Scientific Series

Displaying 3649 - 3660 of 5164

Massive gravitons, the cosmological constant and new directions in gravity
November 14, 2012

PIRSA:12110061
Cosmology
Quasiprobability representations of qubits

November 13, 2012

PIRSA:12110070
Anomaly-induced transport and thermodynamics

Kristan Jensen University of Victoria
November 13, 2012

PIRSA:12110047
Quantum Fields and Strings
Stealthy, Composite Stops

Philip Tanedo Cornell University
November 13, 2012

PIRSA:12110063
Particle Physics
Recent progress on de Sitter S-matrix

Ian Morrison West Chester University
November 13, 2012

PIRSA:12110043
Cosmology
Geometric algebra techniques in flux compactifications

Calin Lazaroiu Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering
November 09, 2012

PIRSA:12110058
Mathematical physics
Dynamical evaporation of quantum horizons
November 08, 2012

PIRSA:12110064
Quantum Gravity
Optimal quantum self-tests based on binary nonlocal XOR games

November 07, 2012

PIRSA:12110067
An introduction to quantum channels and their capacities

Graeme Smith Institute for Quantum Computing (IQC)
November 07, 2012

PIRSA:12110066
Quantum Information
What's an unknown POVM, and what does a two qubit state look like?

Matthew Pusey University of York

November 06, 2012

PIRSA:12110068
Holomorphic Blocks in 3d

Tudor Dimofte University of Edinburgh
November 06, 2012

PIRSA:12110056
Quantum Fields and Strings
Primordial Magnetic Fields & Non-Gaussianity

Martin Sloth University of Southern Denmark
November 06, 2012

PIRSA:12110040
Cosmology

Massive gravitons, the cosmological constant and new directions in gravity
November 14, 2012

PIRSA:12110061
Cosmology
The solutions to the cosmological constant problems may involve modifying the very long-range dynamics of gravity by adding new degrees of freedom. As an example of a conservative and minimal such modification, we consider the possibility that the graviton has a very small mass. Massive gravity has received renewed interest due to recent advances which have resolved its traditional problems. This kind of modification has some peculiar and unexpected features, and it points us towards a universe which looks quite unfamiliar.
Support for this colloquium is provided by The Templeton Frontiers Program.
Quasiprobability representations of qubits

November 13, 2012

PIRSA:12110070

Negativity in a quasi-probability representation is typically interpreted as an indication of nonclassical behavior. However, this does not preclude bases that are non-negative from having interesting applications---the single-qubit stabilizer states have non-negative Wigner functions and yet play a fundamental role in many quantum information tasks. We determine what other sets of quantum states and measurements of a qubit can be non-negative in a quasiprobability representation, and identify nontrivial groups of unitary transformations that permute such states. These sets of states and measurements are analogous to the single-qubit stabilizer states. We show that no quasiprobability representation of a qubit can be non-negative for more than two bases in any plane of the Bloch sphere. Furthermore, there is a single family of sets of four bases that can be non-negative in an arbitrary quasiprobability representation of a qubit. We provide an exhaustive list of the sets of single-qubit bases that are nonnegative in some quasiprobability representation and are also closed under a group of unitary transformations, revealing two families of such sets of three bases. We also show that not all two-qubit Clifford transformations can preserve non-negativity in any quasiprobability representation that is non-negative for the computational basis. This is in stark contrast to the qutrit case, in which the discrete Wigner function is non-negative for all n-qutrit stabilizer states and Clifford transformations. We also provide some evidence that extending the other sets of non-negative single-qubit states to multiple qubits does not give entangled states.
Anomaly-induced transport and thermodynamics

Kristan Jensen University of Victoria
November 13, 2012

PIRSA:12110047
Quantum Fields and Strings
I will discuss recent progress in the study of anomaly-induced transport, focusing on the chiral vortical effect in 3+1 dimensions. Most of my discussion will be framed in light of a larger story, namely progress in making exact statements about finite-temperature quantum field theory, for which the chiral magnetic and vortical effects are instructive prototypes.
Stealthy, Composite Stops

Philip Tanedo Cornell University
November 13, 2012

PIRSA:12110063
Particle Physics
Light third generation superpartners are one way to avoid bounds on new physics from the early LHC. We will review the theory and phenomenology of light stops and highlight a particular UV model based a partially composite electroweak sector through Seiberg duality.
Recent progress on de Sitter S-matrix

Ian Morrison West Chester University
November 13, 2012

PIRSA:12110043
Cosmology
The de Sitter S-matrix provides a gauge-invariant and field redefinition-invariant window into de Sitter QFTs and may provide a crucial entry in any dS/CFT dictionary. In this talk I will summarize recent progress on developing the S-matrix for theories with gauge fields and perturbative gravity. Nonrenormalization theorems, hints of supersymmetry, and perturbative stability will be discussed.
Geometric algebra techniques in flux compactifications

Calin Lazaroiu Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering
November 09, 2012

PIRSA:12110058
Mathematical physics
Using techniques originating in a certain approach to Clifford bundles known as "geometric algebra", I discuss a geometric reformulation of constrained generalized Killing spinor equations which proves to be particularly effective in the study and classification of supersymmetric flux compactifications of string and M-theory. As an application, I discuss the most general N=2 compactifications of M-theory to three dimensions, which were never studied in full generality before. I also touch upon the connection of such techniques with a certain variant of the quantization of spin systems.
Dynamical evaporation of quantum horizons
November 08, 2012

PIRSA:12110064
Quantum Gravity
We describe of the evaporation process as driven by the dynamical evolution of the quantum gravitational degrees of freedom resident at the horizon, as identified by the Loop Quantum Gravity kinematics. Using a parallel with the Brownian motion, we interpret the first law of quantum dynamical horizon in terms of a fluctuation-dissipation relation applied to this fundamental discrete structure. In this way, the horizon evolution is described in terms of relaxation to an equilibrium state balanced by the excitation of Planck scale constituents of the horizon. We show how from this setting the emergence of several conservative scenarios for the final stage of the evaporation process can be microscopically derived. Namely, the leakage of part of the horizon quantum geometry information prior to the Planckian phase and the stabilization of the hole surface shrinkage forming a massive remnant, which can eventually decay, are shown to take place.
Optimal quantum self-tests based on binary nonlocal XOR games

November 07, 2012

PIRSA:12110067

Self-testing a multipartite quantum state means verifying the existence of the state based on the outcomes of unknown or untrusted measurements. This concept is important in device-independent quantum cryptography. There are some previously known results on self-testing which involve nonlocal binary XOR games such as the CHSH test and the GHZ paradox. In our work we expand on these results. We provide a general criterion which, when satisfied, guarantees that a given nonlocal binary XOR game is a robust self-test. The error term in this result is quadratic, which is the best possible. In my talk I will explain the conceptual basis for the criterion and offer some examples. This is joint work with Yaoyun Shi (arXiv:1207.1819).
An introduction to quantum channels and their capacities

Graeme Smith Institute for Quantum Computing (IQC)
November 07, 2012

PIRSA:12110066
Quantum Information
A quantum communication channel can be put to many uses: it can transmit classical information, private classical information, or quantum information. It can be used alone, with shared entanglement, or together with other channels. For each of these settings there is a capacity that quantifies a channel's fundamental potential for communication. In this introductory talk, I will discuss what we known about the various capacities of a quantum channel, including a discussion of synergies between different channels and related additivity questions.
What's an unknown POVM, and what does a two qubit state look like?

Matthew Pusey University of York

November 06, 2012

PIRSA:12110068

If probabilities represent knowledge, what is an "unknown
probability"? De Finetti's theorem licenses the view that it is simply a
convenient metaphor for a certain class of knowledge about a series of
events. There are quantum versions for "unknown states" and "unknown
channels". I will explain how "unknown measurements" can be rehabilitated
too.

I will then move to a totally different topic. The Bloch sphere is handy
for representing qubit states, but the equivalent for two qubits is
15-dimensional! I will advocate instead drawing the set of states that Bob
can steer Alice to, the "steering ellipsoid". I will show how entanglement
and discord look from this perspective, and outline a geometric
classification of separable two qubit states.
Holomorphic Blocks in 3d

Tudor Dimofte University of Edinburgh
November 06, 2012

PIRSA:12110056
Quantum Fields and Strings
Recently techniques have been developed to compute the partition functions of 3d theories with N=2 supersymmetry on curved, compact spaces, in particular S^3 and S^2xS^1 (the latter giving a supersymmetric index). I will discuss how both of these partition functions can be decomposed as products of more fundamental, universal "holomorphic blocks." For 3d gauge theories arising from (auxiliary) 3-manifolds M, these holomorphic blocks are specific Chern-Simons partition functions on M.
Primordial Magnetic Fields & Non-Gaussianity

Martin Sloth University of Southern Denmark
November 06, 2012

PIRSA:12110040
Cosmology
There are indications of a lower bound on magnetic fields in the intergalactic media. Since magnetic fields on such large scales are difficult to generate in the late universe, this might point to inflationary magnetogenesis as the origin of intergalactic magnetic fields. If the magnetic fields are generated during inflation, they are naturally correlated with the inflaton perturbations in a general class of models. This leads to a consistency relation between the power spectrum of primordial magnetic fields and the non-Gaussian three-point cross-correlation of magnetic fields with the inflaton perturbation. The size of non-Gaussianity can be expressed in a new magnetic non-linearity parameter b_NL. In the flattened shape where the non-Gaussianity is maximal, b_NL can be as large as 5000.

Title	Speaker(s)	Date	Talk Type	Info link
Massive gravitons, the cosmological constant and new directions in gravity		2012-11-14	Scientific Series	View details
Quasiprobability representations of qubits		2012-11-13	Scientific Series	View details
Anomaly-induced transport and thermodynamics	Kristan Jensen	2012-11-13	Scientific Series	View details
Stealthy, Composite Stops	Philip Tanedo	2012-11-13	Scientific Series	View details
Recent progress on de Sitter S-matrix	Ian Morrison	2012-11-13	Scientific Series	View details
Geometric algebra techniques in flux compactifications	Calin Lazaroiu	2012-11-09	Scientific Series	View details
Dynamical evaporation of quantum horizons		2012-11-08	Scientific Series	View details
Optimal quantum self-tests based on binary nonlocal XOR games		2012-11-07	Scientific Series	View details
An introduction to quantum channels and their capacities	Graeme Smith	2012-11-07	Scientific Series	View details
What's an unknown POVM, and what does a two qubit state look like?	Matthew Pusey	2012-11-06	Scientific Series	View details
Holomorphic Blocks in 3d	Tudor Dimofte	2012-11-06	Scientific Series	View details
Primordial Magnetic Fields & Non-Gaussianity	Martin Sloth	2012-11-06	Scientific Series	View details

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