to quantum bayesianism, that is ontically agnostic, intersubjective, and concerned with the relationships between experimental design, model construction, and their mutual predictive verifiability. Finally, we propose a procedure for the emergence of space-times from the geometry of quantum correlations and quantum causality structure, and discuss (briefly) the possibility of reconstructing emergent QFTs.
 
Lluis Masanes, University of Bristol
 
A derivation (and quantification) of the third law of thermodynamics
 
The third law of thermodynamics has a controversial past and a number of formulations due to Planck, Einstein, and Nernst. It's most accepted version, the unattainability principle, states that "any thermodynamic process cannot reach the temperature of absolute zero by a finite number of steps and within a finite time". Although formulated in 1912, there has been no general proof of the principle, and the only evidence we have for it is that particular cooling methods become less efficient as a the temperature lowers. Here we provide the first derivation of a general unattainability principle, which applies to arbitrary cooling processes, even those exploiting the laws of quantum mechanics or involving an infinite-dimensional reservoir. We quantify the resources needed to cool a system to any particular temperature, and translate these resources into a minimal time or number of steps by considering the notion of a Cooling Machine which obeys similar restrictions to universal computers. We generally find that the obtainable temperature scales as an inverse power of the cooling time, and place ultimate bounds on the speed at which information can be erased.
 
Markus Mueller, Heidelberg University
 
Quantum theory and spacetime: allies, not enemies
 
It has become conventional wisdom to say that quantum theory and gravitational physics are conceptually so different, if not incompatible, that it is very hard to unify them. However, in the talk I will argue that the operational view of (quantum) information theory adds a very different twist to this picture: quite on the contrary, quantum theory and space-time are highly fine-tuned to fit to each other.
After a recap of ideas by von Weizsacker, Wootters, and Popescu and Rohrlich, I will show how uncertainty relations, the number of degrees of freedom of the Bloch ball, and the existence of entangled states and possibly the Tsirelson bound can be understood from space-time geometry alone. Conversely, I will show how the 3+1 Lorentz group of space-time can be derived from a purely informational communication scenario of two observers that describe local quantum physics in different Hilbert space bases (joint work with Philipp Hoehn).
 
Robert Myers, Perimeter Institute
 
Scanning the Horizon:  Information, Holography and Gravity
 
In science, we often see new advances and insights emerging from the intersection of different ideas coming from what appeared to be disconnected research areas. The theme of my seminar will be an ongoing collision between the three topics listed in my title which has been generating interesting new insights into a variety of fields, eg, condensed matter physics, quantum field theory and  quantum gravity. 
 
Robert Oeckl, Universidad Nacional Autónoma de México (UNAM)
 
Towards new foundations of quantum theory from first principles and from quantum field theory 
 
As is well known, time plays a special role in the standard formulation of quantum theory, bringing the latter into severe conflict with the principles of general relativity. This suggests the existence of a more fundamental and (as it turns out) covariant and timeless formulation of quantum theory. A conservative way to look for such a formulation would be to start from quantum theory as we know it, taken in its experimentally most successful form of quantum field theory, and try to uncover structure in the formalism made for actual physical predictions. A radical way to look for such a formulation would be to forget the standard formulation, take only a few first principles (locality and operationalism turn out to be good ones) and try to construct things from there. Remarkably, approaches following these apparently opposite paths have recently been shown to converge in a single framework. In this talk I want to provide an overview of the current understanding of the resulting "positive formalism", its implications, and the paths that led to it. This includes relations to works of Witten and Segal in mathematical physics and of Aharonov, Hardy and others in quantum foundations.
 
Jonathan Oppenheim, University College
 
The second laws of quantum thermodynamics
 
Ruediger Schack, University of London
 
Agency, causal structure and locality in Qbism
 
In QBism, a quantum state represents an agent's personal degrees of belief regarding the consequences of her actions on any part of her external world. The quantum formalism provides consistency criteria that enable the agent to make better decisions. QBism thus gives a central role to the agent, or user of the theory, and explicitly rejects the ontological model framework introduced by Harrigan and Spekkens. This talk addresses the status of agents and the notion of locality in QBism. Our definition of locality is independent of the assumption of an ontological model. Instead it depends on an appropriate formalization of the idea of a causal structure.
 
Lee Smolin, Perimeter Institute
 
Quantum mechanics from first principles
 
Quantum mechanics is derived from the principle that the universe contain as much variety as possible, in the sense of maximizing the distinctiveness of each subsystem.  This is an expression of Leibniz's principles of sufficient reason and the identity of the indiscernible.
 
The quantum state of a microscopic system is defined to correspond to an ensemble of subsystems of the universe with identical constituents and similar preparations and environments.   A new kind of interaction is posited amongst such similar subsystems which acts to increase their distinctiveness, by extremizing the variety.  In the limit of large numbers of similar subsystems this interaction is shown to give rise to Bohm's quantum potential.  As a result the probability distribution for the ensemble is governed by the Schroedinger equation.
 
The measurement problem is naturally and simply solved.  Microscopic systems appear statistical because they are members of large ensembles of similar systems which interact non-locally.  Macroscopic systems are unique, and are not members of any ensembles of similar systems.  Consequently their collective coordinates may evolve deterministically.  
 
This proposal could be tested by  constructing quantum devices from entangled states of a modest number of quits which, by its combinatorial complexity, can be expected to have no natural copies.
 
Robert Spekkens, Perimeter Institute
 
Nonclassicality as the failure of noncontextuality
 
To make precise the sense in which nature fails to respect classical physics, one requires a formal notion of "classicality".  Ideally, such a notion should be defined operationally, so that it can be subjected to a direct experimental test, and it should be applicable in a wide variety of experimental scenarios, so that it can cover the breadth of phenomena that are thought to defy classical understanding.  Bell's notion of local causality fulfills the first criterion but not the second, because it is restricted to scenarios with two or more systems that are space-like separated.  The notion of noncontextuality fufills the second criterion, because it is applicable to any experiment (even those on a single system), but it is a long-standing question whether it can be made to fulfill the first.  Previous attempts to experimentally test noncontextuality have all presumed certain idealizations that do not hold in real experiments, namely, noiseless measurements and exact operational equivalences.  In this talk, I will describe how one can devise experimental tests that are free of these idealizations using an operational notion of noncontextuality that applies to both preparations and measurements. These new theoretical insights raise the bar significantly for any claim of an experimental demonstration of nonclassicality.  They also provide the means of determining, for any phenomenon that is typically thought to defy classical explanation, which experimentally-testable features of that phenomenon, if any, conflict with the assumption of a noncontextual model. 
 
Daniel Terno, Macquarie University
 
How far can you stretch classical mechanics?
 
Classical and quantum theories are very different, but the gap between them may look narrow particularly if the notion of classicality is broadened. For example, if we do not impose all the classical assumptions at the same time, hidden variable theories reproduce the results of quantum mechanics. If a quantum system is restricted to Gaussian states, evolution and measurements, then classical phase space mechanics with a finite resolution fully reproduces its behavior.
 
We discuss two examples of such extensions. In a version of the delayed-choice experiment we allow an otherwise classical system to exhibit two types of behavior ("P" or "W"), requiring, however, objectivity: the system is at any moment either "P" or "W", but not both. It turns out that the three conditions of objectivity, determinism, and independence of hidden variables are incompatible with any theory, not only with quantum mechanics. We then consider two harmonic oscillators with a Gaussian interaction between them. If  one is treated as quantum and one is described by a classical theory with a finite phase space resolution, no consistent description of this interaction is possible. The lesson is that it is hard to be a little bit quantum: it is either pointless or quantumness takes over altogether.
 
Gerard 't Hooft, Utrecht University
 
The CA interpretation of quantum mechanics
 
The CA interpretation presents a view on the origin of quantum mechanical behavior of physical degrees of freedom, suggesting that, at the Planck scale, bits and bytes are processed, rather than qubits or qubites, so that we are dealing with an ordinary classical cellular automaton. We demonstrate how this approach naturally leads to Born's expression for probabilities, shows how wave functions collapse at a measurement, and provides a natural resolution to Schroedinger's cat paradox without the need to involve vague decoherence arguments. We then continue to discuss the implications of Bell's inequalities, and other issues.
 
Erik Verlinde, University of Amsterdam
 
String Theory, Entropic Gravity and the Dark Universe
 
Recent developments reveal a deep connection between entanglement entropy and the emergence of space time and gravity. In anti-de Sitter space gravity appears to be derived from the first law of thermodynamics for entanglement entropy, which in the large radius limit obeys an area law. Based on insights from string theory, we propose a generalisation of these results to flat space  and de Sitter space. In the latter case, the vacuum entanglement entropy has an additional contribution that scales like the volume of the bulk space time.  We argue that this leads to a modification of Einstein gravity and explains the observed phenomena associated to dark energy and dark matter. 
 
 
 
 

 

Vendredi mai 15, 2015
Speaker(s): 

Perhaps the first use of the mathematical theory of heat to develop another theory was Thomson’s use of Fourier’s equations to formulate equations for electrostatics in the 1840s. After extracting a lesson from this historical case, I will fast forward more than a century to examine the relationship between classical statistical mechanics and QFT that is induced by analytic continuation.

 

Vendredi mai 15, 2015
Speaker(s): 

It is sometimes envisaged that the behaviour of elementary particles can be characterised by the information content it carries, and that exchange of energy and momentum, or more generally the change of state through interactions, can likewise be characterised in terms of its information content. But exchange of information occurs only in the context of a (typically noisy) communication channel, which traditionally requires a transmitter and a receiver; whereas particles evidently are not equipped with such devices.

 

Vendredi mai 15, 2015
Speaker(s): 

The third law of thermodynamics has a controversial past and a number of formulations due to Planck, Einstein, and Nernst. It's most accepted version, the unattainability principle, states that "any thermodynamic process cannot reach the temperature of absolute zero by a finite number of steps and within a finite time". Although formulated in 1912, there has been no general proof of the principle, and the only evidence we have for it is that particular cooling methods become less efficient as a the temperature lowers.

 

Vendredi mai 15, 2015
Speaker(s): 

As is well known, time plays a special role in the standard formulation of quantum theory, bringing the latter into severe conflict with the principles of general relativity. This suggests the existence of a more fundamental and (as it turns out) covariant and timeless formulation of quantum theory. A conservative way to look for such a formulation would be to start from quantum theory as we know it, taken in its experimentally most successful form of quantum field theory, and try to uncover structure in the formalism made for actual physical predictions.

 

Vendredi mai 15, 2015
Speaker(s): 

The theory of causal fermion systems is an approach to describe fundamental physics. It gives quantum mechanics, general relativity and quantum field theory as limiting cases and is therefore a candidate for a unified physical theory. Instead of introducing physical objects on a preexisting space-time manifold, the general concept is to derive space-time as well as all the objects therein as secondary objects from the structures of an underlying causal fermion system. The dynamics of the system is described by the causal action principle.

 

Jeudi mai 14, 2015
Speaker(s): 

The CA interpretation presents a view on the origin of quantum mechanical behavior of physical degrees of freedom, suggesting that, at the Planck scale, bits and bytes are processed, rather than qubits or qubites, so that we are dealing with an ordinary classical cellular automaton. We demonstrate how this approach naturally leads to Born's expression for probabilities, shows how wave functions collapse at a measurement, and provides a natural resolution to Schroedinger's cat paradox without the need to involve vague decoherence arguments.

 

Jeudi mai 14, 2015
Speaker(s): 

Renormalization to low energies is widely used in condensed matter theory to reveal the low energy degrees of freedom of a system, or in high energy physics to cure divergence problems. Here we ask which states can be seen as the result of such a renormalization procedure, that is, which states can “renormalized to high energies". Intuitively, the continuum limit is the limit of this "renormalization" procedure. We consider three definitions of continuum limit and characterise which states satisfy either one in the context of Matrix Product States.

 

Jeudi mai 14, 2015
Speaker(s): 

The modern understanding of quantum field theory underlines its effective nature: it describes only those properties of a system relevant above a certain scale. A detailed understanding of the nature of the neglected information is essential for a full application of quantum information-theoretic tools to continuum theories.

 

Jeudi mai 14, 2015
Speaker(s): 

Our subject is Entropic Dynamics, a framework that emphasizes the deep connections between the laws of physics and information. In attempting to understand quantum theory it is quite natural to assume that it reflects laws of physics that operate at some deeper level and the goal is to discover what these underlying laws might be.

 

Jeudi mai 14, 2015
Speaker(s): 

In the last decade there were proposed several new information theoretic frameworks (in particular, symmetric monoidal categories and "operational" convex sets), allowing for an axiomatic derivation of finite dimensional quantum mechanics as a specific case of a larger universe of information processing theories. Parallel to this, there was an influential development of quantum versions of bayesianism and causality, and relationships between quantum information and space-time structure.

Pages

Scientific Organizers:

Philipp Hoehn, Perimeter Institute
Ryszard Kostecki, Perimeter Institute
Markus Mueller, Heidelberg University