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BOOK OF ABSTRACTS
Charis Anastopoulos (University of Patras, Greece)
Title: Relativistic quantum measurements and tunneling
Abstract: The time it takes a particle to tunnel through a classically forbidden potential
barrier has been debated ever since the early years of quantum theory. The debate involves
two distinct but interconnected problems: (i) there is no unambiguous definition of
tunneling time compatible with the rules of standard quantum theory, and (ii) most
definitions of tunneling time seem to imply that particles may cross the barrier at vanishingly
short times, thus implying the possibility of super-luminal speeds. We address this issue
within a new framework for relativistic quantum measurements that treats the spacetime
coordinates of events as random variables. Our approach leads to a precise definition of
tunneling times, valid also for relativistic systems, and to an explicit quantitative description
of the mechanism through which quantum field theory enforces causality in quantum
tunneling.
Daniel Bedingham (Imperial College, UK)
Title: Relativity and collapse models
Abstract: I will review some recent developments toward understanding how to formulate a
collapse model that is consistent with relativity. In collapse models it is supposed that
quantum state reduction is a genuine physical process, not just something we do when we
make a measurement. The task is to come up with some general equations for the
wavefunction evolution which would approximate well to either the Schrödinger equation or
quantum state reduction in situations where one of those descriptions is more appropriate.
The most famous example of this approach is the non-relativistic GRW or Spontaneous
localization model. I will give an introduction to the GRW model before discussing some
conceptual and technical issues to do with introducing relativity and outlining a proposal for
a relativistic collapse model.
David-Edward Bruschi (University of Leeds, UK)
Title: Towards relativistic quantum technologies
Abstract: In the past few years, the field of Relativistic Quantum Information has gained
attention from the scientific community. Research in the field is aimed towards
understanding how gravity and relativity affect entanglement and quantum information
tasks. Recently, attention was given towards the possible implementations of the
predictions of the theory in experimental settings. We discuss the role of localized devices
and their ability to store, extract and manipulate entanglement of global or local fields. We
discuss future directions and applications.
Theodosios Christodoulakis (University of Athens, Greece)
Title: Canonical quantization of constrained Lagrangians and conditional Symmetries
Abstract: A conditional symmetry is defined, in the phase-space of a quadratic in velocities
constrained action, as a simultaneous conformal symmetry of the supermetric and the
superpotential. It is proven that such a symmetry corresponds to a variational (Noether)
symmetry. The use of these symmetries as quantum conditions on the wave-function entails
a kind of selection rule. As an example, the minisuperspace model ensuing from a reduction
of the Einstein - Hilbert action by considering static, spherically symmetric configurations
and r as the independent dynamical variable, is canonically quantized. The conditional
symmetries of this reduced action are used as supplementary conditions on the wave
function. Their integrability conditions dictate, at a rst stage, that only one of the three
existing symmetries can be consistently imposed. At a second stage one is led to the unique
Casimir invariant, which is the product of the remaining two, as the only possible second
condition on Psi. The uniqueness of the dynamical evolution implies the need to identify this
quadratic integral of motion to the reparametrisation generator. This can be achieved by
fixing a suitable parametrization of the r-lapse function, exploiting the freedom to arbitrarily
rescale it. In this particular parametrization the measure is chosen to be the determinant of
the supermetric. The solutions to the combined Wheeler - DeWitt and linear conditional
symmetry equations are found and seen to depend on the product of the two "scale
factors".
Lajos Diosi (Wigner Research Centre for Physics, Hungary)
Title: Relativistic formulation of multiple localized quantum measurements
Abstract: I consider von Neumann detectors coupled locally to quantized relativistic fields.
The joint outcome statistics of the detectors can be expressed in explicit relativistically
invariant form based on standard field theory concepts like, e.g., time-ordering of the local
fields. Relevance for certain dynamic collapse models is briefly mentioned.
Juliusz Doboszewski (Jagiellonian University, Poland)
Title: Entanglement swapping and retrocausation
Abstract: We begin with Peres' [1999] thought experiment and its experimental realisation
by Ma et al. [2012]. According to the experiment, it is possible to produce entanglement
between two particles after their polarisation had been measured. This may give rise to the
curious view that quantum mechanics implies retrocausation. In Ma et al. words, "there is
never a paradox if the quantum state is viewed as to be no more than a 'catalogue of our
knowledge'", in other words, if the quantum state is to be interpreted statistically.
But another recent result by Pusey, Barrett & Rudolph [2012] forbids the statistical
interpretation. What, then, are quantum states if we take both of these into account? We
note first that (1) this causes serious problems for various proposed in the literature
theories, including branching space-times theory, and that (2) more generally, cobordism in
relativistic spacetimes cannot be exploited to make sense of quantum states. Then we argue
that even under ontic interpretation of quantum states, if there is a retrocausation to be
found in the experiment of Ma et al., it is of very different nature comparing to the
retrocausation considered in the literature either about Bell inequalities (de Bauregard,
Price) or in the closed time-like curves
Fay Dowker (Imperial College, UK)
Title: Dirac’s fork in the road: Spacetime or Hilbert space as the seat for reality?
Astract: In 1932 Dirac identified a "fork in the road" for the foundations of quantum
mechanics. Dirac stated that the lagrangian approach to classical mechanics was probably
more fundamental than the hamiltonian approach because the former is relativistically
invariant whereas the latter is "essentially nonrelativistic". Choosing the hamiltonian
approach leads in quantum theory to canonincal quantisation, Hilbert space, operators and
the textbook rules for state vector "collapse", which are all indeed more or less divorced
from the spacetime nature of the physical world as revealed by relativity. Taking the
"essentially relativistic" lagrangian branch of Dirac's fork however leads to the path integral,
as shown by Dirac in 1932 and developed by Feynman. The interpretation of quantum
mechanics in a path integral framework is based directly on events in spacetime. I will briefly
outline how seeking to extend the path integral from dealing only with "measurement
outcome events" to a quantum theory which treats microscopic and macroscopic physics on
the same footing leads to a second fork in the road. The choice at this fork is whether
ordinary probabilities are fundamental to quantum theory or not.
Demetris Ghikas (University of Patras, Greece)
Title: Some Applications to Quantum Information using tools derived from Quantum
Information Geometry.
Abstract: Quantum Information Geometry is a relatively new area of research that offers
many geometric tools for the analysis of mathematical problems related to Quantum
Information. After a short introduction we present a new metric on the manifold of states
which gives a higher bound of error for certain measurements related to the Quantum
Estimation Problem. Then we discuss various possibilities of Entaglement Quantification in
the framework of Information Geometry.
Joe Henson (Imperial College, UK)
Title: Separability, holism and Bell’s theorem
Abstract: Seperability can be defined in the following way: any statement that can be made
about events in a region of space-time is a logical combination of statements about events in
any given partition of that region. That is, events in large regions are nothing but
combinations of events in smaller regions. It is sometimes claimed in the literature that this
principle is an essential assumption of Bell's theorem, being necessary to the defintition of
any sensible "locality" principle. I will show that this is not the case, and a proof along the
lines of Bell's in "theory of local beables" does not rely on seperability. I will argue that
there is no evidence that Bell or Einstein intended seperability to be at the heart of their
arguments on locality, causality and the completeness of QM. Finally I will draw some wider
conclusions about what constitutes a "plausible response to Bell's theorem", arguing in
particular that it is futile to attack the significance of the theorem on the grounds that Bell's
local causality does not correctly embody "lack of superluminal influence
Beatrix Hiesmayr (University of Vienna, Austria)
Title: Entanglement, Relativistic Observers and Bell inequalities
Abstract: We analyze how entanglement of spin ½ particles changes for a boosted observer
[1]. We show that the change of entanglement arises, because a Lorentz boost on the
momenta of the particles causes a Wigner rotation of the spin, which in certain cases
entangles the spin with the momentum states. We systematically investigate the situation
for different classes of initial spin states and different partitions of the four-qubit space.
Furthermore, we study the behaviour of Bell inequalities for different observers and
demonstrate how the maximally possible degree of violation, using the Pauli-Lubanski spin
observable, can be recovered by any inertial observer.
Finding a meaningful classification of multipartite entanglement is a highly discussed topic.
In Ref.[2] we investigated which general conditions have to be met for any classification of
multipartite entanglement to be Lorentz invariant. This contributes to a physical
understanding of entanglement classification. We show that quantum information in a
relativistic setting requires the partition of the Hilbert space into particles to be taken
seriously. Furthermore, we study exemplary cases and show how the spin and momentum
entanglement transforms relativistically in a multipartite setting.
[1] N. Friis, R.A. Bertlmann, M. Huber, B.C. Hiesmayr Phys. Rev. A 81, 042114 (2010)
[2] M. Huber, N. Friis, A. Gabriel, Ch. Spengler and B.C. Hiesmayr EPL 95, Number 2, 20002
(2011)
Juan Leon (Instituto de Fisica Fundamental, Spain)
Title: Alice passes through a pinhole
Abstract: The emergence of an elementary system through an aperture is a seemingly
innocent phenomenon full of contradictions and apparently at clash with the demands of
locality. I shall use this case to separate mechanical localization (if it is not here, it is zero)
from field localization (if it is not here, there is the vacuum). The goal is to give an
understanding of the possibilities and limits to "putting a qubit somewhere" in spacetime.
Georgios Linardopoulos (National Center for Scientific Research “Demokritos”, Greece)
Title: Rotating Strings and Membranes in AdS/CFT
Abstract: We shall introduce the concept of Gauge/Gravity duality and present some of its
realizations as a correspondence between a quantum theory of gravity and a gauge
(quantum field) theory. The role of classical, bosonic rotating strings and membranes, in
studying the structure of the correspondence, will be stressed.
Nikolaos Pappas (University of Ioannina, Greece)
Title: On the preservation of unitarity during black hole’s evolution and information
extraction from its interior
Abstract: For more than 30 years the discovery that black holes radiate like black bodies of
specific temperature has triggered a multitude of puzzling questions concerning their nature
and the fate of information that goes down the black hole during its lifetime. The most tricky
issue in what is known as information loss paradox is the apparent violation of unitarity
during the formation/evaporation process of black holes. A new idea is proposed based on
the combination of our knowledge on Hawking radiation as well as the Einstein-PodolskyRosen phenomenon, that could resolve the paradox and spare physicists from the
unpalatable idea that unitarity can ultimately be irreversibly violated even under special
conditions.
Stefano Pironio (Université Libre de Bruxelles, Belgium)
Title: Quantum non-locality based on finite-speed causal influences leads to superluminal
signaling
Abstract: The experimental violation of Bell inequalities using spacelike separated
measurements precludes the explanation of quantum correlations through causal influences
propagating at subluminal speed. Yet, the Bell violations observed in such experiments could
always be explained in principle through models based on hidden
influences propagating at a finite speed v>c, provided v is large enough. Here, we show that
for any finite speed v>c, such models predict correlations that can be exploited for fasterthan-light communication. This superluminal communication does not require access to any
hidden physical quantities, but only the manipulation of measurement devices at the level of
our present-day description of quantum experiments. Hence, assuming the impossibility of
using nonlocal correlations for superluminal communication, we exclude any possible
explanation of quantum correlations in terms of influences propagating at any finite speed.
Our result uncovers a new aspect of the complex relationship between multipartite
quantum nonlocality and the impossibility of signaling and illustrates the difficulty to
modify quantum physics while maintaining no-signaling.
Rafael Sorkin (Perimeter Institute, Canada)
Title: Does a quantum particle know its own energy?
Abstract: If a wave function does not describe microscopic reality then what does?
Reformulating quantum mechanics in path-integral terms leads to a notion of "precluded
event" and thence to the proposal that quantal reality differs from classical reality in the
same way as a set of worldlines differs from a single worldline. One can then ask, for
example, which sets of electron trajectories correspond to a Hydrogen atom in its ground
state and how they differ from those of an excited state. I will answer the analogous
questions for simple model that replaces the electron by a particle hopping (in discrete
steps) on a circular lattice.
Ward Struyve (University of Leuven, Belgium)
Title: Semi-classical gravity based on de Broglie-Bohm theory
Abstract: Semi-classical approximations to quantum theory describe part of the system
classically and part quantum mechanically. In the usual approach, one considers the classical
system to move under a mean force, obtained by averaging over the quantum system. We
consider an alternative approach based on de Broglie-Bohm theory. This approach has
shown to yield better results than the mean force approach for certain non-relativistic
systems by e.g. Prezhdo and Brooksby, and Gindensperger et al. We present such semiclassical approximations for quantum electrodynamics and quantum gravity.
Petros Wallden (University of Athens & TEI of Chalkida, Greece)
Title: Interpreting the Quantum Measure
Abstract: Taking Feynman’s view on quantum mechanics, we use histories of the system and
assign to them quantum amplitudes. To recover probabilities, one sums over paths and
takes the mod square of that. Generalizing this view, we can define a quantum measure on
the space of all histories. However, this is not a proper measure and cannot be interpreted
as such. In this talk we first stress the differences between classical and quantum measure
and why we cannot maintain the classical view (as opposed for example in Bohm’s theory).
Furthermore we mention how the quantum measure can be interpreted, either in the
context of consistent histories or in view of the co-event’s formulation which we focus in this
talk.
Silke Weinfurtner (SISSA, Italy)
Title: Spacetime from bits
Abstract: I introduce a binary description for discrete gravity in 1+1 dimensions, focusing on
a particular variant thereof known as causal dynamical triangulations, resting entirely on
binary variables. Furthermore I present an ergodic binary encoding of spacetime manifolds,
and lay out all the necessary steps to evaluate the path integral of discrete gravity directly
from the bits, i.e. the natural language of information processing. Although in 1+1
dimensions the continuum limit of causal dynamical triangulation, i.e. the procedure to
emergence a smooth manifold from the discrete, is well understood, our approach maps
discrete gravity directly to physical systems. Furthermore, the results presented here give
rise to a quantum description of spacetime, by replacing bits with two-state quantummechanical systems. The possibility to express causal dynamical triangulations in terms of
atomic spins hints at the existence of real-life analogue discrete gravity systems.
James Yearsly (University of Cambridge, UK)
Title: Pitfalls of path integrals: amplitudes for spacetime regions and the quantum Zeno
effect
Abstract: Path integrals appear to offer natural and intuitively appealing methods for
defining quantum-mechanical amplitudes for questions involving spacetime regions. For
example, the amplitude for entering a spatial region during a given (large) time interval is
typically defined by summing over all paths between given initial and final points but
restricting them to pass through the region at any time. Such amplitudes play a key role in
consistent histories and quantum measure theory.
I will argue that there is, however, under very general conditions, a significant complication
in such constructions. This is the fact that the concrete implementation of the restrictions on
paths over a range of times corresponds, in an operator language, to sharp monitoring at
every moment of time in the given time interval. Such monitoring processes suffer from the
quantum Zeno effect, in which continual monitoring of a quantum system in a Hilbert
subspace prevents it from leaving that subspace. As a consequence, path integral amplitudes
defined in this seemingly obvious way have physically and intuitively unreasonable
properties and in particular, no sensible classical limit.
I will describe this frequently-occurring but little-appreciated phenomenon in some detail,
showing clearly the connection with the quantum Zeno effect. I will then show that it may
be avoided by implementing the restriction on paths in the path integral in a “softer” way.
The resulting amplitudes then involve a new coarse graining parameter, which may be taken
to be a timescale describing the softening of the restrictions on the paths.
Roman Zapatrin (The State Russian Museum, Russia)
Title: Quantum Contextuality and non-Bayesian Knowledge Revision
Abstract: In general, non-classical correlations (whose manifestation is the failure of
Bayesian law) appear when Kolmogorovian probability model is no longer applicable. In nonrelativistic Quantum Mechanics the structure of events form an orthomodular lattice, this
gives rise to quantum correlations. Recent developments in Computer Science discovered
the existence of stronger-than-quantum correlations in the area of information retrieval. In
order to quantify the bias from classical or quantum correlations I suggest to interpret them
as contextuality and to measure them in terms of the declination from Kochen-Specker
inequalities.
Andreas Zoupas (University of Thessaly, Greece)
Title: Effective Equations of Motion, Decoherence, and Backreaction
Abstract: We analyze the behavior of the density operator propagator for the following class
of systems: two particles coupled to each other and one of them coupled to a thermal bath
of harmonic oscillators. Focusing on the dynamics of the particle which is coupled to the
environment we wish to study its dynamics under the influence of both the environment
and the other particle. We test the following hypothesis: the environment, via the
environment induced decoherence mechanism, leads to classical behavior of the particle it
couples to, called classical particle from now on, while the other particle, called quantum
system from now on, does not retain its quantum nature due to its coupling with classical
particle. Thus, such systems, may be used as toy models for real measuring devices. We may
then study, first whether the classical particle really induces decoherence to the quantum
one, and second what is the effect, of such a coupling, on the equations of motions of the
classical system. This is an attempt to derive from first principles the backreaction of
quantum degrees of freedom to classical ones. We may then attempt to formulate general
rules for the so called effective classical equations of motion. The main result of this work, so
far, is that even in the presence of an environment the combined classical and quantum
system results in a quantum entangled state. This is an explicit result showing that
decoherence cannot solve the measurement problem. It questions both the role of
decoherence in emergent classicality and the model used to study it.