# Abstracts

## Poster Presentations

Please visit this page for poster titles and abstracts.

## Invited Talks

#### Doyeol Ahn (University of Seoul)

**Applicability of Quantum Computation for Solving the Problem of Numerical Fluid Dynamics**

We demonstrate the proof of concept for applying quantum computation to solve the Navier-Stokes equations by implementing a quantum algorithm for the Burgers' equation using a quantum simulator and a variational quantum algorithm on a noisy intermediate-scale quantum (NISQ) computer to solve the Poisson equation. We achieved exponential improvements in resource efficiency by reusing qubits from previous steps, significantly reducing the complexity required to encode non-linear terms. Additionally, we conduct a Poiseuille flow simulation of a bicuspid aortic valve for heart disease patients, which shows strong agreement with clinical results.

In NISQ devices, minimizing the impact of errors and decoherence is critical for practical implementation. While most studies have focused on Markovian noise sources, understanding the relationship between quantum error mitigation (QEM) and non-Markovian noise is essential, as such effects are practically unavoidable in most solid-state quantum computing devices. We also present a non-Markovian noise model for quantum error mitigation, which shows good agreement with experimental results.

#### Chris Akers (University of Colorado, Boulder)

**The reconstruction map in JT gravity**

A key question in holography is how to reconstruct bulk operators in the holographic dual. It is especially interesting to reconstruct operators inside the black hole interior, but also especially difficult to do explicitly. Recently, an explicit form for the bulk-to-boundary `holographic’ map was proposed in JT gravity, by Iliesiu, Levine, Lin, Maxfield, and Mezei, who also proposed and studied an explicit `reconstruction’ map on operators. In this talk, I will discuss various pros and cons of their reconstruction map, and propose an alternative map with arguably nicer properties.

#### Jan de Boer (Universiteit van Amsterdam)

**Cancelled!**

**The dual of semi-classical gravity**

Recent work has produced a consistent picture of the holographic dual description of semi-classical gravity. I will describe this picture, several applications of this picture including the factorization puzzle and the information paradox, and some open questions.

#### David Elkouss Coronas (OIST)

**Pseudo-Entanglement is Necessary for EFI Pairs**

**Pseudo-Entanglement is Necessary for EFI Pairs**

Most of classical cryptography is known to depend on the existence of One-Way Functions (OWFs). However, recent evidence has shown that this is not the case when considering quantum resources. Besides the well known unconditional security of Quantum Key Distribution, it is now known that computational cryptography may be built on weaker primitives than OWFs, e.g., pseudo-random states, one-way state generators, or EFI pairs of states.

We consider a quantum resource, pseudo-entanglement, and show that the existence of EFI pairs, one of the current main candidates for the weakest computational assumption for cryptography (necessary for commitments, oblivious transfer, secure multi-party computation, computational zero-knowledge proofs), implies the existence of pseudo-entanglement. We prove this by constructing a new family of pseudo-entangled quantum states given only EFI pairs.

Our result shows that if pseudo-entanglement does not exist, then most of cryptography cannot exist either. Moreover, it establishes pseudo-entanglement as a new minimal assumption for most of computational cryptography, which may pave the way for the unification of other assumptions into a single primitive.

#### Chisa Hotta (University of Tokyo, Komaba)

**Cluster-projected matrix product state**

Matrix product states (MPS) have long been an ideal variational ansatz for describing the ground states of quantum many-body systems, particularly in one dimension. Due to the limitation of maintaining a finite bond dimension, it was traditionally believed that MPS could only effectively describe states obeying area law entanglement, or those with at most logarithmic corrections. However, it is recently shown that MPS can also capture finite-temperature thermal pure states that follow volume law entanglement [1], as well as various two-dimensional magnetically ordered or spin liquid states, implying that the phase space that the MPS can represent is much broader than the previously thought.

In this work, we propose an algorithm to construct exact solutions for finite size systems using the MPS framework without assuming translational invariance of the MPS. We focus on a class of frustration-free models, where we build the MPS progressively by starting from a single-site MPS and adding site tensors one at a time. The elements of these tensors are determined by successively applying projectors that enforce local constraints, ensuring that specific combinations of local basis states form the desired wave function.

We demonstrate that this approach can describe even gapless or long-range entangled ground states in systems of up to hundred sites, depending on the model, including both one- and two-dimensional cases, and can even capture the long-range entangled spin liquid state in the two-dimensional toric code model. This algorithm allows for the unbiased construction of frustration-free Hamiltonians with explicit exact solutions across various models, and its validity can be numerically verified through energy calculations.

We also show some physical backgrounds of how we derived this scheme and what types of problems they could possibly clarify for a broad range of audiences.

[1] A. Iwaki, A. Shimizu, and C. Hotta, Phys. Rev. Res. 3, L022015 (2021).

[2] H. Saito and C.Hotta, Phys. Rev. Lett, 132 , 166701 (2024)

[3] H. Saito and C. Hotta, arXiv:2406.12357. "

#### Yi-Ping Huang (National Tsing Hua University)

**Interference-caged quantum many-body scars in the 2D U(1) quantum link model**

Quantum many-body scars are excited states characterized by sub-volume law entanglement entropy. Various methods have been developed to construct Hamiltonians that host these scars, often assuming specific algebraic properties of the scar states. In this talk, we explore an alternative approach, starting from the defining feature of sub-volume law entanglement entropy to identify dynamically non-trivial states. Using the 2D U(1) quantum link model, we will demonstrate a novel connection between quantum many-body scars, flat-band physics, and graph theory.

#### Janet Hung (Tsinghua University)

**Building up Space-time with BCFT legos**

Is it possible to read off the quantum gravity dual of a CFT directly from its operator algebra? In this talk, we present a step-by-step recipe synthesizing results and techniques from conformal bootstrap, topological symmetries, tensor networks, a novel symmetry-preserving real-space renormalization algorithm devised originally in lattice models, and the asymptotics of quantum 6j symbols, thereby providing an answer in the affirmative. Quantum 2D Liouville theory serves as a simple and explicit example, illustrating how the quantum gravitational path integral can be built up from local pieces of BCFT correlation functions, which we call the "BCFT Legos." If time allows, we will discuss how the bulk theory derived from TTbar flow of CFTs coincides with the bulk that emerges and how that follows from a general holographic principle that we summarize as symQRG = QG.

#### Etsuko Itou (YITP, Kyoto University)

**Applications of quantum computation and tensor networks to lattice gauge theory**

In recent years, numerical analyses for lattice gauge theories using quantum computation and tensor network have attracted much attention among high-energy physicists as an alternative to lattice Monte Carlo methods. In this talk, I would like to discuss what kind of models and physical observables we aim to calculate and what we are now able to do.

#### Sugumi Kanno (Kyushu University)

**Indirect detection of gravitons through quantum entanglement**

I will discuss our recent idea for indirectly detecting gravitons. We derive a Langevin equation for a system of a macroscopic object surrounded by gravitons and identify the graviton-induced noise in the system. We propose an experiment where the entanglement between two macroscopic mirrors suspended at the ends of an equal-arm interferometer is destroyed by graviton noise through bremsstrahlung. By calculating the noise correlation function, we obtain the decoherence time from the decoherence functional. We estimate that the decoherence time induced by graviton noise in squeezed states stemming from inflation is approximately 20 seconds for 40 km long arms and 40 kg mirrors. Our analysis suggests that observing the decoherence time of quantum entanglement has the potential to indirectly detect gravitons.

#### Joshua Kirklin (Perimeter Institute for Theoretical Physics)

**Gravitational entropy: a tale of five approximations**

The entropy of a gravitational region is its boundary area divided by 4G plus the entropy of interior fields. Since its origin in black hole thermodynamics more than 50 years ago, this formula has guided our exploration of the fascinating links between geometry and quantum information. But it rests on a plethora of interwoven approximations. First, it applies most concretely to perturbative quantum gravity. Second, it has previously relied on the presence of a UV cutoff. By accounting for the role played by observers, recent work has shown this UV cutoff need not be present — but that work only accounts for a tiny subgroup of the full set of diffeomorphism gauge symmetries, and this is the third approximation. Fourth, the fields and the observers have been assumed to be unentangled. And fifth, to recover the area term, one must enter a semiclassical regime in which fluctuations of the observers are suppressed relative to fluctuations of the fields. In this setting, observers are quantum reference frames (QRFs). I will show how the QRF formalism may be employed to completely drop the UV cutoff and unentangled observer approximations. I will also explain how enlarging the subgroup of accounted-for diffeomorphisms allows one to extend the generalised second law (which states that the entropy outside of a horizon increases with time) such that it holds exactly beyond the semiclassical regime. Finally, I will describe the reasons why QRFs should play a fundamental role in going beyond the perturbative regime.

#### Ramis Movassagh (Google)

**Super-critical entanglement in strongly interacting simple models**

TBA

#### Yasha Neiman (OIST)

**Unified Lagrangians for GR and Yang-Mills**

I present a new formulation of gauge theory coupled to gravity with cosmological constant in 4 spacetime dimensions. Its virtue is that it uses the same kind of variables (connection 1-form + curvature 0-form) for both the gravity and gauge sectors. Moreover, the form of the Lagrangian nicely realizes the "GR = YM^2" relation, with Lorentz generators as the color/kinematics dual of the YM gauge generators. The formulation comes in two versions: chiral (more economical), and non-chiral (manifestly real and parity-invariant).

#### Kae Nemoto (OIST)

**Quantum complexity - what complexity does quantum computer create and solve?**

Quantum processors with more than 50 qubits was expected to generate complexity intractable in the conventional computational systems. This has been experimentally shown in some degree. Now, quantum processors are getting larger in size, and it is increasing challenging to characterize such quantum systems. In this talk, we discuss the complexity in quantum systems and what it brings to physics and science.

#### Suvrat Raju (ICTS, Bangalore)

**Massive Particles at Spatial Infinity**

In asymptotically flat space, the principle of holography of information states that, in a theory of quantum gravity, all operators on future (past) null infinity can be represented near its past (future) boundary. However, massive fields do not have a good limit as one approaches null infinity. In this talk, we will discuss a novel asymptotic limit of massive fields at the blowup of spatial infinity that leads to a well-defined algebra of boundary operators. We will show how the extrapolation-procedure must be improved in the presence of interactions and describe the relationship between the algebra at spatial infinity and the standard "in" and "out" algebra. We will briefly discuss a conjecture for how holography of information might be generalized to incorporate massive fields.

#### Renato Renner (ETH Zurich)

**Wigner’s Friend in the Firewall**

One of the most prominent puzzles in quantum theory is Schrödinger’s cat thought experiment, later reconceived as the Wigner’s friend paradox. It was subsequently proposed that the paradox can be resolved by acknowledging that different observers may have different perspectives on the same experiment. A parallel development occurred in quantum gravity, where a paradox arises when considering the fate of information thrown into a black hole. Strikingly, this paradox can be resolved with a similar idea involving the perspectives of different observers, known as black hole complementarity. However, later extensions of these thought experiments — such as multi-agent paradoxes in quantum theory and the firewall paradox in quantum gravity — challenge these solutions. In my talk, I will argue that these extended experiments are closely connected and, more specifically, that lessons learnt from multi-agent paradoxes in quantum theory offer novel insights into the firewall paradox.

#### Allen Scheie (Los Alamos National Laboratory)

**Solid state quantum entanglement witnesses probed with neutron scattering**

This talk is an introduction to spectroscopic entanglement witnesses, whereby quantum spin entanglement can be probed in solid materials (which have uncountably many degrees of freedom) via neutron scattering. I introduce the theory of spectroscopic entanglement witnesses, sketch out the basic derivations, give intuition for what they mean, and show four experimental examples of quantum spin entanglement witnessed in real materials. I end by defining some unsolved problems, the largest of which is defining new witnesses appropriate for quantum entanglement for thermodynamic systems.

#### Antony Speranza (University of Illinois Urbana-Champaign)

**Entropy in gravitational von Neumann algebras**

Entanglement entropy in quantum field theory is UV-divergent, which makes it a challenging quantity to

analyze from an algebraic perspective. In this talk, I will describe how perturbatively coupling to gravity

improves this situation, resulting in a well-defined notion of renormalized entropy in the semiclassical limit. This entropy is constructed using techniques from the theory of von Neumann algebras, and agrees with the generalized entropy of a subregion, consisting of the sum of the quantum field entanglement entropy and the area of the entangling surface. As an application, I will show how to derive the generalized second law for black hole horizons in terms of this renormalized entropy. Time permitting, I will also discuss a construction of a gravitational von Neumann algebra in a slow-roll inflation background, and describe how the background provides an intrinsic notion of a cosmological observer.

#### Tadashi Takayanagi (YITP Kyoto)

**Holographic Entanglement, Pseudo Entropy and Wormholes**

The idea of holographic duality in string theory provides a simple geometric computation of entanglement entropy. This generalizes the celebrated Bekenstein-Hawking formula of black hole entropy and strongly suggests that a gravitational spacetime consists of many qubits with quantum entanglement. Recently, a new extension of entanglement entropy, called pseudo entropy, which depends on both an initial and a final state, was introduced. This quantity turned out to have a clear geometric dual via the holography and also plays a role of a new order parameter of quantum phases. In this talk, after reviewing the above mentioned developments, we would like to point out that pseudo entropy becomes a useful probe in traversable wormhole geometries, where non-hermitian density matrices naturally appear in their CFT duals.

#### Tomonori Ugajin (Rikkyo University)

**Double Holography of Entangled Universes**

We employ double holography to examine a system of two entangled gravitating universes that live on two codimension-one branes in an asymptotically AdS3 spacetime with two disjoint conformal boundaries. There are distinct brane configurations depending on the temperature of the thermofield double (TFD) state between the left and right systems. The topology transition between two branes is naturally identified with the emergence of an Einstein-Rosen bridge connecting the two entangled universes. This doubly holographic construction offers a holographic perspective on gravitational collapse and black hole formation in brane universes. Through this holographic framework, we analyze the quantum information structure of the two gravitating universes. Specifically, we calculate the mutual information between defects present in the boundary theories on the left and right sides. Furthermore, we investigate the decoupling process in the Hayden-Preskill protocol applied to the two copies of the defect field theory and discuss the interpretation of the Yoshida-Kitaev decoding protocol.

#### Aron Wall (University of Cambridge)

**What is the Symmetry Class of Bulk Holography?**

The TTbar deformation is a holographic theory describing holography a finite distance in the bulk. If this theory can be UV completed, it could be a model of nonperturbative bulk quantum gravity. However, it seems to be a non-unitary theory, as the energy eigenvalues lie either on the real axis or the imaginary axis. I will describe the possible symmetry classes of (possibly non-Hermitian) Hamiltonians, and discuss which classes might be compatible with the spectrum of the TTbar deformation.

#### Michael Walter (Ruhr University Bochum)

**Trading Space for Time in Nonlocal Games**

Nonlocal games are a foundational tool in quantum information and complexity. They give an operational perspective on entanglement, which in turn has led to powerful protocols in settings with spatially-separated quantum devices. A recent line of work initiated by Kalai et al (STOC'23) investigates to which extent spatial separation can be replaced by time-like separation, by using cryptography. I will give an introduction to this line of work and its motivations, and present a general result that shows that the performance of players in the (polynomial) time-like setting is always upper bounded by the quantum "commuting operator value," which describes the optimal performance of space-like players in quantum field theory. For XOR games, this achieves a computational version of Tsirelson's theorem. These results show rigorously how spatial separation can emerge through the lens of computational complexity. This may also be of interest in the context of holography. Based on 2408.06711 and 2402.17301.

#### Andreas Winter (ICREA, Barcelona)

**The quest for the laws of (quantum) information theory **

Pippenger originally asked for the determination of all relations between the entropies of subgroups of n random variables, arguing that the collection of these relations comprise the complete "laws of information theory." While Yeung and Zhang initiated great progress on this question since the 1990s in the original classical setting of the Shannon entropy, the analogous problem for the von Neumann entropy has been beset with difficulties. I will review what we know and what has been conjectured about the von Neumann entropy in an n-partite quantum system. Along the way I'll also put into context analogous classification questions for Rényi entropies.

#### Edward Witten (IAS Princeton)

**The Symmetry Generated by The Area Of An Extremal Surface**

It is fairly well known that in some sense, the area of an extremal surface generates, by Poisson brackets, a Lorentz boost. But what precisely does this statement mean, given that in a general spacetime, a Lorentz boost is not a symmetry? I will answer this question at the classical level in somewhat more detail than it has been answered in the literature. Quantum mechanically, as noted previously, the story is somewhat different: the area of an extremal surface is not a well-defined operator and has to be combined with the logarithm of a formal one-sided density operator to make one.

#### Zhen-Sheng Yuan (University of Science and Technology of China)

**Microscopic confinement dynamics of lattice gauge theory with a cold-atom quantum simulator**

Exploring the fundamental structure and basic laws of the universe constitutes an essential drive to physicists. The studies of ultracold atoms have built a bridge between the principles of microscopic world and condensed matter physics. One can prepare and manipulate synthetic quantum material to simulate strongly correlated quantum many-body system with microscopic techniques to solve formidable tasks for the state-of-the-art supercomputers. I will introduce our recent research on one of such synthetic quantum material, the lattice gauge theory (LGT). We implemented a U(1) LGT Hamiltonian with ultracold atoms trapped in optical lattices and studied the relevant properties of gauge invariance, thermalization dynamics and quantum criticality [1-6].

References:

[1] Han-Ning Dai et al. Four-body ring-exchange interactions and anyonic statistics within a minimal toric-code Hamiltonian. Nature Physics 13, 1195 (2017).

[2] Bing Yang et al. Observation of gauge invariance in a 71-site Bose-Hubbard quantum simulator. Nature 587, 392 (2020).

[3] Zhao-Yu Zhou et al. Thermalization dynamics of a gauge theory on a quantum simulator. Science 377, 311 (2022).

[4] Guo-Xian Su et al. Observation of many-body scarring in a Bose-Hubbard quantum simulator. Phys. Rev. Res. 5, 023010 (2023).

[5] Han-Yi Wang et al. Interrelated thermalization and quantum criticality in a lattice gauge simulator, Phys. Rev. Lett. 131, 050401 (2023).

[6] Wei-Yong Zhang et al. Observation of microscopic confinement dynamics by a tunable topological angle, Nature Physics (in press 2024).

## Contributed Talks - 30 minutes

#### Stefan Eccles (OIST)

**Why ETH?**

The eigenstate thermalization hypothesis (ETH) provides the prevailing framework for understanding thermalization in closed quantum systems. An informal expectation is that many “simple” and “local” observables in chaotic systems take the ETH form, and therefore thermalize. However, a complete understanding of which observables and in which systems the ETH form obtains is lacking. I will present a framework for addressing this question in finite systems based on the spectral properties of observables, and a corresponding Hamiltonian decomposition and perturbation problem.

#### Adrian Kent (University of Cambridge)

**Time and Distance Constraints for Mass Interferometry **

I review arguments by Mari et al., Belenchia et al. and Wald et al. on the consistency of mass interferometry with relativistic quantum theory, and offer some critiques and extensions.

#### Barbara Šoda (Perimeter Institute for Theoretical Physics)

**Model for Emergence of Spacetime from Quantum Fluctuations**

We use a result of Hawking and Gilkey to define a Euclidean path integral of gravity and matter which has the special property of being independent of the choice of basis in the space of fields. This property allows the path integral to describe also physical regimes that do not admit position bases. These physical regimes are pre-geometric in the sense that they do not admit a mathematical representation of the physical degrees of freedom in terms of fields that live on a spacetime. In regimes in which a spacetime representation does emerge, the geometric properties of the emergent spacetime, such as its dimension and volume, depend on the balance of fermionic pressure and bosonic and gravitational pull. That balance depends, at any given energy scale, on the number of bosonic and fermionic species that contribute, which in turn depends on their masses. This yields an explicit mechanism by which the effective spacetime dimension can depend on the energy scale.

#### Kotaro Tamaoka (Nihon University)

**Black Hole Singularity and Timelike Entanglement**

We study timelike and conventional entanglement entropy as potential probes of black hole singularities via the AdS/CFT correspondence. Using an analytically tractable example, we find characteristic behavior of holographic timelike entanglement entropy when the geometry involves a curvature singularity. We also observe interesting phenomena that, in some particular setups, holographic timelike and conventional entanglement entropy are determined from multiple complex saddle points, which fall outside the assumptions of the Lewkowycz-Maldacena type argument.

#### Zhenbin Yang (Tsinghua University)

**Comments on the Saad Wormhole**

I will make some comments on how to generalize the Saad Wormhole to higher dimensional black holes.

## Contributed Talks - 15 minutes

#### Cesar Agón (Utrecht University)

**Renyi entropies in the ***n *→ 0 limit, entanglement temperatures and holography

*n*→ 0 limit, entanglement temperatures and holography

In this talk, I will introduce the notion of entanglement temperatures in QFT, a generalization of the Unruh temperatures valid for states reduced onto arbitrary spatial regions. The entanglement temperatures encode the high energy behavior of the state around a point and are determined by the solutions of an Eikonal problem in Euclidean space. I will show that for theories with a UV fixed point, the entanglement temperatures determine the state with a large modular temperature. In particular, I will derive a formula that connects the Renyi entropy in the small Renyi parameter limit and the entanglement temperatures. In two dimensions, the entanglement temperatures are universal and so are the states reduced to an arbitrary number of intervals. I will show that this fact together with holography leads to a simple description of the holographic Renyi entropies in the small Renyi parameter. I will comment on the generalization to arbitrary dimension, as well as, open questions and future directions.

#### Sergio Aguilar Gutierrez (OIST)

**Moving boundaries with the double-scaled SYK model: T^2 deformations, thermodynamics, and Krylov complexity**

Recently, it has been realized that the bulk dual of the double-scaled SYK (DSSYK) model has both positive and negative Ricci curvature and is described by a dilaton-gravity theory with a sin(Phi) potential. We study T^2-deformations in the DSSYK model after performing the ensemble averaging to probe regions of positive and approximately constant curvature. The dual finite cutoff interpretation of the deformation allows us to place the DSSYK model in the stretched horizon of the bulk geometry, realizing a conjecture of Susskind. We show that the energy spectrum is well-defined for a contour reaching these regions. Importantly, the system displays a phase transition from a thermodynamically stable to an unstable configuration by varying its microcanonical temperature; unless the system is located on any of the stretched horizons, always leading to instability. We also evaluate quantum information properties of the deformed model, including Krylov complexity for states and operators, and entanglement entropy for a bipartition of the system, which show an enhanced rate of (hyperfast-)growth as the system approaches the stretched horizon. Lastly, we compare the results with respect to other bulk dual proposals for the DSSYK model under specific constraints.

#### Hugo Camargo (Gwangju Institute of Science and Technology)

**Quantum Chaos and Complexity**

In this talk I will discuss recent developments in the applicability of Krylov operator and state (spread) complexity in the study of quantum chaos in holographic and non-holographic quantum many-body systems. Special emphasis will be given to their sensitivity at different time scales and a comparison will be made with other spectral measures such as the spectral form factor and spectral complexity.

#### Hong Zhe (Vincent) Chen (University of California, Santa Barbara)

**Disentanglement as a strong cosmic censor**

If entanglement builds spacetime, then conversely, disentanglement ought to destroy spacetime. From the quantum null energy condition and quantum focusing conjecture, I derive disentanglement criteria which necessitate infinite energies and strong spacetime singularities. These results are applied to the strong cosmic censorship proposal, where singularities at the Cauchy horizons in black holes are desirable. Using the disentanglement criteria and without resorting to any detailed calculations, I provide an exceedingly general and physically transparent discussion of strong cosmic censorship in semiclassical black holes. I argue that strong cosmic censorship is enforced in asymptotically flat and de Sitter black holes by disentanglement across putative Cauchy horizons and describe how similar disentanglement might be avoided in some anti-de Sitter cases. Time-permitting, I will also present calculations of mutual information in two-dimensional CFTs to explicitly verify some intuition about (dis)entanglement on black hole backgrounds developed in the more general argument.

#### Michele Dall'Arno (Toyohashi University of Technology)

**On the signaling dimension and the no-hypersignaling principle**

The quantum reconstruction program aims at singling out quantum theory, among all physical theories, based on operational constraints on the correlations it can generate. Previous approaches, starting from the well-known no-signaling principle, focused on constraining space-like correlations. Here, we show the existence of theories that are consistent with quantum theory at the level of space-like correlations, but that exhibit anomalies in their time-like correlations. Accordingly, we formulate an operational principle, analog to the no-signaling principle but constraining time-like correlations; we refer to such a principle as the no-hypersignaling principle.

This presentation is based on Phys. Rev. Lett. 119, 020401 (2017), Quantum Views 6, 66 (2022), and Quantum Information & Computation 24, 411 (2024).

#### Julian De Vuyst (OIST)

**Gravitational entropy is observer-dependent**

An essential step in constructing gauge-invariant observables is the splitting of the kinematical degrees of freedom in a physically relevant part and a redundant one. The latter is what will make up our quantum reference frame (QRF). However, there are multiple choices for this splitting into subsystem and QRF; hence, different observers/QRFs will decompose the total gauge-invariant algebra in different ways. A priori, the resulting algebras need not be isomorphic to each other. Consequently, properties defined w.r.t. a subsystem, such as temperature or entropy, typically depend on the observer. One can thus instead see the theory of QRFs as a theory of subsystem relativity. In this short talk we will mainly focus on gravitational algebras and their entropies.

The contents of this talk are complementary to what Josh Kirklin and Fabio Mele will discuss earlier.

#### Jonathan Harper (YITP, Kyoto)

**Multi-invariants and bulk replica symmetry**

We analyze the question of replica symmetry in the bulk for multi-partite entanglement measures in the vacuum state of two dimensional holographic CFTs. We first define a class of multi-partite local unitary invariants, multi-invariants, with a given replica symmetry that acts freely and transitively on the replicas. We look for a subclass of measures such that the dual bulk geometry also preserves replica symmetry. We obtain the most general solution to this problem if we require the bulk to preserve replica symmetry for general configurations of the regions. Orbifolding the bulk solution with the replica symmetry gives us a bulk geometry with a network of conical singularities. Our approach makes it clear that there are infinitely many infinitely large families of multi-invariants such that each family evaluates identically on the holographic state. Geometrically, these are equalities involving volumes of handlebodies, possibly of different genus, at particular points in the moduli space. In certain cases, we check our bulk computation with an explicit calculation in CFT.

#### Yunhyeon Jeong (Tohoku University)

**Analog Universe Expansion using Quantum Hall Edges**

Quantum Hall edges can be regarded as 1+1 dimensional spacetime from their properties of chiral Luttinger liquids. This spacetime is known as one of the conformal fields. We experimentally explore the properties of expanding spacetime of quantum Hall edges and reveal its condition of conformal symmetry. In this presentation, works for determining scale factors on created spacetimes, evaluating if the conformal symmetry survives and future experiments using this system will be shown.

#### Esko Keski-Vakkuri (University of Helsinki)

**Continuous Majorization, Wigner Negativity, and QFT**

In d-dimensional discrete variable quantum computing, states with Wigner negativity (also known as magic states) act as a resource for quantum advantage. The loss of magic can be tracked by various monotones, and computation using "easy gates" gives a majorization order between input and output states. In the continuous variable case (Fock space and QFT), Wigner negativity is similarly a resource, but the rest of the story is more intricate. I discuss a proposal to define continuous majorization in quantum phase space, its role in Gaussian operations, and connection to Wigner negativity. This is based on currently ongoing work with J. de Boer, G. Di Giulio, and E. Tonni.

#### Vinay Malvimat (APCTP, Pohang)

**A new genuine tripartite entanglement measure from reflected entropy**

We introduce a novel measure for genuine tripartite entanglement, with potential applications to many-body systems and holography. While the Markov gap, derived from the lower bound of reflected entropy, has emerged as a new measure, it fails to capture the genuine tripartite entanglement in any GHZ-type states. In contrast, our measure, based on the upper bound of reflected entropy, exhibits maximal values for GHZ states and remains non-vanishing for any state with tripartite entanglement. We illuminate its intriguing behavior in spin chain models, the Sachdev-Ye-Kitaev (SYK) model, and explore its implications in holography.

#### Sean McBride (University of British Columbia)

**Holographic Tensor Networks with Bulk Gauge Symmetries**

Tensor networks are useful toy models for understanding the structure of entanglement in holographic states and reconstruction of bulk operators within the entanglement wedge. They are, however, constrained to only prepare so-called “fixed-area states” with flat entanglement spectra, limiting their utility in understanding general features of holographic entanglement. Here, we overcome this limitation by constructing a variant of random tensor networks that enjoys bulk gauge symmetries. Our model includes a gauge theory on a general graph, whose gauge-invariant states are fed into a random tensor network. We show that the model satisfies the quantum corrected Ryu-Takayanagi formula with a nontrivial area operator living in the center of a gauge-invariant algebra. We also demonstrate nontrivial, n-dependent contributions to the Renyi entropy and Renyi mutual information from this area operator, a feature shared by general holographic states.

#### Fabio Mele (University of Western Ontario)

**Dynamical frames and relational subsystems**

One of the most basic notions in physics is the partitioning of a system into subsystems, and the study of correlations among its parts. Operationally, subsystems are distinguished by physically accessible observables which are often implicitly specified relative to some external frame, such as the laboratory, or a background notion of locality. In absence of external relata (as in Page-Wootters dynamics, gauge theories, and gravity), physical observables must be relationally specified relative to some internal dynamical reference frame. Moving from simple finite-dimensional systems to local subregions in gauge theories, where the dynamical frames are provided by boundary edge modes, in this talk, I discuss how different internal frames identify distinct external-frame-independent/gauge-invariant algebras of subsystem’s observables. As a result, physical properties of subsystems are contingent on the choice of the internal frame. Special attention is reserved to subsystem entropies; in particular, I explain how such a relational definition of subsystems provides an alternative proposal for defining a gauge-invariant notion of entanglement entropy.

#### Yasusada Nambu (Nagoya University)

**Application of partner formula: spatial profile and entanglement**

We present the application of the partner formula and show examples of profiles for local modes defined from quantum fields and their partners. Our main concern in this analysis is to visualize shapes of local modes (detector modes) and partner modes, and obtain qualitative understanding of structure of entanglement of quantum fields. As specific examples of spacetimes, we consider Minkowski spacetime (Rindler mode) and de Sitter spacetime.

#### Pratik Nandy (YITP, Kyoto University; iTHEMS, RIKEN)

**Quantum Dynamics in Krylov Space: Methods and Applications**

The dynamics of quantum systems unfolds within a subspace of the state space or operator space, known as the Krylov space. We present an overview of using Krylov subspace methods to provide a compact and computationally efficient description of quantum evolution. We provide a comprehensive update of recent developments, focused on the quantum evolution of operators in the Heisenberg picture, and explore Krylov complexity and associated metrics as tools for quantifying operator growth, the universal operator growth hypothesis, and its relation to quantum chaos. We also address the possible issues of complexity in quantum field theory and holography.

#### Takuya Okuda (University of Tokyo, Komaba)

**Anomaly inflow for lattice models based on Calderbank-Shor-Steane codes**

Many models with topological or fracton order, such as the toric code and the X-cube model, can be viewed as quantum error-correcting codes of the Calderbank-Shor-Steane (CSS) type. Given a CSS code, a canonical procedure called foliation associates a particularly well-behaved cluster state. In this talk, we explore the phenomenon of anomaly inflow between CSS codes and their corresponding foliated cluster states by showing the equality of the gauge transformations of the bulk and boundary partition functions defined as functionals of defect world volumes. The CSS code and the associated cluster state can be used to construct statistical models with nice duality properties and are realizable via measurement. The cluster state can also be used as a resource state for the measurement-based quantum simulation of a lattice gauge theory, whose deconfined limit is the CSS code. Based on Phys.Rev.Res.6(2024)4,043018 and SciPost Phys.(2024)17,113.

#### Kouichi Okunishi (Niigata University)

**Holographic analysis of boundary correlation functions for the hyperbolic lattice Ising model**

We analyze boundary spin correlation functions of the hyperbolic lattice Ising model from the holographic point of view. Using the corner-transfer-matrix renormalization group, we calculate bulk and boundary spin correlation functions; The boundary correlation function exhibits power-law decay with quasi-periodic oscillations, while the bulk correlation function always decays exponentially. On the basis of the geometric relation between bulk correlation path and distance along the outer edge boundary, we then find scaling dimensions for the boundary correlation function can be explained well by background curvatures inherent to the hyperbolic lattice, where the bulk geodesic line connecting two boundary nodes plays an essential role.

#### Francesco Sartini (OIST)

**Soft Edges: The Link Between Edge and Soft Modes**

I will present a new approach to connecting asymptotic soft modes and finite-distance edge modes. While previous efforts extended edge modes to infinity, we introduce the soft edges: dynamical reference frames that establish this connection without relying on the infinite limit. This enables us to incorporate asymptotic features of the infrared triangle, like the memory effect and Goldstone modes, at finite distance, while clarifying their relationship with edge modes in a gauge-invariant framework.

Our approach also introduces soft boundary conditions that support an infinite-dimensional symmetry algebra, represented by frame reorientations. These reorientations depend on distinguishing intrinsic and extrinsic frames within the region of interest. Crucially, only certain extrinsic frames, which parametrize the full gauge group, qualify as soft edges and enhance symmetries similar to those at infinity. I will demonstrate how this connection is established both formally and explicitly, offering new insights into infrared physics.

#### Nic Shannon (OIST)

**Gravitational wave analogues in spin nematics and cold atoms**

Large-scale phenomena, such as gravitational waves, are notoriously difficult to study in a laboratory setting. None the less, parallels with condensed matter systems can provide a way to access equivalent physics at manageable scale. In this talk, we show how spin nematic phases, realised in spinor condensates, can give access to linearised gravity, and in particular that their Goldstone modes are relativistically-dispersing massless spin-2 Bosons, mathematically-equivalent to gravitational waves.

Starting at the level of the action, we first show that the low-energy effective field theory describing a spin nematic is in one-to-one correspondence with that of linearized gravity. We then identify a microscopic, spin-1 model whose low-energy excitations are relativistically dispersing, massless spin-2 Bosons, providing a direct analogue of gravitational waves in a flat spacetime. Finally, with the aid of simulation, we outline a procedure for observing these analogue gravitational waves in a cold gas of 23Na atoms.

These results suggest that spinor condensates could be used to simulate many of the essential features of linearised gravity.

#### Ayushi Singhania (OIST)

**Emergence of vortex state in the S=1 Kitaev-Heisenberg model with single-ion anisotropy**

The search for Kitaev spin liquid states has recently broadened to include a number of honeycomb materials with integer spin moments. The qualitative difference with their spin-1/2 counterparts is the presence of single-ion anisotropy (SIA). This motivates our investigation of the effects of SIA on the ground state of the spin-1 Kitaev-Heisenberg (KH) model using the density-matrix renormalization group which allows construction of detailed phase diagrams around the Kitaev points. We demonstrate that positive out-of-plane SIA induces an in-plane vortex state without the need for off-diagonal interactions. Conversely, negative SIA facilitates the emergence of a ferromagnetic state in presence of antiferromagnetic Heisenberg interactions, while a Néel state can emerge for ferromagnetic Heisenberg coupling. These findings, pertinent even for weak SIA, not only enhance our theoretical understanding of the spin-1 KH model but also propose experimental prospects for observing these novel magnetic states in material realizations.

#### Hiroyasu Tajima (University of Electro-Communications)

**Gibbs-preserving operations requiring infinite coherence costs**

Gibbs-preserving operations have been studied as one of the standard free processes corresponding to isothermal processes in quantum thermodynamics. Although they admit a simple mathematical structure, their operational significance has been unclear due to the potential hidden cost to implement them using an operatioanlly motivated class of operations, such as thermal operations. Here, we show that this hidden cost can be infinite -- we present a family of Gibbs-preserving operations that cannot be implemented by thermal operations aided by any finite amount of quantum coherence. Our result implies that there are uncountably many Gibbs-preserving operations that require unbounded thermodynamic resources to implement, raising a question about employing Gibbs-preserving operations as available thermodynamics processes. This finding is a consequence of the general lower bounds we provide for the coherence cost of approximately implementing a certain class of Gibbs-preserving operations with a desired accuracy. We find that our lower bound is almost tight, identifying a quantity -- related to the energy change caused by the channel to implement -- as a fundamental quantifier characterizing the coherence cost for the approximate implementation of Gibbs-preserving operations.

#### Daniel Terno (Macquarie University)

**Physical Black Holes: Geometry, Matter, Information**

From the perspective of a distant observer, gravitational collapse may end in one of three ways: proceeding without an actual end, with the event horizon as an asymptotic concept; leading to the formation of a transient or stable ultra-compact object, whose surface remains outside the corresponding gravitational radius; or forming a light-trapping region in finite time, known as physical black holes. Classical black hole solutions, such as Schwarzschild or Kerr, correspond to the first scenario and align with all currently available data. Exotic ultra-compact objects represent the second and are, in principle, distinguishable from the first. However, the occurrence of the third, physical black holes, is necessary to even formulate the information loss problem.

Explicitly stating this requirement and using a weak form of cosmic censorship (curvature scalars are finite at the apparent horizon) provides insights into near-horizon geometry. In spherical symmetry, two dynamic solutions are admissible: evaporating black holes and expanding white holes. We review their properties and implications. The null energy condition is violated near the outer horizon and satisfied near the inner apparent/anti-trapping horizon. These horizons are timelike surfaces with intermediate singular behavior, occasionally showing mild negative energy density firewalls. Similar properties are found in axially symmetric solutions. The generalization of surface gravity, proportional to Hawking temperature in static backgrounds, to dynamic spherically symmetric black holes is discordant and must be zero at the formation and possible evaporation of black holes. These other differences from classical black holes warrant investigation into their potential observational signatures. We conclude by summarizing which of the three models—classical black holes, exotic ultra-compact objects, or physical black holes—describe astrophysical black holes.

#### Michelle Xu (Stanford University)

**Pseudorandom Unitaries from Random Matrix Sums**

Random unitaries are highly useful in quantum algorithms, with diverse applications to benchmarking, tomography, and communication. However, random unitaries are exponentially difficult to produce. The desire to spoof them efficiently in the past few decades has propelled the study of both statistical and computational notions of pseudorandom unitaries — constructions which are both “close” to Haar, and efficient to construct. We present new progress with respect to both notions of pseudorandomness: (i) A natural question is how efficiently one can produce unitary T-designs, the statistical notion of pseudorandom unitaries. The most efficient prior construction of unitary T-designs for n-qudit systems used O(T^5 n^2) quantum gates. In these works, we give new constructions of T-designs via random matrix sums which use merely O(T poly(n)) quantum gates, which yields optimal scaling in T. (ii) The notion of a computational pseudorandom unitary was proposed recently, but not shown to exist. In this work, we also provide the first construction of non-adaptive computational pseudorandom unitaries.

Our constructions derive from random matrix sums, in comparison to commonly studied local random circuits. A central feature of our proof is a new connection between the polynomial method in quantum query complexity and the large-dimension (N) expansion in random matrix theory. In particular, we show that the polynomial method provides exponentially improved bounds on the high moments of certain random matrix ensembles, without requiring intricate Weingarten calculations.