Quantum Physics

Displaying 1453 - 1464 of 2239

Characterizing topological order form a microscopic lattice Hamiltonian

Lukasz Cincio Los Alamos National Laboratory
May 09, 2013

PIRSA:13050042
Quantum Physics

Condensed Matter
Topological Order with a Twist: Ising Anyons from an Abelian Model

Hector Bombin PsiQuantum Corp.
May 06, 2013

PIRSA:13050024
Quantum Physics
From Pauli's Principle to Fermionic Entanglement

Matthias Christandl ETH Zurich
May 03, 2013

PIRSA:13050005
Quantum Physics

Quantum Physics
Quantum measurements constrained by symmetry

Leon Loveridge University of York
April 30, 2013

PIRSA:13040124
Quantum Physics
Laws of thermodynamics beyond the von Neumann regime

Oscar Dahlsten City University of Hong Kong
April 29, 2013

PIRSA:13040112
Quantum Physics
Tensor Networks: an Overview

Lukasz Cincio Los Alamos National Laboratory
April 25, 2013

PIRSA:13040131
Quantum Physics
The continuum limit of tensor networks: a path integral representation

David Jennings Imperial College London
April 22, 2013

PIRSA:13040113
Quantum Physics
The theory of composition in physics

Lucien Hardy Perimeter Institute for Theoretical Physics
April 16, 2013

PIRSA:13040121
Quantum Physics
Continuous-variable entanglement distillation and non-commutative central limit theorems

Earl Campbell University of Sheffield
April 15, 2013

PIRSA:13040122
Quantum Physics
Classical and quantum circuit obfuscation with braids

Stephen Jordan National Institute of Standards and Technology
April 08, 2013

PIRSA:13040111
Quantum Physics
12/13 PSI - Explorations on Quantum Information Lecture 14

David Cory Institute for Quantum Computing (IQC)
April 05, 2013

PIRSA:13040037
Quantum Physics
12/13 PSI - Explorations on Quantum Information Lecture 13

David Cory Institute for Quantum Computing (IQC)
April 04, 2013

PIRSA:13040036
Quantum Physics

Characterizing topological order form a microscopic lattice Hamiltonian

Lukasz Cincio Los Alamos National Laboratory
May 09, 2013

PIRSA:13050042
Quantum Physics

Condensed Matter
In this talk I will show how to obtain a detailed characterization of the emergent topological order starting from microscopic Hamiltonian on a two dimensional lattice. A key step is to obtain a tensor network representation for a complete set of ground states of the Hamiltonian, ﬁrst on an inﬁnite cylinder and then on a ﬁnite torus. As an application of the method I will study lattice Hamiltonians that give rise to selected anyon models, namely chiral semion, Ising as well as Z_3 and Z_5 models.
Topological Order with a Twist: Ising Anyons from an Abelian Model

Hector Bombin PsiQuantum Corp.
May 06, 2013

PIRSA:13050024
Quantum Physics
Anyon models can be symmetric under some permutations of their topological charges. One can then conceive topological defects that, under monodromy, transform anyons according to a symmetry. We study the realization of such defects in the toric code model, showing that a process where defects are braided and fused has the same outcome as if they were Ising anyons.
From Pauli's Principle to Fermionic Entanglement

Matthias Christandl ETH Zurich
May 03, 2013

PIRSA:13050005
Quantum Physics

Quantum Physics
The Pauli exclusion principle is a constraint on the natural occupation numbers of fermionic states. It has been suspected for decades, and only proved very recently, that there is a multitude of further constraints on these numbers, generalizing the Pauli principle. Surprisingly, these constraints are linear: they cut out a geometric object known as a polytope. This is a beautiful mathematical result, but are there systems whose physics is governed by these constraints? In order to address this question, we studied a system of a few fermions connected by springs. As we varied the spring constant, the occupation numbers moved within the polytope. The path they traced hugs very close to the boundary of the polytope, suggesting that the generalized constraints affect the system. I will mention the implications of these findings for the structure of few-fermion ground states and then discuss the relation between the geometry of the polytope and different types of fermionic entanglement.
Quantum measurements constrained by symmetry

Leon Loveridge University of York
April 30, 2013

PIRSA:13040124
Quantum Physics
The Wigner-Araki-Yanase (WAY) theorem delineates circumstances under which a class of quantum measurements is ruled out. Specifically, it states that any observable (given as a self adjoint operator) not commuting with an additive conserved quantity of a quantum system and measuring apparatus combined admits no repeatable measurements. I'll review the content of this theorem and present some new work which generalises and strengthens the existing results. The observation that the WAY constraint vanishes if the observable-to-be-measured is ``relativised'' (in a suitable sense) points to interesting links with quantum reference frames and superselection rules. I'll discuss some of these connections and raise some open questions.
Laws of thermodynamics beyond the von Neumann regime

Oscar Dahlsten City University of Hong Kong
April 29, 2013

PIRSA:13040112
Quantum Physics
A recent development in information theory is the generalisation of quantum Shannon information theory to the operationally motivated smooth entropy information theory, which originates in quantum cryptography research. In a series of papers the first steps have been taken towards creating a statistical mechanics based on smooth entropy information theory. This approach turns out to allow us to answer questions one might not have thought were possible in statistical mechanics, such as how much work one can extract in a given realisation, as a function of the failure-probability. This is in contrast to the standard approach which makes statements about average work. Here we formulate the laws of thermodynamics that this new approach gives rise to. We show in particular that the Second Law needs to be tightened. The new laws are motivated by our main quantitative result which states how much work one can extract or must invest in order to affect a given state change with a given probability of success. For systems composed of very large numbers of identical and uncorrelated subsystems, which we call the von Neumann regime, we recover the standard von Neumann entropy statements.

Joint work with Egloff, Renner and Vedral

http://arxiv.org/abs/1207.0434
Tensor Networks: an Overview

Lukasz Cincio Los Alamos National Laboratory
April 25, 2013

PIRSA:13040131
Quantum Physics
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.
The continuum limit of tensor networks: a path integral representation

David Jennings Imperial College London
April 22, 2013

PIRSA:13040113
Quantum Physics
I will discuss a path-integral representation of continuum tensor networks that extends the continuous MPS class for 1-D quantum fields to arbitrary spatial dimensions while encoding desirable symmetries. The physical states can be interpreted as arising through a continuous measurement process by a lower dimensional virtual field with Lorentz symmetry. The resultant physical states naturally obey entropy area laws, with the expectation values of observables determined by the dissipative dynamics of the boundary field. The class offers the prospect of powerful new analytical and computational tools to describe the physics of strongly interacting field systems.
The theory of composition in physics

Lucien Hardy Perimeter Institute for Theoretical Physics
April 16, 2013

PIRSA:13040121
Quantum Physics
We develop a theory for describing composite objects in physics. These can be static objects, such as tables, or things that happen in spacetime (such as a region of spacetime with fields on it regarded as being composed of smaller such regions joined together). We propose certain fundamental axioms which, it seems, should be satisfied in any theory of composition. A key axiom is the order independence axiom which says we can describe the composition of a composite object in any order. Then we provide a notation for describing composite objects that naturally leads to these axioms being satisfied. In any given physical context we are interested in the value of certain properties for the objects (such as whether the object is possible, what probability it has, how wide it is, and so on). We associate a generalized state with an object. This can be used to calculate the value of those properties we are interested in for for this object. We then propose a certain principle, the composition principle, which says that we can determine the generalized state of a composite object from the generalized states for the components by means of a calculation having the same structure as the description of the generalized state. The composition principle provides a link between description and prediction.
Continuous-variable entanglement distillation and non-commutative central limit theorems

Earl Campbell University of Sheffield
April 15, 2013

PIRSA:13040122
Quantum Physics
Entanglement distillation transforms weakly entangled noisy states into highly entangled states, a primitive to be used in quantum repeater schemes and other protocols designed for quantum communication and key distribution. In this work, we present a comprehensive framework for continuous-variable entanglement distillation schemes that convert noisy non-Gaussian states into Gaussian ones in many iterations of the protocol. Instances of these protocols include the recursive Gaussifier protocol and the pumping Gaussifier protocol. The flexibility of these protocols give rise to several beneficial trade-offs related to success probabilities or memory requirements that can be adjusted to reflect experimental specifics. Despite these protocols involving measurements, we relate the convergence in this protocols to new instances of non-commutative central limit theorems. Implications of the findings for quantum repeater schemes are discussed.
Classical and quantum circuit obfuscation with braids

Stephen Jordan National Institute of Standards and Technology
April 08, 2013

PIRSA:13040111
Quantum Physics
A circuit obfuscator is an algorithm that translates logic circuits into functionally-equivalent similarly-sized logic circuits that are hard to understand. While ad hoc obfuscators have been implemented, theoretical progress has mainly been limited to no-go results. In this work, we propose a new notion of circuit obfuscation, which we call partial indistinguishability. We then prove that, in contrast to previous definitions of obfuscation, partial indistinguishability obfuscation can be achieved by a polynomial-time algorithm. Specifically, our algorithm re-compiles the given circuit using a gate that satisfies the relations of the braid group, and then reduces to a braid normal form. Variants of our obfuscation algorithm can be applied to both classical and quantum circuits.
12/13 PSI - Explorations on Quantum Information Lecture 14

David Cory Institute for Quantum Computing (IQC)
April 05, 2013

PIRSA:13040037
Quantum Physics
12/13 PSI - Explorations on Quantum Information Lecture 13

David Cory Institute for Quantum Computing (IQC)
April 04, 2013

PIRSA:13040036
Quantum Physics

Title	Speaker(s)	Date	Talk Type	Info link
Characterizing topological order form a microscopic lattice Hamiltonian	Lukasz Cincio	2013-05-09	Conference	View details
Topological Order with a Twist: Ising Anyons from an Abelian Model	Hector Bombin	2013-05-06	Conference	View details
From Pauli's Principle to Fermionic Entanglement	Matthias Christandl	2013-05-03	Scientific Series	View details
Quantum measurements constrained by symmetry	Leon Loveridge	2013-04-30	Scientific Series	View details
Laws of thermodynamics beyond the von Neumann regime	Oscar Dahlsten	2013-04-29	Scientific Series	View details
Tensor Networks: an Overview	Lukasz Cincio	2013-04-25	Conference	View details
The continuum limit of tensor networks: a path integral representation	David Jennings	2013-04-22	Scientific Series	View details
The theory of composition in physics	Lucien Hardy	2013-04-16	Scientific Series	View details
Continuous-variable entanglement distillation and non-commutative central limit theorems	Earl Campbell	2013-04-15	Scientific Series	View details
Classical and quantum circuit obfuscation with braids	Stephen Jordan	2013-04-08	Scientific Series	View details
12/13 PSI - Explorations on Quantum Information Lecture 14	David Cory	2013-04-05	Course	View details
12/13 PSI - Explorations on Quantum Information Lecture 13	David Cory	2013-04-04	Course	View details

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Format results

Characterizing topological order form a microscopic lattice Hamiltonian

Topological Order with a Twist: Ising Anyons from an Abelian Model

From Pauli's Principle to Fermionic Entanglement

Quantum measurements constrained by symmetry

Laws of thermodynamics beyond the von Neumann regime

Tensor Networks: an Overview

The continuum limit of tensor networks: a path integral representation

The theory of composition in physics

Continuous-variable entanglement distillation and non-commutative central limit theorems

Classical and quantum circuit obfuscation with braids

12/13 PSI - Explorations on Quantum Information Lecture 14

12/13 PSI - Explorations on Quantum Information Lecture 13

Characterizing topological order form a microscopic lattice Hamiltonian

Topological Order with a Twist: Ising Anyons from an Abelian Model

From Pauli's Principle to Fermionic Entanglement

Quantum measurements constrained by symmetry

Laws of thermodynamics beyond the von Neumann regime

Tensor Networks: an Overview

The continuum limit of tensor networks: a path integral representation

The theory of composition in physics

Continuous-variable entanglement distillation and non-commutative central limit theorems

Classical and quantum circuit obfuscation with braids

12/13 PSI - Explorations on Quantum Information Lecture 14

12/13 PSI - Explorations on Quantum Information Lecture 13