Quantum Matter

Quantum matter physics is the branch of physics that studies systems of very large numbers of particles in a condensed state, like solids or liquids. Quantum matter physics wants to answer questions like: why is a material magnetic? Or why is it insulating or conducting? Or new, exciting questions like: what materials are good to make a reliable quantum computer? Can we describe gravity as the behavior of a material? The behavior of a system with many particles is very different from that of its individual particles. We say that the laws of many body physics are emergent or collective. Emergence explains the beauty of physics laws.

Displaying 493 - 504 of 1229

Quantum Many-Body Scars and Space-Time Crystalline Order from Magnon Condensation

Tom Iadecola University of Maryland, College Park
April 30, 2019

PIRSA:19040131
Condensed Matter
Phase transition of fractional Chern insulators: QED3 and beyond

Yin-Chen He Stony Brook University
April 26, 2019

PIRSA:19040110
Condensed Matter
Application of Tensor Network States to Lattice Field Theories

Stefan Kuhn Deutsches Elektronen-Synchrotron DESY
April 26, 2019

PIRSA:19040109
Condensed Matter
Dynamics of two-point correlation functions in quantum systems

Alvaro Alhambra Universidad Autonoma de Madrid
April 26, 2019

PIRSA:19040108
Condensed Matter
Extracting conformal and superconformal data from critical quantum spin chains
- Ashley Milsted California Institute of Technology
- Yijian Zou Perimeter Institute for Theoretical Physics
April 25, 2019

PIRSA:19040111
Condensed Matter
Topological phases in Kitaev Materials

Yong-Baek Kim University of Toronto
April 25, 2019

PIRSA:19040115
Condensed Matter
Finite Correlation Length Scaling in Lorentz-Invariant Gapless iPEPS Wave Functions

Andreas Lauchli Paul Scherrer Institute
April 25, 2019

PIRSA:19040116
Condensed Matter
Shortcuts in Real and Imaginary Time

Timothy Hsieh Perimeter Institute for Theoretical Physics
April 25, 2019

PIRSA:19040114
Condensed Matter
Isometric Tensor Network States in Two Dimensions

Michael Zaletel University of California, Berkeley
April 25, 2019

PIRSA:19040113
Condensed Matter
From translation symmetry-enriched topological order to fracton phases

Meng Cheng Yale University
April 25, 2019

PIRSA:19040112
Condensed Matter
Spontaneous symmetry breaking from anyon condensation

Yuan-Ming Lu
April 24, 2019

PIRSA:19040105
Condensed Matter
When topology meets strong interactions in quantum matter

Senthil Todadri Massachusetts Institute of Technology (MIT) - Department of Physics
April 24, 2019

PIRSA:19040119
Condensed Matter

Quantum Many-Body Scars and Space-Time Crystalline Order from Magnon Condensation

Tom Iadecola University of Maryland, College Park
April 30, 2019

PIRSA:19040131
Condensed Matter
We study the eigenstate properties of a nonintegrable spin chain that was recently realized experimentally in a Rydberg-atom quantum simulator. In the experiment, long-lived coherent many-body oscillations were observed only when the system was initialized in a particular product state. This pronounced coherence has been attributed to the presence of special "scarred" eigenstates with nearly equally-spaced energies and putative nonergodic properties despite their finite energy density. In this paper we uncover a surprising connection between these scarred eigenstates and low-lying quasiparticle excitations of the spin chain. In particular, we show that these eigenstates can be accurately captured by a set of variational states containing a macroscopic number of magnons with momentum π. This leads to an interpretation of the scarred eigenstates as finite-energy-density condensates of weakly interacting π-magnons. One natural consequence of this interpretation is that the scarred eigenstates possess long-range order in both space and time, providing a rare example of the spontaneous breaking of continuous time-translation symmetry. We verify numerically the presence of this space-time crystalline order and explain how it is consistent with established no-go theorems precluding its existence in ground states and at thermal equilibrium.
Phase transition of fractional Chern insulators: QED3 and beyond

Yin-Chen He Stony Brook University
April 26, 2019

PIRSA:19040110
Condensed Matter
Recent experiments in graphene heterostructures have observed Chern insulators - integer and fractional Quantum Hall states made possible by a periodic substrate potential. Here we study theoretically that the competition between different Chern insulators, which can be tuned by the amplitude of the periodic potential, leads to a new family of quantum critical points described by QED3-Chern-Simons theory. At these critical points, Nf flavors of Dirac fermions interact through an emergent U(1) gauge theory at Chern-Simons level K, and remarkably, the entire family (with any Nf or K) can be realized at special values of the external magnetic field. I will talk about the physical properties and microscopic realization of those critical points. We propose experiments on Chern insulators that could resolve open questions in the study of 2+1 dimensional conformal field theories and test recent duality inspired conjectures.
Application of Tensor Network States to Lattice Field Theories

Stefan Kuhn Deutsches Elektronen-Synchrotron DESY
April 26, 2019

PIRSA:19040109
Condensed Matter
The conventional Euclidean time Monte Carlo approach to Lattice Field Theories faces a major obstacle in the sign problem in certain parameter regimes, such as the presence of a nonzero chemical potential or a topological theta-term. Tensor Network States, a family of ansatzes for the efficient description of quantum many-body states, offer a promising alternative for addressing Lattice Field Theories in the Hamiltonian formulation. In particular, numerical methods based on Tensor Network states do not suffer from the sign problem which makes it possible to study scenarios which are not accessible with standard Monte Carlo methods. In this talk I will present some recent work demonstrating this capability using two (1+1)-dimensional models as a test bed. Studying the O(3) nonlinear sigma model at nonzero chemical potential and the Schwinger model with topological theta-term, I will show how Tensor Networks States accurately describe the low-energy spectrum and that numerical errors can be controlled well enough to make contact with continuum predictions.
Dynamics of two-point correlation functions in quantum systems

Alvaro Alhambra Universidad Autonoma de Madrid
April 26, 2019

PIRSA:19040108
Condensed Matter
We give rigorous analytical results on the temporal behavior of two-point correlation functions (also known as dynamical response functions or Green’s functions) in quantum many body systems undergoing unitary dynamics. Using recent results from large deviation theory, we show that in a large class of models the correlation functions factorize at late times -> , thus proving that dissipation emerges out of the unitary dynamics of the system. We also show that the fluctuations around this late-time value are bounded by the purity of the thermal ensemble, which generally decays exponentially with system size. This conclusion connects the behavior of correlation functions to that of the late-time fluctuations of quenched systems out of equilibrium. For auto-correlation functions such as (as well as the symmetrized and anti-symmetrized versions) we provide an upper bound on the timescale at which they reach that factorized late time value. Remarkably, this bound is a function of local expectation values only, and does not increase with system size. As such it constraints, for instance, the behavior of current auto-correlation functions that appear in quantum transport. We give numerical examples that show that this bound is a good estimate in chaotic models, and argue that the timescale that appears can be understood in terms of an emergent fluctuation-dissipation theorem. Our study extends to further classes of two point functions such as the Kubo function of linear response theory, for which we give an analogous result. Joint work with Luis Pedro Garcia-Pintos and Jonathon Riddell
Extracting conformal and superconformal data from critical quantum spin chains
- Ashley Milsted California Institute of Technology
- Yijian Zou Perimeter Institute for Theoretical Physics
April 25, 2019

PIRSA:19040111
Condensed Matter
Key to characterizing universality in critical systems is the identification of the RG fixed point, which is very often a conformal field theory (CFT). We show how to use lattice operators that mimic the Virasoro generators of conformal symmetry to systematically extract, from a generic critical quantum spin chain, a complete set of the conformal data (central charge, scaling dimensions of primary fields, OPE coefficients) specifying a 2D CFT. We further show that, in the case of an extended superconformal symmetry, one can construct lattice operators that mimic the generators of the superconformal algebra, which allows us to identify superconformal primary states.
Topological phases in Kitaev Materials

Yong-Baek Kim University of Toronto
April 25, 2019

PIRSA:19040115
Condensed Matter
We discuss recent progress in theory and experiment on emergent topological phases in Kitaev materials. Here the competition between different anisotropic spin-exchange interactions may lead to a number of exotic phases of matter. We investigate possible emergence of quantum spin liquid, topological magnons, and topological superconductivity in two and three dimensional systems. We make connections to existing and future experiments.
Finite Correlation Length Scaling in Lorentz-Invariant Gapless iPEPS Wave Functions

Andreas Lauchli Paul Scherrer Institute
April 25, 2019

PIRSA:19040116
Condensed Matter
It is an open question how well tensor network states in the form of an infinite projected entangled-pair states (iPEPS) tensor network can approximate gapless quantum states of matter. In this talk we address this issue for two different physical scenarios: (i) a conformally invariant (2+1)d quantum critical point in the incarnation of the transverse-field Ising model on the square lattice and (ii) spontaneously broken continuous symmetries with gapless Goldstone modes exemplified by the S=1/2 antiferromagnetic Heisenberg and XY models on the square lattice. We find that the energetically best wave functions display finite correlation lengths and we introduce a powerful finite correlation length scaling framework for the analysis of such finite bond dimension (finite-D) iPEPS states. The framework is important (i) to understand the mild limitations of the finite-D iPEPS manifold in representing Lorentz-invariant, gapless many-body quantum states and (ii) to put forward a practical scheme in which the finite correlation length ξ(D) combined with field theory inspired formulas can be used to extrapolate the data to infinite correlation length, i.e., to the thermodynamic limit. The finite correlation length scaling framework opens the way for further exploration of quantum matter with an (expected) Lorentz-invariant, massless low-energy description, with many applications ranging from condensed matter to high-energy physics.
Shortcuts in Real and Imaginary Time

Timothy Hsieh Perimeter Institute for Theoretical Physics
April 25, 2019

PIRSA:19040114
Condensed Matter
In the first half, I will demonstrate an efficient and general approach for realizing non-trivial quantum states, such as quantum critical and topologically ordered states, in quantum simulators. In the second half, I will present a related variational ansatz for many-body quantum systems that is remarkably efficient. In particular, representing the critical point of the one-dimensional transverse field Ising model only requires a number of variational parameters scaling logarithmically with system size. Though optimizing the ansatz generally requires Monte Carlo sampling, our ansatz potentially enables a partial mitigation of the sign problem at the expense of having to optimize a few parameters.
Isometric Tensor Network States in Two Dimensions

Michael Zaletel University of California, Berkeley
April 25, 2019

PIRSA:19040113
Condensed Matter
We introduce an isometric restriction of the tensor-network ansatz that allows for highly efficient contraction of the network. We consider two concrete applications using this ansatz. First, we show that a matrix-product state representation of a 2D quantum state can be iteratively transformed into an isometric 2D tensor network. Second, we introduce a 2D version of the time-evolving block decimation algorithm (TEBD2) for approximating the ground state of a Hamiltonian as an isometric tensor network, which we demonstrate for the 2D transverse field Ising model.
From translation symmetry-enriched topological order to fracton phases

Meng Cheng Yale University
April 25, 2019

PIRSA:19040112
Condensed Matter
Spontaneous symmetry breaking from anyon condensation

Yuan-Ming Lu
April 24, 2019

PIRSA:19040105
Condensed Matter
In the context of quantum spin liquids, it is long known that the condensation of fractionalized excitations will inevitably break certain physical symmetries sometimes. For example, condensing spinons will usually break spin rotation and time reversal symmetries. We generalize these phenomena to generic continuous quantum phase transitions between symmetry enriched topological orders driven by anyon condensation. We provide a generic rule to determine whether a symmetry is enforced to break across an anyon condensation transition. Using a dimensional reduction scheme, we establish a mapping between these symmetry-breaking anyon-condensation transitions in two spatial dimensions, and deconfined quantum criticality in one spatial dimension.
When topology meets strong interactions in quantum matter

Senthil Todadri Massachusetts Institute of Technology (MIT) - Department of Physics
April 24, 2019

PIRSA:19040119
Condensed Matter
The study of strongly interacting quantum matter has been at the forefront of condensed matter research in the last several decades. An independent development is the discovery of topological band insulators. In this talk I will describe phenomena that occur at the confluence of topology and strong interactions. I will first discuss how insights from the study of the relatively simple topological insulators are revolutionizing our theoretical understanding of more complex quantum many body systems. Next I will describe some experimental situations in which both band topology and strong correlations are present, the resulting novel phenomena, and the theoretical challenges they present.

Title	Speaker(s)	Date	Talk Type	Info link
Quantum Many-Body Scars and Space-Time Crystalline Order from Magnon Condensation	Tom Iadecola	2019-04-30	Scientific Series	View details
Phase transition of fractional Chern insulators: QED3 and beyond	Yin-Chen He	2019-04-26	Conference	View details
Application of Tensor Network States to Lattice Field Theories	Stefan Kuhn	2019-04-26	Conference	View details
Dynamics of two-point correlation functions in quantum systems	Alvaro Alhambra	2019-04-26	Conference	View details
Extracting conformal and superconformal data from critical quantum spin chains	Ashley Milsted, Yijian Zou	2019-04-25	Conference	View details
Topological phases in Kitaev Materials	Yong-Baek Kim	2019-04-25	Conference	View details
Finite Correlation Length Scaling in Lorentz-Invariant Gapless iPEPS Wave Functions	Andreas Lauchli	2019-04-25	Conference	View details
Shortcuts in Real and Imaginary Time	Timothy Hsieh	2019-04-25	Conference	View details
Isometric Tensor Network States in Two Dimensions	Michael Zaletel	2019-04-25	Conference	View details
From translation symmetry-enriched topological order to fracton phases	Meng Cheng	2019-04-25	Conference	View details
Spontaneous symmetry breaking from anyon condensation	Yuan-Ming Lu	2019-04-24	Conference	View details
When topology meets strong interactions in quantum matter	Senthil Todadri	2019-04-24	Scientific Series	View details

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Quantum Many-Body Scars and Space-Time Crystalline Order from Magnon Condensation

Phase transition of fractional Chern insulators: QED3 and beyond

Application of Tensor Network States to Lattice Field Theories

Dynamics of two-point correlation functions in quantum systems

Extracting conformal and superconformal data from critical quantum spin chains

Topological phases in Kitaev Materials

Finite Correlation Length Scaling in Lorentz-Invariant Gapless iPEPS Wave Functions

Shortcuts in Real and Imaginary Time

Isometric Tensor Network States in Two Dimensions

From translation symmetry-enriched topological order to fracton phases

Spontaneous symmetry breaking from anyon condensation

When topology meets strong interactions in quantum matter