Conference

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Path Integrals, Reality and Generalizations of Quantum Theory

Adrian Kent
University of Cambridge
May 29, 2013

PIRSA:13050065
Quantum Information

Quantum Foundations
Constraints on generalizations of quantum theory
- Adan Cabello
  Universidad de Sevilla
- Robert Spekkens
  Perimeter Institute for Theoretical Physics
- Joseph Emerson
  Institute for Quantum Computing (IQC)
- Terry Rudolph
  Imperial College London
- Renato Renner
  ETH Zurich
May 28, 2013

PIRSA:13050085
Quantum Information

Quantum Fields and Strings
Collapse and Consequences

Philip Pearle
Hamilton College
May 28, 2013

PIRSA:13050064
Quantum Fields and Strings
Ontology of collapse theories

Wayne Myrvold
Western University

May 28, 2013

PIRSA:13050063
The Quantum-Mechanical Measurement Problem and the Foundations of Statistical Mechanics

David Albert
Columbia University
May 28, 2013

PIRSA:13050062
Quantum Foundations
Phenomenology of spontaneous wave-function collapse models

Angelo Bassi
University of Trieste
May 27, 2013

PIRSA:13050066
Quantum Fields and Strings
Quantum Mechanics and Spacetime

Bill Unruh
University of British Columbia
May 27, 2013

PIRSA:13050060
Quantum Fields and Strings
On the non-extendibility of quantum theory
May 27, 2013

PIRSA:13050059
Quantum Information
Entanglement at strongly-interacting quantum critical points in 2+1D

Roger Melko
University of Waterloo
May 10, 2013

PIRSA:13050051
Quantum Information
A gauge theory generalization of the fermion-doubling theorem

John McGreevy
University of California, San Diego
May 10, 2013

PIRSA:13050050
Quantum Fields and Strings

Condensed Matter
Momentum polarization: an entanglement measure of topological spin and chiral central charge

Xiaoliang Qi
Stanford University
May 10, 2013

PIRSA:13050047
Condensed Matter
Twisted Symmetry in Tensor Network States and Topological Order

Oliver Buerschaper
Multiverse Computing (Germany)
May 10, 2013

PIRSA:13050048
Quantum Information

Condensed Matter

Path Integrals, Reality and Generalizations of Quantum Theory

Adrian Kent
University of Cambridge
May 29, 2013

PIRSA:13050065
Quantum Information

Quantum Foundations
I describe some tentative new ideas on modified versions of quantum theory motivated by the path integral formalism, and on other generalizations, and comment on possible experimental implications.
Constraints on generalizations of quantum theory
- Adan Cabello
  Universidad de Sevilla
- Robert Spekkens
  Perimeter Institute for Theoretical Physics
- Joseph Emerson
  Institute for Quantum Computing (IQC)
- Terry Rudolph
  Imperial College London
- Renato Renner
  ETH Zurich
May 28, 2013

PIRSA:13050085
Quantum Information

Quantum Fields and Strings
Collapse and Consequences

Philip Pearle
Hamilton College
May 28, 2013

PIRSA:13050064
Quantum Fields and Strings
I shall give an introduction to conceptual ideas and equations of the CSL (Continuous Spontaneous Localization) theory of dynamical wave function collapse. Then, I shall discuss various applications of the theory.
Ontology of collapse theories

Wayne Myrvold
Western University

May 28, 2013

PIRSA:13050063

The textbook collapse postulate says that, after a measurement, the quantum state of the system on which the measurement was performed , and becomes an eigenstate of the observable measured. Naively, this is what one would expect of dynamical collapse theories. What one gets, instead, is an approximation to such eigenstates. This leaves us with the question of how to interpret such theories as representing a macroscopically definite world. In this talk, I will review some approaches to the ontology of collapse theories, and raise the question: do these yield rival accounts of the nature of the physical world, or are they mere choices of how to hang talk about ordinary objects onto a theory whose physical import is already clear?
The Quantum-Mechanical Measurement Problem and the Foundations of Statistical Mechanics

David Albert
Columbia University
May 28, 2013

PIRSA:13050062
Quantum Foundations
Phenomenology of spontaneous wave-function collapse models

Angelo Bassi
University of Trieste
May 27, 2013

PIRSA:13050066
Quantum Fields and Strings
Models of spontaneous wave function collapse make predictions, which are different from those of standard quantum mechanics. Indeed, these models can be considered as a rival theory, against which the standard theory can be tested, in pretty much the same way in which parametrized post-Newtonian gravitational theories are rival theories of general relativity. The predictions of collapse models almost coincide with those of standard quantum mechanics at the microscopic level, as these models have to account for the microscopic world, as we know it. Departures become significant when the size of the system increases. However, for larger systems environmental influences become more and more difficult to eliminate. This is the reason why it is tricky to test collapse models experimentally, and so far no decisive test has been performed. We will review the main phenomenological properties of collapse models, in particular the so-called amplification mechanics, as well as the main models, which are debated in the literature (GRW, CSL, QMUPL, DP). We will review the lower bounds on the collapse parameter, and more importantly the upper bounds set by available experimental data. This data come both from experimental tests on earth, and from cosmological observations.
Quantum Mechanics and Spacetime

Bill Unruh
University of British Columbia
May 27, 2013

PIRSA:13050060
Quantum Fields and Strings
On the non-extendibility of quantum theory
May 27, 2013

PIRSA:13050059
Quantum Information
I will present a recent theorem that asserts that there cannot exist an "extension of quantum theory" that allows us to make more informative predictions about future measurable events (e.g., whether a horizontally polarized photon passes a polarization filter with a given orientation) than standard quantum theory. The theorem is based on two assumptions about the extended theory: (i) the theory should be compatible with quantum theory (this means, in practice, that the theory is not falsified by current experimental data); (ii) the theory should not preclude experimenters from freely choosing the measurement settings. More precisely, the latter assumption corresponds to the requirement that measurement settings can be chosen at random such that they are independent of any other events, except of course those that lie in the causal future of the choice (i.e., in its future light cone). In addition, I will discuss a corollary of the non-extendibility theorem which leads to the same conclusions as a recent theorem by Pusey, Barrett, and Rudolph on the "reality of the quantum state", based only on the above assumptions.
Entanglement at strongly-interacting quantum critical points in 2+1D

Roger Melko
University of Waterloo
May 10, 2013

PIRSA:13050051
Quantum Information
In two or more spatial dimensions, leading-order contributions to the scaling of entanglement entropy typically follow the "area" or boundary law. Although this leading-order scaling is non-universal, at a quantum critical point (QCP), the sub-leading behavior does contain universal physics. Different universal functions can be access through entangling regions of different geometries. For example, for polygonal shaped regions, quantum field theories have demonstrated that the subleading scaling is logarithmic, with a universal coefficient dependent on the number of vertices in the polygon. Although such universal quantities are routinely studied in non-interacting field theories, it often requires numerical simulation to access them in interacting theories. In this talk, I discuss quantum Monte Carlo (QMC) and numerical Linked-Cluster Expansion (NLCE) calculations of the Renyi entropies at the transverse-field Ising model QCP on the 2D square lattice. We calculate the universal coefficient of the vertex-induced logarithmic scaling term, and compare to non-interacting field theory calculations by Casini and Huerta. Also, we examine the shape dependence of the Renyi entropy for finite-size toroidal lattices with smooth boundaries. Such geometries provide a sensitive probe of the gapless wave function in the thermodynamic limit, and give new universal quantities that could be examined by future field-theoretical studies in 2+1D.
A gauge theory generalization of the fermion-doubling theorem

John McGreevy
University of California, San Diego
May 10, 2013

PIRSA:13050050
Quantum Fields and Strings

Condensed Matter
This talk is about obstructions to symmetry-preserving regulators of quantum field theories in 3+1 dimensions. New examples of such obstructions can be found using the fact that 4+1-dimensional SPT states are characterized by their edge states.
(Based on work in progress with S.M. Kravec.)
Momentum polarization: an entanglement measure of topological spin and chiral central charge

Xiaoliang Qi
Stanford University
May 10, 2013

PIRSA:13050047
Condensed Matter
Topologically ordered states are quantum states of matter with topological ground state degeneracy and quasi-particles carrying fractional quantum numbers and fractional statistics. The topological spin is an important property of a topological quasi-particle, which is the Berry phase obtained in the adiabatic self-rotation of the quasi-particle by . For chiral topological states with robust chiral edge states, another fundamental topological property is the edge state chiral central charge . In this paper we propose a new approach to compute the topological spin and chiral central charge in lattice models by defining a new quantity named as the momentum polarization. Momentum polarization is defined on the cylinder geometry as a universal subleading term in the average value of a "partial translation operator". We show that the momentum polarization is a quantum entanglement property which can be computed from the reduced density matrix, and our analytic derivation based on edge conformal field theory shows that the momentum polarization measures the combination of topological spin and central charge. Numerical results are obtained for two example systems, the non-Abelian phase of the honeycomb lattice Kitaev model, and the Laughlin state of a fractional Chern insulator described by a variational Monte Carlo wavefunction. The numerical results verifies the analytic formula with high accuracy, and further suggests that this result remains robust even when the edge states cannot be described by a conformal field theory. Our result provides a new efficient approach to characterize and identify topological states of matter from finite size numerics.
Twisted Symmetry in Tensor Network States and Topological Order

Oliver Buerschaper
Multiverse Computing (Germany)
May 10, 2013

PIRSA:13050048
Quantum Information

Condensed Matter

Title	Speaker(s)	Date	Talk Type	Info link
Path Integrals, Reality and Generalizations of Quantum Theory	Adrian Kent	2013-05-29	Conference	View details
Constraints on generalizations of quantum theory	Adan Cabello, Robert Spekkens, Joseph Emerson, Terry Rudolph, Renato Renner	2013-05-28	Conference	View details
Collapse and Consequences	Philip Pearle	2013-05-28	Conference	View details
Ontology of collapse theories	Wayne Myrvold	2013-05-28	Conference	View details
The Quantum-Mechanical Measurement Problem and the Foundations of Statistical Mechanics	David Albert	2013-05-28	Conference	View details
Phenomenology of spontaneous wave-function collapse models	Angelo Bassi	2013-05-27	Conference	View details
Quantum Mechanics and Spacetime	Bill Unruh	2013-05-27	Conference	View details
On the non-extendibility of quantum theory		2013-05-27	Conference	View details
Entanglement at strongly-interacting quantum critical points in 2+1D	Roger Melko	2013-05-10	Conference	View details
A gauge theory generalization of the fermion-doubling theorem	John McGreevy	2013-05-10	Conference	View details
Momentum polarization: an entanglement measure of topological spin and chiral central charge	Xiaoliang Qi	2013-05-10	Conference	View details
Twisted Symmetry in Tensor Network States and Topological Order	Oliver Buerschaper	2013-05-10	Conference	View details

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