Quantum Physics

Displaying 1549 - 1560 of 2289

The structure of meaning in natural language: a big money quantum foundations spin-off.

Bob Coecke Quantinuum
February 12, 2013

PIRSA:13020131
Quantum Physics
A positive and local formalism for quantum theory

Robert Oeckl Universidad Nacional Autónoma De Mexico (UNAM)
February 05, 2013

PIRSA:13020125
Quantum Physics
Pinning of Fermionic Occupation Numbers

Christian Schilling ETH Zurich
January 21, 2013

PIRSA:13010105
Quantum Physics
Exotic topological order from quantum fractal code

Beni Yoshida Perimeter Institute for Theoretical Physics
January 14, 2013

PIRSA:13010101
Quantum Physics
Quantum Chaos, Information Gain and Quantum Tomography.

Vaibhav Madhok Wilfrid Laurier University
December 11, 2012

PIRSA:12120036
Quantum Physics
If no information gain implies no disturbance, then any discrete physical theory is classical

Corsin Pfister
December 04, 2012

PIRSA:12120016
Quantum Physics
Principle of relativity for quantum theory

Marco Zaopo University of Pavia
November 20, 2012

PIRSA:12110073
Quantum Physics
An introduction to quantum channels and their capacities

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

PIRSA:12110066
Quantum Physics
Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

David Jennings Imperial College London
October 23, 2012

PIRSA:12100105
Quantum Physics
The effect of initial correlations on the evolution of quantum states

Mark Byrd Southern Illinois University Carbondale
October 15, 2012

PIRSA:12100045
Quantum Physics
Holographic Mutual Information is Monogamous

Patrick Hayden Stanford University
June 28, 2012

PIRSA:12060070
Quantum Physics
Does Time Exist?

Julian Barbour University of Oxford
June 06, 2012

PIRSA:12060007
Quantum Physics

The structure of meaning in natural language: a big money quantum foundations spin-off.

Bob Coecke Quantinuum
February 12, 2013

PIRSA:13020131
Quantum Physics
A positive and local formalism for quantum theory

Robert Oeckl Universidad Nacional Autónoma De Mexico (UNAM)
February 05, 2013

PIRSA:13020125
Quantum Physics
The general boundary formulation (GBF) is an atemporal, but spacetime local formulation of quantum theory. Usually it is presented in terms of the amplitude formalism, which, in the presence of a background time, recovers the pure state formalism of the standard formulation of quantum theory. After reviewing the essentials of the amplitude formalism I will introduce a new "positive formalism", which recovers instead a mixed state formalism. This allows to define general quantum operations within the GBF and opens it to quantum information theory. Moreover, the transition to the positive formalism eliminates operationally irrelevant structure, making the extraction of measurement probabilities more direct. As a consequence, the probability interpretation takes on a remarkably simple and compelling form. I shall describe implications of the positive formalism, both for our understanding of quantum theory and for the practical formulation of quantum theories. I also observe a certain convergence with Lucien Hardy's operator tensor formulation of quantum theory, on which I hope to comment
Pinning of Fermionic Occupation Numbers

Christian Schilling ETH Zurich
January 21, 2013

PIRSA:13010105
Quantum Physics
The problem of determining and describing the family of 1-particle reduced density operators (1-RDO) arising from N-fermion pure states (viapartial trace) is known as the fermionic quantum marginal problem. We present its solution, a multitude of constraints on the eigenvalues of the 1-RDO, generalizing the Pauli exclusion principle. To explore the relevance of these constraints we study an analytically solvable model of N fermions in a harmonic potential and determine the spectral `trajectory' corresponding to the ground state as function of the fermion-fermion interaction strength.Intriguingly, we find that the occupation numbers are almost, but not exactly, pinned to the boundary of the allowed region (quasi-pinned). Our findings suggest a generalization of the Hartree-Fock approximation.

see also: http://arxiv.org/abs/1210.5531
Exotic topological order from quantum fractal code

Beni Yoshida Perimeter Institute for Theoretical Physics
January 14, 2013

PIRSA:13010101
Quantum Physics
We present a family of three-dimensional local quantum codes with pairs of fractal logical operators. It has two polynomials over finite fields as input parameters which generate fractal shapes of anti-commuting logical operators, and possesses exotic topological order with quantum glassiness which is beyond descriptions of conventional topological field theory. A necessary and sufficient condition for being free from string-like logical operators is obtained under which the model works as marginally self-correcting quantum memory. We also provide theoretical tools to analyze physical and coding properties of translation symmetric stabilizer Hamiltonians.
Quantum Chaos, Information Gain and Quantum Tomography.

Vaibhav Madhok Wilfrid Laurier University
December 11, 2012

PIRSA:12120036
Quantum Physics
Quantum chaos is the study of quantum systems whose classical description is chaotic. How does chaos manifest itself in the quantum world? In recent years, attempts have been made to address this question from the perspective of quantum information theory. It is in this spirit that we study the connection between quantum chaos and information gain in the time series of a measurement record used for quantum tomography. The record is obtained as a sequence of expectation values of a Hermitian operator evolving under repeated application of the Floquet operator of the quantum kicked top on a large ensemble of identical systems. We find an increase in information gain and hence higher fidelities in the process when the Floquet maps employed increase in chaoticity. We make predictions for the information gain using random matrix theory in the fully chaotic regime and show a remarkable agreement between the two.
If no information gain implies no disturbance, then any discrete physical theory is classical

Corsin Pfister
December 04, 2012

PIRSA:12120016
Quantum Physics
(based on http://arxiv.org/abs/1210.0194) It has been suggested that nature could be discrete in the sense that the underlying state space of a physical system has only a finite number of pure states. For example, the Bloch ball of a single qubit could be discretized into small patches and only appear round to us due to experimental limitations. Here, we present a strong physical argument for the quantum theoretical property that every state space (even the smallest possible one, the qubit) has infinitely many pure states. We propose a simple physical postulate which dictates that in fact the only possible discrete theory is classical mechanics. More specifically, we postulate that no information gain implies no disturbance, or read in the contrapositive, that disturbance leads to some form of information gain. In a theory like quantum mechanics where we already know that the converse holds, i.e. information gain does imply disturbance, this can be understood as postulating an equivalence between disturbance and information gain. What is more, we show that non-classical discrete theories are still ruled out even if we relax the postulate to hold only approximately in the sense that no information gain only causes a small amount of disturbance. Finally, our postulate also rules out popular generalizations such as the PR-box that allows non-local correlations beyond the limits of quantum theory.
Principle of relativity for quantum theory

Marco Zaopo University of Pavia
November 20, 2012

PIRSA:12110073
Quantum Physics
In a generic quantum experiment we have a given set of devices analyzing some physical property of a system. To each device involved in the experiment we associate a set of random outcomes corresponding to the possible values of the variable analyzed by the device. Devices have apertures that permit physical systems to pass through them. Each aperture is labelled as "input" or "output" depending on whether it is assumed that the aperture lets the system go inside or outside the device. Assuming a particular input/output structure for the devices involved in a generic experiment is equivalent to assume a particular causal structure for the space-time events constituted by the outcomes happening on devices. The joint probability distribution of these outcomes is usually predicted assuming an absolutely defined input/output structure of devices. This means that all observers of the experiment agree on whether an aperture is labelled as "input" or "output". In this talk we show that the mathematical formalism of quantum theory permits to predict the joint probability distribution of outcomes in a generic experiment in such a way that the input/output structure is indeed relative to an observer. This means that two observers of the same experiment can predict the joint probability distribution of outcomes assuming different input/output labels for the apertures. Since input/output structure is the causal structure of the space-time events constituting the outcomes involved in the experiment we conclude that in quantum theory, the causal structure of events may not be regarded as absolute but rather as relative to the observer. We finally point out that properly extending this concept to the cosmological domain could shed light on the problem of dark energy.
An introduction to quantum channels and their capacities

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

PIRSA:12110066
Quantum Physics
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.
Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

David Jennings Imperial College London
October 23, 2012

PIRSA:12100105
Quantum Physics
I will discuss the central role of correlations in thermodynamic directionality, how strong correlations can distort the thermodynamic arrow and contrast these distortions in both the classical and quantum regimes. These distortions constitute non-linear entanglement witnesses, and give rise to a rich information-theoretic structure. I shall explain how these results are then cast into the language of fluctuation theorems to derive a generalized exchange fluctuation theorem, and discuss the limitations of such a framework.
The effect of initial correlations on the evolution of quantum states

Mark Byrd Southern Illinois University Carbondale
October 15, 2012

PIRSA:12100045
Quantum Physics
Until fairly recently, it was generally assumed that the initial state of a quantum system prepared for information processing was in a product state with its environment. If this is the case,
the evolution is described by a completely positive map. However, if the system and environment are initially correlated, or entangled, such that the so-called quantum discord is non-zero, then the
evolution is described by a map which is not completely positive. Maps that are not completely positive are not as well understood and the implications of having such a map are not completely known. I will discuss a few examples and a theorem (or two) which may help us understand the implications of having maps which are not completely positive.
Holographic Mutual Information is Monogamous

Patrick Hayden Stanford University
June 28, 2012

PIRSA:12060070
Quantum Physics
I'll describe a special information-theoretic property of quantum field theories with holographic duals: the mutual informations among arbitrary disjoint spatial regions A,B,C obey the inequality I(A:BC) >= I(A:B)+I(A:C), provided entanglement entropies are given by the Ryu-Takayanagi formula. Inequalities of this type are known as monogamy relations and are characteristic of measures of quantum entanglement. This suggests that correlations in holographic theories arise primarily from entanglement rather than classical correlations. Moreover, monogamy property implies that the Ryu-Takayanagi formula is consistent with all known general inequalities obeyed by the entanglement entropy, including an infinite set recently discovered by Cadney, Linden, and Winter; this constitutes significant evidence in favour of its validity.
Does Time Exist?

Julian Barbour University of Oxford
June 06, 2012

PIRSA:12060007
Quantum Physics

Title	Speaker(s)	Date	Talk Type	Info link
The structure of meaning in natural language: a big money quantum foundations spin-off.	Bob Coecke	2013-02-12	Scientific Series	View details
A positive and local formalism for quantum theory	Robert Oeckl	2013-02-05	Scientific Series	View details
Pinning of Fermionic Occupation Numbers	Christian Schilling	2013-01-21	Scientific Series	View details
Exotic topological order from quantum fractal code	Beni Yoshida	2013-01-14	Scientific Series	View details
Quantum Chaos, Information Gain and Quantum Tomography.	Vaibhav Madhok	2012-12-11	Scientific Series	View details
If no information gain implies no disturbance, then any discrete physical theory is classical	Corsin Pfister	2012-12-04	Scientific Series	View details
Principle of relativity for quantum theory	Marco Zaopo	2012-11-20	Scientific Series	View details
An introduction to quantum channels and their capacities	Graeme Smith	2012-11-07	Scientific Series	View details
Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.	David Jennings	2012-10-23	Scientific Series	View details
The effect of initial correlations on the evolution of quantum states	Mark Byrd	2012-10-15	Scientific Series	View details
Holographic Mutual Information is Monogamous	Patrick Hayden	2012-06-28	Conference	View details
Does Time Exist?	Julian Barbour	2012-06-06	Public Lectures	View details

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The structure of meaning in natural language: a big money quantum foundations spin-off.

A positive and local formalism for quantum theory

Pinning of Fermionic Occupation Numbers

Exotic topological order from quantum fractal code

Quantum Chaos, Information Gain and Quantum Tomography.

If no information gain implies no disturbance, then any discrete physical theory is classical

Principle of relativity for quantum theory

An introduction to quantum channels and their capacities

Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

The effect of initial correlations on the evolution of quantum states

Holographic Mutual Information is Monogamous

Does Time Exist?

The structure of meaning in natural language: a big money quantum foundations spin-off.

A positive and local formalism for quantum theory

Pinning of Fermionic Occupation Numbers

Exotic topological order from quantum fractal code

Quantum Chaos, Information Gain and Quantum Tomography.

If no information gain implies no disturbance, then any discrete physical theory is classical

Principle of relativity for quantum theory

An introduction to quantum channels and their capacities

Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

The effect of initial correlations on the evolution of quantum states

Holographic Mutual Information is Monogamous

Does Time Exist?