Conference

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Searching for Spin Liquids

Steven White University of California, Irvine
May 09, 2013

PIRSA:13050039
Quantum Fields and Strings

Condensed Matter
Holographic insights into quantum critical transport: from branes to Bose-Hubbard
May 08, 2013

PIRSA:13050037
Condensed Matter
Quantum renormalization group and AdS/CFT

Sung-Sik Lee McMaster University
May 08, 2013

PIRSA:13050036
Quantum Fields and Strings
Propagation of entanglement in strongly coupled systems from gravity

Hong Liu Massachusetts Institute of Technology (MIT) - Department of Physics
May 08, 2013

PIRSA:13050035
Quantum Gravity
Thermodynamical Property of Entanglement Entropy for Excited States

Tadashi Takayanagi Yukawa Institute for Theoretical Physics
May 08, 2013

PIRSA:13050034
Condensed Matter
Impossible symmetry enriched topological phases in 2D and their realization on 3D surface

Xie Chen California Institute of Technology
May 07, 2013

PIRSA:13050033
Quantum Fields and Strings
3D topological lattice models with topologically ordered surface states

Fiona Burnell University of Minnesota
May 07, 2013

PIRSA:13050032
Condensed Matter
Field theory, Wave function, and Defects of Symmetry Protected Topological Phases

Cenke Xu University of California, Santa Barbara
May 07, 2013

PIRSA:13050031
Quantum Fields and Strings
Majorana Ghosts: From topological superconductor to the origin of neutrino mass, three generations and their mass mixing

Zheng-Cheng Gu Chinese University of Hong Kong
May 07, 2013

PIRSA:13050052
Condensed Matter
Fractionalizing Majorana fermions: non-abelian statistics on the edges of abelian quantum Hall states

Erez Berg Weizmann Institute of Science
May 07, 2013

PIRSA:13050029
Condensed Matter
A 3d Boson Topological Insulator and the “Statistical Witten Effect”

Matthew Fisher University of California, Santa Barbara
May 07, 2013

PIRSA:13050028
Condensed Matter
Asymmetry protected emergent E8 symmetry

Brian Swingle Brandeis University
May 06, 2013

PIRSA:13050027
Quantum Fields and Strings

Searching for Spin Liquids

Steven White University of California, Irvine
May 09, 2013

PIRSA:13050039
Quantum Fields and Strings

Condensed Matter
Holographic insights into quantum critical transport: from branes to Bose-Hubbard
May 08, 2013

PIRSA:13050037
Condensed Matter
We discuss the general features of charge transport of quantum critical points described by CFTs in 2+1D. Our main tool is the AdS/CFT correspondence, but we will make connections to standard field theory results and to recent quantum Monte Carlo data. We emphasize the importance of poles and zeros of the response functions. In the holographic setting, these are the discrete quasinormal modes of a black hole/brane; they map to the excitations of the CFT. We further describe the role of particle-vortex or S-duality on the conductivity, which is argued to obey two powerful sum rules.
References (with S. Sachdev): arXiv:1210.4166 (PRB 12); arXiv:1302.0847 (PRB 13)
Quantum renormalization group and AdS/CFT

Sung-Sik Lee McMaster University
May 08, 2013

PIRSA:13050036
Quantum Fields and Strings
In this talk, I will discuss about the notion of quantum renormalization group, and explain how (D+1)-dimensional gravitational theories naturally emerge as dual descriptions for D-dimensional quantum field theories. It will be argued that the dynamical gravitational field in the bulk encodes the entanglement between low energy modes and high energy modes of the corresponding quantum field theory.
Propagation of entanglement in strongly coupled systems from gravity

Hong Liu Massachusetts Institute of Technology (MIT) - Department of Physics
May 08, 2013

PIRSA:13050035
Quantum Gravity
Thermodynamical Property of Entanglement Entropy for Excited States

Tadashi Takayanagi Yukawa Institute for Theoretical Physics
May 08, 2013

PIRSA:13050034
Condensed Matter
We will point out that there is a universal thermodynamical property of entanglement entropy for excited states. We will derive this by using the AdS/CFT correspondence in any dimension. We will also directly confirm this property from direct field theoretic calculations in two dimensions. We will define a new quantity called entanglement density by taking derivatives of entanglement entropy with respect to the shape of subsystem. We will show that this quantity coincides with the energy density by taking the small subsystem limit and show that this is another equivalent statement of the thermodynamical property.
Impossible symmetry enriched topological phases in 2D and their realization on 3D surface

Xie Chen California Institute of Technology
May 07, 2013

PIRSA:13050033
Quantum Fields and Strings
In quantum systems with symmetry, the same topological phase can be enriched by symmetry in different ways, resulting in different symmetry transformations of the superselection sectors in the phase. However, not all symmetry transformations are allowed on the superselection sectors in topological phases in purely 2D systems. In this talk, I will discuss some examples of such symmetry enrichment of topological phases, which seem to be consistent with the fusion and braiding rules of the superselection sectors in the theory but are nonetheless impossible to realize in 2D. Interestingly, we show further that they can be realized on the surface of a 3D gapped system with a topologically trivial bulk.
3D topological lattice models with topologically ordered surface states

Fiona Burnell University of Minnesota
May 07, 2013

PIRSA:13050032
Condensed Matter
I will discuss a family of solvable 3D lattice models that have a ``trivial" bulk, in which all excitations are confined, but exhibit topologically ordered surface states. I will discuss perturbations to these models that can drive a phase transition in which some of these excitations become deconfined, driving the system into a phase with bulk topological order.
Field theory, Wave function, and Defects of Symmetry Protected Topological Phases

Cenke Xu University of California, Santa Barbara
May 07, 2013

PIRSA:13050031
Quantum Fields and Strings
Majorana Ghosts: From topological superconductor to the origin of neutrino mass, three generations and their mass mixing

Zheng-Cheng Gu Chinese University of Hong Kong
May 07, 2013

PIRSA:13050052
Condensed Matter
The existence of three generations of neutrinos and their mass mixing is a deep mystery of our universe. On the other hand, Majorana's elegant work on the real solution of Dirac equation predicted the existence of Majorana particles in our nature, unfortunately, these Majorana particles have never been observed. In this talk, I will begin with a simple 1D condensed matter model which realizes a T^2=-1 time reversal symmetry protected superconductors and then discuss the physical property of its boundary Majorana zero modes. It is shown that these Majorana zero modes realize a T^4=-1 time reversal doubelets and carry 1/4 spin. Such a simple observation motivates us to revisit the CPT symmetry of those ghost particles--neutrinos by assuming that they are Majorana zero modes. Interestingly, we find that a topological Majorana particle will realize a P^4=-1 parity symmetry as well. It even realizes a nontrivial C^4=-1 charge conjugation symmetry, which is a big surprise from a usual perspective that the charge conjugation symmetry for a Majorana particle is trivial. Indeed, such a C^4=-1 charge conjugation symmetry is a Z_2 gauge symmetry and its spontaneously breaking leads to the origin of neutrino mass. We further attribute the origin of three generations of neutrinos to three distinguishable types of topological Majorana zero modes protected by CPT symmetry. Such an assumption leads to an S3 symmetry in the generation space and uniquely determines the mass mixing matrix with no adjustable parameters! In the absence of CP violation, we derive \theta_12=32degree, \theta_23=45degree and \theta_13=0degree, which is intrinsically closed to the current experimental results. We further predict an exact mass ratio of the three mass eigenstate with m_1/m_3~m_2/m_3=3/\sqrt{5}.
Fractionalizing Majorana fermions: non-abelian statistics on the edges of abelian quantum Hall states

Erez Berg Weizmann Institute of Science
May 07, 2013

PIRSA:13050029
Condensed Matter
We study the non-abelian statistics characterizing systems where counter-propagating gapless modes on the edges of fractional quantum Hall states are gapped by proximity-coupling to superconductors and ferromagnets. The most transparent example is that of a fractional quantum spin Hall state, in which electrons of one spin direction occupy a fractional quantum Hall state of $\nu= 1/m$, while electrons of the opposite spin occupy a similar state with $\nu = -1/m$. However, we also propose other examples of such systems, which are easier to realize experimentally. We find that each interface between a region on the edge coupled to a superconductor and a region coupled to a ferromagnet corresponds to a non-abelian anyon of quantum dimension $\sqrt{2m}$. We calculate the unitary transformations that are associated with braiding of these anyons, and show that they are able to realize a richer set of non-abelian representations of the braid group than the set realized by non-abelian anyons based on Majorana fermions. We carry out this calculation both explicitly and by applying general considerations. Finally, we show that topological manipulations with these anyons cannot realize universal quantum computation.
A 3d Boson Topological Insulator and the “Statistical Witten Effect”

Matthew Fisher University of California, Santa Barbara
May 07, 2013

PIRSA:13050028
Condensed Matter
Electron topological insulators are members of a broad class of “symmetry protected topological” (SPT) phases of fermions and bosons which possess distinctive surface behavior protected by bulk symmetries. For 1d and 2d SPT’s the surfaces are either gapless or symmetry broken, while in 3d, gapped symmetry-respecting surfaces with (intrinsic) 2d topological order are also possible. The electromagnetic response of (some) SPT’s can provide an important characterization, as illustrated by the Witten effect in 3d electron topological insulators. Using a 3d parton-gauge theory construction, we have recently developed a dyon condensation approach to access exotic new phases including some 3d bosonic SPT’s. A bosonic SPT with both time-reversal and charge conservation symmetries, is thereby obtained, a phase which supports a gapped, symmetry-unbroken 2d surface with topological order - a toric code with charge one-half anyons. The 3d electromagnetic response of this bosonic SPT phase is quite remarkable - an external magnetic monopole can remain charge neutral, but is statistically transmuted becoming a fermion - a “statistical Witten effect” that characterizes the phase.
Asymmetry protected emergent E8 symmetry

Brian Swingle Brandeis University
May 06, 2013

PIRSA:13050027
Quantum Fields and Strings
The E8 state of bosons is a 2+1d gapped phase of matter which has no topological entanglement entropy but has protected chiral edge states in the absence of any symmetry. This peculiar state is interesting in part because it sits at the boundary between short- and long-range entangled phases of matter. When the system is translation invariant and for special choices of parameters, the edge states form the chiral half of a 1+1d conformal field theory - an E8 level 1 Wess-Zumino-Witten model. However, in general the velocities of different edge channels are different and the system does not have conformal symmetry. We show that by considering the most general microscopic Hamiltonian, in particular by relaxing the constraint of translation invariance and adding disorder, conformal symmetry remerges in the low energy limit. The disordered fixed point has all velocities equal and is the E8 level 1 WZW model. Hence a highly entangled and highly symmetric system emerges, but only when the microscopic Hamiltonian is completely asymmetric.

Title	Speaker(s)	Date	Talk Type	Info link
Searching for Spin Liquids	Steven White	2013-05-09	Conference	View details
Holographic insights into quantum critical transport: from branes to Bose-Hubbard		2013-05-08	Conference	View details
Quantum renormalization group and AdS/CFT	Sung-Sik Lee	2013-05-08	Conference	View details
Propagation of entanglement in strongly coupled systems from gravity	Hong Liu	2013-05-08	Conference	View details
Thermodynamical Property of Entanglement Entropy for Excited States	Tadashi Takayanagi	2013-05-08	Conference	View details
Impossible symmetry enriched topological phases in 2D and their realization on 3D surface	Xie Chen	2013-05-07	Conference	View details
3D topological lattice models with topologically ordered surface states	Fiona Burnell	2013-05-07	Conference	View details
Field theory, Wave function, and Defects of Symmetry Protected Topological Phases	Cenke Xu	2013-05-07	Conference	View details
Majorana Ghosts: From topological superconductor to the origin of neutrino mass, three generations and their mass mixing	Zheng-Cheng Gu	2013-05-07	Conference	View details
Fractionalizing Majorana fermions: non-abelian statistics on the edges of abelian quantum Hall states	Erez Berg	2013-05-07	Conference	View details
A 3d Boson Topological Insulator and the “Statistical Witten Effect”	Matthew Fisher	2013-05-07	Conference	View details
Asymmetry protected emergent E8 symmetry	Brian Swingle	2013-05-06	Conference	View details

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