Dmitry Abanin (U. Geneva) Ergodicity breakdown, entanglement, and non-equilibrium quantum matter We are used to describing systems of many particles by statistical mechanics, and expect a system initially prepared in a non-equilibrium state to reach thermal equilibrium. However, the basic postulate of statistical mechanics - ergodicity -- breaks down in many-body localized systems, where disorder prevents particle transport and thermalization. I will review the current theoretical understanding of many-body localization (MBL), based on the insights from quantum entanglement. Surprisingly, highly excited MBL obey so-called area law, typical of ground states in gapped systems. This property is closely related to the new form of integrability found in MBL systems. Turning to applications, MBL persists in a class of periodically driven (Floquet) many-body systems, which opens the door to distinct Floquet phases with unusual properties such as chiral edge states at high temperature. I will discuss other recently discovered mechanisms of avoiding, or significantly slowing down thermalisation in quantum systems, including quantum many-body scars and Floquet prethermalization. I will close by discussing experimental advances and outstanding challenges in exploring ergodicty and its breakdown in quantum many-body systems. ----------------- Frithjof Anders (TU Dortmund) Strongly correlated multi-impurity models: The crossover from a single-impurity problem to lattice models We present a mapping of correlated multi-impurity Anderson models to a cluster model coupled to a number of effective conduction bands capturing its essential low-energy physics. We can identify the anti-ferromagnetic part of the RKKY interaction and present a mathematical criterion for the number of the effective screening channel, allowing the replacement of the phenomenological exhaustion criterion. This provides a distinction between multi-impurity models of first kind and of second kind. For the latter, there are insufficient screening channels available, so that a singlet ground state must be driven by the inter-cluster spin correlations rather then the Kondo physics. We present applications of the theory to the Kondo-hole problem using Wilsons numerical renormalization group as well as cover the emergent coherence, metallic surface states and quantum phase transitions in Kondo insulators. Using an extended Lieb-Mattis theorem provides a deeper understanding on gapped spectra vs finite density of states in particle-hole symmetric situations. ----------------- Sonia Bacca (U. Mainz) Ab-initio electroweak reactions with nuclei The past decade has witnessed tremendous progress in the theoretical and computational tools that produce our understanding of the nucleus as a compound object of interacting protons and neutrons. A number of ab initio calculations of nuclear electroweak properties that started from interactions and currents obtained from chiral effective field theory have successfully described key experimental observables, yielding a complete picture of how nuclei interact with electroweak probes. The level of accuracy and confidence reached by ab initio calculations opens up the concrete possibility of using nuclear theory to help address open questions in other sub-fields of physics, such as neutrino physics. In this talk, I will present our recent results obtained from coupled-cluster theory for the charge and weak form factors of the 40Ar nucleus and our recent results for electron-scattering cross section of 40Ca. ----------------- Carlo Barbieri (U. Milan) New Advances in self-consistent Green's function with Gorkov propagators The Gorkov-SCGF approach was introduced in Nuclear Physics about 10 years ago as an efficient way to handle pairing and degeneracies in open shell isotopes. It has since been applied to several ab initio computations, reaching up to mass A=140 numbers. Original computations have been limited to second-order truncations of the Gorkov self-energy. In recent months, we have reformulated the formalism in a Nambu-covariant representation, which allows us to extend the Gorkov-SCGF equations to 3rd order truncations of the self-energy and including three-body forces. An order of magnitude increase in the precision of correlation energies and single-particle spectroscopy is expected for semi-magic nuclei. ----------------- Hatem Barghathi (U. Tennessee) A Compact Unary Coding for Bosonic States We introduce a unary coding of bosonic occupation states based on the famous "balls and walls" counting for the number of configurations of N indistinguishable particles on L distinguishable sites. Each state is represented by an integer with a human readable bit string that has a compositional structure allowing for the efficient application of operators that locally modify the number of bosons. By exploiting translational and inversion symmetries, we identify a speedup factor of order L over current methods when generating the basis states of bosonic lattice models. The unary coding is applied to a one-dimensional Bose-Hubbard Hamiltonian with up to L=N=20, and the time needed to generate the ground state block is reduced to a fraction of the diagonalization time. For the ground state symmetry resolved entanglement, we demonstrate that variational approaches restricting the local bosonic Hilbert space could result in large relative errors. ----------------- Thomas Barthel (Duke U.) Criticality and phase transitions in open quantum many-body systems In the thermodynamic limit, the nonequilibrium steady states of open quantum many-body systems can undergo phase transitions due to the competition of unitary and dissipative dynamics. We consider Markovian systems and elucidate structures of the Liouville super-operator that generates the dynamics. In many cases of interest, an operator basis transformation can bring the Liouvillian into block-triangular form, making it possible to assess its spectrum. The super-operator structure can be used to bound gaps, showing that, in a large class of systems, dissipative phase transitions are actually impossible and that the convergence to steady states is exponential [1]. A large class of translation-invariant fermionic and bosonic systems can be characterized almost completely -- ""quadratic"" systems, where the Hamiltonian is quadratic in the ladder operators, and the Lindblad operators are either linear or quadratic and Hermitian [2]. We find that one-dimensional systems with finite-range interactions cannot be critical, i.e., steady-state correlations necessarily decay exponentially. For the quasi-free case without quadratic Lindblad operators, we show that fermionic systems with short-range interactions are non-critical for any number of spatial dimensions and provide bounds on the correlation lengths. Quasi-free bosonic systems in $d>1$ dimensions can be critical. Lastly, we address the question of phase transitions in quadratic systems, finding that, without symmetry constraints beyond particle-hole symmetries, all gapped Liouvillians belong to the same phase [3]. [1] T. Barthel and Y. Zhang, ""Super-operator structures and no-go theorems for dissipative quantum phase transitions"", arXiv:2012.05505 [2] T. Barthel and Y. Zhang, ""Solving quasi-free and quadratic Lindblad master equations for open fermionic and bosonic systems"", arXiv:2112.08344 [3] Y. Zhang and T. Barthel, ""Criticality and phase classification for quadratic open quantum many-body systems"", (to be submitted shortly)" ----------------- Raymond Bishop (U. Manchester) Frustrated spin-1/2 J1–J2–J1perp Heisenberg magnet on a honeycomb bilayer: A high-order study of its phase diagram Raymond F. Bishop1,2 and Peggy H.Y. Li1,2 1Department of Physics & Astronomy, University of Manchester, Manchester, M13 9PL, UK 2School of Physics & Astronomy, University of Minnesota, Minneapolis, MN 55455, USA The frustrated spin-1/2 J1–J2 model on the honeycomb lattice has become a prototypical model in quantum magnetism. After over 30 years of investigation, and several hundreds of papers devoted to it, there is no overall consensus on the details of its quantum phase diagram. By contrast, there are far fewer papers devoted to the even more challenging, analogous bilayer models. Here we employ the coupled cluster method (CCM) [1], which has become one of the most pervasive and most successful of all ab initio formulations of quantum many-body theory. It has been applied to more systems in quantum chemistry (where it has become the "gold standard"), quantum field theory, atomic, nuclear, subnuclear, condensed matter, and other areas of physics than any other competing method. By now it has also very successfully been applied to a wide variety of highly frustrated and strongly entangled spin-lattice systems in quantum magnetism [2]. We present results for the (zero-temperature) quantum phase diagram of a spin-1/2 J1–J2–J1perp Heisenberg magnet on an AA-stacked honeycomb bilayer lattice, using the CCM implemented to very high orders [3]. On each monolayer the spins interact via nearest-neighbor (NN) and frustrating next-nearest-neighbor isotropic antiferromagnetic Heisenberg interactions with respective strength parameters J1 > 0 and J2 \equiv \kappa J1 > 0. The two layers are coupled via NN interlayer pairs of spins interacting via a similar interaction of strength J1perp \equiv \delta J1. We locate with high accuracy the complete phase boundaries in the \kappa-\delta half-plane with \kappa > 0 of the two collinear antiferromagnetic phases with (the two-sublattice) Neel and (four-sublattice) Neel-II magnetic order in each monolayer, and the interlayer NN pairs of spins either anti-aligned (for \delta > 0) or aligned (for \delta < 0) to one another. [1] R.F. Bishop, Theor. Chim Acta 80, 95 (1991). [2] D.J.J. Farnell and R.F. Bishop, in Quantum Magnetism (eds. U. Schollwoeck, J. Richter, D.J.J. Farnell and R.F. Bishop), Lecture Notes in Physics Vol. 645, Springer-Verlag, Berlin (2004), 307. [3] P.H.Y. Li and R.F. Bishop, eprint arXiv:2109.14390 (2021). ----------------- Jordi Boronat (UPC, Barcelona) Finite-range effects in dilute quantum gases Some recent experimental data of different dilute Bose and Fermi gases have shown effects that go beyond the description of these systems with a purely contact interaction. Up to very recently, all the physics of these dilute gases has been studied with interactions that depend only on the value of the s-wave scattering length. We have introduced in the analysis the effective range, which is is the first energy correction to the s-wave scattering. Using quantum Monte Carlo techniques, we have shown that the universality of the equations of state of these systems can be extended if one considers the effective range in addition to the scattering length. With these data we have built a new density functional for attractive Bose mixtures that can explain some experimental data which did not match with existing theory. Similar effects have been observed in the determination of critical numbers for the stability of dipolar drops and in the two-dimensional Fermi polaron. ----------------- Aurel Bulgac (U. Washington) Unraveling The Many Facets of Non-Equilibrium Fission Dynamics: A Real-Time Quantum Approach When comparing nuclear fission at the venerable age of almost 84 years old with other quantum many-body systems (superconductivity, superfluidity, quantum Hall effect, fractional quantum Hall effect, magnetism, etc.) it is surprising to find out how little is known and microscopically justified for this complex quantum non-equilibrium process. In the last decade a significant advancenment was achieved in modeling and disentangling aspects of fission, by means of a pure quantum approach. The level of agreement with observations, without the resort to any unverified theoretical assumptions, uncontrolled numerical approximations, or phenomenology and incorporating only the basic input needed to reproduce most of the well-known properties of nuclei, is surprisingly good. The theoretical framework requires only eight input parameters at most: the nuclear saturation density and energy, surface tension, the symmetry energy and its density dependence to a lesser degree, proton charge, the spin-orbit and the nuclear pairing interaction strengths. Some of our foremost theoretical findings are: i) the strongly- damped character of the large amplitude collective motion beyond the outer saddle-point, ii) the fission fragment excitation energies and its sharing mechanism, and the somewhat surprising excitation energy exchange mechanism between the fission fragments before the fission fragments are fully accelerated, iii) the intrinsic fission fragment spins and their unexpected correlation character, iv) the nature and the properties of the non-equilibrium neutrons emitted before the fission fragments are fully accelerated, v) the strongly damped character of the fission fragment shape evolution after they are spatially separated, vi) the total kinetic energy of the fission fragments, vii) and the evolution of these properties with the initial excitation energy of the compound nucleus. ----------------- Julie Butler (MSU/NSCL) Application of Machine Learning to Many-Body Studies of Infinite Nuclear Matter Neutron stars are extremely cold and dim, making observational astronomy difficult. Therefore, the only way to study them is through many-body studies of their constituent particles using state-of-the-art many-body methods with modern nuclear forces. However, many-body computations of infinite nuclear matter involve a large number of particles and complex potentials. This has a high computational cost, making large studies difficult. Machine learning is emerging as a useful tool in physics that will allow us to tackle problems which are difficult to solve with traditional computational methods. This talk will explore ways in which machine learning can speed up many-body calculations of infinite nuclear matter while still maintaining physically relevant accuracy. Ridge regression and kernel ridge regression will be applied using a variety of algorithms to find converged energies, extrapolate to the thermodynamic limit, and to find coupled cluster correlation energies using only data from many-body perturbation theory calculations. Accuracy compared to full calculations and time savings will be presented to justify the use of machine learning as a valid computational method for these calculations. This project is funded by NSF Grants No. PHY-1404159 and PHY-2013047. ----------------- Zohreh Davoudi (U. Maryland) A quantum-simulation program for QCD? The strong force in nature, described by the quantum and relativistic framework of quantum chromodynamics or QCD, has long generated an active and growing field of research and discovery. In fact, despite its development over many decades ago, it still leaves us with plenty of exciting questions to explore in the 21st century: Can we learn the phase diagram of matter governed by strong interactions? Can we predict how matter evolves and thermalizes after energetic processes such as in the early universe or in terrestrial particle colliders? How do elementary particles in QCD, quarks and gluons, and their interactions give rise to the complex structure of a proton or a nucleus? While an extremely successful theoretical and computational program called lattice QCD has enabled a first-principles look into some properties of matter, we have yet to come up with a computationally more capable tool to predict the complex dynamics of matter from the underlying interactions. Can a large reliable (digital or analog) quantum simulator eventually enable us to study the strong force? What does a quantum simulator have to offer to simulate QCD and how far away are we from such a dream? In this talk, I will describe a vision for how we may go on a journey toward quantum simulating QCD, by taking insights from early to late developments of lattice QCD, by motivating the need for novel theoretical, algorithmic, and hardware approaches to quantum-simulating this unique problem, and by providing examples of the early steps taken to date in establishing a quantum-computational lattice-QCD program. ----------------- Adrian Del Maestro (U. Tennessee) Equivalence of Spatial and Particle Entanglement Growth After a Quantum Quench We analyze fermions after an interaction quantum quench in one spatial dimension and study the growth of the steady-state entanglement entropy density under either a spatial mode or particle bipartition. For integrable lattice models, we find excellent agreement between the increase of spatial and particle entanglement entropy, and for chaotic models, an examination of two further neighbor interaction strengths suggests similar correspondence. This result highlights the generality of the dynamical conversion of entanglement to thermodynamic entropy under time evolution that underlies our current framework of quantum statistical mechanics. ----------------- Yi-Hsien Du (U. Chicago) Decay rate of the Tkachenko mode We construct the nonlinear theory of the Tkachenko mode in a rotating 2D superfluid. We show how the symmetries of the theory determine the behavior of the decay rate of the Tkachenko mode in the long-wavelength limit. ----------------- Florian Ehmann (TU Darmstadt) A Pairing Field Approach to Ultracold Fermi Gases We formulate the dynamics of a two-species Fermi gas in terms of a bosonic pairing field which provides a very natural and direct access to its basic observables like energy and density and to order parameters and correlation functions that allow us to study the phase structure of such Fermi gases. ----------------- Jonathan Engel (UNC Chapel Hill) Solving Nuclear Structure Problems with the Adaptive Variational Quantum Algorithm With the Lipkin model and the valence shell model as examples, I show that the Adaptive Variational Quantum Algorithm works well in nuclear-structure problems that involve phase transitions and symmetry breaking at the mean-field level. The number of quantum operations needed to find the ground-state energy scales linearly with the number of nucleons in these models as long as the noise level is below a certain threshold. The results suggest that near- and intermediate-term quantum computers will be useful for nuclear-structure theory. ----------------- Keisuke Fujii (U. Heidelberg) Universal induced interaction between heavy polarons in superfluids ---Effective field theory approach to polaron physics--- The force between particles is one of the most elementary concepts from condensed-matter physics to high-energy physics. Not only the fundamental interaction mediated by gauge bosons but also the induced interaction between quasiparticles plays an essential role in modern physics. Recently, impurities in superfluids, called polarons, have been attracting much attention in ultracold atom physics. In particular, thanks to the high experimental controllability of ultracold atoms, induced interactions between two polarons of ultracold atoms are an appealing topic with the potential to be confirmed experimentally. In this work, we investigate the long-range behavior of the induced interaction between two spinless heavy impurities in a superfluid. With the help of an effective field theory, we show that the induced interaction universally exhibits power-law behaviors at both zero and finite temperatures and that the magnitude of the potential depends on the medium properties only through the speed of sound [1]. Our formulation provides a new approach to polaron physics using effective field theory and is valid regardless of the interaction strength between the medium particles. We apply our results to the fermionic superfluid showing the BCS-BEC crossover and evaluate the magnitude of the obtained potential using experimental data of the sound velocity. Our results, understood as a phonon-mediated Casimir force, provide new insights not only as polaron physics in ultracold atomic systems but also as induced forces in symmetry-breaking phases. [1] K. Fujii, M. Hongo, and T. Enss, "Universal van der Waals force between heavy polarons in superfluids," arXiv:2206.01048 (2022). ----------------- Thomas Gasenzer (U. Heidelberg) Universal dynamics near non-thermal fixed points Quenched quantum systems can show universal dynamics near non-thermal fixed points, generically in the form of scaling behaviour in space and time [1-3]. Systems where such fixed points can be realized range from post-inflationary evolution of the early universe to low-energy dynamics in cold gases. Effective field theories hold promise to describe the non-perturbative infrared dynamics by allowing to identify the relevant degrees of freedom. The status of different examples and their relevance to near-linear quasiparticle dynamics as well as to the strongly non-linear dynamics of solitary waves and topological defects will be discussed. [1] C.-M. Schmied, A. N. Mikheev, T. Gasenzer, Non-thermal fixed points: Universal dynamics far from equilibrium, Int. J. Mod. Phys. A 34, no. 29 (2019) arXiv:1810.08143 [cond-mat.quant-gas]. [2] M. Pruefer et al., Observation of universal dynamics in a spinor Bose gas far from equilibrium, Nature 563, 217 (2018). [3] S. Erne et al., Universal dynamics in an isolated one-dimensional Bose gas far from equilibrium, Nature 563, 225 (2018). ----------------- Antoine Georges (College de France and Flatiron Institute) What have we learned from Dynamical Mean Field Theory and what lies ahead ? Dynamical Mean-Field Theory (DMFT) provides an original physical perspective on strongly correlated electron materials, as well as an efficient computational framework to understand and predict their properties. In this talk, I will review the main ideas at the heart of the DMFT construction and physical perspective. Through select examples, I will outline how the efforts of a whole community over almost three decades have managed to develop the theory to such a point that it can successfully be applied to a real material, taking into account its structure and chemical composition. I will also outline how the theory is being extended and generalized in many fruitful directions. ----------------- Gaute Hagen (ORNL) Advances in coupled-cluster computations of nuclei High performance computing, many-body methods with polynomial scaling, and ideas from effective-field-theory is pushing the frontier of ab-initio computations of nuclei. Here I report on advances in coupled-cluster computations of nuclei starting chiral Hamiltonians with two- and three-nucleon forces. Global surveys of bulk properties of medium-mass and neutron-rich nuclei from ab-initio approaches are now becoming possible by using reference states that break symmetries. These calculations have revealed systematic trends of charge radii in various isotopic chains, questioned the existence of certain magic shell closures in neutron-rich nuclei, and confrontation with data have exposed challenges for ab-initio theory. The restoration of broken rotational symmetry in coupled-cluster calculations allow us to address rotational structure of nuclei, and with this approach we recently have made predictions for excited states in neutron-rich neon isotopes. New ways to make quantified predictions are becoming possible by the development of accurate emulators of ab-initio calculations. These emulators reduce the computational cost by many orders of magnitude allowing for billions of simulations of nuclei using modest computing resources. This allows us to perform global sensitivity analysis, quantify uncertainties, and use novel statistical tools in predicting properties of nuclei. Using these tools together with delta-full chiral interactions at next-to-next-to leading we made predictions for the neutron-skin of 208Pb, the heaviest nucleus computed within an ab-initio framework to date. Finally, based on arguments from effective field theory we recently renormalized coupled-cluster with singles and doubles to account for short-range triples excitations by adjusting a three-body contact. With this approach we accurately reproduce binding energies from medium mass to heavy nuclei. These developments demonstrate how realistic two- and three-nucleon forces act in atomic nuclei and allow us to make quantitative predictions across the nuclear landscape. ----------------- David Jansen (Georg-August-Universitaet Goettingen) DMRG methods for dynamical properties of electron-phonon systems at finite temperatures We compute the optical conductivity for the Holstein polaron and bipolaron with dispersive phonons at finite temperature using a matrix-product state-based method [1]. We combine purification [2], to obtain the finite-temperature states [3], together with the parallel time-dependent variational principle (pTDVP) [4] algorithm to compute the real-time current-current correlation functions. The pTDVP algorithm utilizes local basis optimization [5] to efficiently treat the phononic degrees of freedom. For the polaron, we find that the phonon dispersion alters the optical conductivity at several temperatures in the weak, intermediate, and strong coupling regimes. In the first two cases, we see that the spectrum goes from being continuous to discrete when going from an upwards to a downwards phonon dispersion relation. In the strong coupling regime, the dispersion leads to a shift of the center of the spectrum. For the bipolaron, we also see that the dispersion shifts the spectrum. The results fit well with an analytical expression derived from the Born-Oppenheimer Hamiltonian. [1] Jansen et al., arXiv:2206.00985 (2022) [2] Verstraete et al., Phys. Rev. Lett. 93, 207204 (2004) [3] Jansen et al., Phys. Rev. B 102, 165155 (2020) [4] Secular et al., Phys. Rev. B 101, 235123 (2020) [5] Zhang et al., Phys. Rev. Lett. 80, 2661 (1998) ----------------- Yosuke Kanai (UNC Chapel Hill) All-electron Bethe-Salpeter equation approach for core electron excitation I will discuss an accurate first-principles computational approach to calculate absolute K-edge core electron excitation energies as measured by X-ray absorption spectroscopy. Our approach employs an all-electron Bethe-Salpeter equation (BSE) formalism based on GW approximation to Hedin's equations (BSE@GW). The many-body perturbation theory formalism has become an increasingly popular method for first-principles computation of neutral valence excitation energies of condensed matter and molecular systems in the last few decades. However, its application to core electron excitation has been largely unexplored. I will discuss the influence of different approximations in the BSE@GW calculation and show its great accuracy with a benchmark set of small organic molecules, previously used for the equation-of- motion coupled cluster method. ----------------- Ribhu Kaul Duality and Domain Wall Dynamics in CoNb2O6 CoNb2O6 is a beautiful realization of a material with weakly coupled one dimensional easy axis magnetism. In this talk I will discuss how the symmetry of the crystal structure of this material creates rich domain wall dynamics, described by the SSH model of polyacetylene. Theoretical studies of a simple model for the spin-orbit coupled magnetism describes the rich structure of THz spectra and its evolution in a transverse field. Close to a critical point the THz data shows universal behavior and the first direct observation of the celebrated Kramers-Wannier duality in a physical system. ----------------- Nitin Kaushal (Oak Ridge National Lab) Magnetic ground states of honeycomb lattice Wigner crystals In recent years, Moire materials constructed using two layers of transition metal dichalcogenides have been used to simulate the Hubbard model on triangular lattice procuring strongly correlated physics in half-filled (n=1) flat bands. Lattice Wigner crystal states, at other fractional fillings like n=2/3, 1/2, and 1/3, are also stabilized by long-range Coulomb interactions in these two-dimensional triangular Moire lattices. Recent ab-initio work on the Gamma-valley transition metal dichalcogenide homobilayers unveiled effective moiré honeycomb lattices near the Fermi level. We employ largescale unrestricted Hartree-Fock techniques to unveil the magnetic phase diagrams of honeycomb lattice Wigner crystals. For the three lattice filling factors with the largest charge gaps, n = 2/3, 1/2, 1/3, the magnetic phase diagrams contain multiple phases, including ones with non-collinear and noncoplanar spin arrangements. We discuss magnetization evolution with the external magnetic field, which has potential as an experimental signature of these exotic spin states. Our theoretical results could potentially be validated in Moire materials formed from group VI transition metal dichalcogenide twisted homobilayers. ----------------- Lex Kemper (NCSU) Lie algebraic generation of quantum circuits Unitary synthesis, e.g. in constructing unitary coupled cluster factors or for evolution under a time dependent Hamiltonian is a key component of quantum simulation on quantum computers. Synthesizing the corresponding quantum circuit is typically done by breaking the operator into small circuit elements, named Trotter decomposition, which leads to circuits whose depth often scales unfavorably. We present two algorithms to help overcome these difficulties. First, it is possible to synthesize exact quantum circuit representations of the desired time evolution unitaries. This is accomplished by considering the Lie algebra generated by the Hamiltonian, and partitioning it via Cartan decomposition. Coupled with an appropriate ansatz, this method yields an exact time evolution unitary, with polynomial or exponential circuit depth depending on the model under consideration. Second, when the circuit elements of the Trotter decomposition are limited to a subset of SU(4) - or equivalently, when the Hamiltonian may be mapped onto free fermionic models - several identities exist that combine and simplify the circuit. Based on this, we present an algorithm that compresses the circuit elements into a single block of quantum gates. This results, for example, in a fixed depth time evolution for certain classes of Hamiltonians. We explicitly show how this algorithm works for several spin models, and demonstrate its use for adiabatic state preparation of the transverse field Ising model. Based on these ideas, we will also present an extension to controlled gates and imaginary time evolution. ----------------- Jane Kim (MSU/NSCL) Neural Network Ansätze for Infinite Matter Artificial neural networks have shown tremendous promise as a flexible ansatz for quantum many-body problems. In this work, we approximately solve the Schroedinger equation by performing variational Monte Carlo calculations with a deep, permutation-invariant neural network as a Jastrow correlator. We discuss the reinforcement learning scheme and the stochastic reconfiguration algorithm which helps stabilize the optimization of the wave function parameters. Ground state energies for the three-dimensional electron gas and infinite neutron matter will be compared to standard variational and diffusion Monte Carlo results. This work is supported by the U.S. National Science Foundation under grants No. PHY-1404159 and PHY-2013047. ----------------- Dean Lee (MSU/FRIB) Lattice simulations for the nuclear many-body problem This talk presents Monte Carlo lattice simulations for the nuclear many-body problem and several new algorithms developed by the Nuclear Lattice Effective Field Theory Collaboration. Some recent results are presented, including the structure of the nuclear states of carbon-12 and a new approach called wave function matching that allows for Monte Carlo simulations using a high-fidelity Hamiltonian that would otherwise produce a severe sign problem. ----------------- Alessandro Lovato (Argonne National Lab) Neural network quantum states for atomic nuclei Artificial neural networks have proven to be a flexible tool to compactly represent quantum many-body states in condensed matter, chemistry, and nuclear physics problems, where non-perturbative interactions are prominent. In this talk, I will present a neural-network quantum ansatz suitable to represent the ground-state wave function of atomic nuclei in a systematically improvable fashion. Using efficient stochastic sampling and optimization schemes, we solve the nuclear many-body Schroedinger equation for a leading-order pionless effective field theory Hamiltonian. The binding energies and point-nucleon densities of nuclei with up to A=16 nucleons are benchmarked against accurate quantum Monte Carlo and hyperspherical harmonics results. ----------------- Piotr Magierski (Warsaw U. of Technology) Spin-polarized vortices with reversed circulation. I will present the analysis of the structure of fermionic vortices with the spin-polarized core from a weak coupling limit to the unitary regime. The mechanism for the generation of the reversed circulation in the vortex core induced by an excess of majority spin particles will be described. Selected issues related to fermionic vortex dynamics in ultracold gases will be discussed in the light of recent experiments. ----------------- Francesco Marino (U. Milan) Ab initio-based nuclear energy functionals: Constraints from the nuclear matter response Ab initio methods [1] hold the promise of allowing to determine all the structural properties of nuclei and infinite nucleonic matter, starting from the individual interactions between protons and neutrons. Despite recent remarkable progress, full-scale studies of heavy nuclei are still out of reach. By contrast, Density Functional Theory (DFT) [2] can be readily applied to ground-state and excited-state properties across the whole nuclear chart. However, the Energy Density Functionals (EDFs), the key quantities in DFT, are phenomenological and biased towards stable nuclei close to magicity. Shortcomings of the empirical EDFs manifest themselves far from the stability valley, e.g. in neutron-rich nuclei or pure neutron matter (PNM). To accompany the growing experimental research efforts devoted to unstable nuclei at the limits of the nuclear chart, there is a strong need for improving the theoretical tools at our disposal. In this contribution, we wish to discuss our approach, inspired by the "Jacob's ladder" of condensed matter DFT [3], that aims at constructing ab initio-constrained EDFs. We shall first present the first rung [4], called local density approximation (LDA), that exploits the equation of state of nucleonic matter as sole input. Then, we describe our current work, in which the static response [5] of both PNM and symmetric nuclear matter to an external potential is computed by means of ab initio techniques, namely the Quantum Monte Carlo and the Self-consistent Green's functions approach, and exploited to constrain the gradient terms of the nuclear EDF. [1] H. Hergert, Front. Phys. 8, 00379 (2020) [2] G. Colò, Advances in Physics: X 5, 1740061 (2020) [3] J. P. Perdew and K. Schmidt, AIP Conf. Proc. 577, 1 (2001) [4] F. Marino et al., Phys. Rev. C 104, 024315 (2021). [5] M. Buraczynski et al., Physics Letters B 818, 136347 (2021) ----------------- Frederic Mila (EPFL, Lausanne, Switzerland) Thermal properties of frustrated quantum magnets The thermal properties of frustrated quantum magnets are a real challenge because, when formulated in the natural configuration basis, Quantum Monte Carlo simulations suffer from a very serious minus sign problem that excludes simulations below temperatures of the order of the coupling constants. In this talk, I will review recent numerical progress made on two fronts: (i) Quantum Monte Carlo simulations in the dimer basis [1]. In this basis, there is no minus sign problem for fully frustrated models, and simulations can be performed down to arbitrarily low temperature. With these simulations, we have identified the presence of a thermal critical point terminating a line of first-order transitions in the fully frustrated bilayer model [1]. (ii) Tensor network simulations [2,3]. Using ancilla spins and a partial trace, the thermal ensemble can be accurately obtained by imaginary time evolution of a purified state, leading to reliable results down to temperatures only a few percents of the coupling constants regardless of the level of frustration. Using this approach, we have been able to show that the peak of the specific heat around 2 GPa and 4 K in SrCu2(BO3)2 is a thermal critical point akin to that of the fully frustrated bilayer [2], and to numerically verify the long-standing prediction that the spin-1/2 J1-J2 model on the square lattice has a thermal Ising transition for large enough J2/J1 [3]. [1] J. Stapmanns, P. Corboz, F. Mila, A. Honecker, B. Normand, and S. Wessel, Phys. Rev. Lett. 121, 127201 (2018). [2] J. Larrea Jimenez, S. P. G. Crone, E. Fogh, M. E. Zayed, R. Lortz, E. Pomjakushina, K. Conder, A. M. Läuchli, L. Weber, S. Wessel, A. Honecker, B. Normand, Ch. Rüegg, P. Corboz, H. M. Ronnow and F. Mila, Nature 592, 370 (2021). [3] O. Gauthe and F. Mila, Phys. Rev. Lett. 128, 227202 (2022)." ----------------- Rubem Mondaini (CSRC) Hamming Distance and the onset of quantum criticality Simulating models for quantum correlated matter unveils the inherent limitations of deterministic classical computations. In particular, in the case of quantum Monte Carlo methods, this is manifested by the emergence of negative weight configurations in the sampling, that is, the sign problem (SP). There have been several recent calculations which exploit the SP to locate underlying critical behavior [1, 2, 3]. In this talk, I plan to show that by utilizing a metric that quantifies phase-space ergodicity in such sampling, the Hamming distance, a significant advance on these ideas to extract the location of quantum critical points in various fermionic models is obtained, in spite of the presence of a severe SP. Combined with other methods, exact diagonalization in our case, it elucidates both the nature of the different phases as well as their location, as we demonstrate explicitly for the honeycomb and triangular Hubbard models, in both their U(1) and SU(2) forms. By directly tackling properties of the auxiliary-fields, our approach exemplifies a possible path to circumvent inherent limitations imposed by the SP, allowing the exploration of the phase diagram of a variety of fermionic quantum models hitherto considered to be impractical via quantum Monte Carlo simulations [4]. [1] Quantum critical points and the sign problem, R. Mondaini, S. Tarat, R Scalettar, Science 375, 418 (2022) [2] Universality and Critical Exponents of the Fermion Sign Problem, R. Mondaini, S. Tarat, R. Scalettar, submitted (2022) [3] Deconvolving the components of the sign problem S. Tarat, B. Xiao, R. Mondaini, R. Scalettar Physical Review B 105, 045107 (2022) [4] Hamming Distance and the onset of quantum criticality, T. Yi, R. Scalettar, R. Mondaini arXiv preprint, arXiv:2111.12936 ----------------- Megan Moss (U. Waterloo) Combining data-driven and Hamiltonian-driven training for learning quantum ground states. Rydberg atom arrays are programmable quantum simulators capable of preparing interacting qubit systems in a variety of quantum states. Due to long experimental preparation times, obtaining projective measurement data can be relatively slow for large arrays, which poses a challenge for state reconstruction methods such as tomography. Today, novel groundstate wavefunction ansätze like recurrent neural networks (RNNs) can be efficiently trained not only from projective measurement data, but also through Hamiltonian-guided variational Monte Carlo (VMC). In the linked paper, we demonstrate how pretraining modern RNNs on even small amounts of data significantly reduces the convergence time for a subsequent variational optimization of the wavefunction. This suggests that essentially any amount of measurements obtained from a state prepared in an experimental quantum simulator could provide significant value for neural-network-based VMC strategies. This talk will focus on how the straight-forward combination of these two training methods (for the same RNN wavefunction) allows one to leverage all available information about a quantum system. ----------------- Mario Motta (IBM) Experimental realization of a measurement-induced entanglement phase transition on a superconducting quantum processor Authors: Jin Ming Koh, Shi-Ning Sun, Mario Motta, and Austin J. Minnich Ergodic many-body quantum systems undergoing unitary dynamics evolve towards increasingly entangled states, characterized by an extensive scaling of entanglement entropies (1). At the other extreme, repeatedly measured quantum systems may be stabilized in a measurement eigenstate, a phenomenon known as the quantum Zeno effect (2). Recently, the intermediate regime in which unitary evolution is interspersed with measurements has become of interest. Numerical studies have reported the existence of distinct phases characterized by volume- and area-law entanglement entropy scaling for low and high measurement rates respectively, separated by a critical measurement rate (3). The experimental investigation of these dynamic quantum phases of matter on near-term quantum hardware is challenging due to the need for repeated high-fidelity mid-circuit measurements and fine control over the evolving unitaries. Here (4), we report the realization of a measurement-induced entanglement transition on superconducting quantum processors with mid-circuit readout capability. We observe extensive and sub-extensive scaling of entanglement entropy in the volume- and area-law phases, respectively, by varying the rate of projective measurements. We further establish the critical nature of the entanglement transition by extracting the critical exponents. Our work paves the way for the use of mid-circuit measurement as an effective resource for quantum simulation on near-term quantum computers, for instance by facilitating the study of dynamic and long-range entangled quantum phases. References: 1) P. Calabrese and J. Cardy, J. Stat. Mech. P04010 (2005) 2) B. Misra and E. C. G. Sudarshan, J. Math. Phys. 18, 756 (1977) 3) B. Skinner et al, Phys. Rev. X 9, 031009 (2019) 4) J. M. Koh et al, arXiv:2203.04338 (2022) ----------------- Takashi Nakatsukasa (U. Tsukuba) Requantization of TDDFT on collective subspace In nuclear physics, the linearized TDDFT often fails to reproduce properties of low-energy modes of excitation. They are basically collective modes of a large amplitude nature, and the failure is due to missing correlations associated with these low-energy collective motions. The microscopic unified description of nuclear structure and reaction is also a big challenge for us. In order to achieve these goals, we adopt a method to "requantize" the TDDFT on a selected collective subspace. In this presentation, I present a basic idea of the methodology, then, show some recent applications, including low-energy nuclear reactions of element synthesis in giant stars. ----------------- Yusuke Nishida (Tokyo Tech.) Nonrelativistic conformality and hydrodynamics I will review the conformal invariance in nonrelativistic systems and its physical consequences relevant to ultracold atom physics. In particular, I will show that the conformal invariance even constrains how the spacetime-dependent scattering length enters hydrodynamic equations, which is found to be useful as a probe of the bulk viscosity. Recent progress on the bulk viscosity regarded as contact correlation will also be discussed. ----------------- Gerardo Ortiz (Indiana U.) Fundamentals of Entangled Probes for Entangled Matter Advancing the frontiers of science often requires the creation of new probes to uncover the underlying microscopic mechanisms giving rise to exotic macroscopic phenomena, such as high-temperature superconductivity. Can quantum entangled probes uncover the inherent entanglement of the target matter? We have recently [1,2] developed an entangled neutron beam where individual neutrons can be entangled in spin, trajectory and energy. To demonstrate entanglement in these beams we crafted neutron interferometric measurements of contextuality inequalities whose violation provided an indication of the breakdown of Einstein's local realism. In turn, the tunable entanglement (spin-echo) length of the neutron beam from nanometers to microns and energy differences from peV to neV opens a pathway to a future era of entangled neutron scattering in matter. What kind of information can be extracted with this novel entangled probe? A recent general quantum many-body entangled-probe scattering theory [3] provides a framework to respond to this question. Interestingly, by carefully tuning the probe's entanglement and inherent coherence properties, one can directly access the intrinsic entanglement of the target material. This theoretical framework supports the view that our entangled beam can be used as a multipurpose scientific tool. We are currently [4] pursuing several ideas and developing new spin-textured entangled beams with OAM for future experiments in candidate quantum spin liquids, unconventional superconductors, and chiral quantum materials. [1] J. Shen {\it et. al.}, Nature Commun. {\bf 11}, 930 (2020). [2] S. Lu {\it et. al.}, Phys. Rev. A {\bf 101}, 042318 (2020). [3] A. A. Md. Irfan, P. Blackstone, R. Pynn, and G. Ortiz, New J. Phys. {\bf 23}, 083022 (2021). [4] Q. Le Thien, S. McKay, R. Pynn, and G. Ortiz, arXiv:2207.12419. ----------------- Aavishkar Patel (Flatiron Institute) Strange Metals: Strongly Correlated Quantum Matter with Spatially Random Interactions Non-Fermi liquid metallic phases are widespread in two-dimensional or quasi two-dimensional materials with strongly correlated electrons, displaying electrical resistances that famously vary linearly with temperature (T) at low temperatures, in stark contrast to the higher powers of temperature predicted by Fermi liquid theory. This robust phenomenon, as well as other experimental observations, suggest that electrons must undergo inelastic collisions that do not conserve momentum, i.e. spatial disorder affects the interactions between electrons. I will describe a body of theoretical work on the controlled computation of the transport properties of non-Fermi liquids, allowing for the careful consideration of the role of interactions, disorder, and disordered interactions, and culminating in a realistic and universal model for the ubiquitous T-linear resistivity. Ongoing work on the study of these models using computational methods will also be touched upon. ----------------- Francesco Pederiva (Trento U.) First baby-steps in the simulation of nuclear reactions on quantum computers Quantum computers are based on the propagating of a quantum state according to a unitary transformation. One of the most straightforward applications of this concept is the study of the time evolution of an arbitrary state, mapped on a set of qubits, which can simulate the time evolution of a physical system of interest. This operation, hard to implement for a many-body system, becomes even harder for a many-nucleon system, where the very nature of the effective nucleon-nucleon force introduces an exponentially growing complexity because of the explicit spin/isospin dependence. In this contribution we want to present some first steps that we have taken in order to develop a practical protocol for simulating on a quantum device a nuclear reaction, starting from the case of two neutrons interacting with a simple LO chiral force. We will present some results focused on the evolution of spins, first considering fixed coordinates, then introducing a classical evolution of the position in order to study the feasibility of the study of a parametrically evolving Hamiltonian on present available NISQ devices, the first step necesary to start thinking of simulating more complex situations. ----------------- Natalia Perkins (U. Minnesota) Disorder in the Kitaev spin liquid Quantum spin liquid (QSL), an exotic magnetic phase with fractionalized spin excitations and intricate entanglement structure, has been pursued both theoretically and experimentally since its first proposal by Anderson in 1973. Theoretical models and candidate materials with strong geometrical or exchange frustration are expected to greatly reduce the ordering temperature and reveal the quantum fluctuations. However, the presence of residual interactions in real systems usually leads to magnetic ordering and shatters the hope for finding QSL. Nevertheless, various compounds were discovered with no magnetic ordering even down to the lowest measurable temperature, and commonly the quenched randomness was found to serve as a potential cause of the sustaining disordered phase and intriguing dynamics of low-energy degrees of freedom. Therefore, the competition between quantum fluctuations and randomness raises a critical question about the true nature of the low-energy phase in those materials. In some Kitaev materials, the so-called second-generation Kitaev materials, experimentally observed peculiar low-energy excitations may be ascribable to spin fractionalization in weakly disordered QSL, but it may also relate to the random singlet (RS) phase in strongly disordered magnets. In my talk, I will discuss these possible scenarios by considering disorder in the exactly solvable Kitaev spin liquid. ----------------- Dmytro Pesin (U. Virginia) Coherence properties of a Raman-coupled pseudospin-1/2 BEC We consider the dynamics of first- and second-order coherences for two Raman-coupled Bose-Einstein condensates. This system was proposed to host a stripe phase with supersolid properties in Li et al., Nature, 543, 91-94 (2017). We show that the existence of the stripes - density modulation induced by the Raman lasers - is determined by the first order coherence between dressed condensates. It typically exists in single-shot experiments, but is a transient phenomenon if averaged over many measurements. However, the Brag scattering signal, actually studied in the work by Li et al., is determined by the second-order coherence, and exists even at long times. ----------------- Pierbiagio Pieri (U. Bologna) FFLO correlations in polarized ultracold Fermi gases M. Pini1,2, P. Pieri 3,4, G. Calvanese Strinati1,5 1 CNR-INO, Istituto Nazionale di Ottica, Sede di Sesto Fiorentino, 50019 (FI), Italy. 2 Max-Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany. 3 Dipartimento di Fisica e Astronomia, Universita di Bologna, I-40127 Bologna (BO), Italy 4 INFN, Sezione di Bologna, I-40127 Bologna (BO), Italy. 5 School of Science and Technology, Physics Division, Universita di Camerino, 62032 Camerino (MC), Italy. Quite generally, an imbalance between the densities of spin-up and spin-down fermions hinders pairing and superfluidity in two-component attractive Fermi gases. The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, in which pairs condense at a finite value of center-of-mass momentum to compensate for the mismatch of the two Fermi surfaces, was proposed many years ago as a possible superfluid phase compatible with a finite polarization. In this talk, I will discuss how significant precursor FFLO fluctuation effects appear already in the normal phase of polarized Fermi gases, and how they could be observed experimentally. At zero temperature, I will also discuss how the quasi-particle parameters of the normal Fermi gas are changed when approaching an FFLO quantum critical point. Within a fully selfconsistent t-matrix approach we find that the quasi-particle residues vanish, and the effective masses diverge at the FFLO quantum critical point, with a complete breakdown of the quasi-particle picture that is similar to what is found in heavyfermion materials at an antiferromagnetic quantum critical point. ----------------- Michael Pottoff (U. Hamburg) Interacting Chern Insulator in Infinite Spatial Dimensions Strong electron correlations and topological classification are two major research frontiers of condensed-matter theory. While much work has been done for noninteracting systems and for correlated one-dimensional models, much less is known for correlated systems in two and higher dimensions. Here, we discuss a generic model of a Chern insulator supplemented by a Hubbard interaction in arbitrary even dimension D and demonstrate that the model remains well defined and nontrivial in the infinite-D limit. Dynamical mean-field theory is applicable and predicts a phase diagram with a continuum of topologically different phases separating a correlated Mott insulator from the trivial band insulator. This provides us with exact results for a topologically nontrivial and strongly correlated system. We discuss various features, such as the elusive distinction between insulating and semimetal states, which are unconventional already in the noninteracting case. Topological phases are characterized by a nonquantized Chern density replacing the Chern number in the infinite-D limit. see: Phys. Rev. Lett. 126, 196401 (2021) ----------------- Khandker Quader (Kent State U.) e-DMFT based Correlation-Temperature Phase Diagram of Prototypical Rare-earth Nickelates Abstract: Materials whose properties are influenced by presence of f- of d-electrons are of current interest in condensed matter as they demonstrate a wide array of novel properties. Interest in the nickelates, RNiO2 (R=La, Nd, Pr) stem from the recent discovery of superconductivity upon doping these systems. Precision many-body methods such as dynamical mean-field theory (DMFT) can be used to study properties at finite temperatures, that can be compared with experiments. In this talk, after a brief discussion of the DMFT scheme, I will discuss, as an example, our recent self-consistent e-DMFT calculations* on the prototypical LaNiO2 compound. We propose a phase diagram based on our results for spin susceptibility, self-energy, scattering rate, spectral function, and magnetization for several values of the correlation U, and a wide range of temperature. The system exhibits a variety of phases in the U-T space, with several temperature scales: Fermi liquid (with screened d-moments) at low-T; Curie-Weiss (CW) with fluctuating d-moment at sufficiently high-T; possible deviation from CW at even higher-T; in-plane anti-ferromagnetism for sufficiently large U. We compare our results with experiments. ----------------- Armin Rahmani (Western Washington U.) Probing Geometric Excitations of Fractional Quantum Hall States on Quantum Computers. Intermediate-scale quantum technologies provide new opportunities for scientific discovery, yet they also pose the challenge of identifying suitable problems that can take advantage of such devices in spite of their present-day limitations. In solid-state materials, fractional quantum Hall (FQH) phases continue to attract attention as hosts of emergent geometrical excitations analogous to gravitons, resulting from the non-perturbative interactions between the electrons. However, the direct observation of such excitations remains a challenge. Here, we identify a quasi-one-dimensional model that captures the geometric properties and graviton dynamics of FQH states. We then simulate geometric quench and the subsequent graviton dynamics on the IBM quantum computer using an optimally-compiled Trotter circuit with bespoke error mitigation. Moreover, we develop an efficient, optimal-control-based variational quantum algorithm that can efficiently simulate graviton dynamics in larger systems. Our results open a new avenue for studying the emergence of gravitons in a new class of tractable models on the existing quantum hardware. ----------------- Carlos Sa de Melo (Georgia Tech) Density induced BCS-Bose evolution in gated two-dimensional superconductors: The role of the interaction range in the Berezinskii-Kosterlitz-Thouless transition Tingting Shi1,2, Wei Zhang1, and C. A. R. Sa de Melo2 1Department of Physics, Renmin University of China, Beijing 100872, China 2School of Physics, Georgia Institute of Technology, Atlanta 30332, USA The evolution from Bardeen-Cooper-Schrieffer (BCS) to Bose superconductivity versus carrier density (n) in two-dimensional (2D) gated superconductors is discussed and the fundamental role that the interaction range plays in the Berezinskii-Kosterlitz-Thouless transition is addressed. [1] The density dependence of the critical temperature (Tc), superfluid density, order parameter, chemical potential and pair size are investigated. The most important finding is that it is essential to include classical and quantum phase fluctuations, as well as finite-ranged interactions to explain the non-monotonic behavior of Tc versus n and to guarantee that the upper bound on Tc is not exceeded in 2D superconductors, as experimentally observed in LixZrNCl [Science 372, 190 (2021)], a lithium intercalated layered nitride, and in magic-angle twisted trilayer graphene [Nature 590, 249 (2021)]. Furthermore, it is shown that the effective mass of charge carriers, their interaction strength and range can be extracted from measurements of Tc and the order parameter. [1] "Density induced BCS-Bose evolution in gated two-dimensional superconductors: The Berezinskii-Kosterlitz-Thouless transition as a function of carrier density", Tingting Shi, Wei Zhang, and C. A. R. Sá de Melo, EPL 139, 36003, (2022); doi:10.1209/0295-5075/ac7ace. See also arXiv:2106.10010v1 (2021). ----------------- Thomas Schaefer (NCSU) Stochastic Fluid Dynamics and Fluctuations in Relativistic Heavy Ion Collisions The search for a critical point in the phase diagram of QCD has motivated an experimental effort to study fluctuation observables in relativistic heavy ion physics, and a theoretical effort to develop tools based on stochastic fluid dynamics. We report on recent progress in constricting effective actions for stochastic fluid dynamics, and in performing real time simulations of stochastic fluids. ----------------- Michael Scherer (Ruhr U., Bochum) Functional RG approach to competing instabilities of the extended Hubbard model on the triangular lattice and application to Moire materials Experimental demonstrations of tunable correlation effects in magic-angle twisted bilayer graphene have put two-dimensional Moire quantum materials at the forefront of condensed-matter research. In particular, bilayers of transition metal dichalcogenides (TMDs) have further enriched the opportunities for analysis and utilization of correlations in such systems. Recently, within the latter material class, the relevance of many-body interactions with an extended range has been demonstrated. Interestingly, the interaction, its range, and the filling can be tuned experimentally by twist angle, substrate engineering and gating. Moiré hetero-bilayer TMDs can be accurately modelled by an effective extended Hubbard model on the triangular superlattice, which defines a starting point for quantum many-body approaches. In my presentation, I will discuss the Fermi surface instabilities and resulting correlated phases of hetero-bilayer TMDs employing a functional renormalization group approach with high momentum resolution. The results from this approach suggest that hetero-bilayer TMDs are unique platforms to realize topological superconductivity with high winding number which reflects in pronounced experimental signatures such as enhanced quantum Hall features. ----------------- Pragya Shukla (IIT Kharagpur) System-dependent random matrix ensembles: an unavoidable tool for many-body theories The ignorance of the detail in a complex system e.g one with many body interactions introduces a degree of randomness in its matrix representation (even in absence of disorder) and it can be modeled by a random matrix (with some or all random entries). While the statistical behavior of many body systems in ergodic regime can be well-modeled by the stationary random matrix ensembles, the non-ergodic regime requires consideration of system-dependent random matrix ensembles: those which take into account the physical constraints on the system e.g. local interactions, dimensionality, symmetry, local conservation laws. For example, the combined effect of nearest neighbor interactions and dimensionality can lead to a sparse random matrix representation of the Hamiltonian in a basis of interest, with sparsity and nature of randomness dependent on system-specific details. The statistical analysis of various many body systems requires, therefore, a thorough probing of a wide range of random matrix ensembles which is not an easy task. It is highly desirable, if possible, to identify a common mathematical structure among the ensembles and analyze it to gain information about the physical properties. Our successful search in this direction leads to Brownian ensembles as the hidden skeleton for a wide range of systems. A complete investigation of Brownian ensembles can then help us in the spectral analysis of a wide range of many body systems. ----------------- Erik Sorensen (McMaster U.) Novel phases of Kitaev Chains and Ladders Today, there is a growing class of magnetic materials where it is believed that the interactions are bond-dependent in a way first imagined by Alexei Kitaev thereby opening a way for realizing topological phases. Bond-dependent interactions are strongly frustrating for the system and hinders conventional ordering. However, in these Kitaev materials other interactions are also often present, among them the well known Heisenberg coupling and also off-diagonal Gamma terms giving rise to an exceptionally rich phase diagram. Even for the simplest models of Kitaev materials it is extremely difficult to arrive at a precise understanding of this complex phase-diagram. Hence, in order to obtain accurate results it is often useful to restrict the analysis to low-dimensions and here we mainly discuss chains and two (and more) leg ladders. Using numerical techniques, it is possible for such models to determine the phase-diagram with very high precision, including the effects of an applied magnetic field. An astonishing abundance of phases arises from the combination of frustration and applied field. In this talk I will focus on some of these phases that appear disordered, without any conventional local magnetic ordering, but where a hidden string-order can be identified. ----------------- Hanna Terletska (Middle Tennessee State U.) Understanding Electron Localization in Quantum Materials Using Quantum Cluster Embedding Tools. Understanding the fundamental mechanisms behind the exotic phases of matter emerging due to many-electron correlations in quantum materials is a grand challenge, which must be overcome to maximize technological advancement. Due to the complexity of the many-electron problem numerical treatment is often required. Over the past decades, numerical analysis has become a very powerful tool for studying strongly correlated electron systems, both clean and materials with defects. The focus of our group is to numerically model electron localization using quantum many-body techniques for strongly-correlated and disordered electron systems. Electron localization (driven by electron interactions or disorder) is a key feature of numerous quantum materials. Various exotic phases of matter with dramatic changes in electronic, magnetic, and transport properties find their roots in electron localized states. Hence, its understanding is critical for further control and optimization of quantum materials and their applications. In this talk, I will first present our results on electron localization in the Hubbard model and beyond using the Dynamical Mean Field Theory and its cluster extension. I will demonstrate how the Mott metal-insulator transition can be described in the framework of the quantum critical phase transition. These theoretical predictions have been recently confirmed experimentally by four independent experimental groups. I will also share our recent results on treating electron localization in disordered electron systems using the typical medium approach. Acknowledgments: This work is supported by NSF CAREER grant # 1944974 and NSF OAC grant # 1931367. ----------------- Alexander Tichai (TU Darmstadt) Ab initio nuclear structure from the density matrix renormalization group I present a novel many-body framework combining the density matrix renormalization group (DMRG) with the valence-space (VS) formulation of the in-medium similarity renormalization group applied to first-principle nuclear structure calculations. This hybrid scheme admits for favorable computational scaling in large-space calculations compared to direct diagonalization. The capacity of the VS-DMRG approach is highlighted in ab initio calculations of neutron-rich nickel isotopes based on chiral two- and three-nucleon interactions. I further discuss orbital entanglement in the VS-DMRG, and investigate nuclear correlation effects in oxygen, neon, and magnesium isotopes. The explored entanglement measures reveal nuclear shell closures as well as pairing correlations. ----------------- Omokuyani Udiani (MSU/FRIB) Convergence Acceleration Using Novel Insights on the In-Medium Similarity Renormalization Group and Unitary Coupled Cluster Theory The in-medium similarity renormalization group (IMSRG) and unitary coupled-cluster (UCC) are iterative operator diagonalization methods used to calculate observables of a nuclear many-body system with a nucleon-nucleon interaction. The IMSRG computes operators (called generators) known to be effective diagonalizers, to gradually eliminate off-diagonal components of a given hamiltonian. In this talk, I will introduce simple perturbative arguments on how a novel generator can be constructed to accelerate the diagonalization of a nuclear hamiltonian. I will present semi-analytic expressions for such a generator. Moreover, I will present results showing the effectiveness of this generator beyond traditional 2nd order many-body perturbation theory. I will argue the power of the generator lies within its unification of UCC and IMSRG theory. Lastly, I will propose a framework for computing this generator with an embarrassingly parallel algorithm. All results presented will be for pure and symmetric nuclear matter in a finite periodic box, using at most 2-body forces from the Minnesota and chiral N2LO-Opt potential. The ultimate aim of this work is to provide computationally efficient expressions that aid IMSRG calculations for the nuclear equation of state. ----------------- Michael Urban (U. Paris-Saclay) Fermi gases and neutron matter with low-momentum interactions We consider a two-component Fermi gas with a contact interaction from the BCS regime to the unitary limit. Starting from the idea that many-body effects should not depend on short-distance or high-momentum physics which is encoded in the s-wave scattering length, but only on momentum scales of the order of the Fermi momentum, we build effective low-momentum interactions that reproduce the scattering phase shifts of the contact interaction below some momentum cutoff. Inspired from recent successes of such methods in nuclear structure theory, we use these interactions to describe the equation of state of the Fermi gas in the framework of Hartree-Fock-Bogliubov theory with perturbative corrections. In the BCS regime, there is a range of cutoffs where we obtain fully converged results. Near unitarity, convergence is not yet reached, but we obtain promising results for the ground-state energies close to the experimental ones [1]. Results obtained in an analogous way for dilute neutron matter will be discussed, too [2]. [1] M. Urban and S. Ramanan, Phys. Rev. A 103, 063306 (2021). [2] V. Palaniappan, S. Ramanan, and M. Urban, in preparation. ----------------- Silvio Vitiello (Unicamp) Kinetic energies of 3He-4He mixtures The mixture 3He-4He is investigated in an attempt to understand discrepancies between experimental [1] and theoretical [2] values still remaining regarding the kinetic energy of the 3He component. Calculations by the variational path-integral Monte Carlo method, that we prefer to call density matrix projection method, are made at zero temperature and both components are treated employing quantum statistics. Improvements are observed, nevertheless, systems formed from 3He-4He atoms continue to offer challenges for its theoretical understanding. Work in collaboration with Sebastian Ujevic, V. Zampronio and B. R. de Abreu. [1] R. Senesi, C. Andreani, A. L. Fielding, J. Mayers, and W. G. Stirling, Phys. Rev. B 68, 214522 (2003-12). [2] M. Boninsegni, J. Chem. Phys. 148, 102308 (2018). ----------------- Dieter Vollhardt (University of Augsburg, Germany) Solving correlated electron problems in infinite dimensions The Hubbard model is the simplest lattice model of interacting electrons. The characteristic local quantum dynamics described by this model is retained even in the limit of infinite spatial dimensions, thus providing a "dynamical mean-field theory" (DMFT) of correlated electrons. In my talk I will sketch the scientific developments in the early 1960s which led to the formulation of the Hubbard model and, 25 years later, to its investigation in infinite dimensions. Then I discuss applications of DMFT to demonstrate some of the insights into the properties of correlated electrons in models and materials obtained by the DMFT community over the last three decades. ----------------- Carolyn Zhang (U. Chicago) Bulk and edge signatures of interacting Floquet systems In many examples of topological phases, there exists a bulk-boundary correspondence that relates topological invariants computed in the edge of the system to topological invariants computed in the bulk of the system. Periodically driven (Floquet) systems that are stabilized by many-body localization can also realize topological phases, some of which have no stationary analogue. It is expected that there also exists a bulk boundary correspondence in these kinds of systems. However, in most cases, only edge invariants have been obtained, and it was not known how, in general, to obtain topological invariants that one can compute in the bulk. In this talk, we present a bulk-boundary correspondence for single-particle and many-body Floquet systems in two spatial dimensions. Our correspondence is based on a general mathematical object that we call a ``flow," and we give concrete recipes for obtaining edge and bulk invariants from a given flow. In particular, we derive bulk invariants for several classes of Floquet systems, including interacting systems without symmetry and with U(1) symmetry. The bulk invariants do not require translation symmetry or flux threading. In systems with $U(1)$ symmetry, the bulk invariant can be related to both a magnetization density and a conserved edge current. ----------------- Shangshun Zhang (U. Minnesota) Ground state and low-energy excitations of a quantum critical superconductor At a quantum critical point of a metal, the critical order parameter fluctuations become soft and mediate singular interactions between electrons. For a large class of models, quantum-critical physics at low energies is described by an effective 0+1 dimensional model with an effective frequency-dependent interaction V (Omega) ~1/Omega^gamma. The value of gamma is determined by a specific microscopic model. This singular interaction gives rise to two competing tendencies towards either a non-Fermi liquid normal state or a superconducting state. In this talk, I show that the pairing of electrons wins the competition. The gap function strongly depends on frequency and possesses an array of dynamical vortices in the complex frequency plane. The vortices enter the upper half-plane one by one upon increasing gamma, and each new vortex gives rise to an additional peak in the density of states. We show that the low-energy excitations above the superconducting ground state display a traditional BCS-like behavior at gamma<1/2 but deviate from BCS behavior at gamma>1/2. These deviations lead to measurable features in the density of states and in the spectral function.