Talks

10321 - 10332 of 16754 Results

Diluted Magnetism in Iridates: Studies of Rh-doped Sr2Ir2O4

Pat Clancy University of Toronto

April 25, 2013

PIRSA:13040137

Condensed Matter
Higgs Boson in Condensed Matter: From Polaron to Topological Insulator

April 25, 2013

PIRSA:13040132

Particle Physics

Condensed Matter
Tensor Networks: an Overview

Lukasz Cincio Los Alamos National Laboratory

April 25, 2013

PIRSA:13040131

Quantum Information
New Neutron Scattering Results on the Enigmatic Ground State of the Pyrochlore Magnet Tb2Ti2O7

Katharina Fristsch McMaster University

April 25, 2013

PIRSA:13040136

Condensed Matter
Absence of Pauling's Residual Entropy in Dy2Ti2O

Jan Kycia University of Waterloo

April 25, 2013

PIRSA:13040130

Condensed Matter
Loop quantization of a weak-coupling limit of Euclidean gravity

Casey Tomlin Pennsylvania State University

April 25, 2013

PIRSA:13040104

Quantum Gravity
Constraining neutron star interior properties with transient events from accreting neutron stars and magnetars

Andrew Cumming McGill University

April 25, 2013

PIRSA:13040138

Strong Gravity
The Quantum von Neumann Architecture and the Future of Quantum Computing with Superconducting Circuits

Matteo Mariantoni Institute for Quantum Computing (IQC)

April 25, 2013

PIRSA:13040135
12/13 PSI - Explorations in String Theory Lecture 14

Pedro Vieira Perimeter Institute for Theoretical Physics

April 25, 2013

PIRSA:13040101

Quantum Fields and Strings
Spin-1/2 Heisenberg Antiferromagnet on the Kagome Lattice: a Z2 Spin Liquid with Fermionic Spinons

Zhihao Hao University of Waterloo

April 25, 2013

PIRSA:13040134

Condensed Matter
12/13 PSI - Explorations in Cosmology Lecture 14

Matthew Johnson York University

April 25, 2013

PIRSA:13040079

Cosmology
Reaching Experimentally Quantum Criticality: A Playground to Explore Novel Correlated Quantum States of Matter

Radu Coldea University of Oxford

April 25, 2013

PIRSA:13040133

Condensed Matter

Diluted Magnetism in Iridates: Studies of Rh-doped Sr2Ir2O4

Pat Clancy University of Toronto

April 25, 2013

PIRSA:13040137

Condensed Matter

The physics of iridium-based 5d transition metal oxides has attracted significant interest due to the potential for exotic magnetic and electronic ground states driven by strong spin-orbit coupling effects. Among the most extensively studied iridates is the layered perovskite Sr2IrO4, which was recently proposed as the first experimental realization of a novel Jeff=1/2 spin-orbital Mott insulating state. Intriguing similarities between Sr2IrO4 and La2CuO4, the parent compound of the high-Tc cuprates, have also led to speculation that it may be possible to induce superconductivity in this system through chemical doping. We have investigated the magnetic properties of the doped system Sr2Ir1-xRhxO4 using a combination of resonant magnetic x-ray scattering (RMXS), resonant inelastic x-ray scattering (RIXS), and x-ray absorption spectroscopy (XAS) techniques. These measurements reveal the effect of Rh-doping on the magnetic structure, phase diagram, and characteristic magnetic excitations of Sr2IrO4, and provide fundamental information about the role of quenched Rh impurities.
Higgs Boson in Condensed Matter: From Polaron to Topological Insulator

April 25, 2013

PIRSA:13040132

Particle Physics

Condensed Matter

In this talk I will briefly review the polaron physics, which has helped theorists to conceive the BCS theory of conventional superconductors as well as experimentalists to discover high temperature superconductors in the cuprates. Specifically I will talk about how charge carriers obtain their
masses from coupling to the phonon field in one, two, three or higher dimensions. More recently, there is increasing interest in topological insulators where a gap can be opened which may suggest new version of Higgs mechanism in condensed matter.
Tensor Networks: an Overview

Lukasz Cincio Los Alamos National Laboratory

April 25, 2013

PIRSA:13040131

Quantum Information

Tensor network algorithms provide highly competitive tools for analyzing ground state properties of quantum lattice models in one and two spatial dimensions. The most notable examples involve matrix product states, projected entangled pair states and multiscale entanglement renormalization ansatz. The key underlying idea of all the approaches is to decompose a quantum many-body state into a carefully chosen network of tensors.
In this talk I will give an introduction to the subject and show how tensor networks can be used to characterize topological order.
New Neutron Scattering Results on the Enigmatic Ground State of the Pyrochlore Magnet Tb2Ti2O7

Katharina Fristsch McMaster University

April 25, 2013

PIRSA:13040136

Condensed Matter

The ground state of the candidate spin liquid pyrochlore magnet Tb2Ti2O7 (TTO) has been long debated. Despite theoretical expectations of magnetic order below ~1K based on classical Ising-like Tb3+ spins, earlier muSR and neutron scattering experiments showed no long range order down to 50mK. This motivated two theoretical scenarios to account for the apparently disordered ground state: a quantum spin ice scenario and a non-magnetic singlet ground state. I will discuss new neutron scattering measurements on TTO that show short range spin correlations developing below ~ 0.5 K with a (½, ½, ½) ordering wavevector, and a concomitant opening of a spin gap across most of the Brillouin zone. Our measurements also refine the crystal field ground state for Tb3+ in TTO and in its sister, “soft” spin ice compound Tb2Sn2O7.
Absence of Pauling's Residual Entropy in Dy2Ti2O

Jan Kycia University of Waterloo

April 25, 2013

PIRSA:13040130

Condensed Matter

The discovery of the spin-ice phase in Dy2Ti2O7 numbers among the most significant findings in magnetic materials in over a decade. The spin-ice model is based on an elegant analogy to Pauling’s model of geometrical frustration in water ice, and predicts the same residual entropy, as confirmed by numerous measurements. Melko, den Hertog and Gingras, with numerical work using a loop algorithm to speed up equilibration times, were able to determine an ordering for this system. This had not been seen experimentally observed by several groups. I will present new experimental results for the specific heat of Dy2Ti2O7, demonstrating why previous measurements were unable to correctly capture its low temperature behaviour. By carefully tracking the flow of heat into and out of the material, we observe a non-vanishing specific heat at low temperatures indicating the residual entropy does not actually agree with the Pauling value.
Loop quantization of a weak-coupling limit of Euclidean gravity

Casey Tomlin Pennsylvania State University

April 25, 2013

PIRSA:13040104

Quantum Gravity

I will describe recent work in collaboration with Adam Henderson, Alok Laddha, and Madhavan Varadarajan on the loop quantization of a certain $G_{\mathrm{N}}\rightarrow 0$ limit of Euclidean gravity, introduced by Smolin. The model allows one to test various quantization choices one is faced with in loop quantum gravity, but in a simplified setting. The main results are the construction of finite-triangulation Hamiltonian and diffeomorphism constraint operators whose continuum limits can be evaluated in a precise sense, such that the quantum Dirac algebra of constraints closes nontrivially and free of anomalies. The construction relies heavily on techniques of Thiemann's QSD treatment, and lessons learned applying such techniques to the loop quantization of parameterized scalar field theory and the diffeomorphism constraint in loop quantum gravity. I will also briefly discuss the status of the quantum constraint algebra in full LQG, and how some of the lessons learned from the present model may guide us in that setting.
Constraining neutron star interior properties with transient events from accreting neutron stars and magnetars

Andrew Cumming McGill University

April 25, 2013

PIRSA:13040138

Strong Gravity

The last few years have seen new opportunities for constraining the physics of neutron star interiors. I will first discuss the current state of neutron star radius measurements and then go on to discuss thermal tomography as a probe of the nuclear, magnetic, and transport properties of neutron star crusts. In each case, I will emphasize the astrophysics that must be understood to make reliable inferences about the properties of dense matter from observations of neutron stars.
The Quantum von Neumann Architecture and the Future of Quantum Computing with Superconducting Circuits

Matteo Mariantoni Institute for Quantum Computing (IQC)

April 25, 2013

PIRSA:13040135

Superconducting quantum circuits have made significant advances over the past decade, allowing more complex and integrated circuits that perform with good fidelity. We have recently implemented a machine comprising seven quantum channels, with three superconducting resonators, two phase qubits, and two zeroing registers. I will explain the design and operation of this machine, first showing how a single microwave photon |1> can be prepared in one resonator and coherently transferred between the three resonators [1]. I will then demonstrate how this machine can be used as the quantum-mechanical analog of the von Neumann computer architecture, which for a classical computer comprises a central processing unit and a memory holding both instructions and data. The quantum version comprises a quantum central processing unit (quCPU) that exchanges data with a quantum random-access memory (quRAM) integrated on one chip, with instructions stored on a classical computer [2]. Finally, I will demonstrate that the quantum von Neumann machine provides one unit cell of a two-dimensional qubit-resonator array that can be used for surface code quantum computing. This will allow the realization of a scalable, fault-tolerant quantum processor with the most forgiving error rates to date [3].
[1] M. Mariantoni et al., Nature Physics 7, 287-293 (2011)
[2] M. Mariantoni et al., Science 334, 61-65 (2011)
[3] A. G. Fowler, M. Mariantoni, J. M. Martinis, and A. N. Cleland, Phys. Rev. A 86, 032324 (2012)
12/13 PSI - Explorations in String Theory Lecture 14

Pedro Vieira Perimeter Institute for Theoretical Physics

April 25, 2013

PIRSA:13040101

Quantum Fields and Strings
Spin-1/2 Heisenberg Antiferromagnet on the Kagome Lattice: a Z2 Spin Liquid with Fermionic Spinons

Zhihao Hao University of Waterloo

April 25, 2013

PIRSA:13040134

Condensed Matter

Motivated by recent numerical and experimental studies of the spin-1/2 Heisenberg antiferromagnet on kagome, we formulate a many-body model for fermionic spinons, which are just uncoupled spins. The spinons interact with an emergent U(1) gauge field and experience strong short-range attraction in the S=0 channel. The ground state of the model is generically a Z(2) liquid. We calculate the edge of the two-spinon continuum and compare the theory to the slave-fermion approach to the Heisenberg model.
12/13 PSI - Explorations in Cosmology Lecture 14

Matthew Johnson York University

April 25, 2013

PIRSA:13040079

Cosmology
Reaching Experimentally Quantum Criticality: A Playground to Explore Novel Correlated Quantum States of Matter

Radu Coldea University of Oxford

April 25, 2013

PIRSA:13040133

Condensed Matter

Realizing experimentally continuous phase transitions in the electronic ground state of materials near zero temperature as a function of tuning some external parameter (magnetic field, pressure etc.) offers a unique opportunity to probe the extreme regime (near the transition point) where strong quantum correlations encompass the macroscopic sample as a whole, so called “quantum criticality” [1]. In this regime of strong correlations small perturbations/interactions can stabilize novel forms order or collective fluctuations that otherwise do not exist. One of the theoretically most studied paradigms for quantum criticality is a chain of Ising spins driven by a transverse field to a critical point separating spontaneous magnetic order and paramagnetic phases. We have realized this system experimentally by applying strong magnetic fields to the quasi-one-dimensional Ising ferromagnet CoNb2O6 and have probed via single-crystal inelastic neutron scattering the evolution of the magnetic order and spin excitation spectrum as a function of applied field at mili-Kelvin temperatures [2]. Near the critical point the spin excitations were theoretically predicted nearly two decades ago to have a set of quantum resonances (collective modes of vibration of the interacting spins) with universal ratios between their frequencies reflecting an exceptional mathematical structure of the quantum many-body eigenstates with a “hidden” E8 symmetry governing the physics in the scaling limit. Experiments indeed observed evidence for a spectrum of resonances and the ratio between the frequencies of the two lowest modes approached the "golden ratio" near the critical point, as predicted by field theory. As a second example of novel physics near quantum criticality I will discuss how an amplitude-modulated incommensurate spin-density wave (SDW) order appears near the field-induced critical point in the quasi-1D spin-1/2 XY antiferromagnet Cs2CoCl4. Incommensurate SDWs are very uncommon in magnetic insulators and are not stable zero-temperature ground states at the classical mean-field level, we propose that here such a state is stabilized by the strong quantum fluctuations associated with the proximity to the critical point and the weak frustrated inter-chain couplings.

Title	Date	Collection	Type	Info
Diluted Magnetism in Iridates: Studies of Rh-doped Sr2Ir2O4	2013‑04‑25	4 Corner Southwest Symposium 2013	Conference	View details
Higgs Boson in Condensed Matter: From Polaron to Topological Insulator	2013‑04‑25	4 Corner Southwest Symposium 2013	Conference	View details
Tensor Networks: an Overview	2013‑04‑25	4 Corner Southwest Symposium 2013	Conference	View details
New Neutron Scattering Results on the Enigmatic Ground State of the Pyrochlore Magnet Tb2Ti2O7	2013‑04‑25	4 Corner Southwest Symposium 2013	Conference	View details
Absence of Pauling's Residual Entropy in Dy2Ti2O	2013‑04‑25	4 Corner Southwest Symposium 2013	Conference	View details
Loop quantization of a weak-coupling limit of Euclidean gravity	2013‑04‑25	Quantum Gravity	Scientific Series	View details
Constraining neutron star interior properties with transient events from accreting neutron stars and magnetars	2013‑04‑25	Strong Gravity	Scientific Series	View details
The Quantum von Neumann Architecture and the Future of Quantum Computing with Superconducting Circuits	2013‑04‑25	4 Corner Southwest Symposium 2013	Conference	View details
12/13 PSI - Explorations in String Theory Lecture 14	2013‑04‑25	12/13 PSI - Eplorations in String Theory	Course	View details
Spin-1/2 Heisenberg Antiferromagnet on the Kagome Lattice: a Z2 Spin Liquid with Fermionic Spinons	2013‑04‑25	4 Corner Southwest Symposium 2013	Conference	View details
12/13 PSI - Explorations in Cosmology Lecture 14	2013‑04‑25	12/13 PSI - Explorations in Cosmology	Course	View details
Reaching Experimentally Quantum Criticality: A Playground to Explore Novel Correlated Quantum States of Matter	2013‑04‑25	4 Corner Southwest Symposium 2013	Conference	View details

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