Quantum Physics

There has been a surge of interest in indefinite causal structure the idea that cause and effect can no longer be sharply distinguished.  Motivated both by experimentation with quantum switches and quantum gravity there can be situations in which there is no matter-of-the-fact as to what the causal structure of spacetime is.  This meeting will bring together workers in Quantum Foundations and Quantum Gravity in both theoretical experimental physics to discuss the state of the art of current research and set new directions for this emerging subdiscipline.

Our conference covers three related subjects: quantum fault-tolerance magic states and resource theories and quantum computational phases of matter. The linking elements between them are (a) on the phenomenological side the persistence of computational power under perturbations and (b) on the theory side symmetry. The latter is necessary for the working of all three. The subjects are close but not identical and we expect cross-fertilization between them.Fault tolerance is an essential component of universal scalable quantum computing.However known practical methods of achieving fault tolerance are extremely resource intensive. Distillation of magic states is in the current paradigm of fault-tolerance the costliest operational component by a large margin. It is therefore pertinent to improve the efficiency of such procedures study theoretical limits of efficiency and more generally to establish a resource theory of quantum state magic. During the workshop we will focus on a fundamental connection between fault-tolerant protocols and symmetries.``Computational phases of matters are a surprising link between quantum computation and condensed matter physics. Namely in the presence of suitable symmetries the ground states of spin Hamiltonians have computational power within the scheme of measurement-based quantum computation and this power is uniform across physical phases. Several computationally universal phases have to date been discovered. This subject is distinct from the above but linked to them by the feature of persistence of computational power under deformations and deviations.

Boundaries and defects play central roles in quantum field theory (QFT) both as means to make contact with nature and as tools to constrain and understand QFT itself. Boundaries in QFT can be used to model impurities and also the finite extent of sample sizes while interfaces allow for different phases of matter to interact in a controllable way. More formally these structures shed light on the structure of QFT by providing new examples of dualities and renormalization group flows.  Broadly speaking this meeting will focus on three areas: 1) formal and applied aspects of boundary and defect conformal field theory from anomalies and c-theorems to topological insulators 2) supersymmetry and duality from exact computations of new observables to the construction of new theories and 3) QFT in curved space and gravity from holographic computations of entanglement entropy to ideas in quantum information theory. Registration for this event is now open.

Machine learning techniques are rapidly being adopted into the field of quantum many-body physics including condensed matter theory experiment and quantum information science.  The steady increase in data being produced by highly-controlled quantum experiments brings the potential of machine learning algorithms to the forefront of scientific advancement.  Particularly exciting is the prospect of using machine learning for the discovery and design of quantum materials devices and computers.  In order to make progress the field must address a number of fundamental questions related to the challenges of studying many-body quantum mechanics using classical computing algorithms and hardware. The goal of this conference is to bring together experts in computational physics machine learning and quantum information to make headway on a number of related topics including: Data-drive quantum state reconstruction Machine learning strategies for quantum error correction Neural-network based wavefunctions Near-term prospects for data from quantum devices Machine learning for quantum algorithm discovery Registration for this event is now closed

The foundations of quantum mechanics have been revitalized in the past few decades by three developments:  (i) the influence of quantum computation and quantum information theory (ii) studies of the interplay between quantum theory and relativity particularly the analysis of indefinite causal structure and (iii) proposals to reconstruct quantum theory from basic axioms.  There have also been very interesting developments in understanding and classifying no=locality and contextuality using tools from sheaf theory and cohomology as well as operator algebras and category theory. The International Congress of Mathematical Physics is a natural forum for the discussion of these topics.  In the past there have been satellite workshops on topics like Operator algebras and quantum statistical mechanics which also address fundamental issues.  The modern study of quantum foundations is very much influenced and informed by mathematics:  sheaf theory and cohomology category theory information theory convex analysis in addition to the continuing interest in operator algebras and functional analysis. The aim of the workshop is to bring together researchers who have made substantial contribution to the recent developments.  The workshop will be held at Perimeter Institute over a five day period from July 30

Our universe is of astonishing simplicity: almost all physical observations can in principle be described by a few theories that have short mathematical descriptions. But there is a field of computer science which quantifies simplicity namely algorithmic information theory (AIT). In this workshop we will discuss emerging connections between AIT and physics some of which have recently shown up in fields like quantum information theory and thermodynamics. In particular AIT and physics share one goal: namely to predict future observations given previous data. In fact there exists a gold standard of prediction in AIT called Solomonoff induction which is also applied in artificial intelligence. This motivates us to look at a broader question: what is the role of induction in physics? For example can quantum states be understood as Bayesian states of belief? Can physics be understood as a computation in some sense? What is the role of the observer i.e. the agent that is supposed to perform the predictions? These and related topics will be discussed by a diverse group of researchers from different disciplines.

Foil theories sometimes called mathematically rigorous science fiction describe ways the world could have been were it not quantum mechanical. Our understanding of quantum theory has been deepened by contrasting it with these alternatives. So far observers in foil theories have only been modeled implicitly for example via the recorded probabilities of observing events. Even when multi-agent settings are considered these agents tend to be compatible in the classical sense that they could always compare their observations. Scenarios where agents and their memories are themselves modeled as physical systems within the theory (and could in particular measure each other as in Wigner's friend experiment) have not yet been considered. In this workshop we will investigate which foil theories allow for the existence of explicit observers and whether they allow for paradoxes in multi-agent settings such as those found in quantum theory. We will also investigate which interpretations of quantum theory would equally well interpret the foil theories and which interpretations are truly quantum. We will gain a deeper understanding of how this can happen by discussing appropriate definitions observers in these theories and seeing how such observers learn about their environment.