| N |
Speeker |
E-mail |
Institution |
Abstract Title |
Abstract Text |
| 1 |
Alex Blatov |
al-blatov@yandex.ru |
|
- |
- |
| 2 |
Maksim Parfenov |
maksimqwery@gmail.com |
|
Spin-to-integer quantum Hall effect crossover in topological superconductors |
Recently, the study of criticality in quantum systems has attracted significant interest. There is theoretical evidence suggesting the existence of the spin quantum Hall effect (sqHe) in two-dimensional superconducting systems with d_(x^2-y^2 )+i d_xy [1]. In such systems, the quantization of spin conductivity (in even integers of e^2/h) has been demonstrated. Since the sqHe is closely related to the integer quantum Hall effect (iqHe), it is natural to consider whether certain symmetry-breaking mechanisms could induce a crossover between them [2].
In this study [3], we develop a theoretical framework for the crossover from the spin quantum Hall effect to the integer quantum Hall effect.
First, we analyze the edge theory of a d_(x^2-y^2 )+i d_xy topological superconductor, as derived in [1]. We demonstrate that the presence of static disorder at the edge leads to the emergence of a topological theta term in the effective diffusive action. This indicates that the quantization of spin conductance remains robust against impurities, and the corresponding action falls within class C of the Altland-Zirnbauer classification [4]. We further show that applying a Zeeman field only at the edge is insufficient to induce a crossover.
Next, we examine the bulk (2D) action for class C in the presence of Zeeman symmetry breaking. We show that bulk topological excitations (instantons) change across the crossover. Specifically, we find that instantons with topological charge W=1 are suppressed by the Zeeman field, while instantons with W=2 transform into two Pruisken instantons [5] with W=1. As a result, the quantization of spin conductivity transitions from even integers to all integers.
We propose that this spin-to-integer quantum Hall effect crossover could potentially be realized in topological superconductors, such as twisted Bi_2 Sr_2 CaCu_2 O_(8+x).
*This work was supported by the Project No. FFWR-2024-0017.
[1] T. Senthil, J. B. Marston, and M. P. A. Fisher, Spin quantum Hall effect in unconventional superconductors, Phys. Rev. B 60, 4245 (1999).
[2] S. Bhardwaj, I. A. Gruzberg, and V. Kagalovsky, Relevant perturbations at the spin quantum Hall transition, Phys. Rev. B 91, 035435 (2015).
[3] M. V. Parfenov, I. S. Burmistrov to be published.
[4] A. P. Schnyder, S. Ryu, A. Furusaki, and A. W. W. Ludwig, Classification of topological insulators and superconductors, AIP Conf. Proc. 1134, 10 (2009).
[5] A. M. M. Pruisken, Quasiparticles in the theory of the integral quantum Hall effect (I), Nucl. Phys. B 285, 719 (1987).
|
| 3 |
Boris Eremin |
Boris.Eremin@skoltech.ru |
|
Conformal bootstrap and A-D-E construction in Gepner Models |
We construct N=2 Superconformal Field Theories with modular invariant partition functions and with central charge c=9. Such theories arising after the compactification in superstring theory. Left and right primary fields in these theories are connected according to A-D-E classification. Orbifolds of the product of Minimal Models connected to Calabi-Yau manifolds of Fermat types are considered. We construct the set of mutually local fields, twisted by the elements of the group of symmetry. |
| 4 |
Asya Aynbund |
aynbund.asya@phystech.edu |
|
Scalar Field Action under 4D Isotropic Cut-off and its Cosmological Impact |
Specific action for isotropic fluctuations of scalar field is derived under the condition of 4D cut-off. It is implemented into the estimates of dark energy scale consistent with current cosmological data. |
| 5 |
Dmitriy Shapiro |
shapiro.dima@gmail.com |
Forschungszentrum Jülich, Germany |
Quantum Simulation of the Dicke-Ising Model via Digital-Analog Algorithms |
The Dicke-Ising model, one of the few paradigmatic models of matter-light interaction, exhibits a superradiant quantum phase transition above a critical coupling strength. However, in natural optical systems, its experimental validation is hindered by a \"no-go theorem\". Here, we propose a digital-analog quantum simulator for this model based on an ensemble of interacting qubits coupled to a single-mode photonic resonator. We analyze the system\\'s free energy landscape using field-theoretical methods and develop a digital-analog quantum algorithm, which disentangles qubit and photon degrees of freedom through a parity-measurement protocol. This disentangling enables the emulation of a photonic Schrödinger cat state -- a hallmark of the superradiant ground state in finite-size systems. The cat state can be unambiguously probed through the Wigner tomography of the resonator\\'s field. Our algorithm features a sequence of analog Jaynes-Cummings gates combined with standard digital single-qubit and two-qubit rotations. This quantum circuit is capable of simulating quench dynamics and the quantum phase transition between the normal and superradiant phases. Additionally, we (i) applied a path-integral description to the model via the bosonic angular representation of spin operators and (ii) formulated a quasi-classical description of fluctuations in the large-spin limit. This approach can be useful for further studies of macroscopic quantum tunneling. Finally, we found that the qubit-qubit interaction leads to an emergent Ising transition driven by the Kibble-Zurek mechanism in imaginary time. The qubit subsystem becomes critical for certain quantum trajectories of the photon field, making the fluctuations in the superradiant phase non-trivial, in contrast to the conventional Dicke model. For further details, see our preprint [1].
[1] D. S. Shapiro, Y. Weber, T. Bode, F. K. Wilhelm, D. Bagrets, \"Quantum Simulation of the Dicke-Ising Model via Digital-Analog Algorithms\", arXiv:2412.14285 (2024). |
| 6 |
Soumya Bera |
soumya.bera@iitb.ac.in |
Indian Institute of Technology Bombay, India |
Pre-localization from fock space fragmentation into resonances |
Many-body localization arises from the interplay of interactions and disorder in closed quantum
systems, forming an emergent integrable phase, which could have potential applications in modern
quantum technologies. In recent years, significant progress has been made in understanding the
fragility of the phase, mainly when studied through ensemble-averaged properties within a reasonable
parameter regime. A key insight from these studies is the presence of strong sample-to-sample
fluctuations in local observables, such as particle density. Here, we take a Fock-space perspective
on thermalization dynamics, developing a geometric description of Fock-space connectivity that
dominates transient dynamics. Even in the weak disorder regime, certain strongly localized samples
can be understood as fragmented Fock-space clusters onto dynamically resonant structures. This
highlights the complexity of disorder ensembles, questioning the notion of many-body localized phase
in generic model. |
| 7 |
Artem Alexandrov |
alexandrov.aa.mipt@gmail.com |
|
Classical phase-locking phenomena and its quantum interpretation |
We discuss how the classical phase-locking phemomena arises in quantum mechanical systems. We provide the correspondence between the Poincare rotation number for the 2D dynamical systems on torus of Mobius type and the Schrodinger equation with periodic potential. This correspondence allows us to treat slow-fast dynamics in systems on torus in terms of exact WKB and vice-versa |
| 8 |
Grigory Budkin |
budkin@mail.ioffe.ru |
|
Ballistic and shift contributions to the photogalvanic effect under Coulomb interactions |
We report on the theoretical study of photocurrents arising in direct optical transitions in semiconductor bulk materials and structures taking into account the Coulomb interaction. In macroscopically homogeneous crystals or laterally uniform two-dimensional systems lacking inversion symmetry, an alternating electromagnetic field can induce a steady photocurrent, a phenomenon known as the photogalvanic effect. We develop a theory of the linear interband photogalvanic effect that precisely accounts for the electron-hole Coulomb interaction.
For the interband optical transitions, there are two contributions to the linear photocurrent: the shift contribution, caused by the displacement of electron wave packets in the real space during quantum transitions, and the ballistic contribution, originating from asymmetry of the photoelectron distribution in the momentum space. While recent studies of the linear photogalvanic effect have been predominantly focused on the shift contribution [1, 2], it is emphasized in Ref. [3] that the ballistic contribution dominates for interband transitions. We present calculations comparing both contributions within a unified band-structure model for systems of different dimensions.
A detailed microscopic theory of shift and ballistic currents is developed, incorporating a self-consistent method to treat Coulomb correlations between the photoexcited electron and hole to all orders of perturbation [4]. The theory is applied to calculate the linear photogalvanic effect in bulk semiconductors with a zinc blende lattice, as well as in two-dimensional materials based on monolayers of transition metal dichalcogenides of the D3h symmetry. It is demonstrated that the Coulomb interaction enhances the shift photocurrent due to an increase in optical absorption due to excitonic effects, although the shift current does exist even neglecting electron-hole scattering. In contrast, the ballistic contribution to the linear photogalvanic effect for direct optical transitions requires an additional scattering to take place, here the Coulomb scattering of a photoexcited electron by a hole. The matrix elements of the velocity operator taken between the Coulomb two-particle functions of the continuous spectrum, including its components off-diagonal in the wave vectors, are calculated in order to obtain the ballistic contribution.
Frequency dependencies of the both contributions to the photocurrent are calculated for bulk semiconductors as well as for two-dimensional monolayer structures. It is demonstrated that the ballistic photocurrent can significantly exceed the shift current in both material classes. It is shown that the ratio of the ballistic contribution to the shift contribution scales as l/aB, where l is the charge carriers mean free path and aB is the exciton Bohr radius. As a result, in a wide range of frequencies where the mean free path of photoexcited charge carriers is longer than the Bohr radius, the ballistic contribution dominates. Thus, accounting for Coulomb interaction to the ballistic mechanism yields a substantially larger total photocurrent than shift-only models predict.
This work was supported by the Russian Science Foundation (project 22-12-00211).
1. Z. Dai and A. M. Rappe // Phys. Rev. B 104, 235203 (2021).
2. Zhenbang Dai and A. M. Rappe // Chem. Phys. Rev. 4, 011303 (2023).
3. B. I. Sturman // Phys.-Usp. 63, 407 (2020).
4. G. V. Budkin, E. L. Ivchenko // JETP 167, 279 (2025). [arXiv:2409.05571] |
| 9 |
Maxim Shishkin |
max.shishckin2011@gmail.com |
|
Dynamics of vesicles under stretching |
Closed lipid membranes (vesicles), being flexible and incompressible, demonstrate a plethora of non-spherical shapes (especially under simple external influences). Within the framework of the hydrodynamic approach, the bilayer is treated as an infinitely thin liquid film with a surface density of free energy. The starting point for this consideration is Helfrich\\\\\\'s energy [W. Helfrich, Z Naturforsch (1973)] , which depends on vesicle shape. Using hydrodynamic Poisson brackets, we can obtain a non-dissipative contribution to the stress tensor from the membrane. Corresponding surface forces cause flows in the viscous surrounding liquid which make the membrane to move. Although such flows occur at low Reynolds numbers, described by the linear hydrodynamic equation (the Stokes equation), vesicle\\\\\\'s shape changes significantly over time.. This makes the system of dynamic equations highly nonlinear. On the one hand, it determines the complexity of the problem, and on the other hand, leads to the need for numerical modelling of the process.
The study investigates the behavior of elongated vesicles under the influence of extending forces, such as uniaxial flow and optical tweezers. There are two critical values of force amplitude: beyond the first, a \\\"dumbbell\\\"-shaped structure forms with a possible infinite elongation, and the second is responsible for the so-called pearling instability, i.e., the formation of beads connected by thin tubes. We also provide a qualitative description of the phenomenon by discussing the variety of stretched shapes and conditions of quasi-stationarity and transition to infinite stretching. In addition, we study the highly nonlinear stage: a slow dynamics remains after the formation of pearls due to the thinness of tubes. Our results qualitatively agree with experimental observations [Kantsler, Segre, and Steinberg (2008)]. |
| 10 |
Gleb Seleznev |
seleznev.gs@phystech.edu |
|
Enhancement of Superconductivity in Dirty Films in an External Magnetic Field |
Thin dirty superconducting films containing magnetic impurities exhibit nontrivial behavior when subjected to an applied magnetic field. This behavior manifests itself in the enhancement of superconductivity, which is attributed to the reduction in the exchange scattering rate due to the polarization of the impurity spins in the presence of the magnetic field. This effect was theoretically predicted in Ref. [1] and then observed experimentally in Ref. [2]. In both studies, the authors concentrated on the dependence of the critical temperature on the magnetic field parallel to the film surface, revealing a nonmonotonic behavior characterized by a maximum at finite field values. However, manifestations of this enhancement for other observable physical quantities, as well as the description of the effect in the presence of a magnetic field component perpendicular to the film surface, have not been investigated. To address this gap, we develop a theoretical framework employing Gorkov\\\\\\'s diagrammatic technique for superconductors. Our work expands the theory of Ref. [1] in two directions: (i) we demonstrate that the enhancement is also reflected in an increase in superfluid density and the spectral energy gap; (ii) we reveal a nonmonotonic dependence of the second critical field (perpendicular to the film surface) on the magnetic field component parallel to the surface.
[1] M.Yu. Kharitonov and M.V. Feigelman, \\\"Enhancement of superconductivity in disordered films by parallel magnetic field\\\", JETP Lett. 82, 421–425 (2005).
[2] Masato Niwata, Ryuichi Masutomi and Tohru Okamoto, \\\"Magnetic-Field-Induced Superconductivity in Ultrathin Pb Films with Magnetic Impurities\\\", Phys. Rev. Lett. 119, 257001 (2017). |
| 11 |
Artem Posadskii |
posadskij.af@phystech.su |
|
Effective action of the Γ-subsystem of the Ising superconductor |
The work is devoted to superconductivity in recently discovered Ising superconductors. This state in them has not yet been fully studied. In particular, the question arises as to which of the valleys in the Brillouin zone play the main role.
The central valley Γ is, under certain assumptions, an independent electron subsystem. In the work, we have obtained and analyzed the gauge-invariant effective action of this subsystem. It includes singlet and triplet pairings, and it is necessary to take into account the locality of these interactions, as well as the symmetry of the lattice. In particular, we obtain an expression for the superconducting weight in the subsystem. |
| 12 |
Artem Polkin |
arpolkin@gmail.com |
|
Conductivity of a superconductor in presence of microwaves |
Nonequilibrium properties of superconducting systems have been studied for a long time. One of such properties is enhancement of superconductivity by microwave irradiation, which was explained theoretically by Eliashberg [1,2] by means of Gorkov equations. In 2018 this theory was extended and refined in [3]. However, recently novel mechanism of microwave absorption was suggested [4]. In their paper authors introduce mechanism of absorption, similar to the Debye absorption in molecular gases, which for non-zero current leads to a large contribution to the ac conductivity, which is proportional to the inelastic scattering time $\\\\tau_{in}$. In present work, we consider quasi-one dimensional diffusive superconductor with finite current bias. Within Keldysh non-linear sigma model approach, we computed conductivity, which for small amplitude of microwave irradiation could be treated within linear response formalism. We found that in presence of dc current conductivity acquires a novel contribution, which is responsible for the so called Debye contribution to the conductivity. We calculated this term for a wide range of frequencies of a microwave and established that results are drastically different for small and large values of $\\\\omega$.
[1] G. M. Eliashberg. Film superconductivity stimulated by a high-frequency field. Sov. Phys. JETP Lett., 11:186, 1970.
[2] B. I. Ivlev and G. M. Eliashberg. Influence of nonequilibrium excitations on the properties of superconducting films in a high-frequency field. Sov. Phys. JETP Lett., 13:464, 1971.
[3] K. S. Tikhonov, M. A. Skvortsov, and T. M. Klapwijk. Superconductivity in the presence of microwaves: Full phase diagram. Phys. Rev. B, 97:184516, May 2018.
[4] M. Smith, A. V. Andreev, and B. Z. Spivak. Debye mechanism of giant microwave absorption in superconductors. Phys. Rev. B, 101:134508, Apr 2020. |
| 13 |
Yuriy Dmitrievtsev |
dmitrievtsev.iua@phystech.edu |
|
Superconducting orbital diode effect in SN bilayers |
In superconducting hybrid structures with broken geometric symmetry and symmetry with respect to time reversal, a diode effect occurs, which consists in different critical currents when an
supercurrent flows in different directions. The system we are considering is an SN bilayer – two layers of superconductor (S) and normal metal (N) brought into contact. The bilayer is located
in an external parallel magnetic field. The properties of the supercurrent flowing along the bilayer perpendicular to the magnetic field are studied. In 2023, an article [1] was published on the study
of the diode effect in such a structure. In it, this effect in the MoN/Cu bilayer was studied numerically and experimentally. Numerical calculation and experiment were carried out for a bilayer
with a thickness of each layer on the order of several coherence lengths, but thin compared to the London penetration depth, in the dirty limit allowing the application of the Usadel equations. The
fact that the thickness of the layers is of the order of the correlation length leads to a nontrivial
distribution of the order parameter, and hence the concentration of superconducting electrons along
the thickness of the sample. This makes the problem analytically unsolvable in the general case.
Our goal is to consider a similar system in extreme cases that allow an analytical solution, in which,
nevertheless, many qualitative patterns for critical currents are preserved, as well as to consider the
effect of interface resistance on the diode effect.
In particular, the dependences of critical currents on the magnetic field are found. A nonmonotonic dependence of the efficiency of the diode effect on the resistance of the interface with the maximum at a certain optimal resistance has also been established.
1. Finite momentum superconductivity in superconducting hybrids: Orbital mechanism / M. Yu. Levichev, I. Yu. Pashenkin, N. S. Gusev, D. Yu. Vodolazov // Phys. Rev. B. — 2023. — Sep. — Vol. 108. — P. 094517. https://link.aps.org/doi/10.1103/ PhysRevB.108.094517. |
| 14 |
Alexey Mikhaylenko |
mikhajlenko.ag@phystech.edu |
|
Non-Gaussian Initial Correlations in Non-Equilibrium Quantum Field Theory |
This work is devoted to the role of initial correlations in the nonequilibrium evolution of observables in quantum field theory. We show that information about the initial state of the system can be represented as an additional term in the Keldysh action. This term is expressed in terms of the generating functional of the cumulants of the initial Wigner functional. The presence of non-Gaussian correlations manifests itself in the form of additional vertices, each of which is proportional to the corresponding cumulant. Since, generally speaking, there can be infinitely many nonzero non-Gaussian cumulants, it becomes necessary to somehow limit ourselves to a finite number of them. We show that this can be achieved using the formalism of a two-particle irreducible (2PI) effective action. Namely, we demonstrate that only a finite number of cumulants contribute to the equations of motion in the approximation with a finite number of loops in the diagrammatic representation of an effective action. This makes it possible to systematically take into account the cumulants of higher degrees, gradually increasing the number of loops in approximation to effective action. In addition, we show how non-Gaussian initial correlations can generate a non-zero average field in the process of quantum evolution even if it’s value was zero at the initial moment of time. |
| 15 |
Grachik Simonyan |
simonyan.grachik@gmail.com |
|
Calculation of correlation functions for nonequilibrium quantum systems with non-Gaussian initial conditions |
A non-perturbative technique within the Schwinger-Keldysh formalism is applied for nonequilibrium quantum systems with non-Gaussian initial conditions. The system has a free part in the form of an oscillator and a quartic interaction term. The correlation function is computed under specific non-Gaussian initial conditions using the Kadanoff-Baym equations in a two-loop approximation. The same results are also derived using perturbation theory, and a comparison is made between the two approaches. Additionally, we present integral-differential equations in phase space for multiple degrees of freedom, applicable to quantum field systems, and calculate the corresponding correlation function. |
| 16 |
Sergey Potashin |
sergeypotashin@gmail.com |
|
Thermoelectric and viscous contributions to the hydrodynamic ratchet effect |
We study the hydrodynamic regime of the ratchet effect, i.e., radiation-induced generation of a direct electric current, $J_{\\\\rm rat}$, in an asymmetric dual-grating gate structure without an inversion center. Recently, it was demonstrated that the frequency dependence of $J_{\\\\rm rat}$ is essentially different within the hydrodynamic (HD) and drift-diffusion (DD) regimes of electron transport: $J_{\\\\rm rat}^{\\\\rm HD} \\\\propto 1/\\\\omega^6$ and $J_{\\\\rm rat}^{\\\\rm DD} \\\\propto 1/\\\\omega^2$ for $\\\\omega \\\\to \\\\infty$. Here, we analyze the previously neglected thermoelectric contribution to the ratchet current, $J_{\\\\rm th}$, which arises due to inhomogeneous heating of the electron liquid. We demonstrate that this contribution dominates at sufficiently low electron-phonon scattering rates, yields a high-frequency asymptotic $J_{\\\\rm th} \\\\propto 1/\\\\omega^2$ even in the HD regime, and can change the sign of the response at certain frequency intervals. We analyze the plasmonic resonance in $J_{\\\\rm rat}$, which has the shape of an asymmetric Fano peak, and find that the asymmetry increases with increasing thermoelectric contribution. We also study the effect of finite viscosity of the electron liquid, as well as the manifestation of the plasmonic drag phenomena and inhomogeneous rectification effects in the ratchet current. We demonstrate that viscosity suppresses plasmonic resonance but unexpectedly enhances the Drude peak due to the interference nature of the ratchet effect.
This work was supported by the Russian Science Foundation (project 25-12-00212) |
| 17 |
ELIZAVETA SAFONOVA |
safonova.ea1@gmail.com |
Ljubljana University |
Density correlation function L\'evy Rosenzweig-Porter model via supersymmetric approach |
We present an analytical calculation of the density of states correlation
function in the L´evy-Rosenzweig-Porter random matrix ensemble which off-diagonal elements are strongly non-Gaussian with power-law tails. In order to obtain the results on all the energy scales we use supersymmetry approach. Power-law distribution tails makes the standard Hubbard-Stratonovich transformation inapplicable to such problems. We used, instead, the functional Hubbard-Stratonovich transformation which allowed to solve the problem analytically for large sizes of matrices. |
| 18 |
Valentin Mylnikov |
m-u-u27@yandex.ru |
|
Critical slowing down in two-photon dissipative oscillator |
In this study, we investigate the critical slowing down of dissipative phase transition, which is observed in a parametric oscillator with two-photon drive and both linear and nonlinear dissipation. Using the numerical calculations, complex P-representation and the perturbative, we determine the exponentially small eigenvalue of the Liouville operator that determines small relaxation of the system towards the steady state.
Acknowledgment
This research was supported by RSF (project No. 21-72-30020).
|
| 19 |
Mikhail Pavlov |
michaelmorgn@gmail.com |
|
Classical Virasoro blocks with heavy and light operators |
In this note we study differential equations for classical blocks with heavy and light operators from different perspectives. We present ODEs for the 4-pt blocks, generalizing the ODE for the 4-pt identity block, found by Fitzpatrick, Kaplan, Walters, and Wang. |
| 20 |
Aleksei Radkevich |
radkevichaa@lebedev.ru |
|
Gutzwiller trace formula for potentials with tunneling |
Tunneling is a quantum phenomenon, the essence of which is that the wave function of a system in the course of its dynamics penetrates into the energetically inaccessible region of configuration space. This phenomenon is essentially semiclassical and can be described within the framework of the semiclassical approximation in quantum mechanics by solving the Schrödinger equation by the WKB method. At the same time, there is a wide class of systems for which the description of tunneling within the framework of the Feynman path integral is of interest, in particular, dissipative systems, where the description of the system using the wave function is completely impossible. In such systems, tunneling can be described using the path integral in imaginary time, where the so-called instanton solutions are responsible for tunneling; however, being tied to imaginary time, this formalism is suitable only for studying the characteristics of a system in a state of thermodynamic equilibrium and is not applicable to significantly nonequilibrium phenomena. Hence, it is necessary to develop an approach that takes into account instanton solutions in the framework of the path integral in real time. In this work, a step in this direction is made, consisting in generalizing the Gutzwiller trace formula (which is usually derived in the real-time formalism) for the density of states of a quantum-mechanical particle in a potential with tunneling. |
| 21 |
Konstantin Turyshev |
turyshev.konstantin@gmail.com |
HSE University |
Current-phase relation of an S-TI-S Josephson junction with a Majorana edge mode |
We consider a long and narrow S-TI-S Josephson junction on top of a 3D
topological insulator in magnetic field [1,2], surrounded by a layer of insulating
magnetic material. Majorana zero modes are predicted to be localized at Josephson
vortices in the junction, while the outer edge of the junction supports a 1D
Majorana edge mode. Parity of the number of vortices inside of the junction
determines the boundary conditions for the edge mode, and in the case of the
odd number of vortices, the edge contains a Majorana zero mode. As the global
phase difference between the superconductors is varied, the vortices move along
the junction. When a vortex approaches the edge of the junction, corresponding
Majorana zero mode may hybridize with the Majorana zero mode on the outer
edge, acquiring non-zero energy and contributing to the current through the
junction. Considering the edge mode scattering problem, we find analytical
expression for the energy of Majorana zero modes hybridization. We also discuss
the current contribution of the hybridization of higher-energy modes, based on
numerical solutions.
References
[1] Potter A. C., Fu L., Phys. Rev. B 88, 121109 (2013)
[2] Yue G. et al.., Phys. Rev. B 109, 094511 (2024) |
| 22 |
Viacheslav Krivorol |
v.a.krivorol@gmail.com |
|
First-order GLSM construction in sigma models |
Sigma models form a class of field theories that play a crucial role in various branches of modern theoretical and mathematical physics. However, studying these models is challenging due to the highly nonlinear nature of their Lagrangians. There are some specific methods, such as the background field method, that can be used to study these models, but they have some limitations.
There is an alternative recently proposed method, called \\\"the first-order GLSM formulation\\\" (or \\\"Gross-Neveu formalism\\\"), for studying sigma models. In this method one cast these models as gauge theories with a finite number of interactions using the idea of symplectic reduction. I will present how this method works for target spaces that are homogeneous Hermitian complex spaces associated with classical Lie groups.
Based on joint works with Dmitri Bykov: https://arxiv.org/abs/2306.04555, https://arxiv.org/abs/2407.20423, see also https://arxiv.org/abs/2502.07612 |
| 23 |
Ilya Gorbenko |
spbdriliya@gmail.com |
|
Current-induced instability in 2D electron liquid |
Several possible mechanisms of current-induced instability have been discovered in 2D electron liquid: amplification of plasma waves due to asymmetric boundary conditions of Dyakonov and Shur [1], change of sign of the radiative decay rate resulting in negative absorption coefficient [2], Cherenkov-type instability arising when drift velocity of current exceeds plasma wave velocity [3] and interplay of different dispersion laws of gated and ungated plasmons [4].
We investigate current-induced plasma wave instability in 2D electron liquid with periodically modulated concentration which creates lateral plasmonic crystal (LPC), recently discussed in [5]. We found that solutions with largest instability increment are excited in particular interval of currents, which is fully determined with electron concentration profile. In this regime, three types of unstable solutions were discovered: the Cherenkov-type instability ω=ω_I+i λ_I with a small increment (ω_I≫λ_I), a new type of unstable solutions with a large increment ω=ω_II+i λ_II (λ_II>ω_II), and a purely imaginary solution ω=i λ_III. Increase of current outside the interval preserves only the first Cherenkov-type instability.
This work was supported by the Russian Science Foundation (project 25-12-00212).
[1] Dyakonov, Shur // PRL 71, 2465 (1993).
[2] Mikhailov // PRB 58, 1517 (1998).
[3] Kachorovskii, Shur // APL 100, 232108 (2012).
[4] Petrov, Svintsov, Ryzhii, Shur // PRB 95, 045405 (2017).
[5] Gorbenko, Kachorovskii // PRB 110, 155406 (2024). |
| 24 |
Anton Selemenchuk |
selemenchyk@icloud.com |
|
Fluctuations of Young diagrams for symplectic groups and semiclassical orthogonal polynomials |
Consider an $n\\\\\\\\times k$ matrix of i.i.d. Bernoulli random numbers with some value of $p$. Dual RSK algorithm gives a bijection of this matrix to a pair of Young tableaux of conjugate shape, which is manifestation of skew Howe $\\\\\\\\GL_{n}\\\\\\\\times \\\\\\\\GL_{k}$-duality. Thus the probability measure on zero-ones matrix leads to the probability measure on Young diagrams propor-tional to the ratio of the dimension of $\\\\\\\\GL_{n}\\\\\\\\times \\\\\\\\GL_{k}$-representation and the dimension of the exterior algebra $\\\\\\\\bigwedge\\\\\\\\left(\\\\\\\\CC^{n}\\\\\\\\otimes\\\\\\\\CC^{k}\\\\\\\\right)$.
Similarly, by applying Proctor\\\\\\\\\\\\\\'s algorithm based on Berele\\\\\\\\\\\\\\'s modification of the Schensted insertion, we get skew Howe duality for the pairs of groups $\\\\\\\\Sp_{2n}\\\\\\\\times \\\\\\\\Sp_{2k}$. In the limit when $n,k\\\\\\\\to\\\\\\\\infty$ $\\\\\\\\GL$-case is relatively easily studied by use of free-fermionic representation for the correlation kernel. But for the symplectic groups there is no convenient free-fermionic representation. We use Christoffel transformation to obtain the semiclassical orthogonal polynomials for $\\\\\\\\Sp_{2n}\\\\\\\\times \\\\\\\\Sp_{2k}$ from Krawtchouk polynomials that describe $\\\\\\\\GL_{2n}\\\\\\\\times\\\\\\\\GL_{2k}$ case. We derive an integral representation for semiclassical polynomials. The study of the asymptotic of this integral representation gives us the description of the limit shapes and fluctuations of the random Young diagrams for symplectic groups.
The studied problem is closely connected with describing the moduli space of isomonodromic deformations of rational d-connections as a Sakai surface for discrete Painlevé equations. |
| 25 |
Daniil Lopatin |
lopatin.daniil2014@mail.ru |
|
Local quantum quench in interacting field theories |
Nonequilibrium quantum field theory is an important area of modern physics, where many arising problems require consideration of the unitary evolution of observables from some initial
state of the system, which is not, generally speaking, an proper state for the corresponding Hamiltonian. In this case, the system, being in a nonequilibrium initial state, evolves over time to some equilibrium. One way to specify an initial nonequilibrium state is to instantly change the parameters of the system at the initial moment of time. In such case of creating nonequilibrium, we speak of a quantum quench. In this paper, we study the evolution of a quantum scalar field (and others) as a result of a local quantum quench, i.e. as a result of a rapid perturbation in the vicinity of a certain point. The problem is studied in the formalism of the Keldysh technique, which is convenient for considering nonequilibrium quantum systems. We study the semiclassical approximation, which is exact for
non-interacting systems. To calculate the values of observables in the
semiclassical approximation, a numerical code is used that calculates a
functional integral using the Monte Carlo method. In the general case, to find a
semiclassical solution, it is necessary:
Find classical trajectories as functions of the initial conditions
Calculate the desired observables on the obtained trajectories
Average the obtained expressions over the initial conditions with a weight specified by the
Wigner functional corresponding to the problem being solved
By considering various types of quantum local quenches for various initial states,
we study the properties of the corresponding system when a disturbance propagates in it. |
| 26 |
Mikhail Sharov |
sharov.mr22@physics.msu.ru |
|
Horndeski theory on a dynamical spherically-symmetric background |
We study the stability of classical solutions in Horndeski theory. In this work, we address a general dynamical spherically symmetric background. We derive the set of stability conditions in the cubic subclass of Horndeski theory and formulate the no-go theorem for this subclass.
For full Horneski theory and beyond Horndeski theory we formulate a set of linear stability conditions for high energy odd parity perturbation modes above an arbitrary solution. In this general setting we derive speeds of propagation in both radial and angular directions for gravity waves and compare them with the speed of light in the case of minimally coupled photon. In particular, we find that the class of beyond Horndeski theories, which satisfy the equality of gravity waves’ speed to the speed of light over a cosmological background, feature gravity waves propagating at luminal speeds above a time-dependent inhomogeneous background as well.
We revisit the models recently derived from a Kaluza-Klein compactification of higher dimensional Horndeski theory, where the resulting electromagnetic sector features non-trivial couplings to Horndeski scalar. In particular, this class of theories admits the electromagnetic waves propagating at non-unit speed, which in turn allows to relax the constraints on Horndeski theories following from multi-messenger speed test. In this work we prove that both gravitational wave and its electromagnetic counterpart propagate at the same, although non-unit, speed above an arbitrarily time-dependent, spherically symmetric background within the theories in question. Hence, we support the statement that several subclasses of Horndeski theories are not necessarily ruled out after the GW170817 event provided the photon-Galileon couplings are allowed. We also formulate the set stability conditions based on odd parity perturbations for an arbitraty solution within the discussed theoretical setting.
|
| 27 |
Maxim Chepurnoi |
chepurnoi.ma22@physics.msu.ru |
|
Tau-functions beyond the group elements |
Non-petrubative partition functions of quantum theories constitute a class of τ −functions, which satisfy Hirota’s bilinear identities. To make this statement general, there must be a proper definition of τ −function, that gives rise to a set of bilinear identities. In the classical definition of τ −function for integrable Toda or KP hierarchies, there is a restriction on matrix elements to be based on group elements with the following comultiplication ∆(g) = g ⊗ g. This restriction cannot be straightforwardly transferred to the q-deformed case because there are no group elements in q-deformed UEA, except for its Cartan subalgebra. The new approach to the τ −function is to remove the restriction on the group elements and replace it with X, where ∆(X) = \\\\sum(X′α ⊗ X′′α) . The main result of this work is the derivation of the set of bilinear identities and τ −functions for Uq (sl3) in both fundamental representations for non-group elements. |
| 28 |
Ivan Ryzhkov |
iwanryzhkov@ya.ru |
|
Baker-Akhiezer functions for twisted rays in DIM-algebra’s representation (0, 0) |
t is known, that Macdonald polynomials are eigen functions of the relativistic generalization of the Calogero-Sutherland hamiltonian. This hamiltonian can be viewed as a part of an integrable system, that corresponds to a certain ”ray” in the representation of DIM-algebra, where central charges have values (0, 0). These ray is nothing but a representation of a commutative subalgebra in
DIM, and thus it is possible to construct a complete set of their eigen functions, Baker-Akhiezer functions. It is also possible to generalize this by considering some other commutative subalgebras and their Baker-Akhiezer functions. But an expression for these generalized Baker-Akhiezer functions is only known up to coefficients.
In this paper a set of approaches to obtain an expression for these coefficients will be considered. The main idea is to use properties of double affine Hecke algebra (DAHA), which appears to be closely related to this representation.
References:
[1] A. Mironov, A. Morozov, A. Popolitov. On Chalykh’s approach to eigen-
functions of DIM-induced integrable Hamiltonians.
[2] A. Mironov, A. Morozov, A. Popolitov. Commutative families in DIM alge-
bra, integrable many-body systems and q,t matrix models
[3] I. Cherednik. Double Affine Hecke Algebras.
[4] O. Chalykh. Macdonald polynomials and algebraic integrability. |
| 29 |
Sergei Aksenov |
asv@itp.ac.ru |
|
Transport phenomena in a dissipative superconducting system |
We have studied the transport properties of a system including a superconducting wire interacting with an arbitrary number of normal Fermi reservoirs (leads) and baths. The presence of the latter results in the appearance of a dissipative component of the dynamics in the equation for the density matrix. Within the quantum-field approach with a quadratic Liouvillian, we have obtained expressions for the particle and energy currents in the arbitrary lead, as well as the loss current caused by dissipative processes. Equations for nonequilibrium occupation numbers are obtained taking into account the particle gain/loss processes due to the baths. Based on the conductance analysis, the possibility to probe the degeneracy of a nonequilibrium steady state induced by the nontrivial topology of a closed system is investigated. |
| 30 |
Maksim Shustin |
mshustin@yandex.ru |
|
Majorana-driven nonequilibrium steady states in dissipative topological superconductors |
The search for conditions supporting degenerate steady states in nonequilibrium topo-
logical superconductors is important for advancing dissipative quantum engineering, a
field that has attracted significant research attention over the last decades [1, 2, 3]. In
this study, we address this problem by investigating topological superconductors hosting
unpaired Majorana modes under the influence of environmental dissipative fields. Within
the Gorini-Kossakowski-Sudarshan- Lindblad (GKSL) framework and the third quantiza-
tion formalism, we establish a correspondence between equilibrium Majorana zero modes
and nonequilibrium master zero modes. We further derive a simple algebraic relation
between the numbers of these excitations, expressed in terms of hybridization between
the single-particle wavefunctions and linear dissipative fields. Based on these findings, we
propose a practical recipes to stabilize degenerate steady states in topological supercon-
ductors through controlled dissipation engineering. To demonstrate their applicability, we
implement our general framework in the class-BDI Kitaev chain with long-range hopping
and pairing terms — a system known to host a robust edge-localized Majorana modes [4].
Our analysis reveals that while master zero modes formally generalize Majorana modes to
nonequilibrium settings, key entanglement features of the later can be suppressed under
dissipative effects.
The work was funded by Russian Ministry of Science and Higher Education (Project
No. FFWR-2024-0017). The authors acknowledge personal support from the Foundation
for the Advancement of Theoretical Physics and Mathematics “BASIS”
References:
[1] S. Diehl, A. Micheli, A. Kantian, B. Kraus, H. P. Buchler, and P. Zoller, Nat. Phys.
4, 878–883 (2008).
[2] F. Thompson and A. Kamenev, Ann. Phys. (N.Y.) 455, 169385 (2023).
[3] L. M. Sieberer, M. Buchhold, J. Marino, and S. Diehl, arXiv:2312.03073 (2023).
[4] L. Fidkowski, A. Kitaev, Phys. Rev. B 83, 075103 (2023) |
| 31 |
Chenan Wei |
chenanwei@physics.umass.edu |
Alikhanyan National Science Laboratory |
Chaotic non-fermi liquids in flatband systems: SYK model and beyond |
We demonstrate how disorder and strong interactions in flat‐band systems provide a unified route to Sachdev-Ye-Kitaev (SYK) physics and non-Fermi-liquid behavior across two complementary platforms. In an optical Kagome lattice, randomly positioned immobile impurities localize a flat band into a tunable, all-to-all complex Fermion network, allowing direct equilibrium and non-equilibrium measurements. In magic-angle twisted bilayer graphene on disordered substrates, inhomogeneities fragment the nearly flat moiré bands into mesoscopic \"SYK bundles,\" whose incoherent interbundle tunneling yields linear-in-T transport. Together, these realizations establish disordered interacting flat bands as a versatile experimental arena for exploring quantum chaos, strange‐metal transport, and emergent holographic dualities. |
| 32 |
Anastasia Lyublinskaya |
lyublinskaya@itp.ac.ru |
|
Instability of the engineered dark state in two-band fermions under number-conserving dissipative dynamics |
Correlated quantum many-body states can be created and controlled by the dissipative protocols. Among these, particle number-conserving protocols are particularly appealing due to their ability to stabilize topologically nontrivial phases. Is there any fundamental limitation to their performance? We address this question by examining a general class of models involving a two-band fermion system subjected to dissipation designed to transfer fermions from the upper band to the lower band. By construction, these models have a guaranteed steady state — a dark state — with a completely filled lower band and an empty upper band. In the limit of weak dissipation, we derive equations governing the long-wavelength and long-time dynamics of the fermion densities and analyze them numerically. These equations belong to the Fisher-Kolmogorov-Petrovsky-Piskunov reaction-diffusion universality class. Our analysis reveals that the engineered dark state is generically unstable, giving way to a new steady state with a finite density of particles in the upper band. We also estimate the minimum system sizes required to observe this instability in finite systems. Our results suggest that number-conserving dissipative protocols may not be a reliable universal tool for stabilizing dark states. |
| 33 |
Nikita Ignatyuk |
ignatyuk.na@phystech.edu |
|
Integrable structure of gl(2) Affine Yangian in Wakimoto realisation |
In this paper, we consider a quantum integrable system related to the affine Yangian Y(gl(2)), in the Wakimoto realization of the underlying space. Starting from the Lax operator, we compute R-matrix at the lowest levels and reveal a nice sl(2) structure on the vacuum subspace. Furthermore, we establish a correspondence between a zero-twist frame and stripped two-sheaved partitions. Finally, we construct Bethe vectors and derive Bethe Ansatz equations. |
| N |
Speeker |
E-mail |
Institution |
Abstract Title |
Abstract Text |
| 1 |
Mikhail Skvortsov |
skvor@itp.ac.ru |
|
Thermal phase slips in superconducting films |
A dissipationless supercurrent state in superconductors can be destroyed by thermal fluctuations. Thermally activated phase slips provide a finite resistance of the sample and are also responsible for dark counts in superconducting single photon detectors. The activation barrier for a phase slip is determined by a space-dependent saddle-point (instanton) configuration of the order parameter. In the one-dimensional wire geometry, such a saddle point has been analytically obtained by Langer and Ambegaokar in the vicinity of the critical temperature, $T_c$, and for arbitrary bias currents below the critical current $I_c$. In the two-dimensional geometry of a superconducting strip, which is relevant for photon detection, the situation becomes much more complicated. Depending on the ratio $I/I_c$, several types of saddle-point configurations have been proposed, with their energies being obtained numerically. We demonstrate that the saddle-point configuration for an infinite superconducting film at $I\to I_c$ is described by the exactly integrable Boussinesq equation solved by Hirota's method. The instanton size is $L_x\sim\xi(1-I/I_c)^{-1/4}$ along the current and $L_y\sim\xi(1-I/I_c)^{-1/2}$ perpendicular to the current, where $\xi$ is the Ginzburg-Landau coherence length. The activation energy for thermal phase slips scales as $\Delta F^\text{(2D)}\propto (1-I/I_c)^{3/4}$. For sufficiently wide strips of width $w\gg L_y$, it is energetically favorable to form a half-instanton near the boundary, with the activation energy being 1/2 of $\Delta F^\text{(2D)}$. |
| 2 |
Yakov Fominov |
fominov@itp.ac.ru |
|
Superconducting diode effect |
I will present a concise overview of the rapidly developing field of nonreciprocal effects in superconducting transport, also known as the superconducting diode effect. The essence of this phenomenon lies in the asymmetry of a system’s properties when a supercurrent flows in opposite directions. Such an effect requires the simultaneous breaking of time-reversal and inversion symmetries. The underlying physical mechanisms can vary significantly, including effects of magnetic (and, more specifically, exchange) fields, spin-orbit interactions, and geometric asymmetry of the system. These effects can lead to nonreciprocal charge transport both in systems homogeneous along the current direction and in Josephson junctions.
The work was supported by the Russian Science Foundation (Grant No. 24-12-00357).
Literature:
[1] Ya.V. Fominov, D.S. Mikhailov, Asymmetric higher-harmonic SQUID as a Josephson diode, Phys. Rev. B 106, 134514 (2022).
[2] G.S. Seleznev, Ya.V. Fominov, Influence of capacitance and thermal fluctuations on the Josephson diode effect in asymmetric higher-harmonic SQUIDs, Phys. Rev. B 110, 104508 (2024).
[3] D.S. Kalashnikov, G.S. Seleznev, A. Kudriashov, Y. Babich, D.Yu. Vodolazov, Ya.V. Fominov, V.S. Stolyarov, Diode effect in Shapiro steps in an asymmetric SQUID with a superconducting nanobridge, in preparation.
[4] Yu.A. Dmitrievtsev, Ya.V. Fominov, Superconducting orbital diode effect in SN bilayers, in preparation.
[5] D.A. Chuklanov, Ya.V. Fominov, Diode effect in superconductors with spin-orbit interaction, in preparation. |
| 3 |
Vladimir Zyuzin |
zyuzin.vova@gmail.com |
|
zyuzin.vova@gmail.com |
We propose and study a theoretical model of insulators which show de Haas-van Alphen oscillations as well as periodic dependence of the magnetization on inverse temperature. The insulating behavior is due to the Coulomb interaction driven hybridization of fermions at the crossing point of their energy bands. We show that the leading contribution to the oscillations at small magnetic fields is due to the oscillatory dependence of the hybridization gap on the magnetic field. In order to see this the hybridization is derived from a self-consistent non-linear equation. We show that the amplitude of the de Haas-van Alphen is periodic in inverse temperature with a period defined by a combination of the hybridization gap and magnetic field. Based on these findings, we present arguments that a modification of our model to the heavy fermion system may explain the giant temperature peak experimentally observed in SmB$_6$.
|
| 4 |
Yurii Makhlin |
makhlin@itp.ac.ru |
|
Bound states on Josephson vortices in planar topological junctions |
Josephson vortices in planar junctions on top of a topological insulator material in weak magnetic fields may bind electronic states. The Dirac spectrum of surface states in the topological insulator produces subgap states in the junction, which correspond to Landau levels, with a Majorana mode at zero energy. These zero modes are carried by vortices, with their location controlled via the magnetic field and phase bias. Interference of local Josephson currents can be used to demonstrate the presence of MZMs as well as to probe their quantum state. At integer flux values, the standard Fraunhofer interference demonstrates vanishing critical current, and the observed non-zero critical current can be linked to contribution of MZMs. Moreover, in the Corbino geometry flux quantization allows to probe only integer flux values. However, similar effects may arise from imperfections, including nonuniform geometry. We discuss effects of the geometric disorder and compare them to experiments. We further analyze other possibilities to probe physics of the bound states including spectroscopy.
|
| 5 |
Alexei Litvinov |
litvinov@itp.ac.ru |
|
On dual regime in Yang-Baxter deformed $\mathrm{O}(2N)$ sigma models |
We explore a new class of integrable sigma models, which we refer to as the "dual regime" of the Yang-Baxter (YB) deformed $\mathrm{O}(2N)$ sigma models. This dual regime manifests itself in the conformal perturbation approach. Namely, it is well known that the conventional YB-deformed $\mathrm{O}(N)$ sigma models are described in the UV by a collection of free bosonic fields perturbed by some relevant operators. The holomorphic parts of these operators play the role of screening operators which define certain integrable systems in the free theory. All of these integrable systems depend on a parameter $b$, which parameterizes the central charge, and are known to possess the duality under $b^2\longleftrightarrow -1-b^2$. While $\mathrm{O}(2N+1)$ integrable systems are self-dual, $\mathrm{O}(2N)$ systems are not. In particular, the $\mathrm{O}(2N)$ integrable systems provide new perturbations of the sigma model type. We identify the corresponding one-loop metric and $B-$field and show that they solve the generalized Ricci flow equation. |
| 6 |
Vadim Geshkenbein |
dimagesh@itp.phys.ethz.ch |
Institute for Theoretical Physics, ETH Zurich, CH-8093 Zurich, Switzerland |
Abbrikosov vortices switching Josephson current in magic angle graphene |
Planar Josephson junctions made from atomically thin films exhibit poor transverse screening, causing the magnetic-field dependence of the Josephson current Ic(B) to deviate from the standard Fraunhofer pattern of conventional junctions. The relevant flux determining the oscillations in Ic(B) is not the usual flux Φλ = 2BWλL penetrating the junction but the larger flux ΦW = 2BW2, including the lead areas near the junction, with W the junction width.
The envelope of the Fraunhofer-like pattern also differs, with maxima decaying slowly ∝1∕√B rather than the usual ∝1/B.
Given the weak screening, the junction is highly sensitive to Pearl vortices in the leads. Vortices alter the phase pattern and affect the Josephson current. Thermal fluctuations can cause vortices to jump in and out of the leads, leading to shifts in the Fraunhofer-like pattern, as observed in the recent experiment. Our model quantitatively explains these jumps, whose timescale depends on magnetic field, current, temperature, and superfluid stiffness. At elevated temperatures, fast vortex jumps may wash out the Fraunhofer pattern well below Tc. By analyzing the timescale of these jumps, we can determine the superfluid stiffness and the Berezinskii-Kosterlitz-Thouless transition temperature of magic-angle twisted four-layer graphene. These values are in agreement with recent kinetic inductance measurements. |
| 7 |
Hrant Topchyan |
hranttopchyan1@gmail.com |
"A. I. Alikhanyan national science laboratory (Yerevan Physics Institute)" foundation |
S-matrix approach and Harris criterion in the Integer quantum Hall effect |
One of the topics open to discussion in the Integer quantum Hall effect (IQHE) is the theory for the plateau transitions. The widely accepted Chalker-Coddingtion model shows a mismatch with the experiment (the value of the localization length exponent). Recent numerical studies show that the mismatch can be fixed by introducing network disorder (two-dimensional quantum gravity), however the accuracy of those calculations were questioned due to the seemingly imperfect methods employed. Moreover, the fact of fixing the mismatch itself contradicts the Harris criterion. Hereby we confirm the previously done study, by introducing an S-matrix calculation approach which doesn't contain any of the imperfections in previous methods, and is better in general. We also address the Harris criterion issue, by showing its inapplicability in this case. We conjecture that the cornerstone of this phenomenon are the scale-free networks that emerge in IQHE. They are widely used in various fields of science, but are purely studied in condensed matter physics.
|
| 8 |
Alex Kamenev |
kamen002@umn.edu |
Fine Theoretical Physics lnstitute, University of Minnesota. US |
Discrete optimization and neural networks training with quantum computers |
I will discuss the physics of quantum optimization algorithms and their implementation with a 5000-qubit D-Wave device. It brings questions about computational complexity of finding the ground state of 3D spin glasses. I will show how successful resolution of these issues allows us to implement an efficient quantum training of neural networks, which can be uploaded and used on conventional computers. |
| 9 |
Ilya Gruzberg |
gruzberg.1@osu.edu |
|
Quantum Hall transitions on random networks and exact results from quantum gravity. |
The paradigmatic Chalker-Coddington network model for the integer quantum Hall transition (QHT) has been generalized to random networks. Numerical studies of the random networks showed that critical exponents of the integer QHT are modified by the geometric randomness. It was conjectured that the changes are similar to the ones induced by random geometry (two-dimensional quantum gravity) at critical points of conventional statistical mechanics models (Ising, Potts, O(N), etc.) and described by the so called Knizhnik-Polyakov-Zamolodchikov (KPZ) scaling relation. Here we investigate these issues for the spin QHT which can be mapped to classical percolation. The mapping works even in the presence of geometric disorder, and we solve the spin QHT on random networks as percolation on certain random graphs using methods of discrete quantum gravity (matrix models and loop equations). We confirm that the KPZ scaling works in this case. We also discuss how our findings are related to the Harris criterion and the Chase-Chase-Fisher-Spencer inequality.
|
| 10 |
Dima Gangardt |
d.m.gangardt@bham.ac.uk |
|
Limit shapes and their phase transitions: classical and quantum |
I will present examples of Limit Shapes - the most probable macroscopic shape with sharp boundaries separating frozen and fluctuating regions - which arise in a variety of classical and quantum systems. I will explain a special role played by analytic functions defining a Riemann surface whose topology can be changed abruptly across phase transitions. Most of the examples
are based on free fermionic models; however, recently we studied a notable exception from this rule - the Polytropic Gas with a power-law equation of state. The analytic approach to Emptiness Formation Probability in Politropic Gas will be discussed.
[1] J. Pallister, D.M. Gangardt and A. Abanov, "Limit shape phase transitions: a merger of arctic circles", J. Phys. A 55, 304001, 2022
[2] James S. Pallister, Samuel H. Pickering, Dimitri M. Gangardt and Alexander G. Abanov, "Phase transitions in full counting statistics of free fermions and directed polymers", Phys. Rev. Research 7, L022008, 2025
[3] Alexander G. Abanov, Dimitri M. Gangardt, "Emptiness instanton in quantum polytropic gas", SciPost Phys. 18, 122, 2025
|
| 11 |
Andrea Cappelli |
andrea.cappelli@fi.infn.it |
INFN and University of Florence, Italy |
Bosonizations and dualities in 2+1 dimensions |
We discuss two methods for relating bosonic and fermionic relativistic field theories in 2+1 dimensions, the Z_2 gauging and the flux attachment. The first is primarily a correspondence between topological theories. Its inverse map, fermionization, shows how spin structures and Z_2 fermion parity emerge from a bosonic theory equipped with a dual Z_2^(1) generalized symmetry. The second method, flux attachment, is obtained by coupling to a Chern-Simons theory, and is at the basis of Abelian dualities. We illustrate the two bosonizations with explicit results in a solvable semiclassical, yet non-trivial conformal theory. We also combine the two bosonizations to obtain further duality relations. |
| 12 |
Igor Gornyi |
igor.gornyi@kit.edu |
Karlsruhe Institute of Technology |
Scaling of many-body localization transitions: Fock-space correlations, spectral observables, and dynamics |
Many-body-localization (MBL) models can be viewed as tight-binding models in manybody Hilbert space (Fock space). We study MBL transitions in a family of single-spin-flip spin-1
2 models. They include the one-dimensional (1D) chain with nearest-neighbor interactions and the quantum dot (QD) model with all-to-all pair interactions. In addition, we consider their modifications (uQD and u1D models) with removed correlations of the off-diagonal matrix elements, as well a quantum random-energy model (QREM) with no correlations at all. This allows
us to explore the role of correlations between matrix elements of the effective Fock-space Hamiltonians in the scaling of MBL critical disorder Wc(n) with the number of spins n [1]. Our numerical results based on many-body spectral observables are in excellent agreement with analytical arguments predicting a power-law (with logarithmic factors) growth of Wc(n) for QREM, u1D, uQD, and QD models. This growth is in stark contrast to the 1D model, where Wc(n) is essentially independent of n. Our findings demonstrate that the scaling of Wc(n) for MBL transitions is governed by a
combined effect of Fock-space correlations of diagonal and off-diagonal matrix elements. We further investigate [2] the Fock-space and real-space dynamics in the single-spin-flip models. Specifically, we focus on the generalized imbalance that characterizes propagation in Fock space out of an initial basis state and, at the same time, can be efficiently probed by real-space measurements. For all models considered (1D, QD, and QREM), the average imbalance and its quantum and mesoscopic fluctuations provide excellent indicators for the position of the MBL transition Wc(n). The obtained results are in full consistency with those obtained from spectral observables [1]. We thus determine phase diagrams of the MBL transitions in the n-W plane, with clear evidence for a direct transition between the ergodic and MBL phases for each of the models, without any intermediate phase. We also determine the scaling of the transition width ∆W (n)/Wc(n) and estimate the system size n needed to study the asymptotic scaling behavior. Our results indicate the feasibility of experimental studies of n-W phase diagrams and scaling properties of MBL transitions in models of 1D and QD type and their extensions to other spatial geometry or distance-dependent interactions.
[1] T. Scoquart, I.V. Gornyi, and A.D. Mirlin, Phys. Rev. B 109, 214203 (2024).
[2] T. Scoquart, I.V. Gornyi, and A.D. Mirlin, arXiv:2502.16219. |
| 13 |
Moshe Goldstein |
mgoldstein@tauex.tau.ac.il |
|
Entanglement with symmetry: From record high to record low |
Symmetries and the corresponding conservation laws, as well as entanglement, are two central pillars of quantum many body physics and field theory. Only relatively recently their interplay started to be studies by our group and others. In this talk I will provide two examples, showing that such an interplay can lead to both record-low and record-high entanglement. The first example concerns lattice gauge theories, which play a central role in high energy physics, condensed matter physics, and quantum error correction. Due to the nontrivial structure of the Hilbert space of such systems, entanglement is tricky to define. However, when one limits oneself to superselection resolved entanglement, that is, entanglement corresponding to specific gauge symmetry sectors, the entanglement becomes well-defined. Moreover, when gauge symmetry is strictly obeyed, superselection-resolved entanglement becomes the only distillable contribution to the entanglement. Employing a tensor network construction for gauge-invariant systems as defined by Zohar and Burrello we find that, in a vast range of cases, the leading term in the uperselection-resolved entanglement depends on the number of corners in the partition an unprecedently small corner-law (rather than area law) entanglement. The second example deals the steady state of noninteracting fermions, occupying a 1D lattice that hosts a generic scatterer at its center. It is coupled at its ends to two reservoirs biased by either voltage or temperature, leading to steady flows of the conserved particle number and energy. We show that disjoint intervals located on opposite sides of the scatterer, and within similar distances from it, maintain volume-law entanglement and total correlations regardless of their separation, as measured by their fermionic negativity and mutual information, respectively. Interestingly, this implies that if the position of one of the intervals is kept fixed, then the quantum correlation measures depend non-monotonically on the distance between the intervals. We derive exact analytical expressions for the extensive terms of these measures, which allow us to demonstrate that the strong long-range entanglement is generated by the coherence between the transmitted and reflected parts of propagating particles within the bias energy window. |
| 14 |
Alexander Mirlin |
alexander.mirlin2@kit.edu |
Karlsruhe Institute of Technology, Germany |
Measurement-induced phase transitions in fermionic systems |
We develop [1-5] a theory of measurement-induced phase transitions (MIPT) for d-dimensional lattice fermions subject to random measurements of local site occupation numbers. Our nalytical approach is based on Keldysh path-integral formalism and replica trick. For free fermions, we derive a non-linear sigma model (NLSM) as an effective field theory of the problem. Its replica-symmetric sector is a U(2)/U(1)xU(1) NLSM corresponding to observables linear in the density matrix; it describes diffusive behavior of average density fluctuations. The most interesting is the replica-asymmetric sector corresponding to observables that are non-linear in the density matrix. In particular, it describes propagation of quantum correlations of charge and of quantum information in a system. It is given by a (d+1)-dimensional isotropic NLSM defined of a chiral symmetry class AIII or BDI, with the target manifold SU(R) or SU(2R)/USp(2R), depending on presence of an additional effective time-reversal symmetry, with a replica limit R à 1. This establishes a close relation between MIPT and Anderson transitions. On the Gaussian level, the NLSM predicts diffusive behavior, implying that the entanglement entropy grows with system size as logarithm times area. However, the renormalization-group analysis shows that, for d=1, the "weak localization of information" develops asymptotically into strong localization, implying that the system is in the area-law phase even for a small measurement rate [1]. The corresponding localization length is however exponentially large for rare measurements. For d>1, we obtain a MIPT between the "diffusive" and "localized" phases of information and charge correlations [2]. The charge covariance G (linked to mutual information) in our theory is a counterpart of conductance in Anderson transitions. The "metallic" phase is characterized by "universal conductance fluctuations" of G and the critical point by scale-invariant distribution of G and by multifractality of two-point "conductance" [5]. Including interaction between fermions induce additional terms in the NLSM that affect the physics in a dramatic way [3]. First, this leads to the “information-charge separation”: charge cumulants get decoupled from entanglement entropies. Second, the interaction stabilizes the volume-law phase for the entanglement. Third, for spatial dimensionality d=1, the interaction stabilizes the phase with logarithmic growth of charge cumulants. We also explore a model of free fermions in d=1, subject to non-commuting local measurements across adjacent sites, which resolves the fermions into non-orthogonal orbitals, misaligned from the underlying lattice [4]. For maximal misalignment, superdiffusive behavior emerges from the vanishing of the measurement-induced quasiparticle decay rate at one point in the Brillouin zone, which generates fractal-scaling entanglement entropy S ∝ ℓ1/3 for a subsystem of length ℓ. We derive an effective NLSM with long-range couplings responsible for Lévy flights in entanglement propagation. When the misalignment is reduced, the entanglement exhibits, with increasing ℓ, consecutive regimes of superdiffusive, diffusive, and localized behavior. All analytical results are supported by numerical simulations [1-5].
[1] I. Poboiko, P. Pöpperl, I.V. Gornyi, A.D. Mirlin, Phys. Rev. X 13, 041046 (2023)
[2] I. Poboiko, I.V. Gornyi, A.D. Mirlin, Phys. Rev. Lett. 132, 110403 (2024)
[3] I. Poboiko, P. Pöpperl, I.V. Gornyi, A.D. Mirlin, Phys. Rev. B 111, 024204 (2025)
[4] I. Poboiko, M. Szyniszewski, C.J. Turner, I.V. Gornyi, A.D. Mirlin, and A. Pal,
arXiv:2501.12903
[5] I. Poboiko, I.V. Gornyi, A.D. Mirlin, in preparation |
| 15 |
Dmitry Bagrets |
d.bagrets@fz-juelich.de |
Forschungszentrum Juelich and University of Cologne, Germany |
On chiral Majoranas and BTZ black holes |
A celebrated realization of the holographic principle posits an approximate duality between the quantum mechanical SYK model and two-dimensional Jackiw-Teitelboim gravity, mediated by the Schwarzian action as an effective low energy theory common to both systems. In this talk, I discuss a generalization of this holographic correspondence to one dimension higher [1]. Starting from a microscopic realization of an effectively chiral (1+1) dimensional generalization of the SYK model, I will demonstrate that one can derive its reduction to the Alekseev-Shatashvilli (AS) action, a minimal extension of the Schwarzian action which has been proposed as the effective boundary action of three-dimensional gravity. Remarkably, in the bulk the same action describes fluctuations around the Euclidean BTZ black hole configuration, the dominant stationary solution of three-dimensional AdS gravity. These two constructions allow one to match bulk and boundary coupling constants, and to compute observables. Specifically, I outline a semiclassical technique inspired by condensed matter physics to the computation of a two-point function of Majoranas and their out-of-time-order correlation function (OTOC), the latter demonstrating maximal chaos in the chiral SYK model and its gravity dual.
[1] A. Altland, D. Bagrets, N. Callebaut and K. Weisenberger, arXiv:2502.19370 |
| 16 |
Andreas Klümper |
kluemper@uni-wuppertal.de |
University of Wuppertal, Germany |
Chiral Basis for Qubits and Spin-Helix Decay |
We propose a qubit basis composed of transverse spin helices with kinks. Unlike the usual computational basis, this chiral basis is well suited for describing quantum states with nontrivial
topology. Choosing appropriate parameters the operators of the transverse spin components, $\sigma_n^x$ and $\sigma_n^y$, become diagonal in the chiral basis, which facilitates the study of problems focused on transverse spin components. As an application, we study the temporal decay of the transverse polarization of a spin helix in the XX model that has been measured in recent cold atom experiments. We obtain an explicit universal function describing the relaxation of helices of arbitrary wavelength. |
| 17 |
Tigran Sedrakyan |
tsedrakyan@physics.umass.edu |
University of Massachusetts, Amherst |
Unveiling chiral states in the XXZ chain |
In this talk, I will present a detailed study of the low-energy properties of the one-dimensional spin-1/2 XXZ chain with time-reversal symmetry-breaking pseudo-scalar chiral interaction. I will propose a phase diagram for the model, focusing on the integrable case of the isotropic Heisenberg model with the chiral interaction. By employing the thermodynamic Bethe ansatz, I will discuss the concept of “chiralization”—the response of the ground state to the strength of the pseudo-scalar chiral interaction in a chiral Heisenberg chain. Notably, the chirality of the ground state remains zero until a critical coupling, α_c = (2/π)J, is reached, where J denotes the antiferromagnetic spin-exchange interaction. The two distinct phases, characterized by zero and finite chirality, are described by central-charge c = 1 conformal field theories (CFTs). Despite having identical central charges, I will argue that the difference between these emergent CFTs lies in the symmetry of their ground-state primary fields, leading to symmetry-enriched CFTs. Furthermore, at finite but small temperatures, the non-chiral Heisenberg phase acquires a finite chirality at finite but small temperatures that scales with the temperature quadratically. Finally, I will discuss how finite-size effects near the transition point provide a sensitive probe of the phase transition, offering insights into the underlying physics. |
| 18 |
Alexander Gorsky |
shuragor@mail.ru |
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Phase-locking in dynamical systems and quantum mechanics |
We discuss the relation between the dynamical system on the torus and the Hill equation, which is interpreted as either the equation of motion for the parametric oscillator or the Schr\"{o}dinger equation with periodic potential. The structure of phase-locking domains in the dynamical system on torus is mapped into the band-gap structure of the Hill equation. For the parametric oscillator, we provide the relation between non-adiabatic Hannay angle and the Poincar\'{e} rotation number of the corresponding dynamical system. In terms of quantum mechanics, the integer Poincar\'{e} rotation number is connected to the quantization number via the Milne's quantization approach and exact WKB. Using recent results concerning the exact WKB approach in quantum mechanics, we discuss the non-perturbative effects in the dynamical systems on the torus and for parametric oscillator. The semiclassical WKB is interpreted in the framework of a slow-fast dynamical system. The link between the classification of the coadjoint Virasoro orbits and the Hill equation yields a classification of the phase-locking domains in the parameter space in terms of the classification of Virasoro orbits. Our picture is supported by numerical simulations for the model of the Josephson junction and Mathieu equation.
Joint paper with A. Alexandrov and A. Glutsyuk |
| 19 |
Nikolay Gromov |
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| 20 |
Leon Balents |
balents@spinsandelectrons.com |
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Symmetry breaking patterns of 2+1d U(1) gauge theory with an SU(N) chemical potential and application to quantum antiferromagnets |
We study the response of U(1) gauge theory on the lattice in 2+1 dimensions to an applied chemical potential coupling to a conserved SU(N) flavor charge. This mimics the physics of an applied Zeeman field coupling to a U(1) Dirac spin liquid. We observe several different symmetry breaking patterns and discuss the associated observable orders. We also investigate trial wavefunctions for antiferromagnets inspired by the gauge theory. |
| 21 |
Sergei Nechaev |
sergei.nechaev@gmail.com |
LPTMS, Universite Paris-Saclay |
Fractional Brownian motion meets polymer topology |
We investigate statistical and topological properties of fractional Brownian polymers with the fractal dimension D_f > 2 in the tree-dimensional space. Our study is motivated by an attempt to mimic the statistics of collapsed unknotted polymer rings, which are known to form hierarchical crumpled globules (CG) with D_f=3 at large scales. We demonstrate that with the increase of D_f, typical conformations become less knotted. Distribution of the knot complexity for various fractal dimensions of chains suggests a relationship between fractal dimension and polymer topology. This finding could have an important practical impact: replacing topology by a fractal dimension would tremendously simplify the problem of generating compact self-avoiding polymer conformations since topological constraints are washed out of the consideration. |
| 22 |
Ferdinand Evers |
eversfh@gmail.com |
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A Perspective on (Many-Body) Localization in Fock Space — Facts and Work in Progress |
The talk will present numerical investigations of many-body localization (MBL) from a Fock-space perspective. The first part reviews the current status of the field, focusing on the dynamical behavior of entanglement entropy and sublattice imbalance. The second part explores certain analogies between the Fock-space dynamics of many-body systems and the dynamics of non-interacting particles on a high-dimensional regular graph with on-site disorder. We will highlight, in particular, analogies in the patterns of local current densities that arise in a quasi-stationary flow. Potential implications for MBL phase diagrams will be briefly discussed. |
| 23 |
Yuval Gefen |
yuval.gefen@weizmann.ac.il |
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Effective linear response for non-equilibrium anyonic systems |
The low-energy dynamics of two-dimensional topological matter hinges on its one-dimensional edge modes. Tunneling between fractional quantum Hall edge modes facilitates the study of anyonic statistics: it induces time-domain braiding that dominates signals from dilute anyon beams. We develop a framework for characterizing one-dimensional out-of-equilibrium anyonic states and define their effective chemical potential and temperature, both arising from anyonic braiding; these quantities depend on the effective (fractional) charge of the anyons and on their braiding phase. We further define electric and thermal transport coefficients in non-equilibrium anyonic setups. We show that in the extremely dilute limit, where contributions due to direct collisions of non-equilibrium anyons are negligible, the off-diagonal thermoelectric transport coefficients, i.e., Seebeck and Peltier coefficients, both vanish due to the symmetry between particle and hole distributions. This symmetry, however, is broken when deviating from this dilute limit. It follows that finite Seebeck and Peltier coefficients represent a
smoking gun evidence of anyonic collisions.
[1] Gu Zhang, Igor Gornyi, and Yuval Gefen, arXiv:2407.14203 and to be
published. |
| 24 |
Felix von Oppen |
onoppen@physik.fu-berlin.de |
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Random fields in the Floquet quantum Ising model |
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| 25 |
Elio Koenig |
elio.koenig@physics.wisc.edu |
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Topologically enabled superconductivity and possible implications for rhombohedral graphene |
We present a topological mechanism for superconductivity emerging from Chern-2 insulators. While, naively, time reversal symmetry breaking is expected to prevent superconductivity it turns out that the opposite is the case: An explicit model calculation for a generalized attractive-U Haldane-Hubbard model demonstrates that superconductivity is only stabilized near the quantum anomalous Hall state, but not near a trivial, time reversal symmetrical band insulator. We explain this using an effective fractionalized field theory involving fermionic chargeons, bosonic colorons and an emergent U(1) gauge field. When chargeons form a topological band structure, they prevent monopole proliferation ensuring a gapless photon. We argue that this photon should be interpreted as the Goldstone boson of the superfluid. Using random phase approximation on top of extensive slave-rotor mean-field calculations we characterize coherence length and stiffness of the superconductor. Thereby, we deduce the phase diagram in parameter space along with the universal nature of the superconducting transitions. We furthermore discuss the effect of doping and external magnetic field. We complement the fractionalized theory with calculations using an effective spin model and Gutzwiller projected wavefunctions. While mostly based on a simple toy model, we argue that our findings pave the way to a better understanding of superconductivity emerging out of spin- and valley polarized rhombohedral multilayer graphene in a parameter regime with nearby quantum anomalous Hall insulators. |
| 26 |
Nikita Nekrasov |
nikitastring@gmail.com |
Simons Center for Geometry and Physics Stony Brook University Stony Brook NY 11794-3636 USA |
The magic of two dimensional Yang-Mills : strings, anyons and graphene |
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| 27 |
Victor Galitski |
galitski@umd.edu |
University of Maryland, College ParkUniversity of Maryland |
Glasses: From Physical Hamiltonians to Neural Networks and Back |
This talk will review our recent work on classical and quantum glasses. I will start with a discussion of spin glasses from the perspective of chaos theory. The Thouless-Anderson-Palmer (TAP) formalism will be introduced to "visualize" the landscape of metastable energy minima in such systems. The quantization of the TAP equations will be introduced and used to explore the spectral form factor (SFF)—a key metric of quantum chaos—in certain models of quantum glasses. It will be shown that the hallmark of quantum chaos—a ramp in the SFF—is rescaled by the exponential of complexity compared to the standard chaotic (random matrix) model. I will briefly mention the realization of such models in glassy quantum circuits, which exhibit slow thermalization. Next, a one-to-one correspondence between classical spin models and neural networks (NNs) will be established. Training a NN in this mapping corresponds to a family of spin Hamiltonians parameterized by training time. TAP equations will be used to show that training a NN on a classification task physically implies the destruction of the spin glass and the emergence of hidden order, whose melting temperature increases as a power law with training time. This provides an appealing physical picture of training neural networks as a search for hidden order associated with the task. Finally, a natural quantization of neural networks will be introduced, and I will argue that some test cases are readily deployable on present-day quantum computers. |
| 28 |
Boris Khesin |
boris.khesin@gmail.com |
Univ. of Toronto, Canada |
Geometry behind fluids |
In 1966 V.Arnold suggested a group-theoretic approach to ideal hydrodynamics via the geodesic flow of the right-invariant energy metric on the group of volume-preserving diffeomorphisms of the flow domain. We describe several recent ramifications of this approach related to compressible fluids, optimal mass transport, as well as Newton's equations on diffeomorphism groups and smooth probability densities. It turns out that various important PDEs of hydrodynamical origin can be described in this geometric framework in a natural way. This is a joint work with G.Misiolek and K.Modin. |
| 29 |
Gabriel Cardoso |
gabriel.jg.cardoso@outlook.com |
Nordita, Stockholm University, and KTH Royal Institute of Technology, Hannes Alfv´ens v¨ag 12, 106 91 Stockholm, Sweden |
Gapless Floquet Topology |
Symmetry-protected topological (SPT) phases in insulators and superconductors are known for hosting robust edge modes, linked via the bulk-boundary correspondence to topological invariants derived from bulk wavefunctions. While traditionally formulated for gapped systems, this correspondence can persist in gapless phases. We develop a framework for gapless Floquet topology in one-dimensional systems with chiral symmetry, extending the classification of fermionic Floquet SPTs in classes AIII and BDI to cases where the bulk quasienergy spectrum is gapless at 0 and/or π. The topological invariants are constructed from the half-period evolution operator, sidestepping the ambiguities that arise in definitions based on the Floquet Hamiltonian. These invariants admit a geometric interpretation as linking numbers between loops in the three-sphere; in the gapless case, our construction corresponds to the generalization of linking numbers to oriented intersecting loops. We prove a bulk-boundary correspondence relating these invariants to the number of edge-localized zero and π modes, even when the bulk is gapless at the corresponding quasienergies. Explicit examples include generalized Kitaev chains and spin models. In the spin-chain realizations, these edge modes manifest as boundary autocorrelations with exponentially diverging lifetimes in the thermodynamic limit. We also examine the effects of interactions, showing that edge-mode lifetimes become finite and consistent with Fermi’s golden rule. Our results uncover new classes of topological Floquet phases without bulk gaps and open a path toward identifying intrinsically gapless Floquet SPTs.
References
[1] Cardoso, G., Yeh, H. C., Korneev, L., Abanov, A. G., & Mitra, A. (2025). Gapless Floquet topology.
Physical Review B, 111(12), 125162. |
| 30 |
Rubik Poghossian |
poghos@yerphi.am |
"A. I. Alikhanyan national science laboratory (Yerevan Physics Institute)" foundation |
On 5-point conformal block with level 2 degenerate insertion and its AGT dual |
In my talk I will present a new recursive method for studying the 5-point conformal Liouville block with degenerate level 2 insertion and its AGT dual. First, the solution of the BPZ differential equation satisfied by the conformal block is represented as a double series expansion. From the 2-node quiver gauge theory side, this expansion corresponds to the instanton series. It will be shown that the expansion coefficients are uniquely determined by a recursive relation. This series can be partially resummed, leading to an elegant expression in terms of a single hypergeometric function and its derivative. This new representation makes it straightforward to relate different asymptotic regions. As a by-product, we get a simple derivation of the fusion and braiding coefficients. It will be shown how a subtle procedure of merging the degenerate field with the outgoing state provides an alternative way of calculating the general 4-point block, which on the gauge theory side corresponds to the partition function of the SU(2) gauge theory with four massive hypermultiplets in the Omega background. These results are confirmed by comparison with known results obtained either from 2d conformal field theory or from the instanton count. |
| 31 |
Alexander Zamolodchikov |
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| 32 |
Boris Svistunov |
svistunov@physics.umass.edu |
University of Massachusetts, Amherst |
Transverse Quantum Superfluids |
Even when ideal solids are insulating, their states with crystallographic defects may have superfluid properties. It became clear recently that edge dislocations in He-4 featuring a combination of microscopic quantum roughness and superfluidity of their cores may represent a new paradigmatic class of quasi-one-dimensional superfluids. The new state of matter, termed transverse quantum fluid (TQF), is found in a variety of physical setups. The key ingredient defining the class of TQF systems is infinite compressibility, which is responsible for all other unusual properties such as the quadratic spectrum of normal modes (or even the absence of sharp quasiparticles), irrelevance of the Landau criterion, off-diagonal long-range order at T = 0, and the exponential dependence of the phase slip probability on the inverse flow velocity. From a conceptual point of view, the TQF state is a striking demonstration of the conditional character of many dogmas associated with superfluidity, including the necessity of elementary excitations, in general, and the ones obeying the Landau criterion in particular. |
| 33 |
Alexey Lunkin |
lunk112514@gmail.com |
Nanocenter CENN |
Local Density of States Correlations in the Lévy-Rosenzweig-Porter random matrix ensemble |
We present an analytical calculation of the local density of states correlation function β(ω) in the Lévy-Rosenzweig-Porter random matrix ensemble at energy scales larger than the level spacing but smaller than the bandwidth. The only relevant energy scale in this limit is the typical level width Γ. We show that β(ω≪Γ)∼W/Γ (here W is width of the band) whereas β(ω≫Γ)∼(W/Γ)(Γ/ω)^μ where μ is an index characterising the distribution of the matrix elements. We also provide an expression for the average return probability at long times: ln[R(t≫Γ)]∼−(Γt)^μ/2. Numerical results based on the pool method and exact diagonalization are also provided and are in agreement with the analytical theory. |
| 34 |
Michael (Misha) Chertkov |
chertkov@math.arizona.edu |
University of Arizona |
Non-Equilibrium Statistical Mechanics of/for AI |
This talk presents a unifying applied mathematics/theoretical physics framework that bridges core components of modern generative AI -- diffusion models, reinforcement learning, and transformers -- through the lens of contemporary applied mathematics. Central to this framework are the concepts of Decision Flows and Path Integral Diffusions, which offer structured approaches to sequential sampling over discrete, continuous, and hybrid spaces. These approaches are rooted in Green-function-based control, Schrödinger bridges, and non-equilibrium statistical physics. Building on recent work, we explore analytically tractable and algorithmically efficient regimes -- often requiring minimal use of neural networks -- where sampling from complex distributions becomes both explainable and extrapolative. We highlight connections between score-based diffusion, linearly-solvable Markov Decision Processes, and energy-based models, including emerging insights into phase transitions in generative AI (e.g., memorization and speciation dynamics). Applications span inference/sampling in Ising models, CIFAR-10 image generation, physics-informed reinforcement learning in turbulent flows, and auto-regressive modeling of statistical hydrodynamics. We also touch on decision-making under uncertainty in energy systems. |