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String Theory Journal Club

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Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 10:00

Bartłomiej Czech (IAS Tsinghua)

The gauge theory of measurement-based quantum computation

The gauge theory of measurement-based quantum computationAbstract: Measurement-Based Quantum Computation (MBQC) is a model ofquantum computation, which uses local measurements instead of unitarygates. Here we explain that the MBQC procedure has a fundamental basisin an underlying gauge theory. This perspective provides a theoreticalfoundation for global aspects of MBQC. The gauge symmetry reflects thefreedom of formulating the same MBQC computation in different localreference frames. The main identifications between MBQC and gauge theoryconcepts are: (i) the computational output of MBQC is a holonomy of thegauge field, (ii) the adaption of measurement basis that remedies theinherent randomness of quantum measurements is effected by gaugetransformations. The gauge theory of MBQC also plays a role incharacterizing the entanglement structure of symmetry-protectedtopologically (SPT) ordered states, which are resources for MBQC. Ourframework situates MBQC in a broader context of condensed matter andhigh energy theory.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 11:30

Michał P. Heller (Ghent University)

Towards deriving a gravity dual to complexity

Holographic complexity proposals are interesting because, onone hand, they express universal properties of black hole interiors and,on the other, they go beyond the area-centric view on quantum gravity.Our best take on complexity in quantum field theory is based onassigning a cost to circuits generated by time-dependent Hamiltoniansand its minimization. I will discuss recent progress on understandinghow the relevant circuits are realized in holography and what arepossible gravity duals to good costs. Based on 2112.12158 and2203.08842.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 15:00

Michał Oszmaniec (CFT, PAN)

Saturation and recurrence of complexity in random quantum circuits

Quantum complexity is a measure of the minimal number ofelementary operations required to approximately prepare a given state orunitary channel. Recently, this concept has found applications beyondquantum computing—in studying the dynamics of quantum many-body systemsand the long-time properties of AdS black holes. In this context Brownand Susskind conjectured that the complexity of a chaotic quantum systemgrows linearly in time up to times exponential in the system size,saturating at a maximal value, and remaining maximally complex untilundergoing recurrences at doubly-exponential times. In this work weprove the saturation and recurrence of the complexity of quantum statesand unitaries in a model of chaotic time-evolution based on randomquantum circuits, in which a local random unitary transformation isapplied to the system at every time step. Importantly, our findings holdfor quite general random circuit models, irrespective of the gate setand geometry of qubit interactions. Our results advance an understandingof the long-time behaviour of chaotic quantum systems and could shedlight on the physics of black hole interiors. From a technicalperspective our results are based on establishing new quantitativeconnections between the Haar measure and high-degree approximatedesigns, as well as the fact that random quantum circuits ofsufficiently high depth converge to approximate designs.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Pedram Karimi (IFT UW)

Superintegrability in (deformed) Gaussian matrix models

The Gaussian Hermitian matrix model has the peculiar property that the averages of Schur functions of the eigenvalues take purely factorized forms, and can be written solely in terms of Schur functions evaluated at certain special values. This property, commonly referred to as superintegrability, has also been conjectured in the case of beta-deformed and q/t-deformed matrix models, which involve the Jack and Macdonald polynomials respectively. In this seminar, I will review these notions, and outline a proof of superintegrability in the case of beta-deformed matrix models. This is based on a joint work with A. Bawane and P. Sulkowski.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Adam Bzowski (IFT UW)

Logarithmic CFTs and holography, part 2

First, we will analyze the essential structure of the bulk physics required for the emergence of a dual logarithmic CFT. We will solve simple examples involving scalar operators, see e.g., hep-th/9807034. Next, we will look at bulk models containing gravity, including Topological Massive Gravity and/or higher order curvature models. We will analyze their holographic duals, see e.g., 0906.4926 or 1205.5804. I will use 1302.0280 as the compact review of the holographic models having dual logarithmic CFTs.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 10:30

Kurt Hinterbichler (Case Western Reserve University)

Symmetries and anomalies at the IR fixed point of gravity

I will discuss symmetries that arise at the infrared fixed point of the RG flow of Einstein gravity, including conformal vs. scale invariance in various dimensions, as well as 1-form generalized global symmetries and new anomalies that arise among them.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Claire Zukowski (University of Amsterdam)

Complexity for Conformal Field Theories in General Dimensions

In this talk I will describe circuit complexity for conformal field theories in arbitrary dimensions. I will consider gates built from a unitary representation of the Lorentzian conformal group, two different circuit cost functions, and paths that start from an initial primary state. The results can be understood in terms of the geometry of coadjoint orbits of the conformal group. I will also explain how these methods can be extended to study circuits in other symmetry groups using a group theoretic generalization of the notion of coherent states. Finally, I will describe a connection to timelike geodesics in anti-de Sitter spacetimes.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Adam Bzowski (IFT UW)

Logarithmic CFTs and holography

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Dongsheng Ge (IFT UW)

Introduction to Logarithmic CFT: Basics, part 3

In this journal club, I will introduce some basics on logarithmic CFT, following the review by Gurarie. I will first introduce the logarithmic operators and then study them in two models: c=-2 and c=0.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Dongsheng Ge (IFT UW)

Introduction to Logarithmic CFT: Basics, part 2

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Dongsheng Ge (IFT UW)

Introduction to Logarithmic CFT: Basics

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Piotr Sułkowski (IFT UW)

Very short summary of 2d CFT, part 2

I will present a very brief summary of 2d CFT, which is supposed to provide a background for the forthcoming series of our journal club discussions.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Falk Hassler (Uniwersytet Wrocławski)

An Algebraic Classification of Solution Generating Techniques

I will discuss a two-fold problem: on the one hand, the classification of a family of solution-generating techniques in (modified) supergravity and, on the other hand, the classification of a family of canonical transformations of 2-dimensional σ-models giving rise to integrability-preserving transformations. Assuming a generalised Scherk-Schwarz ansatz, in fact, the two problems admit essentially the same algebraic formulation, emerging from an underlying double Lie algebra. After presenting the derivation of the classification, we discuss in detail the relation to modified supergravity and the additional conditions to recover the standard (unmodified) supergravity. Starting from a master equation - that encodes all the possible continuous deformations allowed in the family of solution-generating techniques - I show that these are classified by the Lie algebra cohomologies H^2(h,R) and H^3(h,R) of the maximally isotropic subalgebra h of the double Lie algebra. Finally, I introduce a non-trivial example, the integrable bi-Yang-Baxter-Wess-Zumino model.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Mykola Dedushenko (Simons Center for Geometry and Physics, Stony Brook, USA)

Quantum algebras and SUSY interfaces

I will talk about certain supersymmetric interfaces in gauge theories and their role in the Bethe/gauge correspondence. On the "Bethe" side of this correspondence, there is an integrable model, whose Hilbert space V furnishes a representation of the quantum spectrum generating algebra (such as Yangian), while on the "gauge" side there is a family of supersymmetric gauge theories, whose space of SUSY vacua is V. Supersymmetric Janus interfaces for masses give natural linear maps between the spaces of SUSY vacua V, realizing stable envelopes and chamber R-matrices (both due to Maulik-Okounkov and Aganagic-Okounkov), which ultimately encode the action of quantum algebra on the "gauge" side. Further applications will be mentioned as well. Based on the recent and upcoming works with N.Nekrasov.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Piotr Sułkowski (IFT UW)

Very short summary of 2d CFT

I will present a very brief summary of 2d CFT, which is supposed to provide a background for the forthcoming series of our journal club discussions.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Jacek Pawełczyk (IFT UW)

Bosonic string as an integrable model, part 2

I shall show that finite volume spectrum of the free bosonic string can be reconstructed by a simple integrable model by means of thermodynamic Bethe Ansatz.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Jacek Pawełczyk (IFT UW)

Bosonic string as an integrable model

I shall show that finite volume spectrum of the free bosonic string can be reconstructed by a simple integrable model by means of thermodynamic Bethe Ansatz.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 11:00

Jan Boruch (IFT UW)

Recent developments on near-extremal black holes

In this talk, I will review some of the recent developments in understanding black holes near-extremality. For such black holes, below a certain temperature, one expects a breakdown of black hole thermodynamics. In the past, this had led to the prediction of the existence of a mass gap between the mass of an extremal black hole and its lightest excited state. Following https://arxiv.org/abs/2003.02860, I will discuss how the problem of higher dimensional near extremal black holes can be reduced to a well-studied model of JT gravity, and subsequently, show how one can probe the existence of the mass gap in different models.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Dimitris Patramanis (IFT UW)

Taming quantum chaos with symmetry

Understanding the time evolution of quantum operators is hardly a new topic in physics. In fact, for simple systems such as the harmonic oscillator this is a problem reserved for undergraduate students. However, what happens when we consider more complex systems that are, for example, described by many body dynamics or QFTs? How can we approach the same type of problem in the case of chaotic theories for which the tools at our disposal are limited? In my talk I will discuss a general method, called the Lanczos algorithm, which allows us to make progress in these directions by providing us with a clever way of decomposing a quantum operator in a convenient basis. I will then show that for systems with symmetry we can obtain analytical results for an operator at arbitrary times by combining the Lanczos algorithm with the formalism of coherent states. This turns out to be an efficient way of treating chaotic systems (and not only!), since it makes information about the operator evolution that is generally difficult to access readily available. In this sense we obtain a way to "tame" quantum chaos through symmetry considerations.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Neetu (Dublin Institute for Advanced Studies)

Asymptotics of Young diagrams through matrix models

Growth of Young diagrams is an important topic of study in asymptotic representation theory. In this seminar, we will talk about a matrix model description of growth processes of Young diagrams. In particular, we will see that the Plancherel growth process and its generalisations can be described through unitary matrix models. The classical solutions of unitary matrix models capture the asymptotic behaviour of Young diagrams growing according to (q-deformed) Plancherel probability. We will also talk about a Hilbert space description of unitary matrix models and Young diagrams.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Aditya Bawane (IFT UW)

Conformal bootstrap in Liouville theory, part 2

I will go over the bootstrap derivation of the structure constant ("the DOZZ formula") of Liouville theory. Following this, I will consider boundary conditions in Liouville theory, with particular focus on the FZZT boundary, and derive some of the structure constants in this boundary theory. I will then summarize the timelike analogs of these results, including some recent progress in boundary timelike Liouville theory in hep-th/2111.04715. Much of the talk will be an overview of well-known and established results, and the presentation will be pedagogical, geared towards graduate students.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Aditya Bawane (IFT UW)

Conformal bootstrap in Liouville theory

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:00

Sinong Liu (IFT UW)

Quantum quench in c = 1 matrix model and emergent space-times, part 2

We consider quantum quench in large-N singlet sector quantum mechanics of a single hermitian matrix in the double scaling limit. The time dependent parameter is the self-coupling of the matrix. We find exact classical solutions of the collective field theory of the eigenvalue density with abrupt and smooth quench profiles which asymptote to constant couplings at early and late times, and with the system initially in its ground state. With adiabatic initial conditions we find that adiabaticity is always broken regardless of the quench speed. In a class of quench profiles the saddle point solution for the collective field diverges at a finite time, and a further time evolution becomes ambiguous. However the underlying matrix model expressed in terms of fermions predict a smooth time evolution across this point. By studying fluctuations around the saddle point solution we interpret the emergent space-times. They generically have spacelike boundaries where the couplings of the fluctuations diverge and the semi-classical description fails. Only for very finely tuned quench profiles, the space-time is normal. This talk is based on the work arXiv: 1910.00123.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:15

Sinong Liu (IFT UW)

Quantum quench in c = 1 matrix model and emergent space-times

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:15

Adam Bzowski (IFT UW)

Breaking the spell of the tensor product

In my talk I will argue that the Hilbert space of states dual to a traversable wormhole is smaller than the tensor product of the independent Hilbert spaces of the boundary field theories. From the point of view of semiclassical physics, the decrease in the number of states is perceived as an emergent, non-local interaction stabilizing the wormhole. This presents new possibilities for models of radiating black holes. I will present a simple quantum-mechanical model, where the factorization of the Hilbert space is only approximate at low energies. I will show how quantum `weirdness' of the black holes physics follows from such models.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:15

Oleksandr Gamayun (IFT UW)

Modeling finite entropy states with free fermions, part 2

I will overview the "microscopic" bosonization approach to the evaluation of correlation functions in one-dimensional quantum fluids. The essence of this method lies in exact accounting for the soft-mode excitations around the vacuum state. I will try to explain how this is related to conformal field theory, Riemann-Hilbert problem, Painleve equations, Integrable systems, etc. My main example will be a Fredholm determinant of the sine kernel, which is also nicely connected to the Hermitian Matrix Models. Finally, if time permits, I will explain how to generalize this machinery for the computation of correlation functions on the finite entropy state.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:15

Oleksandr Gamayun (IFT UW)

Modeling finite entropy states with free fermions

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:15

Kento Osuga (IFT UW)

Algebraic Curves in Mathematical and Theoretical Physics, part 2

Algebraic curves play very important roles in mathematical and theoretical physics including topological string theory, Seiberg-Witten theory, matrix models, 2d gravity, and more. For a wide variety of examples, it has been conjectured or even proven that one can compute the partition function and correlation functions of a physical theory without referring to the path integral, but purely in terms of geometric properties of the corresponding algebraic curve. In this introductory talk, I will present an overview of how such algebraic curves arise in physics and also how we can use them to compute invariants in physics. If time permits, I will briefly mention about recent and ongoing results of my research with collaborators.

Zapraszamy do sali 5.42, ul. Pasteura 5 o godzinie 12:15

Kento Osuga (IFT UW)