- Jackson R Fliss (University of Cambridge)
- "Keeping matter in the loop in 3d quantum gravity"
[Abstract] [pdf]
Abstract
Chern-Simons theory provides an attractive framework for quantizing 3d gravity. But how do we describe matter in CS gravity while retaining its useful features? In this talk, I will introduce a "Wilson spool," which provides an effective description of massive one-loop determinants directly as a gauge-invariant object. The spool can be heuristically viewed as a collection of Wilson loops winding in the Euclidean spacetime. I will illustrate its utility for reproducing the one-loop determinants of massive scalar fields in both Anti-de Sitter and de Sitter backgrounds. In the context of de Sitter quantum gravity, exact results in Chern-Simons theory allow one to calculate the spool at finite G_N. This provides a method for investigating how dynamical gravity renormalizes the physics of massive matter.
- Keiichiro Furuya (Northeastern University)
- "Information loss, mixing and emergent type III_1 factors"
[Abstract]
Abstract
A manifestation of the black hole information loss problem is that the two-point function of probe operators in a large Anti-de Sitter black hole decays in time, whereas, on the boundary CFT, it is expected to be an almost periodic function of time. We point out that the decay of the two-point function (clustering in time) holds important clues to the nature of observable algebras, states, and dynamics in quantum gravity.
We argue that, from the point of view of quantum error correction (QEC), a decorrelating flow is a dynamical process that secretly creates approximate QEC codes. The preparation is secret, in the sense that observers in either split subsystem cannot detect the process.
In gravity, quite generally, there seems to be a regime where the split flow stretches the space decorrelating subsystems in time. For infinite volume subsystems, as the space stretches the systems decorrelate asymptotically in time. Whereas finite volume subsystems decorrelate at the finite time undergoing phase transitions. We argue that from the point of view of quantum mechanics, monotonic decorrelation or phase transitions are unexpected, and correspond to a density matrix version of the black hole information loss problem.
- Elliott Gesteau (California Institute of Technology)
- "Large N von Neumann algebras and the renormalization of Newton's constant"
[Abstract]
Abstract
In holography, the quantum extremal surface formula relates the entropy of a boundary state to the sum of two terms: the area term and the entropy of bulk fields inside the entanglement wedge. As the bulk effective field theory suffers from UV divergences, the second term must be regularized. It has been conjectured since the work of Susskind and Uglum that the renormalization of Newton’s constant in the area term exactly cancels the difference between different choices of regularization for bulk entropy. In this talk, I will explain how the recent developments on von Neumann algebras appearing in the large N limit of holography allow to prove this claim within the framework of holographic quantum error correction, and to reinterpret it as an instance of the ER=EPR paradigm. This talk is based on the paper arXiv:2302.01938.
- Kohei Kawabata (Institute for Solid State Physics, University of Tokyo)
- "Symmetry Classification of Typical Quantum Entanglement"
[Abstract] [pdf]
Abstract
Entanglement entropy of typical quantum states, also known as the Page curve, plays an important role in quantum many-body systems and quantum gravity. However, the role of symmetry has remained largely unclear. Here, we establish the classification of typical quantum entanglement for free fermions, or equivalently the quadratic Sachdev-Ye-Kitaev model with symmetry, on the basis of the tenfold fundamental symmetry classes of time reversal, charge conjugation, and chiral transformation. Through both analytical and numerical calculations of random matrix theory, we show that the volume-law contribution to average entanglement entropy is robust and remains unaffected by symmetry. Conversely, we uncover that the constant terms of the average and variance of entanglement entropy yield tenfold universal values unique to each symmetry class. These constant terms originate from the combination of a global scaling of the entanglement spectrum due to time-reversal symmetry and a singular peak at the center of the entanglement spectrum due to chiral or particle-hole symmetry.
- Masamichi Miyaji (Nagoya University)
- "Fluctuations in the Entropy of Hawking Radiation"
[Abstract]
Abstract
Recent study revealed that the inclusion of Euclidean wormhole into the gravitational path integral renders the entropy of Hawking radiation consistent with unitarity, deriving the Page curve of the Hawking radiation. On the other hand, since the gravitational path integral with Euclidean wormhole computes quantities of ensemble average of theories, it is possible that the entropy of Hawking radiation of each gravity theory fluctuate wildly around the ensemble average. In this talk we show that such fluctuation is as small as the dimension of the system, ensuring the answer from the ensemble average is typical. We use the gravitational path integral to compute the fluctuations of the Hawking radiation entropy around the Page curve, in a two-dimensional model introduced by Penington \emph{et al}. Before the Page time, we find that $\delta S = e^{-S}/\sqrt{2}$, where $S$ is the black hole entropy. This result agrees with the Haar-averaged entropy fluctuations of a bipartite system, which we also compute at leading order. After the Page time, we find that $\delta S = O(1)e^{-S}$. This is not symmetric under exchange of subsystem sizes and so does not agree with the Haar average for a subsystem of fixed Hilbert space dimension. We show that the discrepancy can be attributed to an additive $O(1)$ fluctuation in the number of black hole states in a given energy band. As a by-product, our result gives a refinement on the known upper bound on the subsystem entropy fluctuation in Haar random pure state.
- Vladimir Narovlansky (Princeton University)
- "Semiclassical geometry in double-scaled SYK"
[Abstract]
Abstract
Double-scaled SYK (DSSYK) has a tunable coupling constant related to the number of fermions taking part in the basic interaction. We argue that weak coupling corresponds to a semiclassical approximation governed by a non-trivial saddle point. The classical value gives the `large q’ SYK theory. To gain insight into finite coupling, we go beyond the classical limit. We describe a two dimensional gravitational theory, where every observable of DSSYK has a corresponding observable in this theory. In the classical limit of DSSYK the metric is that of AdS with negligible fluctuations. We compute analytically the 1-loop correction, showing that the geometry deviates from AdS as we go into the bulk, and compare to numerics at finite coupling. On the quantum mechanics side, the two dimensional curvature is encoded in energy fluctuations in light operators. We also describe the entanglement entropy in the semiclassical limit.
- Cheng Peng (Kavli Institute for Theoretical Sciences, UCAS)
- "On covariant SYK models"
- Kazuaki Takasan (University of Tokyo)
- "Quantum active matter: A new class of nonequilibrium phases of matter"
[Abstract]
Abstract
Active matter is an ensemble of self-propelled entities, such as flocks of birds and schools of fish, that has attracted significant attention for its various phase transitions and pattern formations that are not present in equilibrium systems [1]. The physics of active matter has been studied mainly in classical systems. In particular, its application to biophysics has been successful, helping to understand the nature of biological systems [2]. In contrast, the study of active matter in quantum systems has been limited due to the lack of open quantum many-body systems in experiments. Recently, however, such systems have become accessible through advances in atomic-molecular-optical experiments [3]. Thus, it is now reasonable to consider the quantum versions of active matter physics.
Recently, we proposed a quantum many-body model that resembles active matter and exhibits several activity-induced quantum phase transitions [4]. The model consists of two-component hard-core bosons on a lattice with a non-Hermitian hopping term, mimicking the activity in classical systems. Through exact diagonalization and quantum Monte Carlo simulation, we obtained a phase diagram that includes several nonequilibrium phases, including motility-induced phase separation and polar flocking. Furthermore, we proposed an experimental setup to realize this model using ultracold atoms in optical lattices. In addition, we present more recent studies on another quantum active matter model containing spin-spin interaction in this talk [5]. If time allows, we would like to address a possible application of quantum active matter to quantum information processing. Our work opens a new direction to explore nonequilibrium quantum phases of matter and the physics of quantum simulation.
This talk is based on the collaboration works [4, 5] with Kyosuke Adachi (RIKEN) and Kyogo Kawaguchi (RIKEN).
[1] M. C. Marchetti et al., Rev. Mod. Phys. 85, 1143 (2013). [2] K. Kawaguchi et al., Nature 545, 327 (2017). [3] T. Tomita et al., Sci. Adv. 3, e1701513 (2017). [4] K. Adachi, KT, K. Kawaguchi, Phys. Rev. Research 4, 013194 (2022). [5] KT, K. Kawaguchi, K. Adachi, in preparation.
- Zhuo-Yu Xian (Julius-Maximilians-Universität Würzburg)
- "Universal chaotic dynamics from Krylov space"
[Abstract]
Abstract
The Krylov complexity measures the spread of the wavefunction in the Krylov basis, which is constructed using the Hamiltonian and an initial state. We investigate the evolution of the maximally entangled state in the Krylov basis for both chaotic and non-chaotic systems in our paper arXiv:2303.12151. Our findings suggest that neither the linear growth nor the saturation of Krylov complexity is necessarily associated with chaos. However, for chaotic systems, we observe a universal rise-slope-ramp-plateau behavior in the transition probability from the initial state to a Krylov basis, which is a characteristic of chaos in the spectrum of the Hamiltonian. Additionally, the long ramp in the transition probability is directly responsible for the late-time peak of Krylov complexity observed in previous literature. On the other hand, for non-chaotic systems, the transition probability exhibits a different behavior without the long ramp. Therefore, our results help to clarify which features of the wave function time evolution in Krylov space characterize chaos.
- Yang Zhenbin (Institute for Advanced Study, Tsinghua University)
- "Firewalls from wormholes"
[Abstract]
Abstract
Spacetime wormholes can lead to surprises in black hole physics. We show that a very old black hole can tunnel to a white hole/firewall by emitting a large baby universe. We study the process for a perturbed thermofield double black hole in Jackiw-Teitelboim (JT) gravity, using the lowest order (genus one) spacetime wormhole that corresponds to single baby-universe emission. The probability for tunneling to a white hole is proportional to t^2e^{-2S} where t is the age of the black hole and S is the entropy of one black hole.
- Takanori Anegawa (Osaka University)
- "Shock waves and delay of hyperfast growth in de Sitter complexity"
[Abstract] [pdf]
Abstract
We study the holographic complexity in de Sitter spacetime, especially how the hyperfast growth of holographic complexity in de Sitter spacetime is affected under a small and early perturbation. The perturbed geometry is de Sitter spacetime with shock waves. We find that the critical time, at which de Sitter holographic complexity diverges, becomes always greater in the presence of the shock waves, which satisfies the averaged null energy conditions. This means that the hyperfast property of de Sitter complexity is delayed by small perturbations.
- Shoto Aoki (Osaka university)
- "Curved domain-wall fermion and its anomaly inflow"
[Abstract]
Abstract
We investigate a fermion system with a curved domain-wall mass term.
In the same way as the conventional flat domain-wall fermion, the
chiral edge modes appear localized at the wall, but the Dirac operator
contains a nontrivial gravitational potential. In the case of S^1
domain-wall fermion on a two-dimensional flat lattice with U(1)
electrio-magnetic field, we find a competition between the
Aharonov-Bohm(AB) effect and gravitational gap in the Dirac eigenvalue
spectrum, which leads to anomaly of the time-reversal (T) symmetry.
Our numerical result shows a good consistency with the
Atiyah-Patodi-Singer index theorem on a disk inside the S^1
domain-wall, which describes the cancellation of the T anomaly between
the bulk and edge. When the U(1) flux is squeezed inside one
plaquette, and the AB phase takes a quantized value π mod 2 π Z, the
anomaly inflow drastically changes: the strong flux creates another
domain-wall around the flux to make the two zero modes coexist.
- Sinya Aoki (Yukawa Institute for Theoretical Physics, Kyoto University)
- "Conserved charge in general relativity"
[Abstract] [pdf]
Abstract
For a system invariant under time-translation, energy is defined as its Noether charge and thus dynamically conserved. For a curved spacetime in general relativity, however, the energy is not necessary to be conserved since the time-translation invariant is broken in general. In this talk, we propose a conserved charge in general relativity, which is defined from the matter energy momentum tensor together with an introduction of a new scalar function. By applying this definition to the FLRW expanding Universe, we argue that this conserved charge as well as the scalar function are interpreted as an entropy and an local inverse temperature in the spacetime, respectively.
- Goncalo Araujo-Regado (University of Cambridge / Okinawa Institute of Science and Technology)
- "Cauchy Slice Holography - From Basics to a Taste of Quantum Cosmology"
[Abstract]
Abstract
In this talk I will introduce the formalism of Cauchy Slice Holography, which provides a holographic description of Wheeler-DeWitt states in the canonical formulation of quantum gravity in terms of partition functions of T^2-deformed CFTs. The field theory lives on a spatial slice of the bulk. I will then explore some of the consequences of such a description of quantum gravity for a closed Universe with a positive cosmological constant. It turns out that a general solution comes as a superposition of two field theory branches, which are CPT duals of each other. Unlike in AdS/CFT, both of them are important in this case. I will end by explaining how the choice of superposition of branches is related to the contour problem in quantum cosmology, referring to minisuperspace toy models for concreteness.
- Jaydeep Kumar Basak (National Sun Yat-sen University, Taiwan)
- "Reflected entropy and Markov gap in non-inertial frame"
[Abstract] [pdf]
Abstract
I will explain the result of our upcoming article on the reflected entropy and Markov gap between two modes of a free fermionic field as observed by two accelerating observers. This is done for both bipartite system which is described by Bell state and tripartite systems which are represented by W and GHZ states. The reflected entropy degrades monotonically as a result of the Unruh effect, eventually reaching a non-zero minimum value in the limit of infinite acceleration. Markov gap is a measure of multipartite entanglement measure which increase for Bell and GHZ states with respect to acceleration. On the other hand, W state shows decreasing characteristics with increasing acceleration. For all the cases, Markov gap show non zero values at infinite acceleration limit which indicates the possibility of three party quantum information processing task. In addition, we also propose a $\sigma$-function for reflected entropy which decreases monotonically with decreasing Unruh temperature irrespective of the states under consideration.
- Jan Boruch (University of Warsaw)
- "Indices from the gravitational path integral: new forms of attraction"
[Abstract]
Abstract
In recent years, the Euclidean gravitational path integral has proven to be a reliable tool for studying quantum mechanical aspects of black holes. An important quantity that can help us probe whether black holes behave like conventional quantum mechanical systems is the supersymmetric index computed directly from the gravitational path integral. In this talk, I will discuss the issue of multicentered black hole contributions to the Euclidean path integral that computes the supersymmetric index at finite temperature. In the context of Einstein-Maxwell theory in 4d, I will explain how the multicentered generalization of the Kerr-Newman black hole, called the Israel-Wilson solution, can be seen to satisfy the boundary conditions of the supersymmetric index and yields a regular contribution to the index. I will show how even though we perform the computations at finite temperature, the construction makes the value of the on-shell action depend only on the black hole charges, which can be viewed as a new form of the attractor mechanism. Finally, I will describe how we can extend the analysis to the most general solutions of N=2 4d supergravity, where the on-shell action becomes independent of the boundary values of the scalars. Based on the upcoming work with Luca Iliesiu, Sameer Murthy and Joaquin Turiaci.
- Aidan Chatwin-Davies (Okinawa Institute of Science and Technology)
- "Predictions for Quantum Gravitational Signatures from Inflation"
[Abstract] [pdf]
Abstract
The huge separation between the Planck scale and typical laboratory scales makes it extremely difficult to detect quantum gravitational effects; however, the situation is in principle much more favourable in cosmology, which motivates looking for present-day signatures of Planck-scale physics from the early universe. The question, then, is what quantum gravitational effects should we look for, and what are their observational signatures? Here I will discuss how quantum gravitational and information theoretic considerations lead to an extended Nyquist-Shannon sampling theorem for fields on Lorentzian manifolds. Applying the results to the physics of cosmological perturbations leads to predictions for signatures of quantum gravity in primordial power spectra that will allow experiments to place new rigorous bounds on the scale at which quantum gravity effects become important.
- Giuseppe Di Giulio (Julius-Maximilians Universität Würzburg)
- "Symmetry-resolved modular correlation functions in free fermionic theories"
[Abstract] [pdf]
Abstract
Recently there has been a huge research activity on the interplay between symmetries and entanglement, exploiting the block-diagonal structure of the reduced density matrix (RDM) in each charge sector. The goal of this talk is to study how the presence of a global U(1) charge affects the modular flow, a central object in the algebraic description of quantum field theory. Roughly speaking, the modular flow is given by a generalized time evolution induced by a RDM of a given spatial region. I will discuss the symmetry resolution of the modular flow and the modular correlation function of U(1)-invariant operators. I will provide a consistent definition of symmetry-resolved modular flow defined for a local algebra of operators associated with a sector with a fixed charge. I will also discuss the symmetry-resolved modular correlation functions, showing that they satisfy the KMS condition in each symmetry sector. In order to complement this analysis with an example, I will provide a toolkit for computing the symmetry-resolved modular correlation function of the charge density operator in free fermionic theories. I will show that, in a 1 + 1-dimensional free massless Dirac field theory, this quantity is independent of the charge sector at leading order in the ultraviolet cutoff expansion. This feature can be regarded as an equipartition of the modular correlation function.
- Kazuki Doi (Yukawa Institute for Theoretical Physics, Kyoto University)
- "dS/CFT and Pseudoentropy"
[Abstract]
Abstract
We study holographic entanglement entropy in dS/CFT. This takes complex values in general and we argue that it is correctly understood as pseudoentropy. We find that the imaginary part of pseudoentropy implies an emergence of time in dS/CFT. This work was published as Phys. Rev. Lett. 130 (2023) 3, 031601 and is based on collaboration with Harper, Mollabashi, Takayanagi, and Taki.
- Stefan V. Ecclers (Okinawa Institute of Science and Technology)
- "Gravitational edge modes as reference frames"
[Abstract]
Abstract
I will discuss the interpretation of gravitational edge modes as dynamical reference frames. I will introduce a framework [arXiv:2205.00913] based on the covariant phase space formalism that identifies these "new" degrees of freedom at a subregion boundary as originating from the field content of the complement region and encoding relational information about the embedding of the subregion into the global theory. A systematic post-selection procedure is invoked to identify consistent subregion theories associated with different choices of gauge invariant boundary conditions. Requiring conservation of the subregion presymplectic structure leads to an essentially unique prescription and unambiguous Hamiltonian charges, which can be understood as the generators of frame reorientations. I will compare and contrast this proposal for presymplectic structure with related proposals in the literature.
- Chen-Hsuan Hsu (Institute of Physics, Academia Sinica, Taiwan)
- "Unconventional states of matter in the quantum-wire network of moiré systems"
[Abstract] [pdf]
Abstract
We theoretically investigate the unconventional quantum matter in the quantum-wire network, a model used to describe the low-energy physics of moiré bilayer systems. We construct a general operator describing various scatterings based on conservation laws and identify generalized umklapp scatterings in twisted moiré bilayer structures, which result in correlated states at fractional fillings. Remarkably, we uncover scattering processes that lead to a gapped bulk with chiral edge modes, resembling the recently observed quantum anomalous Hall effect in twisted bilayer graphene. We demonstrate that our description can be useful by predicting observable features in the proposed setups, including spectroscopic probes and edge transport measurements.
- Yichen Hu (Princeton University)
- "LOOP HOMOTOPY OF CLIFFORD CIRCUITS"
[Abstract]
Abstract
Lagrangian submodules of hyperbolic modules over Laurent polynomial rings with
coefficients in prime fields encode one of the simplest types of translationally invariant invertible many-body systems. In this talk, we investigate the homotopy classes of loops of Clifford circuits by analyzing their action on lagrangians. The main tool we use is the hermitian K-theory and, in particular, the Maslov index of a loop of free lagrangians.
- Youka Kaku (Department of physics, Nagoya University)
- "Blackhole shadow of a spatially superposed Schwarzchild spacetime"
[Abstract] [pdf]
Abstract
In 2017, a thought experiment observing gravity-induced superposition of a probe particle was proposed as a first step to look into quantum nature of gravity. However, most of these thought experiment suppose that gravity is weak enough and consider Newton gravity in non-relativistic regime, so that a character of gravity did not appear in their observable. In this talk, we consider blackhole shadow of a spatially superposed Schwarzchild spacetime. We clearly consider a strong gravitational field, which we expect to capture a quantum feature unique to gravity.
- Naoto Kan (Osaka University)
- "Curved domain-wall fermion and its applications"
[Abstract]
Abstract
A domain-wall fermions has played a key role in formulating chiral symmetric theories in particle physics mainly on a flat spacetime. Recently it was shown that when the domain-wall of the mass term is curved, the chiral edge modes feel a nontrivial gravitational potential through the induced spin connection. In this talk, we discuss possible applications of this curved domain-wall fermion system to condensed matter physics with nontrivial geometry, as well as to effective gravity theory.
- Surbhi Khetrapal (University of Hyderabad, India)
- "Quantum Chaos and K-complexity in Conformal Field Theory"
[Abstract]
Abstract
We study the out-of-time-ordered correlator (OTOC) in a zero temperature 2d large-c CFT under evolution by a Liouvillian composed of the Virasoro generators. A bound was conjectured in Parker et. al., 2018 on the growth of the OTOC set by the Krylov complexity which is a measure of operator growth. The latter grows as an exponential of time with exponent which sets an upper bound on the Lyapunov exponent. We find that for a two dimensional zero temperature CFT, the OTOC decays exponentially with a Lyapunov exponent which saturates this bound. We show that these Virasoro generators form the modular Hamiltonian of the CFT with half space traced out. Therefore, evolution by this modular Hamiltonian gives rise to thermal dynamics in a zero temperature CFT. Leveraging the thermal dynamics of the system, we derive this bound in a zero temperature CFT using the analyticity and boundedness properties of the OTOC. Based on https://arxiv.org/abs/2210.15860
- Akira Matsumoto (Yukawa Institute for Theoretical Physics, Kyoto University)
- "Three ways of calculating mass spectra for composite particles in the Hamiltonian formalism"
[Abstract] [pdf]
Abstract
We propose three independent methods to compute the mass of composite particles (hadrons) of gauge theories in the Hamiltonian formalism.
Determination of hadron masses is one of the key issues in QCD, which has been precisely calculated by Monte Carlo calculations based on the Lagrangian formalism.
We newly show how to calculate the mass spectra in Hamiltonian formalism, which is suitable for quantum calculations and tensor networks.
The three methods, by examining correlation functions, the one-point function, and the dispersion relation, are tested with DMRG in the 2-flavor Schwinger model,
which shares important properties with QCD. We show that the results of these methods are consistent with each other, and discuss their potential applications.
- Takato Mori (Yukawa Institute for Theoretical Physics, Kyoto University)
- "Probing quantum correlations in holography via measurements"
[Abstract]
Abstract
In this talk, I discuss the holographic quantum correlation between one side of the eternal AdS black hole and a subregion at the asymptotic boundary on the other side based on low and high-complexity measurements. The quantum correlation is quantified by quantum discord (QD). This includes non-entanglement quantum correlations while it excludes classical correlations. Remarkably, it is likely to be a good measure for quantum correlation of mixed states while discontinuity is absent unlike entanglement wedge cross section. Furthermore, by using an information theoretic inequality for entanglement of formation calculated from QD, it is shown that QD is sensitive to the (a)typicality of black hole microstates. Finally, it tells us not only about bipartite quantum correlations but tripartite entanglement and the complexity of measurements. By comparing two measurements with different complexity, it is suggested that ignorance and complexity are interchangeable.
- Mitsuhiro Nishida (Pohang University of Science and Technology)
- "Krylov complexity in the IP matrix model"
[Abstract] [pdf]
Abstract
The IP matrix model is a simple large N quantum mechanical model made up of an adjoint harmonic oscillator plus a fundamental harmonic oscillator. It is a model introduced previously as a toy model of the gauge theory dual of an AdS black hole. In the large N limit, one can solve the Schwinger-Dyson equation for the fundamental correlator, and at sufficiently high temperature, this model shows key signatures of thermalization and information loss; the correlator decays exponentially in time, and the spectral density becomes continuous and gapless. We study the Lanczos coefficients in this model and at sufficiently high temperature, it grows linearly in n with logarithmic corrections, which is one of the fastest growth under certain conditions. As a result, the Krylov complexity grows exponentially in the square root of time. These results indicate that the IP model at sufficiently high temperature is chaotic.
- Yuki Osawa (Nagoya University)
- "Information Channel in the Spacetime with Moving Boundary"
[Abstract]
Abstract
We investigate the method to understand Hawking radiation and the information paradox by using the communication channel via quantum field.
In this talk, we construct the communication protocol using quantum field and we see that the effect of Hawking radiation can be understood as the noise of the communication channel.
We will also discuss the relation between the possibility of removing channel noise and the information loss paradox.
- Juan W. Pedersen (The University of Tokyo)
- "Schwinger model at finite temperature and density using quantum imaginary time evolution"
[Abstract]
Abstract
We have studied the chiral and confinement-screening phase transitions in the Schwinger model at finite temperature and density using the quantum algorithm.
The theoretical exploration of the phase diagram for strongly interacting systems at finite temperature and density remains incomplete mainly due to the sign problem in the conventional Lattice Monte Carlo method.
However, quantum computation offers a promising solution to circumvent the sign problem as it deals with quantum field theories in the Hamiltonian formalism.
The preparation of thermal states on quantum circuits is a non-trivial challenge.
We have successfully implemented the thermal state preparation on quantum circuits using a theoretical framework known as Thermal Pure Quantum states (TPQs) and the Quantum Imaginary Time Evolution (QITE) algorithm.
The details of the algorithm, our improvements, and the results will be presented in the talk.
- Enrico Rinaldi (Quantinuum KK)
- "Classical sampling algorithms for estimating quantum computing resources for bosonic systems"
[Abstract] [pdf]
Abstract
To simulate bosons on a qubit- or qudit-based quantum computer, one
has to regularize the theory by truncating infinite-dimensional local
Hilbert spaces to finite dimensions.
In the search for practical quantum applications, it is important to
know how big the truncation errors can be. In general, it is not easy
to estimate errors unless we have a good quantum computer.
In this paper we show that traditional sampling methods on classical
devices, specifically Markov Chain Monte Carlo, can address this issue
with a reasonable amount of computational resources available today.
As a demonstration, we apply this idea to the scalar field theory on a
two-dimensional lattice, with a size that goes beyond what is
achievable using exact diagonalization methods.
This method can be used to estimate the resources needed for realistic
quantum simulations of bosonic theories, and also, to check the
validity of the results of the corresponding quantum simulations.
- Abhisek Sahu (University of British Columbia)
- "Bubbles of Cosmology in AdS/CFT"
[Abstract] [pdf]
Abstract
We propose a microscopic description for a specific class of cosmological spacetimes with negative cosmological constant using the AdS/CFT correspondence.
The spacetimes under consideration consist of spherically symmetric bubbles with homogeneous and isotropic cosmologies embedded within a Schwarzschild-AdS spacetime, separated by thin domain walls. We argue that these spacetimes can be effectively described by a single copy of a conformal field theory (CFT) residing on the asymptotic boundary of the black hole.
A key feature of our approach is the time-reversal symmetry of the bubble-of-cosmology spacetime, which allows for a well-defined Euclidean spacetime via analytic continuation about the time-reversal symmetric slice. We analyse our parameter space to obtain regions where this continuation yields non-trivial boundary conditions, and the resulting Euclidean solution serves as the saddle point of a gravitational path integral. The corresponding dual CFT description involves a path integral that characterizes the natural state of the CFT, representing a specific microstate of the bulk black hole geometry that encompasses a patch of cosmological spacetime within its interior.
We provide explicit examples of bubbles filled with dust and/or radiation, featuring simple surface stress-energy on the thin domain wall. Importantly, our construction allows for sufficiently large interiors that encompass the entire causal patch accessible to a single observer in the cosmology. Additionally, we demonstrate that Ryu-Takayanagi surfaces, which encode the entanglement entropy in the CFT, can probe the cosmological region in certain cases.
- Sunil Kumar Sake (Osaka University)
- "Local SYK - A sparse version of SYK"
[Abstract]
Abstract
We study a model of fermions with random couplings similar to conventional SYK with N number of flavours of fermions, at large N. Unlike the conventional SYK model, which has all-to-all couplings, the model we study, which we call local SYK, has a much less number of random couplings, just N in number and with only local interactions. It is shown that there exists a limit in which the local SYK model can be solved using the chord diagram techniques, analogous to the double-scaled limit of conventional SYK. This limit corresponds to taking the size of the fermion coupling terms, q, to scale linearly with N.
- Yusuke Taki (Yukawa Institute for Theoretical Physics, Kyoto University)
- "Complex saddles of three-dimensional de Sitter gravity via holography"
[Abstract]
Abstract
We determine complex saddles of three-dimensional gravity with a positive cosmological constant by applying the recently proposed holography. It is sometimes useful to consider a complexified metric to study quantum gravity as in the case of the no-boundary proposal by Hartle and Hawking. However, there would be too many saddles for complexified gravity, and we should determine which saddles are taken. At the leading order in the Newton constant, the holographic dual is given by Liouville theory with a large imaginary central charge. We examine geometry with a conical defect from a Liouville two-point function and find the allowed saddles. Also we extend the analysis to higher-point functions.
- Mao Tian Tan (Asia Pacific Center for Theoretical Physics)
- "Information Scrambling and Recovery in Inhomogeneous Quenches: An Exploration in Two-dimensional Conformal Field Theories"
[Abstract] [pdf]
Abstract
In recent years, analytically tractable models of quench and Floquet dynamics have been constructed in two-dimensional conformal field theories by considering the time evolution generated by a family of inhomogeneous Hamiltonians which includes the sine-squared-deformed (SSD) Hamiltonian where the energy density profile is given by a sine-squared function.
When the thermal state is quenched by the SSD Hamiltonian, we find that all the quantum information in the system gets concentrated about a particular fixed point. We dub these agglomerations of quantum information "black hole-like" excitations and they carry as much information as the thermal entropy of the total system. Away from this fixed point, the rest of the system "reverse thermalizes" from the uniform thermal state into the ground state.
We also consider the quench of the thermofield double state which is equivalent to studying the operator entanglement of the unitary time evolution operator. This quantity measures the amount of information scrambled by the system's dynamics. It was previously shown that holographic CFTs scramble information maximally. By introducing a sine-squared deformation, this information scrambling can be reduced and information can be recovered. Furthermore, genuine tripartite entanglement which is not shared by any two parties is produced in the process.
- Seiji Terashima (Yukawa Institute for Theoretical Physics, Kyoto University)
- "Rindler bulk reconstruction and subregion duality in AdS/CFT"
[Abstract] [pdf]
Abstract
We study the AdS-Rindler reconstruction. The CFT operators naively given by the holographic dictionary for the AdS-Rindler reconstruction contain tachyonic modes, which are inconsistent with the causality and unitarity of the CFT. Therefore, the subregion duality and the entanglement wedge reconstruction do not hold. We also find that the tachyonic modes in the AdS-Rindler patch lead to arbitrary high-energy or trans-Planckian modes in the global AdS. It means that the mode expansion of the Rindler patch is sensitive to the UV limit of the theory, that is, quantum gravity. In addition, the tachyonic modes are related to the existence of null geodesics connecting the past and future horizons.
- Hiromasa Watanabe (Yukawa Institute for Theoretical Physics, Kyoto University)
- "An extension of Replica-Exchange Monte Carlo methods applying to matrix geometry"
[Abstract] [pdf]
Abstract
The efficient exploration of minimal solutions can be performed by the simulated annealing that exchanges configurations among multiple replicas that introduce virtual temperature. In this talk, we demonstrate that further efficiency gains can be achieved by preparing replica actions more suitably. Through this technique, we expect a clearer determination of the positions of D-branes can be extracted from the field configurations of the corresponding supersymmetric gauge theory. We discuss the physical background and application methodology of this approach.
- Cynthia Yan (Stanford Institute for Theoretical Physics, Stanford University)
- "Chords and the ground state sector of N=2 SYK + A Black Hole Information Paradox for BPS States"
[Abstract] [pdf]
Abstract
The N=2 supersymmetric SYK model has the unusual feature that in the double scaling limit, the number of BPS ground states is a finite fraction of the total number of states. This fraction has a remarkably simple bulk interpretation as the probability that the Hartle-Hawking state has zero length. Using chord techniques, we compute the zero-temperature Hartle-Hawking wavefunction; the resulting answer agrees with index computations, including non-perturbative corrections. Along the way, we improve the construction of the N=2 chord Hilbert space and show that the transfer matrix enjoys an enhanced N=4 supersymmetry. We also obtain expressions for the 2-pt function at zero temperature.
Understanding how to prepare and count BPS black hole micro-states by using the gravitational path integral is one of the most important problems in quantum gravity. Nevertheless, a state-by-state count of the degeneracy of such black holes is difficult because the apparent number of degrees of freedom available in the gravitational effective theory can vastly exceed the entropy of the black hole. In this paper, we show that we can use the gravitational path integral to prepare a basis for the Hilbert space of all BPS black hole microstates. The dimension of this Hilbert space computed by an explicit state count is in complete agreement with the degeneracy obtained from the Gibbons-Hawking prescription. Specifically, this match includes all non-perturbative corrections in 1/G_N; such corrections are, in turn, necessary in order for the degeneracy of BPS states to match the predicted count from string theory.
- Junggi Yoon (Asia Pacific Center for Theoretical Physics)
- "Gravitational edge mode in JT gravity for asymptotically AdS2"
[Abstract]
Abstract
In this talk, I will discuss the gravitational edge mode of the Jackiw-Teitelboim (JT) gravity and the constrained sl(2,R) BF theory for the asymptotically AdS2. I will revisit the derivation of the Schwarzian theory from the wiggling boundary as an action for the gravitational edge mode. In addition, I will present an alternative description for the gravitational edge mode from the metric fluctuation with the fixed boundary, which is also known as the would-be gauge mode in the gravity. After clarifying the relation between the wiggling boundary and the would-be gauge mode, I will demonstrate a natural top-down derivation of PSL(2,R) gauging and the path integral measure of the Schwarzian theory. In the constrained sl(2, R) BF theory, I will present a method for incorporating the gravitational edge mode in the BF theory where I will derive the Schwarzian theory with PSL(2,R) gauging. I will show that the Haar measure for the Iwasawa decomposition of PSL(2,R) leads to the path integral measure.
- Atis Yosprakob (Department of Physics, Niigata University)
- "Grassmann tensor network study of Nf-flavor gauge theory"
[Abstract]
Abstract
In order to treat the 2D gauge theory with Nf fermions in the Grassmann tensor network formalism, the site tensor is separated into multiple layers associated with each flavor, effectively making the tensor network three-dimensional. To also make the gauge field local, it is also separated into several replicas, which are connected via the delta function. We also propose a compression scheme that truncates the size of the initial tensor with high efficiency for larger gauge groups. We demonstrate the effectiveness of the formulation by computing the observables at finite fermion density with up to Nf = 4. The Silver Blaze phenomenon is clearly observed.
- Mengyang Zhang (Princeton University)
- "Solve 3d gravity with Virasoro TQFT"
[Abstract] [pdf]
Abstract
We propose a precise reformulation of 3d quantum gravity with negative cosmological constant in terms of a topological quantum field theory based on the quantization of the Teichmüller space of Riemann surfaces that we refer to as "Virasoro TQFT". We explain how together with standard TQFT surgery techniques this leads to a fully algorithmic procedure for the computation of the gravity partition function on a fixed topology exactly in the central charge. We demonstrate the explicit calculation of gravity partition function for various hyperbolic manifolds, e.g. hyperbolic knots, multi-boundary wormholes, etc.
JSPS KAKENHI No. JP21H05187 "Quantum Cosmology from Quantum Information"