Talks

10753 - 10764 of 16543 Results

Causal Constraints on Possible Measurements

Leron Borsten
Heriot-Watt University

June 28, 2012

PIRSA:12060078

Quantum Fields and Strings
Holographic Mutual Information is Monogamous

Patrick Hayden
Stanford University

June 28, 2012

PIRSA:12060070

Quantum Information
Quantum Tasks in Minkowski Space

Adrian Kent
University of Cambridge

June 28, 2012

PIRSA:12060062

Mathematical physics
Entanglement Generation in Relativistic Quantum Fields

June 28, 2012

PIRSA:12060068
On the Preparation of States in Nonlinear Quantum Mechanics

Nicolas Menicucci
Royal Melbourne Institute of Technology University (RMIT)

June 28, 2012

PIRSA:12060048

Quantum Fields and Strings
Photon Location in Rindler Coordinates

June 28, 2012

PIRSA:12060066
Any Quantum State Can be Cloned in the Presence of a Closed Timelike Curve

June 28, 2012

PIRSA:12060075
Quantum Communication Between Localized, Non-Inertial Observers

Tim Ralph
University of Queensland

June 28, 2012

PIRSA:12060065
Future-past Correlations in Relativistic Quantum Information

Jorma Louko
University of Nottingham

June 28, 2012

PIRSA:12060064
Uncertainty Relations on a Planck Lattice and Black Hole Temperature

Fabio Scardigli
Politecnico Milano

June 27, 2012

PIRSA:12060063
TBA

Sandu Popescu
University of Bristol

June 27, 2012

PIRSA:12060071
Quantum Limits to the Measurement of Spacetime Geometry

Seth Lloyd
Massachusetts Institute of Technology (MIT) - Center for Extreme Quantum Information Theory (xQIT)

June 27, 2012

PIRSA:12060061

Causal Constraints on Possible Measurements

Leron Borsten
Heriot-Watt University

June 28, 2012

PIRSA:12060078

Quantum Fields and Strings

A crucial question in any approach to quantum information processing is: first, how are classical bits encoded physically in the quantum system, second, how are they then manipulated and, third, how are they finally read out? These questions are particularly challenging when investigating quantum information processing in a relativistic spacetime. An obvious framework for such an investigation is relativistic quantum field theory. Here, progress is hampered by the lack of a universally applicable rule for calculating the probabilities of the outcomes of ideal measurements on a relativistic quantum field in a collection of spacetime regions. Indeed, a straightforward relativistic generalisation of the non-relativistic formula for these probabilities leads to superluminal signalling.

Motivated by these considerations we ask what interventions/ideal measurements can we in principle make, taking causality as our guiding criterion. In the course of this analysis we reconsider various aspects of ideal measurements in QFT, detector models and the probability rules themselves. In particular, it is shown that an ideal measurement of a one–particle wave packet state of a relativistic quantum field in Minkowski spacetime enables superluminal signalling. The result holds for a measurement that takes place over an intervention region in spacetime whose extent in time in some frame is longer than the light crossing time of the packet in that frame.
Holographic Mutual Information is Monogamous

Patrick Hayden
Stanford University

June 28, 2012

PIRSA:12060070

Quantum Information

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.
Quantum Tasks in Minkowski Space

Adrian Kent
University of Cambridge

June 28, 2012

PIRSA:12060062

Mathematical physics

The fundamental properties of quantum information and its applications to computing and cryptography have been greatly illuminated by considering information-theoretic tasks that are provably possible or impossible within non-relativistic quantum mechanics. In this talk I describe a general framework for defining tasks within (special) relativistic quantum theory and illustrate it with examples from relativistic quantum cryptography.
Entanglement Generation in Relativistic Quantum Fields

June 28, 2012

PIRSA:12060068

We present a general, analytic recipe to compute the entanglement that is generated between arbitrary, discrete modes of bosonic quantum fields by Bogoliubov transformations. Our setup allows the complete characterization of the quantum correlations in all Gaussian field states. Additionally, it holds for all Bogoliubov transformations. These are commonly applied in quantum optics for the description of squeezing operations, relate the modedecompositions of observers in different regions of curved spacetimes, and describe observers moving along non-stationary trajectories. We focus on a quantum optical example in a cavity quantum electrodynamics setting: an uncharged scalar field within a cavity provides a model for an optical resonator, in which entanglement is created by non-uniform acceleration.We show that the amount of generated entanglement can be magnified by initialsingle-mode squeezing, for which we provide an explicit formula.Applications to quantum fields in curved spacetimes, such as an expanding universe, are discussed.
On the Preparation of States in Nonlinear Quantum Mechanics

Nicolas Menicucci
Royal Melbourne Institute of Technology University (RMIT)

June 28, 2012

PIRSA:12060048

Quantum Fields and Strings

Recent analysis of closed timelike curves from an information-theoretic perspective has led to contradictory conclusions about their information-processing power. One thing is generally agreed upon, however, which is that if such curves exist, the quantum-like evolution they imply would be nonlinear, but the physical interpretation of such theories is still unclear. It is known that any operationally verifiable instance of a nonlinear, deterministic evolution on some set of pure states makes the density matrix inadequate for representing mixtures of those pure states. We re-cast the problem in the language of operational quantum mechanics, building on previous work to show that the no-signalling requirement leads to a splitting of the equivalence classes of preparation procedures. This leads to the conclusion that any non-linear theory satisfying certain minimal conditions must be regarded as inconsistent unless it contains distinct representations for the two different kinds of mixtures, and incomplete unless it contains a rule for determining the physical preparations associated with each type. We refer to this as the `preparation problem' for nonlinear theories.
Photon Location in Rindler Coordinates

June 28, 2012

PIRSA:12060066

Bases of orthonormal localized states are constructed in Rindler coordinates and applied to an Unruh detector with good time resolution and an accelerated rod-like array detector.
Any Quantum State Can be Cloned in the Presence of a Closed Timelike Curve

June 28, 2012

PIRSA:12060075

Using the Deutsch approach, we show that the no-cloning theorem can be circumvented in the presence of closed timelike curves, allowing the perfect cloning of a quantum state chosen randomly from a finite alphabet of states. Further, we show that a universal cloner can be constructed that when acting on a completely arbitrary qubit state, exceeds the no-cloning bound on fidelity. Since the “no cloning theorem” has played a central role in the development of quantum information science, it is clear that the existence of closed timelike curves would radically change the rules for quantum information technology.
Quantum Communication Between Localized, Non-Inertial Observers

Tim Ralph
University of Queensland

June 28, 2012

PIRSA:12060065

An unsolved problem in relativistic quantum information research is how to model efficient, directional quantum communication between localised parties in a fully quantum field theoretical framework. We propose a tractable approach to this problem based on calculating expectation values of localized field observables in the Heisenberg Picture. We illustrate our approach by analysing, and obtaining approximate analytical solutions to, the problem of communicating quantum states between an inertial sender, Alice and an accelerated homodyne receiver, Rob. We discuss the effect on quantum protocols carried out over such a communication channel.
Future-past Correlations in Relativistic Quantum Information

Jorma Louko
University of Nottingham

June 28, 2012

PIRSA:12060064

In the Unruh effect, long-distance correlations in a pure quantum state cause accelerated observers to experience the state as a thermal bath. We discuss a similar phenomenon for quantum states that contain correlations between the distant future and the distant past. Examples include Minkowski half-space with a static mirror and an eternal black hole with an unusual global structure behind the horizon. The question of utilising the future-past correlations in quantum information tasks is raised.
Uncertainty Relations on a Planck Lattice and Black Hole Temperature

Fabio Scardigli
Politecnico Milano

June 27, 2012

PIRSA:12060063

After an introduction to generalized uncertainty principle(s), we study uncertainty relations as formulated in a crystal-like universe, whose lattice spacing is of order of Planck length. For Planckian energies, the uncertainty relation for position and momenta has a lower bound equal to zero. Connections of this result with 't Hooft's deterministic quantization proposal, and with double special relativity are briefly presented. We then apply our formulae to (micro) black holes, we derive a new mass-temperature relation for Schwarzschild black holes, and we discuss the new thermodynamic entropy and heat capacity. In contrast to standard results based on Heisenberg and stringy uncertainty relations, we obtain both a finite Hawking's temperature and a zero rest-mass remnant at the end of the (micro) black hole evaporation. [Ref.Paper: PRD 81, 084030 (2010). arXiv:0912.2253]
TBA

Sandu Popescu
University of Bristol

June 27, 2012

PIRSA:12060071
Quantum Limits to the Measurement of Spacetime Geometry

Seth Lloyd
Massachusetts Institute of Technology (MIT) - Center for Extreme Quantum Information Theory (xQIT)

June 27, 2012

PIRSA:12060061

This talk analyzes the limits that quantum mechanics imposes on the accuracy to which spacetime geometry can be measured. By applying the fundamental physical bounds to measurement accuracy ensembles of clocks and signals, as in the global positioning system, I present a covariant version of the quantum geometric limit, which states that the total number of ticks of clocks and clicks of detectors that can be contained in a four volume of spacetime of radius R and temporal extent is less than or equal to RT divided by the Planck length times the Planck time. The quantum geometric bound limits the number of events or `ops' that can take place in a four-volume of spacetime and is consistent with and complementary to the holographic bound which limits the number of bits that can exist within a three-volume of spacetime.

Title	Date	Collection	Type	Info
Causal Constraints on Possible Measurements	2012‑06‑28	Relativistic Quantum Information - 2012	Conference	View details
Holographic Mutual Information is Monogamous	2012‑06‑28	Relativistic Quantum Information - 2012	Conference	View details
Quantum Tasks in Minkowski Space	2012‑06‑28	Relativistic Quantum Information - 2012	Conference	View details
Entanglement Generation in Relativistic Quantum Fields	2012‑06‑28	Relativistic Quantum Information - 2012	Conference	View details
On the Preparation of States in Nonlinear Quantum Mechanics	2012‑06‑28	Relativistic Quantum Information - 2012	Conference	View details
Photon Location in Rindler Coordinates	2012‑06‑28	Relativistic Quantum Information - 2012	Conference	View details
Any Quantum State Can be Cloned in the Presence of a Closed Timelike Curve	2012‑06‑28	Relativistic Quantum Information - 2012	Conference	View details
Quantum Communication Between Localized, Non-Inertial Observers	2012‑06‑28	Relativistic Quantum Information - 2012	Conference	View details
Future-past Correlations in Relativistic Quantum Information	2012‑06‑28	Relativistic Quantum Information - 2012	Conference	View details
Uncertainty Relations on a Planck Lattice and Black Hole Temperature	2012‑06‑27	Relativistic Quantum Information - 2012	Conference	View details
TBA	2012‑06‑27	Relativistic Quantum Information - 2012	Conference	View details
Quantum Limits to the Measurement of Spacetime Geometry	2012‑06‑27	Relativistic Quantum Information - 2012	Conference	View details

Format results