BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//CERN//INDICO//EN
BEGIN:VEVENT
SUMMARY:A gravitational collapse singularity theorem which does not requir
e chronology
DTSTART;VALUE=DATE-TIME:20190924T085000Z
DTEND;VALUE=DATE-TIME:20190924T092500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5181@indico.ict.inaf.it
DESCRIPTION:Speakers: Ettore Minguzzi\nI present a new gravitational colla
pse singularity theorem which improves Penrose's and which does not assume
predictability (global hyperbolicity) while it is compatible with chronol
ogy violation (closed timelike curves) and black hole evaporation.\nhttps:
//indico.ict.inaf.it/event/751/contributions/5181/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5181/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Testing Gravitational Redshifts with Galileo 5 and 6
DTSTART;VALUE=DATE-TIME:20190925T085500Z
DTEND;VALUE=DATE-TIME:20190925T092500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5825@indico.ict.inaf.it
DESCRIPTION:Speakers: Christophe Le Poncin-Lafitte (SYRTE’ Deputy-Direc
tor\, Observatoire de Paris\, PSL Research University\, CNRS\, Sorbonne Un
iversités\, UPMC Univ. Paris 06\, LNE)\nhttps://indico.ict.inaf.it/event/
751/contributions/5825/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5825/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum entanglement near open timelike curves: theory and experi
mental simulation
DTSTART;VALUE=DATE-TIME:20190925T153000Z
DTEND;VALUE=DATE-TIME:20190925T153100Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-6203@indico.ict.inaf.it
DESCRIPTION:Speakers: Enrico Rebufello (INRiM)\nClosed timelike curves are
striking predictions of general relativity allowing for time-travel. They
are afflicted by notorious causality issues (e.g. grandfather’s paradox
). Quantum models where a qubit travels back in time solve these problems\
, at the cost of violating quantum theory’s linearity—leading e.g. to
universal quantum cloning. Interestingly\, linearity is violated even by o
pen timelike curves (OTCs)\, where the qubit does not interact with its pa
st copy\, but is initially entangled with another qubit. Non-linear dynami
cs is needed to avoid violating entanglement monogamy. Here we propose an
alternative approach to OTCs\, allowing for monogamy violations. Specifica
lly\, we describe the qubit in the OTC via a pseudo-density operator—a u
nified descriptor of both temporal and spatial correlations. We also simul
ate the monogamy violation with polarization-entangled photons\, providing
a pseudo-density operator quantum tomography. Remarkably\, our proposal a
pplies to any space-time correlations violating entanglement monogamy\, su
ch as those arising in black holes.\nhttps://indico.ict.inaf.it/event/751/
contributions/6203/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/6203/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Black Holes are Time Machines
DTSTART;VALUE=DATE-TIME:20190923T090000Z
DTEND;VALUE=DATE-TIME:20190923T094000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5482@indico.ict.inaf.it
DESCRIPTION:Speakers: Francesca Vidotto (University of Western Ontario\, C
anada)\nWhat would happen if you could enter inside a black hole? You woul
d travel to the future\, coming out of a white hole! In fact\, the huge gr
avitational redshift distinguish two characteristic time for such a proces
s: the one of the infalling observer\, that is fast\, and the one of an ex
ternal observer\, that is extremely long. I discuss how such a process is
allowed by gluing classical metrics without violation of causality. On the
other hand\, the full process is a characteristic non-perturbative quantu
m phenomenon\, that involve the superposition of different geometries. I d
iscuss the condition for this to happen\, including an intriguing realisat
ion in the remnant phase of the black hole.\nhttps://indico.ict.inaf.it/ev
ent/751/contributions/5482/
URL:https://indico.ict.inaf.it/event/751/contributions/5482/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Conjectures on SpaceTime
DTSTART;VALUE=DATE-TIME:20190925T105500Z
DTEND;VALUE=DATE-TIME:20190925T110000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5182@indico.ict.inaf.it
DESCRIPTION:Speakers: Alessandro Capurso\nIntroduction\n------------\n\nTh
e current description of SpaceTime follows Quantum Mechanics principles at
the smallest scales\, while it is commonly associated to General Relativi
ty in cosmological terms. The opposite perspectives eventually differ in t
erms of discrete *versus* continuum analysis.\nTime seems *vanishing* in t
he latest formulations of Quantum theories (Loop Quantum Gravity)\, as a s
tatic spin-foam that describes spatially entangled loops and *forgets* the
importance of *Memory*. On the other hand\, Time is described in relativi
ty terms as a *continuum existing block*\, of which we perceive instants t
hat are part of an always existing word-line\, like *worms* in a 4D-pancak
e with the tail on the birth and the head on the last instant of existence
. \nIt seems that our latest descriptions of Time point at *everything* (i
n relativity) or *nothing* (in quantum) but still strive to understand ent
anglement\, coherence and eventually evolution in Time.\n\nRecently\, seve
ral efforts have been done to reestablish a more *natural perspective* on
Science\, able to better face not only SpaceTime fabric description\, but
also debate on deeper *philosophical questions* concerning Time and its ro
le in the Universe. \nAn extended review of the importance of Time in elem
entary physics\, as well as in many other disciplines\, is given by Lee Sm
olin in [1]. \nThe coming ideas follow a similar path\, trying to continue
the effort towards a physical description of SpaceTime that seems to *fra
me better* quantum and cosmological scales with natural evolution.\n\n\n\n
\nAbstract and Summary\n--------------------\n\nThe aim of this contributi
on is to propose new conjectures on SpaceTime variables and their descript
ion\, through the concepts of *network*\, *entropy* and *coherent decoding
* (borrowed from Information Theory and quantum computation) and to offer
a possible wider perspective on SpaceTime fabric and evolution.\nGiven the
*unnatural physical existence* of a *Real continuum* and consequent *infi
nities*\, in the context of a discrete universe on space and even time on
a Planck scale (as discussed in [2])\, starting from the definition of a *
new reference frame* based on an Absolute Time T[k]\, an imaginary time *i
ct* and on the relative *momenta*\, a possible interpretation of AdS/CFT c
orrespondence\, SpaceTime fabric and elementary particles behavior is prop
osed.\n\nThe Absolute Time is described in the *AdS bulk* of the Maldacena
correspondence. It is represented as *entangled memory links* (between im
aginary points on the surface) that develop highlighting *surface correlat
ion* in a wavelet decomposition of the local pulse (phase shift info in re
spect to the Absolute Time reference pulse). \nThe memory links are descri
bed as well as a *deep neural network* (growing in T[k]) that *stores and
project* the evolving surface information\, as discussed in [3]. The infor
mation stored and projected through the Absolute Time is interpreted in th
e context of SpaceTime fabric as the *most efficient quantum computation n
etwork*\, as proposed also in [4]\, [5] and [6].\n\nImaginary time\, follo
wing Hawking intuition\, maps the *surface* of the AdS/CFT correspondence
to a *diffusive space distance* in a relativistic and flat space\, in cohe
rence *c* with the pulse of T[k]. It defines\, at any given k (*Now*)\, th
e full *current 3D space*\, from -∞@T[k-1] to +∞@T[k+1]. \nIn an evolv
ing 4D-SpaceTime\, the perceived 3D Space is interpreted as *emerging*\, i
n each *current Now*\, as the current configuration of *SpaceTime informat
ion*. It is distributed on the Universe *Surface of Existence* along *ict*
at a given k\, giving 2 probabilistic Real degrees of freedom in each sur
face bit and the correlation derived on the memory-links\, entangled along
the past instants in the Absolute Time.\n\nThe *momenta* involved represe
nt the *phase variations* (along both times in respect to the relative *re
ference of coherence*) and develop as in a logarithmic spiral\, following
a relativistic description of the *information space* and *coherent time*
on the surface of the bulk. \nA mathematical description of the mentioned
momenta in relativistic terms is proposed.\n\nBosons are described as *sin
gle qubits of information* and *elementary vibrating strings*\, flowing wi
th no *inertia* on the surface defined by the imaginary time.\nMatter elem
entary particles\, as *Entities* in SpaceTime\, are described as *Networks
* of imaginary points sharing a *common beat* (decoding as a *coherent-Sel
f* in T[k]). They emerge from the entanglement in the Absolute Time of sur
face strings\, that reduce their local degrees of freedom to become *inter
connected in the bulk*\, pulsing as a single\, persisting Self (debated in
[7]\, [8]).\n\nFollowing the conjectures proposed and the parallel with *
information encoded* in the entanglement of surface strings in T[k]\, the
Dirac equation is mapped to Shannon *Entropy*\, as a *summary* of the info
rmation content *shown on the surface*\, mathematically expressed as the s
um of the information derived over the variations along the *past loopy ti
cks* of the Absolute Time.\nThe geometry proposed is then applied to Dark
Matter\, interpreted as diffusive *wrinkles* in the local fabric\, and to
Black Holes\, as coherent Self and quantum networks showing maximum surfac
e entropy at current T[k]. \nBlack holes are described\, on the horizon\,
as *1 tick away* from the *coherent Now* (as a result of the *SpaceTime de
coding algorithm* local computation on both *momenta*). \nThe horizon resu
lts *too out of phase* in the local *current T[k] coherence* to be *decode
d* in the surrounding 3D local space (consequently with very little chance
of receiving\, on the outside\, any information).\nFurther reasoning on S
paceTime *info compression algorithm* and relative computational efficienc
y as a quantum computer are presented in the context of fabric entanglemen
t (as *living memory-roots* through past events) and maximum entropy on th
e surface (as equivalent to Shannon max *info compression*).\n\nTo illustr
ate possible wider similarities and consequences of the proposed conjectur
es\, the *Evolution* of Network-Entities and of information is described a
s cycles of transformation in *ict* and new gained persistence in T[k]\, i
n a growing of global surface entropy and local complexities\, levels of a
bstraction\, efficiency in equilibrium and Self-gained emerging properties
.\nFinally\, a possible interpretation of the *Origin* is proposed\, rewin
ding back both times\, in the context of Absolute Time and imaginary time
emerging from a *no-boundary* alike model (Hartle and Hawking).\n\nFurther
developments on the proposed conjectures are still required. \nA wider ma
thematical and physical analysis is suggested to extend the comprehension
of information in SpaceTime and to evaluate the implications on telecommun
ication and energy production. \nA deeper philosophical understanding is e
xpected.\n\nThe full paper is available at [9].\n\n \n\n\n\n\n\nReferences
\n----------\n\n[1] L. Smolin\, Time Reborn: From the Crisis in Physics t
o the Future of the Universe\, 2013. \n[2] C. Rovelli and M. Christodoulo
u\, “On the possibility of experimental detection of the discreteness of
time” arXiv:1812.01542v2\, 2018. \n[3] X.-L. Qi\, “Exact holographic
mapping and emergent space-time geometry” arXiv:1309.6282v1\, 2013. \n[
4] L. Zhou and X. Dong\, “Geometrization of deep networks for the inter
pretability of deep learning systems” arXiv:1901.02354v2\, 2019. \n[5]
L. Zhou and X. Dong\, “Spacetime as the optimal generative network of qu
antum states: a roadmap to QM=GR?”arXiv:1804.07908v1\, 2018. \n[6] P. C
aputa and J. M. Magan\, “Quantum Computation as Gravity” PHYSICAL REVI
EW LETTERS\, pp. 122\, 231302\, 2019. \n[7] G. Jaroszkiewicz and J. Eakin
s\, “Particle decay processes\, the quantum Zeno effect and the continui
ty of time” arXiv:quant-ph/0608248\, 2006. \n[8] T. Ullrich\, D. Kharze
ev and Z. Tu\, “The EPR paradox and quantum entanglement at sub-nucleoni
c scales” arXiv:1904.11974\, 17 May 2019. \n[9] A. Capurso\, “Conject
ures on SpaceTime” \nAvailable: http://www.tempiodicrono.net/download/Ca
purso-Conjectures_paper.pdf.\nhttps://indico.ict.inaf.it/event/751/contrib
utions/5182/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5182/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Locally Covariant Quantum Field Theory on Causally Compatible Sets
DTSTART;VALUE=DATE-TIME:20190925T153200Z
DTEND;VALUE=DATE-TIME:20190925T161100Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5755@indico.ict.inaf.it
DESCRIPTION:Speakers: James Vickers (Mathematical Sciences\, University of
Southampton\, UK)\nIn this talk I describe the mathematics required in or
der to provide a description of the observables for quantum fields on low-
regularity spacetimes. The first step involves constructing low-regularity
advanced and retarded Green operators as maps between suitable function s
paces. In specifying these we need to use graph norms on Sobolev spaces t
o ensure that the Green operators are well-defined inverses. The causal pr
opagator is then used to define a symplectic form on a topological vector
space $V(M)$. A key point is the way in which the causal propagator on a (
non-smooth) globally hyperbolic spacetime restricts to the causal propagat
or on a smaller causally compatible submanifold and therefore induces a sy
mplectic map between the vector spaces. This property enables one to provi
de a locally covariant description of the quantum fields in terms of the e
lements of quasi-local $C^*$-algebras on which one may define canonical co
mmutation relations. I end with a brief discussion on the choice of Sobole
v micro-local spectrum condition used to single out the physical states in
the low-regularity setting.\nhttps://indico.ict.inaf.it/event/751/contrib
utions/5755/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5755/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum field measurements without superluminal signalling
DTSTART;VALUE=DATE-TIME:20190924T145000Z
DTEND;VALUE=DATE-TIME:20190924T151000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5183@indico.ict.inaf.it
DESCRIPTION:Speakers: Jose de Ramon Rivera (University of Waterloo)\, Edua
rdo Martin-Martinez (University of Waterloo)\, Jason Pye (University of Wa
terloo)\nAlthough quantum field theory inherits much of the basic structur
e laid out by the postulates of ordinary quantum mechanics\, it is known t
hat the measurement theory cannot go through unscathed. There are examples
of idealised measurements in quantum field theory which produce superlumi
nal signalling. These examples indicate that endowing quantum theory with
a relativistic spacetime structure restricts the set of admissible quantum
operations. There is\, as of yet\, no characterisation of these operation
s. To this end\, here we proceed to clarify the causality issues which ari
se in measurements of quantum fields\, as well as characterise a class of
permissible measurements.\nhttps://indico.ict.inaf.it/event/751/contributi
ons/5183/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5183/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dynamical wormholes in Robinson-Trautman class
DTSTART;VALUE=DATE-TIME:20190925T074500Z
DTEND;VALUE=DATE-TIME:20190925T080500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5207@indico.ict.inaf.it
DESCRIPTION:Speakers: Otakar Svitek\nWe present wormholes based on the Ro
binson–Trautman class of spacetimes generally containing geometries with
out symmetries. We focus on a model sourced by a ghost scalar field invest
igating its asymptotics\, stability and other issues. Within the same fami
ly of geometries one can construct a thin-shell model which approaches sim
ple spherically symmetric wormhole in the distant future. The generalizati
on of the second model to higher dimensions provides a possibility of avoi
ding the energy condition violation.\nhttps://indico.ict.inaf.it/event/751
/contributions/5207/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5207/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Conditional probabilities\, relativistic quantum clocks\, and the
trinity of relational quantum dynamics
DTSTART;VALUE=DATE-TIME:20190925T145000Z
DTEND;VALUE=DATE-TIME:20190925T151000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5206@indico.ict.inaf.it
DESCRIPTION:Speakers: Alexander R. H. Smith (Department of Physics and Ast
ronomy\, Dartmouth College)\nWhat allowed Einstein to transcend Newton’s
conception of absolute time was his insistence on an operational definiti
on of time in terms of the measure- ment of a clock. Quantum theory has ye
t to be liberated from this absolute time as evidenced by the Schr ̈oding
er equation in which time appears as an external classical parameter.\nIn
this talk I will introduce an operational formulation of quantum theory kn
own as the conditional probability interpretation of time (CPI) in which t
ime is defined in terms of an observable on a quantum system functioning a
s a clock\; in some contexts\, the CPI is known as the Page and Wootters m
echanism. This clock and the system whose dynamics it is tracking\, do not
evolve with respect to any external time. Instead\, they are entangled an
d as a consequence a relational dynamics emerges between them.\nI will pre
sent a generalization of the CPI to the case when the clock and system int
eract [1]\, which should be expected at some scale when the gravita- tiona
l interaction between them is taken into account. I will demonstrate how s
uch clock-system interactions result in a time-nonlocal modification to th
e Schro ̈dinger equation. I will then examine relativistic particles with
internal degrees of freedom that constitute a clock which tracks their pr
oper time [2]. By examining the conditional probability associated with tw
o such clocks reading different proper times\, I will show that these cloc
ks exhibit both classical and quantum time dilation effects. Moreover\, in
connection with quantum metrol- ogy\, it will be seen that the Helstrom-H
olevo lower bound requires that these clocks satisfy a time-energy uncerta
inty relation between the proper time they measure and their rest mass. Fi
nally\, I will show how the CPI constitutes one out of a trinity of distin
ct but equivalent formulations of the same relational quantum dynamics [3]
.\n\nReferences:\n[1] Quantizing time: Interacting clocks and systems\nA.
R. H. Smith and M. Ahmadi\, Quantum 3 160 (2019)\n[2] Relativistic quantum
clocks observe classical and quantum time dilation A. R. H. Smith and M.
Ahmadi\, arXiv:1904.12390 (2019)\n[3] The trinity of relational quantum dy
namics\nA. R. H. Smith\, M. P. E. Lock\, and P. A. Ho ̈hn\, Forthcoming (
2019)\nhttps://indico.ict.inaf.it/event/751/contributions/5206/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5206/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gravitational lensing hundred years after the Eddington expedition
DTSTART;VALUE=DATE-TIME:20190923T070000Z
DTEND;VALUE=DATE-TIME:20190923T074500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5480@indico.ict.inaf.it
DESCRIPTION:Speakers: Volker Perlick (ZARM\, University of Bremen\, German
y)\nExactly hundred years ago\, in May 1919\, Arthur Eddington and three c
olleagues observed the gravitational light deflection\, as predicted by Al
bert Einstein\, during a total Sun eclipse. After a historical introductio
n\, I'll discuss the relevance of gravitational lensing as an important to
ol for present-day astrophysics. In the last part of the talk I will inves
tigate in some detail the pictures of the shadow of the black-hole candida
te at the centre of M87\, which were released to the public on 10 April 20
19\, just hundred years after the Eddington expedition.\nhttps://indico.ic
t.inaf.it/event/751/contributions/5480/
URL:https://indico.ict.inaf.it/event/751/contributions/5480/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Probing regular black hole spacetimes with scalar fields
DTSTART;VALUE=DATE-TIME:20190923T094000Z
DTEND;VALUE=DATE-TIME:20190923T100000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5208@indico.ict.inaf.it
DESCRIPTION:Speakers: Tayebeh Tahamtan\nWe study the properties of regul
ar black holes using both test and gravitating scalar fields. The main mot
ivation being to discover features that distinguish them from real black h
oles. One such characteristic is regularity of horizon which is spoilt by
scalar field in spherically symmetric static cases.\nhttps://indico.ict.in
af.it/event/751/contributions/5208/
URL:https://indico.ict.inaf.it/event/751/contributions/5208/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum Measurements of time
DTSTART;VALUE=DATE-TIME:20190923T125500Z
DTEND;VALUE=DATE-TIME:20190923T134000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5218@indico.ict.inaf.it
DESCRIPTION:Speakers: Lorenzo Maccone (Univ. degli Studi di Pavia)\nWe pro
pose a time-of-arrival operator in quantum mechanics by conditioning on a
quantum clock. This allows us to bypass some of the problems of previous p
roposals\, and to obtain a Hermitian time of arrival operator whose probab
ility distribution arises from the Born rule and which has a clear physica
l interpretation. The same procedure can be employed to measure the "time
at which some event happens" for arbitrary events (and not just specifical
ly for the arrival time of a particle).\nhttps://indico.ict.inaf.it/event/
751/contributions/5218/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5218/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The temporally nonlocal character of the quantum computational spe
edup
DTSTART;VALUE=DATE-TIME:20190923T161000Z
DTEND;VALUE=DATE-TIME:20190923T163000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5038@indico.ict.inaf.it
DESCRIPTION:Speakers: Avshalom Elitzur (Institute for Quantum Studies\, Ch
apman University\, Orange\, CA 92866\, USA and Iyar\, The Israeli Institut
e for Advanced Research\, POB 651\, Zichron\, Ya’akov 3095303\, Israel)\
, Elihau Cohen (Faculty of Engineering and the Institute of Nanotechnology
and Advanced Materials\, Bar Ilan University\, Ramat Gan 5290002\, Israel
)\, Artur Ekert (‡Mathematical Institute\, University of Oxford and Cen
tre for Quantum Technologies\, National University of Singapore )\, Giusep
pe Castagnoli (Elsag Bailey ICT Division and Quantum information Laborator
y)\nOne says that there is a *quantum computational speedup* when the comp
utation of the solution of a problem is more efficient quantumly than clas
sically. Let us consider\, as an example\, the simplest case that Bob\, th
e problem setter\, hides a ball in a chest of four drawers. Alice\, the pr
oblem solver\, is to locate in by opening drawers (by querying the oracle:
is the ball in that drawer?). While in the classical case Alice may need
to open up to three drawers\, with the quantum algorithm devised by Grover
she only needs to open one.\nThe usual representation of quantum algorith
ms is limited to the computation of the solution of the problem. We extend
it to the process of setting the problem. Bob\, who operates on the quant
um register B\, randomly selects the problem-setting (the number of the dr
awer with the ball) by an initial measurement in a (possibly incoherent) s
uperposition of all the possible problem-settings. He could then unitarily
change it into a desired setting but for simplicity we omit this operatio
n. Alice\, who operates on the quantum register A initially in an arbitra
ry sharp state (standing for a blank blackboard)\, unitarily computes the
corresponding solution and reads it by the final measurement. With probabi
lity one of reading the solution\, the process between the initial and fin
al measurement outcomes is reversible – no information is destroyed alon
g it. \nWe physically represent the fact that the problem-setting selected
by Bob must be hidden from Alice (it would tell her the solution of the p
roblem) by relativizing the extended representation to her. In the represe
ntation with respect to Alice\, the projection of the quantum state associ
ated with the initial measurement is postponed till the end of the unitary
part of her problem-solving action. After the initial measurement\, the q
uantum state of register B to Alice remains the quantum superposition of a
ll the possible problem settings. It represents her complete ignorance of
the problem setting selected by Bob. Alice unitarily changes the tensor pr
oduct of this superposition and the sharp state of register A into a super
position of tensor products\, each a problem setting in B multiplied by th
e corresponding solution in A. Then she selects the problem setting alread
y selected by Bob by the final measurement of the solution. \nWe represent
the reversibility of the process between the initial and final measuremen
t outcomes by time-symmetrizing it. In this kind of process\, and in the u
sual way of seeing\, the information that specifies the initial measuremen
t outcome and consequently the final one (in the present example\, both th
e number of the drawer with the ball) is all selected by the initial measu
rement\; its outcome (encoding the problem setting selected by Bob in regi
ster B) undergoes the time forward unitary transformation until becoming t
he state before the final measurement (encoding the solution in register A
). The latter measurement just reads the solution encoded in A\, without s
electing anything. However\, the thing could be seen in the time-symmetric
way. The initial measurement does not select anything\, the initial state
superposition undergoes the unitary transformation that represents Alice
’s problem solving action and the final measurement performs all the sel
ection. The measurement outcome\, which encodes the solution in register A
\, by the Parisian Zigzag propagates backwards in time by the inverse unit
ary transformation until becoming the outcome of the initial measurement\,
encoding the problem setting in register B. \nHowever\, either way of see
ing\, introducing a preferred direction of time\, is not symmetric in time
. According to the tenet of the Two-State-Vector Formalism\, we assume tha
t the initial and final measurements evenly contribute to determining the
process in between\, namely to selecting the information that specifies ei
ther measurement outcome. The half information selected by the initial mea
surement propagates forward in time\, that selected by the final measureme
nt backwards in time according to the Parisian Zigzag. Since there are man
y ways of halving the information\, we should take all the corresponding t
ime-symmetrization instances in quantum superposition. \nThis time-symmetr
ization procedure leaves the extended representation of the quantum algori
thm\, which is ordinary in character since no observer is shielded from an
y measurement outcome\, unaltered.\nIt shows that the representation of th
e quantum algorithm relativized to Alice is a superposition of (partly ove
rlapping) superpositions\, the time-symmetrization instances\, each a quan
tum algorithm by itself. In each instance\, Alice remains shielded from th
e information coming to her from the initial measurement\, not from that c
oming to her from the final measurement. The computational complexity of t
he problem to be solved by her is correspondingly reduced. All is as if sh
e knew in advance\, before performing the unitary part of her problem-solv
ing action\, half of the information that specifies the problem-setting an
d thus the solution of the problem and could use this information to reach
the solution with fewer oracle queries. This accounts for the quantum com
putational speedup. The fact that the final measurement non-locally change
s the state of register B to Alice at the beginning of the unitary part of
the quantum algorithm\, from a superposition of all the problem setting t
o that of a reduced part thereof\, is of course a form of temporal nonloca
lity. It cannot be seen in the usual representation of quantum algorithm\,
which\, by an application of the principle of locality\, replaces the ini
tial measurement by its measurement outcome.\nThe above accounts for the c
omputational speedup of all the quantum algorithms examined. These compris
e the major quantum algorithms and cover both the quadratic and exponentia
l speedups. More generally\, given an oracle problem\, the number of oracl
e queries required to solve it in an optimal quantum way is that of a clas
sical algorithm (a Turing machine) endowed with the advanced knowledge of
half of the information that specifies the setting and the corresponding s
olution of the problem.\nThe fact that\, in each time-symmetrization insta
nce\, Alice knows in advance half of the solution she will read in the fut
ure and uses this information to reach the solution with fewer oracle quer
ies is a half causal loop. Its physical viability is discussed. The fact t
hat there is apparently information going back in time from the final to t
he initial measurement is compensated for by the fact that one has to take
the superposition of all the instances (apparent backward causality is co
mpensated for by the indeterminacy inherent in the very notion of quantum
superposition). This superposition – the quantum algorithm to Alice back
again – is an ordinary quantum mechanical superposition\, where apparen
tly no information is sent back in time.\n**References**\nEkert\, A. K. an
d Jozsa\, R.: Quantum Algorithms: Entanglement Enhanced Information Proces
sing arXiv:quant-ph/9803072 (1998)\nDolev\, S. and Elitzur\, A. C.: Non-se
quential behavior of the wave function. arXiv:quant-ph/0102109 v1 (2001) \
nCastagnoli\, G. and Finkelstein\, D. R.: Theory of the quantum speedup. P
roc. Roy. Soc. A 1799\, 457\, 1799-1807 (2001) \nCastagnoli\, G.: The quan
tum correlation between the selection of the problem and that of the solut
ion sheds light on the mechanism of the quantum speed up. Phys. Rev. A 82\
, 052334-052342 (2010)\nAharonov\, Y.\, Cohen\, E.\, and Elitzur\, A. C.:
Can a future choice affect a past measurement outcome? Ann. Phys. 355\, 25
8-268 (2015)\nElitzur\, A.C.\, Cohen\, E.\, Okamoto\, R. and Takeuchi\, S.
: Nonlocal position changes of a photon revealed by quantum routers. Sci.
Rep. 8\, 7730 (2018)\nhttps://indico.ict.inaf.it/event/751/contributions/5
038/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5038/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The role of causality in quantum gravity
DTSTART;VALUE=DATE-TIME:20190924T070000Z
DTEND;VALUE=DATE-TIME:20190924T074500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5222@indico.ict.inaf.it
DESCRIPTION:Speakers: Sumati Surya (Raman Research Institute)\nThe notion
of causality\, both local or global\, is tied inextricably to the Lorentzi
an character of spacetime.\nThis is embodied by the causal structure poset
which\, given weak causality constriants\, determines the conformal\nspac
etime geometry. This is the starting point for the causal set approach to
quantum gravity\, where the\nunderlying continuum is replaced by a locally
finite partially ordered set. In this talk I will discuss the role played
by\ncausality both kinematically and dynamically in quantum gravity\, wit
h a focus on the causal set approach.\nhttps://indico.ict.inaf.it/event/75
1/contributions/5222/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5222/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Remote time manipulation
DTSTART;VALUE=DATE-TIME:20190924T143000Z
DTEND;VALUE=DATE-TIME:20190924T145000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5041@indico.ict.inaf.it
DESCRIPTION:Speakers: Benjamin Dive (IQOQI-Vienna)\, Miguel Navascues (IQO
QI-Vienna)\, David Trillo (IQOQI-Vienna)\nHarnessing the flow of proper ti
me of arbitrary external systems over which we exert little or no control
has been a recurring theme in both science and science-fiction. Unfortunat
ely\, all relativistic schemes to achieve this effect beyond mere time dil
ation are utterly unrealistic. In this work\, we find that there exist non
-relativistic scattering experiments which\, if successful\, freeze out\,
speed up or even reverse the free dynamics of any ensemble of quantum syst
ems present in the scattering region. This "time warping" effect is univer
sal\, i.e.\, it is independent of the particular interaction between the s
cattering particles and the target systems\, or the (possibly non-Hermitia
n) Hamiltonian governing the evolution of the latter. The protocols requir
e careful preparation of the probes which are scattered\, and success is h
eralded by projective measurements of these probes at the conclusion of th
e experiment. We fully characterize the possible time translations which w
e can effect on n target systems through a scattering protocol of fixed du
ration\; the core result is that time can be freely distributed between th
e systems\, and reversed at a small cost. For high n\, our protocols allow
one to quickly send a single system to its far future or past. In this se
nse\, we have devised a time machine for very small stuff.\nhttps://indico
.ict.inaf.it/event/751/contributions/5041/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5041/
END:VEVENT
BEGIN:VEVENT
SUMMARY:On the unique evolution of solutions to wave equations
DTSTART;VALUE=DATE-TIME:20190924T074500Z
DTEND;VALUE=DATE-TIME:20190924T082000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5042@indico.ict.inaf.it
DESCRIPTION:Speakers: Jan Sbierski\nThe well-known theorem of Choquet-Bruh
at and Geroch states that for given smooth initial data for the Einstein e
quations there exists a unique maximal globally hyperbolic development. In
particular\, the time-evolution of globally hyperbolic solutions is uniqu
e. This talk investigates whether the same results hold for quasilinear wa
ve equations defined on a fixed background. We first present an example of
a quasilinear wave equation for which unique evolution of smooth globally
hyperbolic solutions in fact fails and contrast this case with the Einste
in equations. We then proceed by presenting conditions which guarantee uni
que evolution. This talk is based on joint work with Felicity Eperon and H
arvey Reall.\nhttps://indico.ict.inaf.it/event/751/contributions/5042/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5042/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sound Propagation in the Ellis Wormhole
DTSTART;VALUE=DATE-TIME:20190925T080500Z
DTEND;VALUE=DATE-TIME:20190925T082500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5043@indico.ict.inaf.it
DESCRIPTION:Speakers: Zaza Osmanov (Free University of Tbilisi)\nFor the s
implest case of Ellis Wormhole (WH) the fluid moving through the mentioned
metrics is considered. For this purpose\, the set of linearized equations
composed of the Euler and continuity equations is examined. The propagati
on of sound waves has been considered and corresponding non-trivial analyt
ical and numerical results – obtained.\nhttps://indico.ict.inaf.it/event
/751/contributions/5043/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5043/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Locality and causality in the Aharonov-Bohm effect
DTSTART;VALUE=DATE-TIME:20190925T122000Z
DTEND;VALUE=DATE-TIME:20190925T130000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5227@indico.ict.inaf.it
DESCRIPTION:Speakers: Chiara Marletto (University of Oxford\, ISI\, Nation
al University of Singapore)\nI will expose a local\, fully quantum-field-t
heory compliant model of the Aharonov-Bohm effect\, where the Aharonov-Boh
m phase is gradually and locally acquired. I will explore the theoretical
and experimental implications of this model\, especially in regard to loca
lity and causality in quantum theory.\nhttps://indico.ict.inaf.it/event/75
1/contributions/5227/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5227/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Changing the interpretation of time
DTSTART;VALUE=DATE-TIME:20190924T103500Z
DTEND;VALUE=DATE-TIME:20190924T104000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5035@indico.ict.inaf.it
DESCRIPTION:Speakers: Luigi Foschini (Istituto Nazionale di Astrofisica (I
NAF))\nI would like to explore a change in the interpretation of time. By
thinking time as a cut\, and no more like a lapse\, there could be interes
ting opportunities. Particularly\, with such interpretation\, quantum grav
ity theories based on 3+1 spacetime (e.g. Kuchar or Ellis' evolving block
universe) may open unexpected and fruitful views. Among the many consequen
ces\, there will be no possibility for time machines.\nhttps://indico.ict.
inaf.it/event/751/contributions/5035/
URL:https://indico.ict.inaf.it/event/751/contributions/5035/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Preemptive chronology protection and superluminal travel.
DTSTART;VALUE=DATE-TIME:20190924T125500Z
DTEND;VALUE=DATE-TIME:20190924T134000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5229@indico.ict.inaf.it
DESCRIPTION:Speakers: Stefano Liberati (SISSA)\nIn this talk I shall revie
w the implications of superluminal travel and the means by which it can be
achieved in classical General Relativity. We shall then see in the specif
ic case of superluminal warp drives how it seems that a preemptive form of
chronological protection is at work once their dynamics it is analysed wi
thin quantum field theory in curved spacetime. Finally\, we shall discuss
the robustness of this chronological protection with respect the details o
f the spacetime structure.\nhttps://indico.ict.inaf.it/event/751/contribut
ions/5229/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5229/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Contrary Inferences for Classical Histories in the Consistent Hist
ories Approach
DTSTART;VALUE=DATE-TIME:20190925T143000Z
DTEND;VALUE=DATE-TIME:20190925T145000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5066@indico.ict.inaf.it
DESCRIPTION:Speakers: Petros Wallden (Laboratory for Foundations of Comput
er Science (LFCS)\, School of Informatics\, Unversity of Edinburg)\, Georg
ios Pavlou (Nuclear & Particle Physics Section\,\, Physics Department\, Na
tional and Kapodistrian University of Athens)\, Adamantia Zampeli (Charles
University)\nTitle: Contrary Inferences for Classical Histories in the Co
nsistent Histories Approach\n\n\nThe non-relativistic quantum theory is on
e of the most successful theories in the history of science\, since it has
been verified experimentally in several different situations and with ext
remely high precision. Despite the fact that its mathematical formalism is
universally accepted\, its conceptual foundations have always been a subj
ect of scientific dispute. The standard interpretation is that of the Cope
nhagen school which has many conceptual and practical problems. One of the
most prominent is the distinction between the classical and quantum world
\, as well as the issue of the quantum-to-classical transition. Closely re
lated to these is also the famous measurement problem. \n\nAn alternative
interpretation of quantum theory based on the histories approach is the co
nsistent histories theory [1-5]. The space of states consists of all the p
ossible histories of a quantum system and the aim is to derive probabiliti
es for the realization of a (coarse-grained) history of this system. The p
robability of a history\, which is defined in relation to the other histor
ies belonging to the corresponding partition of the histories space\, are
assigned only when a condition defined on this coarse-grained-histories se
t holds. When such a set satisfies the consistency condition\, it is calle
d consistent histories set (CHS). Unfortunately\, there are many CHS which
are not mutually compatible. This leads to the existence of contrary infe
rences\, which are defined as two contradictory arguments both implied wit
h probability one [6]. Of course\, this issue does not arise in the classi
cal world. The existence of contrary inferences comes from the existence o
f zero covers [7]\; specifically\, by covering the full histories space wi
th two (overlapping) zero quantum measure sets. It is known that\, in quan
tum theory\, many interpretational problems arise because of the existence
of zero quantum measure covers\, e.g. the Kochen-Specker theorem and the
contextuality [8]. The strangeness of contrary inferences is typically jus
tified by proponents of the consistent histories\, by arguing that these a
ppear in the small scale (far from the classical domain)\, where counterin
tuitive properties are expected to appear. Then the technical way to avoid
such issues is to focus on and compare propositions belonging to a single
CHS\, an assumption justified in the microscopic world\, but much less in
classical scales. \n\nIn this talk\, we give an example of two contrary c
lassical propositions in the context of consistent histories approach. We
analyze the arrival time of a (semi-) classical free particle in an infini
te square well. By selecting two different partitions of the histories spa
ce\, we find a quantum measure of zero cover\, which consists of two coars
e-grained sets. Thus\, we end up with contrary inferences for a classical
particle. The consequences of this example for histories formulations of q
uantum theory will be shortly discussed. \n\n\nReferences\n\n[1] M. Gell-M
ann and J. B. Hartle. Classical equations for quantum systems. Phys. Rev.\
, D 47:3345–3382\, 1993.\n[2] R. B. Griffiths. Consistent histories and
the interpretation of quantum mechanics. J. Statist. Phys.\, 36:219–272\
, 1984.\n[3] R. Omnes. Logical Reformulation of Quantum Mechanics. 1. Foun
dations. J. Statist. Phys.\, 53:893–932\, 1988.\n[4] R. Omnes. Logical R
eformulation of Quantum Mechanics. 2. Interferences and the Einstein-Podol
sky- Rosen Experiment. J. Statist. Phys.\, 53:933–955\, 1988.\n[5] R. Om
nes. Logical Reformulation of Quantum Mechanics. 3. Classical Limit and Ir
reversibility. J. Statist. Phys.\, 53:957–975\, 1988.\n[6] A. Kent. Cons
istent sets and contrary inferences: Reply to Griffiths and Hartle. Phys.
Rev. Lett.\, 81:1982\, 1998.\n[7] P. Wallden. Contrary Inferences in Consi
stent Histories and a Set Selection Criterion. Found.Phys.\, 44(11):1195
–1215\, 2014.\n[8] S. Surya and P. Wallden. Quantum covers in quantum me
asure theory\,arxiv: 0809.1951 [quant-ph]\, 2008.\nhttps://indico.ict.inaf
.it/event/751/contributions/5066/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5066/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Causal set theory and quantum fields
DTSTART;VALUE=DATE-TIME:20190924T134000Z
DTEND;VALUE=DATE-TIME:20190924T140000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5067@indico.ict.inaf.it
DESCRIPTION:Speakers: Dionigi Benincasa\, Stefano Liberati (SISSA)\, Aless
io Belenchia (Queen's University Belfast)\, Marco Letizia (University of W
aterloo and Perimeter Institute)\nIn this talk I will discuss the properti
es of quantum fields in causal set theory\, a theory of quantum gravity in
which nonlocality emerges as a consequence of discreteness and local Lore
ntz invariance. In particular I will present some recent results regarding
the computation of entanglement entropy in this context and consider some
comparisons with other models of quantum spacetime with particular attent
ion to the fate of Lorentz symmetries.\nhttps://indico.ict.inaf.it/event/7
51/contributions/5067/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5067/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dirac tunneling: superluminal velocities and closed time-like curv
es?
DTSTART;VALUE=DATE-TIME:20190924T121000Z
DTEND;VALUE=DATE-TIME:20190924T125500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5216@indico.ict.inaf.it
DESCRIPTION:Speakers: Randall Dumont (McMaster University\, Hamilton\, On
t.\, Canada)\nThe Hartman effect – first discovered by MacColl\, in 1932
– is the claimed observation that\, when a particle tunnels\, it arrive
s at the opposite side of the barrier the moment it encounters the barrier
. If this is so\, then sufficiently wide barriers and fast particles shoul
d produce superluminal effective velocities. However\, such superluminal e
ffective velocities have been dismissed as attributable solely to uncertai
nty in the initial position of the particle. We examine this position\, an
d further investigate this motif for superluminal velocities\, and associa
ted backward time travel – the latter expected in the particle frame of
reference\, when the particle travels superluminally in the barrier frame.
\nhttps://indico.ict.inaf.it/event/751/contributions/5216/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5216/
END:VEVENT
BEGIN:VEVENT
SUMMARY:New Classes of Warp Drive Solutions in General Relativity
DTSTART;VALUE=DATE-TIME:20190924T151000Z
DTEND;VALUE=DATE-TIME:20190924T153000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5483@indico.ict.inaf.it
DESCRIPTION:Speakers: Alexey Bobrick\nWe report on the results of our ongo
ing work on reducing the energy requirements of classical warp drives. The
existing warp drive solutions by van den Broek and Alcubierre assume sphe
rical symmetry. We show that by considering their counterparts of arbitrar
y shape\, one can reduce the energy requirements by orders of magnitude. F
urther\, I will outline a method of constructing more general classes of w
arp drives. As a demonstration\, we have constructed\, for the first time\
, a warp drive solution with a region resembling the ergosphere region of
Kerr black holes. I will present on the properties of such drives and disc
uss the possibility of applying the Penrose process to them.\nhttps://indi
co.ict.inaf.it/event/751/contributions/5483/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5483/
END:VEVENT
BEGIN:VEVENT
SUMMARY:On Closed Timelike Curves\, Cosmic Strings and Conformal Invaria
nce
DTSTART;VALUE=DATE-TIME:20190923T100000Z
DTEND;VALUE=DATE-TIME:20190923T102000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5034@indico.ict.inaf.it
DESCRIPTION:Speakers: Reinoud Slagter (Univ of Amsterdam and ASFYON\, The
Netherlands)\nAbstract \nIn general relativity theory (GRT) one can constr
uct solutions which are related to real physical objects. The most famous
one is the black hole solution. One now believes that in the center of man
y galaxies there is a rotating super-massive black hole\, the Kerr black h
ole. Because there is an axis of rotation\, the Kerr solution is a member
of the family of the axially symmetric solutions of the Einstein equations
. A legitimate question could be: are there other axially or cylindrically
symmetric asymptotically flat solutions of the equations of Einstein with
a classical or non-classical matter distribution and with correct asympto
tical behavior\, just as the Kerr solution? Many attempts are made\, such
as the Weyl-\, Papapetrou- and Van Stockum solution. None of these attempt
s result is physically acceptable solution. Often\, these solutions posses
s closed timelike curves (CTC's). The possibility of the formation of CTC
's in GRT seems to be an obstinate problem to solve in GRT. At first glanc
e\, it seems possible to construct in GRT causality violating solutions. C
TC's suggest the possibility of time-travel with its well-known paradoxes.
Although most physicists believe that Hawking's chronology protection con
jecture holds in our world\, it can be alluring to investigate the mathem
atical underlying arguments of the formation of CTC's. There are several s
pacetimes that can produce CTC's. Famous is the Tipler-cylinder. Most of t
hese spacetimes can easily characterized as un-physical. \nThe problems ar
e\, however\, more deep-seated in the vicinity of a (spinning) cosmic stri
ng or in the so-called Gott-spacetime. These cosmic string models gained m
uch attention the last decades. Two cosmic strings\, approaching each othe
r with high velocity\, could produce CTC's. If an advanced civilization co
uld manage to make a closed loop around this Gott pair\, they will be retu
rned to their own past. However\, the CTC's will never arise spontaneously
from regular initial conditions through the motion of spinless “cosmons
” ( “Gott’s pair”): there are boundary conditions that has CTC's
also at infinity or at an initial configuration. If it would be possibl
e to fulfil the CTC condition at t0\, then at sufficiently large times t
he cosmons will have evolved so far apart that the CTC's would disappear.
The chronology protection conjecture seems to be saved for the Gott spacet
ime. There are still some unsatisfied aspects around spinning cosmic stri
ngs. If the cosmic string has a finite dimension\, one needs to consider t
he coupled field equations\, i.e.\, besides the Einstein equations\, also
the scalar and gauge field equations. It came as a big surprise that there
exists a vortex-like solution in GRT comparable with the magnetic flux li
nes in type II superconductivity. Many of the features of the Nielsen-Oles
en vortex solution and superconductivity will survive in the self-gravitat
ing situation. These vortex lines occur as topological defects in an abeli
an U(1) gauge model\, where the gauge field is coupled to a charged scalar
field. It can easily be established that the solution must be cylindrica
lly symmetric\, so independent of the z-coordinate and the energy per unit
length along the z-axis is finite. There are two types\, local (gauged) a
nd global cosmic strings. We are mainly interested in local cosmic strings
\, because in a gauge model\, strings were formed during a local symmetry
breaking and so have a sharp cutoff in energy\, implying no long range in
teractions. It turns out that spinning cosmic string solutions can cause
serious problems when CTC's are formed which are not hidden behind a horiz
on\, as is the case for the Kerr metric. One can "hide" the presence of th
e spinning string by suitable coordinate transformation in order to get th
e right asymptotic behaviour and without a residue of the angle deficit.
One obtains then a helical structure of time\, not desirable. Further\, it
is not easy to match the interior on the vacuum exterior and to avoid the
violation of the weak energy condition (WEC). Many attempts are made to f
ind a physically acceptable solutions\, but all failed. It is clear that
an additional field must be added to compensate for the energy failure clo
se to the core of the string. That part of the mass density of a rotating
string due to its angular deficit is insufficient. In general one can conc
lude that there is an urgent need for a satisfying physical interpretation
of CTC’s in this spacetime.\nIn my talk I will consider the spinning st
ring in conformal gravity\, where the interior consists of a gauged scalar
field. Conformal invariance in GRT considered as exact at the level of t
he Lagrangian but spontaneously broken\, is an approved alternative for d
isclosing the small-distance structure when one tries to describe quantum-
gravity problems. Moreover\, the conformal invariant cosmological models c
ould solve the dark energy/matter problem.\nWe will write the metric as g
_μν=ω^2 g ̃_μν \, with ω a dilaton field\, handled on equal foo
ting with the Higgs field and g ̃_μν the “unphysical” metric. By de
manding regularity of the action\, no problems emerge when ω→0. For the
vacuum exterior\, exact (Ricci-flat) solutions are found with the correc
t asymptotic features which can be matched on the numerical interior solut
ion. For global cosmic strings\, the existence of CTC's can be avoided or
pushed to infinity by suitable values of the integration constants. These
constants can be used to fix the parameters of the cosmic string by the sm
ooth matching of the solutions at the boundary. There seems to be no probl
ems in order to fulfil the weak energy condition.\nOur result could be a
new possible indication that local conformal invariance and spontaneously
broken in the vacuum\, can be a promising method for studying quantum effe
cts in GR\, as was found in many other studies.\nR. J. Slagter and S. Pan\
, 2016\, Found of Phys\, 46\, 1075\nR. J. Slagter\, 2019\, Phys of the Da
rk Universe\, 24\, 100282\nR. J. Slagter and C. L. Duston\, 2019\, ArXiv:
gr-qc/190206088 [subm to Ann of Phys\nhttps://indico.ict.inaf.it/event/751
/contributions/5034/
URL:https://indico.ict.inaf.it/event/751/contributions/5034/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Traversable Casimir Wormholes
DTSTART;VALUE=DATE-TIME:20190925T070000Z
DTEND;VALUE=DATE-TIME:20190925T074500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5039@indico.ict.inaf.it
DESCRIPTION:Speakers: Remo Garattini (Università degli Studi di Bergamo)\
nTraversable Wormholes are a prediction of General Relativity. After the d
iscovery of the Gravitational Wave signals detected in 2015\, Traversable
Wormholes have had another renaissance\, because they can be considered as
Black Hole Mimickers.\nIn this talk we give a pedagogical introduction an
d we present some theoretical aspects at classical and semiclassical level
\, namely when the source has quantum mechanical origin. A brief descripti
on of a Self-Sustained Traversable Wormhole\, namely a Traversable Wormhol
e ehich is sustained by its own quantum fluctuations is also presented.\nh
ttps://indico.ict.inaf.it/event/751/contributions/5039/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5039/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Entangled histories\, the two-state-vector and the pseudo-de
nsity formalisms: Towards a better understanding of quantum temporal corre
lations.
DTSTART;VALUE=DATE-TIME:20190923T134000Z
DTEND;VALUE=DATE-TIME:20190923T140000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5049@indico.ict.inaf.it
DESCRIPTION:Speakers: Marcin Nowakowski (Department of Theoretical Physics
and Quantum Information\, Gdansk University of Technology )\nThe two-stat
e-vector formalism\, the entangled histories and the pseudo-density formal
isms are attempts to better understand quantum correlations in time. These
formalisms share some similarities\, but they are not identical\, having
subtle differences in their interpretation and manipulation of quantum tem
poral structures [1\, 2]. I will show\, for instance\, that they treat ope
rators and states on equal footing\, leading to the same statistics for al
l measurements. I will discuss the topic of quantum correlations in time a
nd show how they can be generated and analysed in a consistent way using t
hese formalisms. I will also elaborate on an unconventional behaviour of t
emporal monogamic structures and quantum histories of evolving multipartit
e systems which do not exhibit global nonlocal correlations in time but ne
vertheless can lead to entangled reduced histories characterizing evolutio
n of an arbitrarily chosen subsystem.\n\n\n[1] M. Nowakowski\, E. Cohen\,
P. Horodecki\, Entangled Histories vs. the Two-State-Vector Formalism -Tow
ards a Better Understanding of Quantum Temporal Correlations\, Phys. Rev.
A 98\, 032312 (2018).\n[2] M. Nowakowski\, Quantum Entanglement in Time\,
AIP Conference Proceedings 1841\, 020007 (2017).\nhttps://indico.ict.inaf.
it/event/751/contributions/5049/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5049/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The quantum theory of time: from formalism to experimental test
DTSTART;VALUE=DATE-TIME:20190923T150500Z
DTEND;VALUE=DATE-TIME:20190923T154500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5219@indico.ict.inaf.it
DESCRIPTION:Speakers: Joan A. Vaccaro (Griffith University)\nThe violation
of the discrete symmetries of charge conjugation (C)\, parity inversion (
P)\, and time reversal (T) observed in high energy physics are clearly fun
damental aspects of nature. A new quantum theory [1\,2] has been introduc
ed to demonstrate the possibility that the violations have large-scale phy
sical effects. The new theory does not assume any conservation laws or equ
ations of motion. In particular\, if T violation is turned off\, matter i
s represented in terms of virtual particles that exist momentarily only. H
owever\, with T violation turned on\, what was the mathematical structure
of a virtual particle now traces out an unbounded world line that satisfie
s conservation laws and an equation of motion. The theory is then analogou
s to the 5 dimensional "proper time" formalism introduced by Feynman [3]\,
extended by Nambu [4] in the 1950's\, and developed as "parameterized rel
ativistic quantum theories" [5]. The important point here is that time evo
lution and conservation laws are not built into the new theory\, but rathe
r they emerge _phenomenologically_ from T violation. In other words\, the
new theory proposes that T violation is the _origin of dynamics and conser
vations laws_. It has experimentally testable predictions and offers new
insight into the quantum nature of time.\n\nThe talk will include an analy
sis of the nature of the T violation from known and expected sources such
as mesons\, neutrinos\, and a Higgs-like scalar field. In appropriate par
ameter regimes\, the commutator of the time-reversed versions of the assoc
iated T violating Hamiltonian\, $\\hat{H}_F$ and $\\hat{H}_B$\, is found t
o approach the canonical form $[\\hat{H}_F\,\\hat{H}_B]=i\\lambda \\hat{1}
$ where $\\hat{H}_B=\\hat{T}\\hat{H}_F\\hat{T}^{-1}$\, $\\hat{T}$ is Wigne
r's time reversal operator\, $\\hat{1}$ is the identity operator\, and $\\
lambda=\\langle i[\\hat{H}_F\,\\hat{H}_B]\\rangle$ represents the amount o
f T violation.\n\n[1] J.A. Vaccaro\, Quantum asymmetry between time and sp
ace\, _Proc. R. Soc. A_ __472__\, 20150670 (2016). \nhttps://dx.doi.org/1
0.1098/rspa.2015.0670\n\n[2] J.A. Vaccaro\, The quantum theory of time\, t
he block universe\, and human experience\, _Phil. Trans. R. Soc. Lond. A_
__376__\, 20170316 (2018). https://dx.doi.org/10.1098/rsta.2017.0316\n\n[3
] R.P. Feynman\, Mathematical Formulation of the Quantum Theory of Electro
magnetic Interaction\, _Phys. Rev._ __80__\, 440-457 (1950)\, Appendix A.
https://dx.doi.org/10.1103/PhysRev.80.440\n\n[4] Y. Nambu\, The Use of the
Proper Time in Quantum Electrodynamics I\, _Prog. Theor. Phys._ __5__\, 8
2 (1950). https://dx.doi.org/10.1143/ptp/5.1.82\n\n[5] J.R. Fanchi\, Revie
w of invariant time formulations of relativistic quantum theories\, _Found
. Phys._ __23__\, 487-548 (1993). https://dx.doi.org/10.1007/BF01883726\nh
ttps://indico.ict.inaf.it/event/751/contributions/5219/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5219/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Interrelations between local correlations\, nonlocal correlations
and causality
DTSTART;VALUE=DATE-TIME:20190923T142500Z
DTEND;VALUE=DATE-TIME:20190923T150500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5221@indico.ict.inaf.it
DESCRIPTION:Speakers: Eliahu Cohen (Faculty of Engineering\, Bar Ilan Uni
versity)\nThe set of quantum mechanical nonlocal correlations is unique an
d intriguing in many ways. Characterizing this set is expected to cast lig
ht on the fundamental physical principles governing quantum theory\, those
from which the mathematical structure of the theory arises. Recently\, we
have shown ([A. Carmi and E. Cohen\, Sci. Adv. eaav8370 (2019)] and follo
wup works) that this set may largely be derived from the requirement that
uncertainty relations\, broadly understood\, are local in the sense of bei
ng independent of the choices made by other parties. Relativistic independ
ence\, as we have named this condition\, treats nonlocal correlations and
uncertainty relations on an equal footing. Furthermore\, it implies that q
uantum mechanics can be as nonlocal as it is without violating relativisti
c causality thanks to the existence of intrinsic uncertainty.\nThe notion
of relativistic independence can be also encoded in a new kind of nonlocal
hidden variables we term "pseudolocal". We have shown that different kind
s of quantum hidden variables lead to backwards in time signaling if known
[A. Carmi\, E. Cohen\, L. Maccone\, and H. Nikolic\, arXiv:1903.01349].\n
In this talk we shall briefly present these previous works and then build
upon them to show how this view gives rise to causal structures. We will d
emonstrate how such a causal structure tightens the bounds on the set of n
onlocal correlations in any physical theory as the number of experimenters
\, measuring devices and incorporated statistical moments increases. Final
ly\, we will connect the failure of counterfactual definiteness with time-
irreversibility and discuss a sense in which entanglement gives rise to th
e arrow of time.\nhttps://indico.ict.inaf.it/event/751/contributions/5221/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5221/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum field theories with quantum causal structure
DTSTART;VALUE=DATE-TIME:20190925T151000Z
DTEND;VALUE=DATE-TIME:20190925T153000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5037@indico.ict.inaf.it
DESCRIPTION:Speakers: Ding Jia (Perimeter Institute: University of Waterlo
o)\nWe study quantum gravity induced quantum causal structure in the conte
xt of quantum field theories. We argue both conceptually and numerically t
hat when spacetime is treated quantumly\, (1) exact microcausality conditi
on\, (2) exact causal boundaries\, and (3) the distinction between particl
es and antiparticles cannot be maintained. These suggest possibilities of
"time travel" and "tunneling out of black holes"\, but to examine whether
such possibilities can be realized\, concrete calculations are needed. We
present a method to conduct calculations for quantum field theories on qua
ntum spacetime based on the expansion of Feynman diagrams into worldline d
iagrams. As a first application\, we show that quantum causal structure re
gularizes matter field UV singularities. This result reinforces previous s
uggestions from analyzing entanglement in the presence of quantum causalit
y.\nhttps://indico.ict.inaf.it/event/751/contributions/5037/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5037/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Reversible time travel with freedom of choice
DTSTART;VALUE=DATE-TIME:20190924T094500Z
DTEND;VALUE=DATE-TIME:20190924T101500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5215@indico.ict.inaf.it
DESCRIPTION:Speakers: Ämin Baumeler (Institute for Quantum Optics and Q
uantum Information)\nGeneral relativity allows for the existence of closed
time-like curves\, along which a material object could travel back in tim
e and interact with its past self. Previous studies by Thorne and others s
howed that for any choice of initial conditions\, consistent dynamics —
even in the presence of closed time-like curves — exist. Moreover and co
unterintuitively\, they showed that the examples with self-interaction lea
d to an infinite number of consistent dynamics. While in these previous st
udies initial conditions only where subject to the experimenter’s choice
\, we allow for arbitrary operations to be performed in local space-time r
egions. We find that any such dynamics can be realised through reversible
interactions. We further find that consistency with local operations is co
mpatible with non-trivial time travel: Three parties can interact in such
a way to be all both in the future and in the past of each other\, while b
eing free to perform arbitrary local operations. Finally\, the states desc
ribed in our framework are uniquely determined.\nhttps://indico.ict.inaf.i
t/event/751/contributions/5215/
URL:https://indico.ict.inaf.it/event/751/contributions/5215/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A time machine allowing travel to the past by free fall
DTSTART;VALUE=DATE-TIME:20190924T092500Z
DTEND;VALUE=DATE-TIME:20190924T094500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5484@indico.ict.inaf.it
DESCRIPTION:Speakers: Livio Pizzocchero (Dipartimento di Matematica\, Un
iversit`a degli Studi di Milano and INFN\, Sezione di Milano )\nThis talk
illustrates a model of spacetime with closed timelike curves proposed in a
recent paper (D. Fermi and L. Pizzocchero\, Class. Quantum Grav. 35 (2018
)\, 165003\, 42pp). This spacetime is diﬀeomorphic to R4 and carries an
ad hoc metric\; it consists of a ﬂat outer region and of a “time machi
ne”\, formed by a toroidal interface and by an inner ﬂat region. The t
imelike geodesics of this model\, representing motions in free fall\, can
be analyzed qualitatively and computed analytically by quadratures\; in th
is way\, it is shown that a freely falling observer can start from the out
er Minkowskian region\, travel across the time machine and then return to
its initial position at an earlier time\, as evaluated by an inertial fram
e for the outer region with a clock ﬁxed in the initial position. With a
suitable choice of the initial conditions\, the amount of time travelled
in the past according to this ﬁxed clock can be made arbitrarily large\,
while keeping non large the duration of the trip according to the travell
er’s clock\; quantitative examples are given.\nThe price for the above f
eatures of the model is the violation of the standard energy conditions in
the interface of the time machine. Another problem are the tidal forces e
xperienced by the traveller within this interface: as shown by a quantitat
ive analysis\, these are non destructive for a human being only if the siz
e of the machine (and of the interface) is astronomical. A time machine of
this size also has a non large interfacial mass-energy density\, much sma
ller (in absolute value) than the density of water\; the energy density is
much below the Planck scale even for a machine of size comparable with th
e human scale\, which ensures that the treatment of these objects via clas
sical physics is correct.\nhttps://indico.ict.inaf.it/event/751/contributi
ons/5484/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5484/
END:VEVENT
BEGIN:VEVENT
SUMMARY:introductory round table
DTSTART;VALUE=DATE-TIME:20190923T183000Z
DTEND;VALUE=DATE-TIME:20190923T190000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5880@indico.ict.inaf.it
DESCRIPTION:Speakers: Mariateresa Crosta (Istituto Nazionale di Astrofisic
a (INAF))\, Lorenzo Maccone (Univ. degli Studi di Pavia)\, Stefano Liberat
i (SISSA)\nProf. Stefano Liberati (SISSA) and Prof. Lorenzo Maccone (Univ
. Pavia)\; \n\nModerators: Mariateresa Crosta (INAF-OATo)\nhttps://indico.
ict.inaf.it/event/751/contributions/5880/
LOCATION:Sala Soldati\, Cinema Massimo
URL:https://indico.ict.inaf.it/event/751/contributions/5880/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Screening of "Time Bandits"\, original version
DTSTART;VALUE=DATE-TIME:20190923T190000Z
DTEND;VALUE=DATE-TIME:20190923T210000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5927@indico.ict.inaf.it
DESCRIPTION:https://indico.ict.inaf.it/event/751/contributions/5927/
LOCATION:Sala Soldati\, Cinema Massimo
URL:https://indico.ict.inaf.it/event/751/contributions/5927/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Introduction
DTSTART;VALUE=DATE-TIME:20190924T153000Z
DTEND;VALUE=DATE-TIME:20190924T154000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5819@indico.ict.inaf.it
DESCRIPTION:Speakers: Mariateresa Crosta (Istituto Nazionale di Astrofisic
a (INAF))\nhttps://indico.ict.inaf.it/event/751/contributions/5819/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5819/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBD
DTSTART;VALUE=DATE-TIME:20190924T160000Z
DTEND;VALUE=DATE-TIME:20190924T162000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5820@indico.ict.inaf.it
DESCRIPTION:Speakers: Sumati SURYA (Raman Research Institute)\nhttps://ind
ico.ict.inaf.it/event/751/contributions/5820/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5820/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBD
DTSTART;VALUE=DATE-TIME:20190924T154000Z
DTEND;VALUE=DATE-TIME:20190924T160000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5823@indico.ict.inaf.it
DESCRIPTION:Speakers: Susanna TERRACINI (Dip. of Mathematics)\nhttps://ind
ico.ict.inaf.it/event/751/contributions/5823/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5823/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Discussion - Closing remarks
DTSTART;VALUE=DATE-TIME:20190924T162000Z
DTEND;VALUE=DATE-TIME:20190924T163000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5824@indico.ict.inaf.it
DESCRIPTION:https://indico.ict.inaf.it/event/751/contributions/5824/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5824/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Superpositions of Mesoscopic Objects for Sensing Quantum Gravity a
nd Gravitational Waves
DTSTART;VALUE=DATE-TIME:20190925T092500Z
DTEND;VALUE=DATE-TIME:20190925T101000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5826@indico.ict.inaf.it
DESCRIPTION:Speakers: Sougato Bose (Department of Physics and Astronomy\,
University College London)\nWe will show two fundamental applications of q
uantum superpositions of spatially separated states of mesoscopic objects
(nano- and micro-spheres). Firstly we are going to show how convenient it
may be to prepare and probe such superpositions through a pure ancillary s
ystem such as a spin. Next\, we are going to show how an entanglement betw
een two such interferometers can be generated purely through the Newtonian
interaction between the masses and that this can be probed\, at the end o
f the interferometry\, purely by measuring the correlations between spins.
We are going to justify why\, under the assumption of locality of physica
l interactions and under a reasonable definition of classicality\, the abo
ve entanglement signifies the qualitatively quantum nature of gravity. We
are also going to discuss how the same spin-induced and probed superposit
ions will open up the ability to detect low frequency gravitational waves\
, immune to initial thermal noise\, with a meter-scale apparatus.\nhttps:/
/indico.ict.inaf.it/event/751/contributions/5826/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5826/
END:VEVENT
BEGIN:VEVENT
SUMMARY:“Time” replaced by quantum correlations: experimental visualiz
ation.
DTSTART;VALUE=DATE-TIME:20190923T154500Z
DTEND;VALUE=DATE-TIME:20190923T161000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5220@indico.ict.inaf.it
DESCRIPTION:Speakers: Ekaterina MOREVA (INRiM)\nThe description of time
in quantum mechanics and in particular in connection with quantum gravity
and cosmology has always presented significant difficulties. One of descri
ptions based on Page and Wootters (PaW) mechanism which considers “time
” as a quantum degree of freedom[1]. Here we give a complete review of t
he Page and Wootters' quantum time mechanism and provide experimental illu
strations that are able to describe time as an emergent property of quantu
m correlations and giving us access to the possibility of a test of the Le
ggett-Garg inequalities.\n
\n[1] D.N. Page and W.K. Wootters\, Phys. Rev
. D 27\, 2885 (1983). \n[2] E. Moreva\, M. Gramegna\, G. Brida\, L. Maccon
e\, M. Genovese\, “Quantum time: Experimental multitime correlations”\
, Physical Review D 96 (10)\, 102005 (2017)\nhttps://indico.ict.inaf.it/ev
ent/751/contributions/5220/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5220/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Superpositions of causal orders in a timeless universe
DTSTART;VALUE=DATE-TIME:20190925T101000Z
DTEND;VALUE=DATE-TIME:20190925T105500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5226@indico.ict.inaf.it
DESCRIPTION:Speakers: Vlatko Vedral (University of Oxford\, ISI\, National
University of Singapore)\nI will first review the timeless Page-Wootters
picture of the quantum universe in which there is no overall dynamics\, bu
t where the states of quantum fields evolve relative to the quantum states
of the underlying space. I will then introduce the concept of superposing
different causal orders – a notion that could be naturally motivated wi
thin some approaches to quantum gravity – and ask if and how this phenom
enon could be incorporated within the Page-Wootters formalism. I hope to f
inish by speculating about some possible experimental implications.\nhttps
://indico.ict.inaf.it/event/751/contributions/5226/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5226/
END:VEVENT
BEGIN:VEVENT
SUMMARY:What is the surface of a (dynamical) black hole?
DTSTART;VALUE=DATE-TIME:20190923T074500Z
DTEND;VALUE=DATE-TIME:20190923T083000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5481@indico.ict.inaf.it
DESCRIPTION:Speakers: José M.M. Senovilla (UPV/EHU)\nBlack holes in equil
ibrium are fundamental objects predicted by General Relativity. However\,
real black holes form\, evolve and eventually evaporate\, thus they are dy
namical. Do they have a well-defined boundary? Where? The usual Event Hori
zon is global and teleological\, thus not well defined for dynamical black
holes. The concepts of dynamical and trapping horizons\, based on closed
trapped surfaces\, are promising alternatives. I will show\, however\, the
fundamental problems inherent to dynamical or trapping horizons. I will t
hen introduce the concept of Core of a black hole\, and discuss the possib
ility that they can select a unique horizon.\nhttps://indico.ict.inaf.it/e
vent/751/contributions/5481/
URL:https://indico.ict.inaf.it/event/751/contributions/5481/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Causal nature and dynamics of trapping horizons in black hole coll
apse
DTSTART;VALUE=DATE-TIME:20190923T102000Z
DTEND;VALUE=DATE-TIME:20190923T104000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5440@indico.ict.inaf.it
DESCRIPTION:Speakers: Ilia Musco (Institut de Ciències del Cosmos\, Univ
ersitat de Barcelona\, Facultat de Física)\nIn calculations of gravitatio
nal collapse to form black holes\, trapping horizons (foliated by marginal
ly trapped surfaces) make their first appearance either within the collaps
ing matter or where it joins on to a vacuum exterior. Those which then mov
e outwards with respect to the matter have been proposed for use in defini
ng black holes\, replacing the global concept of an event horizon\, which
has some serious drawbacks for practical applications. I here present resu
lts from a study of the properties of both outgoing and ingoing trapping h
orizons\, assuming strict spherical symmetry throughout. Their causal natu
re (i.e. whether they are spacelike\, timelike or null) is investigated\,
following two different approaches\, one using a geometrical quantity rela
ted to expansions of null geodesic congruences\, and the other using the h
orizon velocity measured with respect to the collapsing matter. The models
treated are simplified\, but do include pressure effects in a meaningful
way and we analyze how the horizon evolution depends on the initial condit
ions of energy density and pressure of the collapse. (NOTE: This work has
been published in Classical and Quantum Gravity 34 (2017) no.13\, 135012 )
\nhttps://indico.ict.inaf.it/event/751/contributions/5440/
URL:https://indico.ict.inaf.it/event/751/contributions/5440/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matrix Product State Simulations of Quantum Fields in Curved 1+1 S
pacetime
DTSTART;VALUE=DATE-TIME:20190924T101500Z
DTEND;VALUE=DATE-TIME:20190924T103500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5231@indico.ict.inaf.it
DESCRIPTION:Speakers: Adam Lewis (Perimeter Institute\, Waterloo Ontario
)\nWhile the dynamics of black hole evaporation and closed-timelike-curve
physics in the presence of quantum fields are to some extent understood in
principle\, the computations necessary to produce concrete predictions fr
om them are often intractable in practice. Here we show how tensor-network
based numerics\, which assign a manageably sparse representation to certa
in quantum states\, can be used to perform them. As a first step wecompute
the Hadamard-regularized stress-energy tensor of a 1+1-D massive Dirac fi
eld in various quantum states\, demonstrating the Unruh effect in flat and
curved spacetime.\nhttps://indico.ict.inaf.it/event/751/contributions/523
1/
URL:https://indico.ict.inaf.it/event/751/contributions/5231/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Pseudodensity Matrix of a quatum optical system as a tool for visu
alizing open timelike curves.
DTSTART;VALUE=DATE-TIME:20190925T130000Z
DTEND;VALUE=DATE-TIME:20190925T133000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5827@indico.ict.inaf.it
DESCRIPTION:Speakers: Marco Genovese (INRiM)\nQuantum optical systems pres
ent several interesting properties that allow using them as a tool for vis
ualizing physical phenomena otherwise subject of theoretical speculation o
nly\, as Bose Einstein condensation for Hawking radiation [1] or Page Woot
ters model [2-5].\n\nClosed Time-like Curves (CTC)\, one of the most strik
ing predictions of general relativity\, are notorious for generating parad
oxes\, such as the grandfather's paradox\, but these paradoxes can be solv
ed in a quantum network model [6]\, where a qubit travels back in time and
interacts with its past copy. However\, there is a price to pay. The reso
lution of the causality paradoxes requires to break quantum theory's linea
rity. This leads to the possibility of quantum cloning\, violation of the
uncertainty principle and solving NP-complete problems in polynomial time.
Interestingly\, violations of linearity occur even in an open time-like
curve (OTC)\, when the qubit does not interact with its past copy\, but it
is initially entangled with another\, chronology-respecting\, qubit. The
non-linearity is needed here to avoid violation of the monogamy of entangl
ement. To preserve linearity and avoid all other drastic consequences\, we
discuss how the state of the qubit in the OTC is not a density operator\,
but a pseudo-density operator (PDO) - a recently proposed generalisation
of density operators\, unifying the description of temporal and spatial qu
antum correlations. Here I present an experimental simulation of the OTC u
sing polarization-entangled photons\, also providing the first full quantu
m state tomography of the PDO describing the OTC\, verifying the violation
of the monogamy of entanglement induced by the chronology-violating qubit
. At the same time the linearity is preserved since the PDO already contai
ns both the spatial degrees of freedom and the linear temporal quantum evo
lution. These arguments also offer a possible solution to black hole entro
py problem.\n\n[1] J.Steinahauer et al.\, Nature Physics volume12\, 959
–965 (2016)\n\n[2] D.N. Page and W.K. Wootters\, Phys. Rev. D 27\, 2885
(1983)\; W.K. Wootters\, Int. J. Theor. Phys. 23\, 701 (1984).\n\n[3] E.Mo
reva\,M.Gramegna\,G.Brida\,L.Maccone\,M.Genovese\, Phys. Rev. A 89\, 05212
2 (2014).\n\n[4] V.Giovannetti\, S.Lloyd\, L.Maccone\, Phys. Rev. D\, 92
\, 045033 (2015).\n\n[5] E.Moreva\,M.Gramegna\,G.Brida\,L.Maccone\,M.Genov
ese\, Phys. Rev.D in press. arXiv:1710.00707\n\n[6] D. Deutsch\, Phys. Rev
. D 44\, 10\, 1991.\n\n[7] C. Marletto\, V. Vedral\, S. Virzì\, E.Rebufel
lo\,A.Avella\,M.Gramegna\, I.P. Degiovanni\,M.Genovese\, in press.\nhttps:
//indico.ict.inaf.it/event/751/contributions/5827/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5827/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Updates from the future
DTSTART;VALUE=DATE-TIME:20190923T121000Z
DTEND;VALUE=DATE-TIME:20190923T125500Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5836@indico.ict.inaf.it
DESCRIPTION:Speakers: Seth Lloyd (MIT)\nThe possibility of closed timelike
curves in general relativity opens up the physical possibility of\ntime t
ravel. This talk reviews the different quantum mechanical theories of clos
ed timelike curves\, and\ndiscusses their various advantages and drawbacks
. We will discuss whether it is possible to use closed \ntimelike curves
to build a time machine.\nhttps://indico.ict.inaf.it/event/751/contributi
ons/5836/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5836/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum enhanced correlated interferometry for Planck scale phys
ics
DTSTART;VALUE=DATE-TIME:20190925T133000Z
DTEND;VALUE=DATE-TIME:20190925T140000Z
DTSTAMP;VALUE=DATE-TIME:20210927T081400Z
UID:indico-contribution-5228@indico.ict.inaf.it
DESCRIPTION:Speakers: Elena Losero\nRecently\, hypothetical faint effects
in interferometers connected to non-commutativity of position variables in
different directions originating at the Planck scale have been consider
ed\, as a possible signature of quantum gravity. In particular\, this idea
led to the realization of a double 40 m interferometer at Fermilab with s
tate of the art sensitivity in the MHz domain. Although instruments such
as optical interferometers represent probably the most sensitive devices c
urrently available\, their performance are still limited by shot noise\, i
f operated with classical light. Quantum metrology\, allows to overcame t
hese limits\, by exploiting quantum properties of light\, therefore repres
enting a promising avenue for enabling new discoveries. \n\nHere we presen
t an experiment of quantum-enhanced correlated interferometry\, showing an
improved sensitivity with respect to a single interferometer in revealin
g faint stochastic noise\, such as the ones predicted by some Planck scale
model. Using quantum-enhanced correlation techniques between two Michelso
n interferometers\, we reach a sensitivity of 10-17 m/(Hz)1/2 at 13.5 MHz
in a few seconds of integration time\, which is 20 times better than the
one of a single device. Moreover\, by injecting bipartite quantum correla
ted states\, we also demonstrated a sub shot noise sensitivity in the com
parison of different interferometers' signals. In perspective\, the propos
ed technique could allow either to reduce the size to a table top scale or
to further improve the sensitivity of large setup such as the Fermilab f
acility.\nhttps://indico.ict.inaf.it/event/751/contributions/5228/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5228/
END:VEVENT
END:VCALENDAR