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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
12/13 PSI - Explorations in Condensed Matter Lecture 14
- Guifre Vidal Alphabet (United States)
- Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
April 25, 2013

PIRSA:13040060
Condensed Matter
Electronic Liquid Crystalline Phases of Highly Correlated Electronic Systems
April 24, 2013

PIRSA:13040116
Condensed Matter
12/13 PSI - Explorations in String Theory Lecture 13

Pedro Vieira Perimeter Institute for Theoretical Physics
April 24, 2013

PIRSA:13040100
Quantum Fields and Strings

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.
12/13 PSI - Explorations in Condensed Matter Lecture 14
- Guifre Vidal Alphabet (United States)
- Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
April 25, 2013

PIRSA:13040060
Condensed Matter
Electronic Liquid Crystalline Phases of Highly Correlated Electronic Systems
April 24, 2013

PIRSA:13040116
Condensed Matter
In one extreme, where the interactions are sufficiently weak compared to the interactions, electrons form a “Fermi liquid” – the state that accounts for the properties of simple metals. In the other extreme, where the interactions are dominant, the electrons form various “Mott” insulating or “Wigner crystalline” phases, often characterized by broken spatial and/or magnetic symmetries. Corresponding charge and/or magnetically ordered insulating phases are common in nature. Between these two extremes lie highly correlated electronic fluids, and correspondingly a host of interesting and perplexing materials, including such diverse systems as the cuprate and iron-based high temperature superconductors, the failed metamagnet Sr3Ru2O7, and a variety of quantum Hall fluids. Some insight into electron fluids in this rich intermediate coupling regime can be obtained from viewing them as partially melted electron solids, rather than as strongly interacting gases. Here, analogies with the liquid crystalline phases of complex classical fluids provide useful guidance for a new approach to this key problem in condensed matter physics.
12/13 PSI - Explorations in String Theory Lecture 13

Pedro Vieira Perimeter Institute for Theoretical Physics
April 24, 2013

PIRSA:13040100
Quantum Fields and Strings

Title	Date	Collection	Type	Info
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
12/13 PSI - Explorations in Condensed Matter Lecture 14	2013‑04‑25	12/13 PSI - Explorations in Condensed Matter	Course	View details
Electronic Liquid Crystalline Phases of Highly Correlated Electronic Systems	2013‑04‑24	Colloquium	Scientific Series	View details
12/13 PSI - Explorations in String Theory Lecture 13	2013‑04‑24	12/13 PSI - Eplorations in String Theory	Course	View details

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