Quantum Matter

436 talks

S021

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Displaying 301 - 312 of 436

Spin-charge scattering in Luttinger Liquids

Alex Levchenko Michigan State University (MSU)
November 04, 2014

PIRSA:14110096
Condensed Matter
Numerical Study of a Bosonic Topological Insulator in Three Dimensions

Scott Geraedts California Institute of Technology
October 21, 2014

PIRSA:14100113
Condensed Matter
Bulk Entanglement Spectrum: From Topological States to Quantum Criticality

Timothy Hsieh Perimeter Institute for Theoretical Physics
October 14, 2014

PIRSA:14100075
Condensed Matter
Irreversibility and Entanglement Spectrum Statistics in Quantum Circuits

Eduardo Mucciolo University of Central Florida
September 30, 2014

PIRSA:14090028
Condensed Matter
Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography
September 19, 2014

PIRSA:14090072
Quantum Fields and Strings

Condensed Matter

Strong Gravity
Irreversibility, Entropy Production, and and Self-organization far from Equilibrium

Jeremy England Massachusetts Institute of Technology (MIT)
September 17, 2014

PIRSA:14090073
Condensed Matter
Self-assembling tensor networks and holography in disordered spin chains

Andrew Goldsborough RWTH Aachen University
September 16, 2014

PIRSA:14090029
Condensed Matter
Stripes and pairing in t-J and Hubbard models

Steven White University of California, Irvine
September 11, 2014

PIRSA:14090074
Condensed Matter
Many-Body Localization in translation invariant systems?

Francois Huveneers University of Paris-Saclay

September 09, 2014

PIRSA:14090027
Monogamy of entanglement and improved mean-field ansatz for spin lattices

Ralf Schuetzhold Helmholtz-Zentrum Dresden-Rossendorf
September 02, 2014

PIRSA:14090069
Condensed Matter
TBA

Senthil Todadri Massachusetts Institute of Technology (MIT) - Department of Physics
August 19, 2014

PIRSA:14080036
Condensed Matter
Reconstructing quantum states from local data

Isaac Kim University of California, Davis
August 12, 2014

PIRSA:14080007
Condensed Matter

Spin-charge scattering in Luttinger Liquids

Alex Levchenko Michigan State University (MSU)
November 04, 2014

PIRSA:14110096
Condensed Matter
I will discuss the violation of spin-charge separation in generic Luttinger liquids and investigate its effect on the relaxation, thermal and electrical transport of genuine spin-1/2 electron liquids in ballistic quantum wires. We will identify basic scattering processes compatible with the symmetry of the problem and conservation laws that lead to the decay of plasmons into the spin modes and also discuss Brownian backscattering of spin excitations. I will present a closed set of coupled kinetic equations for the spin-charge excitations and solve the problem of electrical and thermal conductance of interacting electrons for an arbitrary relation between the quantum wire length and spin-charge thermalization length.
Numerical Study of a Bosonic Topological Insulator in Three Dimensions

Scott Geraedts California Institute of Technology
October 21, 2014

PIRSA:14100113
Condensed Matter
We construct a model which realizes a (3+1)-dimensional symmetry-protected topological phase of bosons with U(1) charge conservation and time reversal symmetry, envisioned by A. Vishwanath and T. Senthil [PRX 4 011016]. Our model works by introducing an additional spin degree of freedom, and binding its hedgehogs to a species of charged bosons. We study the model using Monte Carlo and determine its bulk phase diagram; the phase where the bound states of hedgehogs and charges condense is the topological phase, and we demonstrate this by observing a Witten effect. We also study the surface phase diagram on a (2+1)-dimensional boundary between the topological and trivial insulators. We find a number of exotic phases on the surface, including exotic superfluids, a phase with a Hall conductivity quantized to half the value possible in 2D, and a phase with intrinsic topological order. We also find a new bulk phase with intrinsic topological order.
Bulk Entanglement Spectrum: From Topological States to Quantum Criticality

Timothy Hsieh Perimeter Institute for Theoretical Physics
October 14, 2014

PIRSA:14100075
Condensed Matter
A quantum phase transition is usually achieved by tuning physical parameters in a Hamiltonian at zero temperature. Here, we demonstrate that the ground state of a topological phase itself encodes critical properties of its transition to a trivial phase. To extract this information, we introduce a partition of the system into two subsystems both of which extend throughout the bulk in all directions. The resulting bulk entanglement spectrum (BES) has a low-lying part that resembles the excitation spectrum of a bulk Hamiltonian, which allows us to probe a topological phase transition from a single wavefunction by tuning either the geometry of the partition or the entanglement temperature. As an example, this remarkable correspondence between topological phase transition and entanglement criticality is rigorously established for integer quantum Hall states. We also implement BES using tensor networks, derive the universality classes of topological phase transitions from the spin-1 chain Haldane phase, and demonstrate that the AKLT wavefunction (and its generalizations) remarkably contains critical six-vertex (and in general eight-vertex) models within it.
Irreversibility and Entanglement Spectrum Statistics in Quantum Circuits

Eduardo Mucciolo University of Central Florida
September 30, 2014

PIRSA:14090028
Condensed Matter
We show that for a system evolving unitarily under a stochastic quantum circuit, the notions of irreversibility, universality of computation, and entanglement are closely related. As the state of the system evolves from an initial product state, it becomes increasingly entangled until entanglement reaches a maximum. We define irreversibility as the failure to find a circuit that disentangles a maximally entangled state. We show that irreversibility occurs when maximally entangled states are generated with a quantum circuit formed by gates from a universal quantum computation set. We find that irreversibility is also associated to a Wigner-Dyson statistics in the fluctuations of spacings between adjacent eigenvalues of the system’s reduced density matrix. In contrast, when the system is evolved with a non-universal set of gates, the statistics of the entanglement spacing deviates from Wigner-Dyson and the disentangling algorithm succeeds. We discuss how these findings open a new way to characterize non-integrability in quantum systems.
Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography
September 19, 2014

PIRSA:14090072
Quantum Fields and Strings

Condensed Matter

Strong Gravity
We discuss properties of 2-point functions in CFTs in 2+1D at finite temperature. For concreteness, we focus on those involving conserved flavour currents, in particular on the associated conductivity. At frequencies much greater than the temperature, ω >> T, the ω dependence of the conductivity can be computed from the operator product expansion (OPE) between the currents and operators which acquire a non-zero expectation value at T > 0. Such results are found to be in excellent agreement with quantum Monte Carlo studies of the O(2) Wilson-Fisher CFT. Results for the conductivity and other observables are also obtained in vector 1/N expansions. We match these large ω results to the corresponding correlators of holographic representations of the CFT: the holographic approach then allows us to extrapolate to small ω/T. Other holographic studies implicitly only used the OPE between the currents and the energy-momentum tensor, and this yields the correct leading large ω behavior for a large class of CFTs. However, for the Wilson-Fisher CFT a relevant “thermal” operator must also be considered, and then consistency with the Monte Carlo results is obtained without a previously needed ad hoc rescaling of the T value [1]. We also use the OPE to prove sum rules obeyed by the conductivity. **In collaboration with A. Katz, S. Sachdev and E. Sørensen** [1] WWK, E. Sørensen, S. Sachdev, Nat. Phys. 10, 361 (2014)
Irreversibility, Entropy Production, and and Self-organization far from Equilibrium

Jeremy England Massachusetts Institute of Technology (MIT)
September 17, 2014

PIRSA:14090073
Condensed Matter
In the last few decades, substantial advances have been made in our ability to make general statements about the thermodynamics of systems driven far from thermal equilibrium. In this talk, I will give a brief overview of some the most basic results in this area and explain their connection to classic results in linear response theory. I will then describe how to formally construct the generalization of free energy for macrostates in a far-from-equilibrium system and discuss possible connections to self-organization phenomena in both biological and other contexts.
Self-assembling tensor networks and holography in disordered spin chains

Andrew Goldsborough RWTH Aachen University
September 16, 2014

PIRSA:14090029
Condensed Matter
We show that the numerical strong disorder renormalization group algorithm (SDRG) of Hikihara et.\ al.\ [{Phys. Rev. B} {\bf 60}, 12116 (1999)] for the one-dimensional disordered Heisenberg model naturally describes a tree tensor network (TTN) with an irregular structure defined by the strength of the couplings. Employing the holographic interpretation of the TTN in Hilbert space, we compute expectation values, correlation functions and the entanglement entropy using the geometrical properties of the TTN. We find that the disorder averaged spin-spin correlation scales with the average path length through the tensor network while the entanglement entropy scales with the minimal surface connecting two regions. Furthermore, the entanglement entropy increases with both disorder and system size, resulting in an area-law violation. Our results demonstrate the usefulness of a self-assembling TTN approach to disordered systems and quantitatively validate the connection between holography and quantum many-body systems.
Stripes and pairing in t-J and Hubbard models

Steven White University of California, Irvine
September 11, 2014

PIRSA:14090074
Condensed Matter
This has been a leading question in condensed matter physics since the discovery of the cuprate superconductors. In this talk I will review some of the DMRG and tensor network results for the ground states of these models. A key question I'll address is the issue of stripes: are the ground states striped? Do stripes compete with or induce d-wave superconductivity? Another question I'll address is: how well does 2D DMRG do in comparison with iPEPS and quantum Monte Carlo. I will also show recent results for a standard 3-band Hubbard model for the cuprates. The asymmetry between hole and electron doped systems which is seen in the cuprates arises naturally from this model.
Many-Body Localization in translation invariant systems?

Francois Huveneers University of Paris-Saclay

September 09, 2014

PIRSA:14090027

Roughly speaking, Many-Body Localization (MBL) refers to the state of a material that fails to thermalize. Though MBL has mostly been studied in quenched disordered systems, several authors have recently proposed that this phase could be realized in clean (translation invariant) systems too. In this talk, I will discuss this idea and ask to which extent an MBL phase can indeed be expected in systems without quenched disorder. Hopefully, the discussion shed also some light on the localization-delocalization transition for more generic many-body systems. From joint work with W. De Roeck (Leuven), M. Mueller (Trieste), M. Schiulaz (Trieste).
Monogamy of entanglement and improved mean-field ansatz for spin lattices

Ralf Schuetzhold Helmholtz-Zentrum Dresden-Rossendorf
September 02, 2014

PIRSA:14090069
Condensed Matter
We consider rather general spin-1/2 lattices with large coordination numbers Z.
Based on the monogamy of entanglement and other properties of the concurrence C,
we derive rigorous bounds for the entanglement between neighboring spins,
which show that C decreases for large Z. In addition, the concurrence C measures the deviation from mean-field behavior and can only vanish if the mean-field ansatz yields an exact ground state of the Hamiltonian. Motivated by these findings, we propose an improved mean-field ansatz by adding entanglement
TBA

Senthil Todadri Massachusetts Institute of Technology (MIT) - Department of Physics
August 19, 2014

PIRSA:14080036
Condensed Matter
Reconstructing quantum states from local data

Isaac Kim University of California, Davis
August 12, 2014

PIRSA:14080007
Condensed Matter
We consider the problem of reconstructing global quantum states from local data. Because the reconstruction problem has many solutions in general, we consider the reconstructed state of maximum global entropy consistent with the local data. We show that unique ground states of local Hamiltonians are exactly reconstructed as the maximal entropy state. More generally, we show that if the state in question is a ground state of a local Hamiltonian with a degenerate space of locally indistinguishable ground states, then the maximal entropy state is close to the ground state projector. We also show that local reconstruction is possible for thermal states of local Hamiltonians. Finally, we discuss a procedure to certify that the reconstructed state is close to the true global state. We call the entropy of our reconstructed maximum entropy state the "reconstruction entropy", and we discuss its relation to emergent geometry in the context of holographic duality. This is a joint work with Brian Swingle.

Title	Speaker(s)	Date	Talk Type	Info
Spin-charge scattering in Luttinger Liquids	Alex Levchenko	2014-11-04	Scientific Series	View details
Numerical Study of a Bosonic Topological Insulator in Three Dimensions	Scott Geraedts	2014-10-21	Scientific Series	View details
Bulk Entanglement Spectrum: From Topological States to Quantum Criticality	Timothy Hsieh	2014-10-14	Scientific Series	View details
Irreversibility and Entanglement Spectrum Statistics in Quantum Circuits	Eduardo Mucciolo	2014-09-30	Scientific Series	View details
Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography		2014-09-19	Scientific Series	View details
Irreversibility, Entropy Production, and and Self-organization far from Equilibrium	Jeremy England	2014-09-17	Scientific Series	View details
Self-assembling tensor networks and holography in disordered spin chains	Andrew Goldsborough	2014-09-16	Scientific Series	View details
Stripes and pairing in t-J and Hubbard models	Steven White	2014-09-11	Scientific Series	View details
Many-Body Localization in translation invariant systems?	Francois Huveneers	2014-09-09	Scientific Series	View details
Monogamy of entanglement and improved mean-field ansatz for spin lattices	Ralf Schuetzhold	2014-09-02	Scientific Series	View details
TBA	Senthil Todadri	2014-08-19	Scientific Series	View details
Reconstructing quantum states from local data	Isaac Kim	2014-08-12	Scientific Series	View details

Quantum Matter

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