Scientific Series

Displaying 3109 - 3120 of 5090

ADMX: The Axion Dark Matter Experiment

Gray Rybka University of Washington
September 30, 2014

PIRSA:14090067
High Energy Physics
From Black Holes to Big Bang, and Back

Niayesh Afshordi University of Waterloo

September 30, 2014

PIRSA:14090088
Fault-tolerant logical gates in quantum error-correcting codes

Beni Yoshida Perimeter Institute for Theoretical Physics
September 24, 2014

PIRSA:14090032
Quantum Physics
Lifshitz Field Theories, Anomalies and Hydrodynamics

Shira Chapman University of Amsterdam

September 23, 2014

PIRSA:14090083
Algebraic characterization of entanglement classes

Markus Grassl Max Planck Institute for the Science of Light
September 19, 2014

PIRSA:14090070
Quantum Physics
Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography
September 19, 2014

PIRSA:14090072
High Energy Physics

Condensed Matter

General Relativity & Quantum Cosmology
Observables and Change in Totally Constrained Systems

Karim Thebault Ludwig-Maximilians-Universität München (LMU)
September 18, 2014

PIRSA:14090004
General Relativity & Quantum Cosmology
Evolution of quantum field, particle content, and classicality in the three stage universe

Suprit Singh IUCAA - The Inter-University Centre for Astronomy and Astrophysics
September 18, 2014

PIRSA:14090082
Astrophysics
A magic bullet for numerous quantum-informational tasks

Mark Howard University of Waterloo

September 17, 2014

PIRSA:14090006
Boltzmann's Dog and Darwin's Finch: The statistical thermodynamics of self-replication and evolution

Jeremy England Massachusetts Institute of Technology (MIT)

September 17, 2014

PIRSA:14090003
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

ADMX: The Axion Dark Matter Experiment

Gray Rybka University of Washington
September 30, 2014

PIRSA:14090067
High Energy Physics
Axions are an exceptionally well-motivated dark matter candidate in addition to being a consequence of the Peccei-Quinn solution to the strong CP problem. ADMX (Axion Dark Matter eXperiment) has recently been selected as the axion search for the US DOE Second-Generation Dark Matter Program. I will discuss the imminent upgrade of ADMX to a definitive search for micro-eV mass dark matter axions as well as the ongoing research and development of new technologies to expand the reach of ADMX to the entire plausible dark matter axion mass range.
From Black Holes to Big Bang, and Back

Niayesh Afshordi University of Waterloo

September 30, 2014

PIRSA:14090088

By now, both black hole astrophysics and big bang cosmology are empirically well-established disciplines of physics and astronomy. They are also the only circumstances in nature where Einstein's general relativity can be seen in its full glory, and yet contain within them, its eventual and inevitable folly. Here, I will outline subtle lines evidence for why a phenomenologically successful description of big bang cosmology and black hole horizons may be intimately connected. These lines include a holographic description of big bang, thermal tachyacoustic cosmology, and the firewall controversy. Astrophysical observations, ranging from CMB and dark energy probes, to astrophysical neutrinos could shed further light on these potential connections.
Fault-tolerant logical gates in quantum error-correcting codes

Beni Yoshida Perimeter Institute for Theoretical Physics
September 24, 2014

PIRSA:14090032
Quantum Physics
Recently, Bravyi and Koenig have shown that there is a tradeoff between fault-tolerantly implementable logical gates and geometric locality of stabilizer codes. They consider locality-preserving operations which are implemented by a constant depth geometrically local circuit and are thus fault-tolerant by construction. In particular, they shown that, for local stabilizer codes in D spatial dimensions, locality preserving gates are restricted to a set of unitary gates known as the D-th level of the Clifford hierarchy. In this paper, we elaborate this idea and provide several extensions and applications of their characterization in various directions. First, we present a new no-go theorem for self-correcting quantum memory. Namely, we prove that a three-dimensional stabilizer Hamiltonian with a locality-preserving implementation of a non-Clifford gate cannot have a macroscopic energy barrier. Second, we prove that the code distance of a D-dimensional local stabilizer code with non-trivial locality-preserving m-th level Clifford logical gate is upper bounded by L^{D+1-m}. For codes with non-Clifford gates (m>2), this improves the previous best bound by Bravyi and Terhal. Third we prove that a qubit loss threshold of codes with non-trivial transversal m-th level Clifford logical gate is upper bounded by 1/m. As such, no family of fault-tolerant codes with transversal gates in increasing level of the Clifford hierarchy may exist. This result applies to arbitrary stabilizer and subsystem codes, and is not restricted to geometrically-local codes. Fourth we extend the result of Bravyi and Koenig to subsystem codes. A technical difficulty is that, unlike stabilizer codes, the so-called union lemma does not apply to subsystem codes. This problem is avoided by assuming the presence of error threshold in a subsystem code, and the same conclusion as Bravyi-Koenig is recovered. This is a joint work with Fernando Pastawski. arXiv:1408.1720
Lifshitz Field Theories, Anomalies and Hydrodynamics

Shira Chapman University of Amsterdam

September 23, 2014

PIRSA:14090083

I will review various aspects of field theories that posses a Lifshitz scaling symmetry. I will detail our study of the cohomological structure of anisotropic Weyl anomalies (the equivalent of trace anomalies in relativistic scale invariant field theories). I will also analyze the hydrodynamics of Lifshitz field theories and in particular of Lifshitz superfluids which may give insights into the physics of high temperature superconductors.
Algebraic characterization of entanglement classes

Markus Grassl Max Planck Institute for the Science of Light
September 19, 2014

PIRSA:14090070
Quantum Physics
Entanglement is a key feature of composite quantum system which is directly related to the potential power of quantum computers. In most computational models, it is assumed that local operations are relatively easy to implement. Therefore, quantum states that are related by local operations form a single entanglement class. In the case of local unitary operations, a finite set of polynomial invariants provides a complete characterization of the entanglement classes. Unfortunately, one faces the problem of combinatorial explosion so that computing such a complete set of invariants becomes difficult already for quite small system. The two main problems in this context are to compute invariants and to decide completeness, i.e., whether a given set of invariants generates the full invariant ring. Important tools are both univariate and multivariate Hilbert series which are already difficult to compute. We will also address computational aspects of these problems and techniques for showing completeness of a set of invariants.
Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography
September 19, 2014

PIRSA:14090072
High Energy Physics

Condensed Matter

General Relativity & Quantum Cosmology
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)
Observables and Change in Totally Constrained Systems

Karim Thebault Ludwig-Maximilians-Universität München (LMU)
September 18, 2014

PIRSA:14090004
General Relativity & Quantum Cosmology
We isolate an important physical distinction between gauge symmetries which exist at the level of histories and states, and those which exist at the level of histories and not states. This distinction is characterised explicitly using a generalized Hamilton-Jacobi formalism within which a non-standard prescription for the observables of classical totally constrained systems is developed. These ideas motivate a `relational quantization' procedure which is different from the standard `Dirac quanization'. In particular, relational quantization of totally constrained systems leads to a formalism with superpositions of energy eigenstates and an enlarged set of quantum observables. These `Kucha\v{r} observables' can change independently of each other, and thus are associated with measurable quantities in excess of the `perennials' of the standard Dirac approach.
Evolution of quantum field, particle content, and classicality in the three stage universe

Suprit Singh IUCAA - The Inter-University Centre for Astronomy and Astrophysics
September 18, 2014

PIRSA:14090082
Astrophysics
I will discuss the evolution of a quantum scalar field in a toy universe which has three stages of evolution, viz., (i) an early (inflationary) de Sitter phase (ii) radiation-dominated phase and (iii) late-time (cosmological constant dominated) de Sitter phase. Using the Schr\"odinger picture, the scalar field equations are solved separately for the three stages and matched at the transition points. The boundary conditions are chosen so that field modes in the early de Sitter phase evolve from the Bunch-Davies vacuum state. I shall look the (time-dependent) particle content of this quantum state for the entire evolution of the universe and describe the various features both numerically and analytically. I shall also describe the quantum to classical transition in terms of a classicality parameter which tracks the particle creation and its effect on phase space correlation of the quantum field.
A magic bullet for numerous quantum-informational tasks

Mark Howard University of Waterloo

September 17, 2014

PIRSA:14090006

A class of d-level quantum states called "magic states", whose initial purpose was to enable universal fault-tolerant computation within error-correcting codes, has a surprisingly broad range of applications. We begin by describing their structure with respect to the Clifford hierarchy, and in terms of convex geometry before proceeding to their applications. They appear to have some relevance to the search for SIC-POVMs in certain prime dimensions. A version of the CHSH non-local game, using a d-ary alphabet and Pauli measurements, has an optimal quantum strategy using magic states. Finally, magic states exhibit nice symmetries (balanced, minimum uncertainty) with respect to Pauli measurements and consequently could find applications in areas like cryptography.
Boltzmann's Dog and Darwin's Finch: The statistical thermodynamics of self-replication and evolution

Jeremy England Massachusetts Institute of Technology (MIT)

September 17, 2014

PIRSA:14090003

Living things operate according to well-known physical laws, yet it is challenging to discern specific, non-trivial consequences of these constraints for how an organism that is a product of evolution must behave. Part of the difficulty here is that life lives very far from thermal equilibrium, where many of our traditional theoretical tools fail us. However, recent developments in nonequilibrium statistical mechanics may help light a way forward. The goal of this talk will be to explain some of these developments, and show how they begin to offer a new perspective on the physics of self-replication, natural selection, and evolution.
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.

Title	Speaker(s)	Date	Talk Type	Info link
ADMX: The Axion Dark Matter Experiment	Gray Rybka	2014-09-30	Scientific Series	View details
From Black Holes to Big Bang, and Back	Niayesh Afshordi	2014-09-30	Scientific Series	View details
Fault-tolerant logical gates in quantum error-correcting codes	Beni Yoshida	2014-09-24	Scientific Series	View details
Lifshitz Field Theories, Anomalies and Hydrodynamics	Shira Chapman	2014-09-23	Scientific Series	View details
Algebraic characterization of entanglement classes	Markus Grassl	2014-09-19	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
Observables and Change in Totally Constrained Systems	Karim Thebault	2014-09-18	Scientific Series	View details
Evolution of quantum field, particle content, and classicality in the three stage universe	Suprit Singh	2014-09-18	Scientific Series	View details
A magic bullet for numerous quantum-informational tasks	Mark Howard	2014-09-17	Scientific Series	View details
Boltzmann's Dog and Darwin's Finch: The statistical thermodynamics of self-replication and evolution	Jeremy England	2014-09-17	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

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ADMX: The Axion Dark Matter Experiment

From Black Holes to Big Bang, and Back

Fault-tolerant logical gates in quantum error-correcting codes

Lifshitz Field Theories, Anomalies and Hydrodynamics

Algebraic characterization of entanglement classes

Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography

Observables and Change in Totally Constrained Systems

Evolution of quantum field, particle content, and classicality in the three stage universe

A magic bullet for numerous quantum-informational tasks

Boltzmann's Dog and Darwin's Finch: The statistical thermodynamics of self-replication and evolution

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

Self-assembling tensor networks and holography in disordered spin chains

ADMX: The Axion Dark Matter Experiment

From Black Holes to Big Bang, and Back

Fault-tolerant logical gates in quantum error-correcting codes

Lifshitz Field Theories, Anomalies and Hydrodynamics

Algebraic characterization of entanglement classes

Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography

Observables and Change in Totally Constrained Systems

Evolution of quantum field, particle content, and classicality in the three stage universe

A magic bullet for numerous quantum-informational tasks

Boltzmann's Dog and Darwin's Finch: The statistical thermodynamics of self-replication and evolution

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

Self-assembling tensor networks and holography in disordered spin chains