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BEGIN:VEVENT
SUMMARY:Giulio Chiribella (The University of Hong Kong)
DTSTART:20210531T130000Z
DTEND:20210531T133000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/1
DESCRIPTION:Title: Quantum operations with indefinite direction of time: the quantum tim
e flip\nby Giulio Chiribella (The University of Hong Kong) as part of
BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbst
ract\nThe standard operational framework of quantum theory is time-asymmet
ric. This asymmetry reflects the capabilities of ordinary agents\, who are
able to deterministically pre-select the states of quantum systems\, but
not to deterministically post-select the outcomes of quantum measurements.
However\, the fundamental dynamics of quantum particles is time-symmetric
\, and is compatible with a broader class of operations where pre-selectio
ns and post-selections are combined in general ways that do not presuppose
a definite direction of time. In this talk I introduce a framework for qu
antum operations with indefinite time direction\, providing an example\, c
alled the quantum time flip\, where an unknown\, time-symmetric process is
accessed in a coherent superposition of two alternative time directions.
In certain information-theoretic tasks\, a hypothetical agent with access
to the quantum flip can in principle outperform all agents who operate in
a definite time direction. \n\nRelated paper: G. Chiribella an Z. Liu\,
The quantum time flip\, https://arxiv.org/abs/2012.03859\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Aleks Kissinger (University of Oxford)
DTSTART:20210531T133000Z
DTEND:20210531T140000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/2
DESCRIPTION:Title: The Logic of Influence and Causation\nby Aleks Kissinger (Univers
ity of Oxford) as part of BIRS workshop : Quantum Foundations\, Gravity\,
and Causal Order\n\n\nAbstract\nI will talk about some recent developments
in the framework of "black box causal reasoning". In this minimal setting
\, we assume access to some abstract process and attempt to describe\, qua
ntify\, or prove properties about the causal relationships between its inp
uts and outputs. This works both for first-order processes\, which can cap
ture e.g. a device shared by multiple agents\, or higher-order processes\,
which capture the environment in which those agents live. This higher-ord
er picture leads naturally to a particular categorical structure that has
long been studied in theoretical computer science called a *-autonomous ca
tegory. Whereas first order processes (e.g. quantum gates) only have two n
atural notions of composition (in series and in parallel)\, higher-order p
rocesses have an extremely rich and multi-faceted notion of composition gu
ided by the "internal logic" of a *-autonomous category. In this talk\, I
will highlight some aspects of this logic\, show how they can be used for
causal reasoning\, and discuss some recent extensions and open problems.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gavin Morley (University of Warwick)
DTSTART:20210531T141000Z
DTEND:20210531T144000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/3
DESCRIPTION:Title: Levitating nanodiamond experiments: towards a test of quantum gravity
\nby Gavin Morley (University of Warwick) as part of BIRS workshop : Q
uantum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nWe are buil
ding an experiment in which a nitrogen-vacancy-centre electron spin would
be used to put a levitated nanodiamond into a spatial quantum superpositio
n [1-3]. This would be able to test theories of spontaneous wavefunction c
ollapse and is the first step of a much more ambitious experiment to test
if gravitational effects can be in a quantum superposition [4\, 5]. This t
alk will describe our current experimental design [6-11]\, and our latest
experimental progress: the first steps on a long journey.\n\n[1] A. T. M.
A. Rahman\, A. C. Frangeskou\, M. S. Kim\, S. Bose\, G. W. Morley & P. F.
Barker\, Sci. Rep. 6\, 21633 (2016).\n[2] A. T. M. A. Rahman\, A. C. Frang
eskou\, P. F. Barker & G. W. Morley\, RSI 89\, 023109 (2018).\n[3] A. C. F
rangeskou\, A. T. M. A. Rahman\, L. Gines\, S. Mandal\, O. A. Williams\, P
. F. Barker & G. W. Morley\, NJP 20\, 043016 (2018).\n[4] S. Bose\, A. Maz
umdar\, G. W. Morley\, H. Ulbricht\, M. Toroš\, M. Paternostro\, A. A. Ge
raci\, P. F. Barker\, M. S. Kim & G. Milburn\, PRL 119\, 240401 (2017).\n[
5] C. Marletto & V. Vedral\, PRL 119\, 240402 (2017).\n[6] S. Bose & G. W.
Morley\, arXiv:1810.07045 (2018).\n[7] M. Scala\, M. S. Kim\, G. W. Morle
y\, P. F. Barker & S. Bose\, PRL 111\, 180403 (2013).\n[8] C. Wan\, M. Sca
la\, G. W. Morley\, A. T. M. A. Rahman\, H. Ulbricht\, J. Bateman\, P. F.
Barker\, S. Bose & M. S. Kim\, PRL 117\, 143003 (2016).\n[9] J. S. Pederna
les\, G. W. Morley & M. B. Plenio\, PRL 125\, 023602 (2020).\n[10] R. J. M
arshman\, A. Mazumdar\, G. W. Morley\, P. F. Barker\, S. Hoekstra & S. Bos
e\, NJP 22\, 083012 (2020).\n[11] Z.-q. Yin\, T. Li\, X. Zhang & L. M. Dua
n\, PRA 88\, 033614 (2013).\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Philip Walther (University of Vienna)
DTSTART:20210531T144000Z
DTEND:20210531T151000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/4
DESCRIPTION:Title: Shining light on the interface of gravity and quantum physics: precis
ion measurements using photonic quantum interferometry\nby Philip Walt
her (University of Vienna) as part of BIRS workshop : Quantum Foundations\
, Gravity\, and Causal Order\n\n\nAbstract\nQuantum mechanics and general
relativity are two fundamentally different theories and have both been tes
ted independently with very high precision. However\, even after a century
of research\, the interplay of those two very different theories has neve
r been tested experimentally. Within this talk I will present the experim
ental research aiming to explore this interface between quantum mechanics
and general relativity by performing high-precision experiments at the lev
el of single quanta of light\, the photons. Such quantum systems allow one
to examine the influence of gravity on interference effects. For this pur
pose\, a high-precision interferometer whose paths are subject to differen
t gravitational potentials will be used.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fabio Costa (University of Queensland)
DTSTART:20210531T220000Z
DTEND:20210531T223000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/5
DESCRIPTION:Title: Background independent quantum causal structures\nby Fabio Costa
(University of Queensland) as part of BIRS workshop : Quantum Foundations\
, Gravity\, and Causal Order\n\n\nAbstract\nThe process matrix formalism f
ormalises non-classical causal structures\, which are expected to emerge i
n a theory that combines quantum indeterminacy with the dynamical causal s
tructure of general relativity. The framework relies on the notion of loca
l laboratories—an abstraction of spacetime events or regions—where loc
al operations and measurements can be performed. In a theory of quantum gr
avity\, we expect that it should not be possible to label laboratories a p
riori: this requires a background reference frame (although possibly non-c
lassical)\, while general relativity is background independent. I will pre
sent a background independent formulation of the process matrix formalism
that incorporates a discrete version of background independence: invarianc
e under permutations. Although the formalism abandons an absolute notion o
f “local operation”\, such a notion re-emerges as relative to a physic
al reference frame. Permutation symmetry also implies some type of superse
lection rule\, although\, for quantum processes\, this cannot be interpret
ed as implying the existence of a conserved charge with a definite value.
Finally\, I will comment on the possibility to extend the approach to incl
ude quantum coordinate transformations.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Laura Henderson (University of Waterloo)
DTSTART:20210531T223000Z
DTEND:20210531T230000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/6
DESCRIPTION:Title: Entanglement Harvesting with a Twist\nby Laura Henderson (Univers
ity of Waterloo) as part of BIRS workshop : Quantum Foundations\, Gravity\
, and Causal Order\n\n\nAbstract\nPrevious work has shown that a single Un
ruh-DeWitt (UDW) detector can distinguish between a black hole and geon ev
en through the topological differences are hidden behind a horizon. We ext
end this work to two detectors to study the effects of topology on the ent
anglement harvesting protocol by placing a pair of UDW detectors outside o
f an RP2 geon and comparing resulting entanglement to a similar pair place
d outside of a BTZ black hole. The detectors are stationary\, located at d
ifferent radii from the horizon the interact with the Hartle-Hawking vacuu
m of a conformally coupled massless scalar field. We find that the two spa
cetimes are distinguishable by this protocol only when the black hole has
a small mass. We also find the difference in the amount entanglement harve
sted is highly dependent on the energy gap of the detector: detectors with
a large gap harvest more entanglement outside of a geon\, while detectors
with a small energy gap harvest more entanglement outside of a black hole
. This may suggest a frequency dependent difference in the entanglement st
ructure of quantum field.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrew White (University of Queensland)
DTSTART:20210531T231000Z
DTEND:20210531T234000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/7
DESCRIPTION:by Andrew White (University of Queensland) as part of BIRS wor
kshop : Quantum Foundations\, Gravity\, and Causal Order\n\nAbstract: TBA\
n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Markus Müller (Austrian Academy of Sciences)
DTSTART:20210601T130000Z
DTEND:20210601T133000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/8
DESCRIPTION:Title: Quantum reference frame transformations as symmetries and the paradox
of the third particle\nby Markus Müller (Austrian Academy of Science
s) as part of BIRS workshop : Quantum Foundations\, Gravity\, and Causal O
rder\n\n\nAbstract\nIn a quantum world\, reference frames are ultimately q
uantum systems too -- but what does it mean to "jump into the perspective
of a quantum particle"? In this work\, we show that quantum reference fram
e (QRF) transformations appear naturally as symmetries of simple physical
systems. This allows us to rederive and generalize known QRF transformatio
ns within an alternative\, operationally transparent framework\, and to sh
ed new light on their structure and interpretation. We give an explicit de
scription of the observables that are measurable by agents constrained by
such quantum symmetries\, and apply our results to a puzzle known as the `
paradox of the third particle'. We argue that it can be reduced to the que
stion of how to relationally embed fewer into more particles\, and give a
thorough physical and algebraic analysis of this question. This leads us t
o a generalization of the partial trace (`relational trace') which arguabl
y resolves the paradox\, and it uncovers important structures of constrain
t quantization within a simple quantum information setting\, such as relat
ional observables which are key in this resolution. While we restrict our
attention to finite Abelian groups for transparency and mathematical rigor
\, the intuitive physical appeal of our results makes us expect that they
remain valid in more general situations.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marios Christodoulou (University of Vienna)
DTSTART:20210601T133000Z
DTEND:20210601T140000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/9
DESCRIPTION:Title: Quantum Superpositions of Graphs\nby Marios Christodoulou (Univer
sity of Vienna) as part of BIRS workshop : Quantum Foundations\, Gravity\,
and Causal Order\n\n\nAbstract\nGraphs are a discrete topological canvas
that in many applications can completely replace a continuous manifold. Ne
vertheless\, invariance of dynamics defined on graphs under changes of re
ference frames is typically attempted by embedding the graph in an ambient
manifold. This seems superfluous as node names already label points simil
arly to a choice of coordinates in continuous space. As node names are fid
ucial\, graph renamings can be seen as a change of coordinates on the gr
aph. Thus\, graph renamings correspond to a natively discrete analogue of
diffeomorphisms. In quantum theory\, node names become even more important
. We first provide a robust notion of quantum superpositions of graphs and
argue with a simple example that in quantum theory in order to avoid inst
antaneous signalling it is necessary to use node names to define the ‘lo
calisation’ of a node\, rather than values of a physical field. We propo
se renaming invariance as a symmetry principle of similar weight to diffeo
morphism invariance and show how to impose it at the level of quantum supe
rpositions of graphs.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Esteban Castro Ruiz (ETH Zurich)
DTSTART:20210601T141000Z
DTEND:20210601T144000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/10
DESCRIPTION:Title: Relative subsystems and quantum reference frame transformations\
nby Esteban Castro Ruiz (ETH Zurich) as part of BIRS workshop : Quantum Fo
undations\, Gravity\, and Causal Order\n\n\nAbstract\nTransformations betw
een reference frames play a crucial role in our understanding of physical
processes. In practice\, reference frames are realised by physical systems
\, which are standardly treated as classical. However\, assuming that ever
y physical system is ultimately quantum\, it is interesting to ask how a t
heory of transformations wrt quantum reference frames would look like\, an
d what implications it would have for our description of spacetime. Recent
ly\, there has been a lot of effort towards developing a quantum generalis
ation of reference frame transformations\, unveiling novel phenomena that
are absent in the classical treatment of reference frames. Here\, we devel
op a first-principles framework for quantum reference frame transformation
s which clarifies important conceptual issues of previous treatments. Bas
ed on the algebra of relative observables between a system and a reference
frame\, our operational perspective leads naturally to a mixed-state appr
oach (incoherent twirling)\, in contrast to current pure-state approaches
(coherent twirling). Within our framework\, the full invariant quantum sub
system contains not only the algebra of relative observables between the s
ystem and the reference frame but also an “extra particle\,” related t
o the invariant degrees of freedom of the reference frame itself. Importan
tly\, this extra particle contains information about the “quantumness”
of the reference frame and is essential to the unitarity of quantum refer
ence frame transformations. Our approach is general\, in the sense that it
can be applied to a vast set of symmetry groups and to any type of system
. We illustrate the physical meaning of the concepts developed by analysin
g quantum reference frame transformations with respect to the (centrally e
xtended) Galilei group.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ognyan Oreshkov (Université libre de Bruxelles)
DTSTART:20210601T144000Z
DTEND:20210601T151000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/11
DESCRIPTION:Title: Quantum processes on time-delocalised systems\nby Ognyan Oreshko
v (Université libre de Bruxelles) as part of BIRS workshop : Quantum Foun
dations\, Gravity\, and Causal Order\n\n\nAbstract\nTransformations betwee
n reference frames play a crucial role in our understanding of physical pr
ocesses. In practice\, reference frames are realised by physical systems\,
which are standardly treated as classical. However\, assuming that every
physical system is ultimately quantum\, it is interesting to ask how a the
ory of transformations wrt quantum reference frames would look like\, and
what implications it would have for our description of spacetime. Recently
\, there has been a lot of effort towards developing a quantum generalisat
ion of reference frame transformations\, unveiling novel phenomena that ar
e absent in the classical treatment of reference frames. Here\, we develop
a first-principles framework for quantum reference frame transformations
which clarifies important conceptual issues of previous treatments. Based
on the algebra of relative observables between a system and a reference f
rame\, our operational perspective leads naturally to a mixed-state approa
ch (incoherent twirling)\, in contrast to current pure-state approaches (c
oherent twirling). Within our framework\, the full invariant quantum subsy
stem contains not only the algebra of relative observables between the sys
tem and the reference frame but also an “extra particle\,” related to
the invariant degrees of freedom of the reference frame itself. Importantl
y\, this extra particle contains information about the “quantumness” o
f the reference frame and is essential to the unitarity of quantum referen
ce frame transformations. Our approach is general\, in the sense that it c
an be applied to a vast set of symmetry groups and to any type of system.
We illustrate the physical meaning of the concepts developed by analysing
quantum reference frame transformations with respect to the (centrally ext
ended) Galilei group.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexander Smith (Saint Anselm College)
DTSTART:20210601T220000Z
DTEND:20210601T223000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/12
DESCRIPTION:Title: Relational dynamics and quantum time dilation\nby Alexander Smit
h (Saint Anselm College) as part of BIRS workshop : Quantum Foundations\,
Gravity\, and Causal Order\n\n\nAbstract\nThe lesson of general relativity
is background independence\, which results in a Hamiltonian constraint. T
his presents a challenge for quantum gravity because the quantization of t
his constraint demands that physical states of geometry and matter are fro
zen\, leading to the problem of time. We must then explain how the convent
ional notion of time evolution emerges\, which motivates the need for a re
lational description of quantum dynamics. Using quantum clocks and covaria
nt time observables\, I will introduce a formulation of relational quantum
dynamics that allows for a probabilistic notion of relativistic time dila
tion. This framework will then be used to describe a quantum time dilation
effect that occurs when a clock moves in a superposition of different rel
ativistic momenta. I will argue that this time dilation effect may be obse
rvable with present-day technology and offers a new test of relativistic q
uantum mechanics. Implications for causal structure will be discussed.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eduardo Martin-Martinez (University of Waterloo)
DTSTART:20210601T223000Z
DTEND:20210601T230000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/13
DESCRIPTION:Title: A tale of two detector models: Causal structure and measurements in
quantum field\nby Eduardo Martin-Martinez (University of Waterloo) as
part of BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n
\n\nAbstract\nWe will discuss how relativistic causality and covariance pl
ay a role in the measurement problem in quantum fields and even in our abi
lity to put information into a quantum field. We will compare the Fewster-
Verch formalism with the Unruh-DeWitt-like (UDW) particle detector models.
We will discuss the limitations of both measurement frameworks as well a
s the typical abuses that are often made with Unruh-DeWitt-like detector m
odels and how they matter in general relativistic scenarios. Finally we w
ill discuss the claim in [arXiv:2103.13400] that weakly coupled detectors
cannot harvest entanglement and show what is the effect of that claim\, if
any\, on the feasibility of entanglement harvesting with particle detecto
rs.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Magdalena Zych (University of Queensland)
DTSTART:20210601T231000Z
DTEND:20210601T234000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/14
DESCRIPTION:Title: Clocks and detectors for characterising quantum causal structures\nby Magdalena Zych (University of Queensland) as part of BIRS workshop :
Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nUnderstan
ding and characterising causal structures which posses provably non-classi
cal features is of direct relevance for the research on quantum theory wit
h indefinite causal order as well as for quantum gravity. Due to diffeomor
phism invariance of general relativity (GR)\, causal structure of spacetim
e in GR requires an operational description — in terms of physical syste
ms and their ability to exchange information. In quantum theory such syste
ms can be taken as composite quantum particles\, modelling ideal clocks as
well as particle detectors. I will discuss how such particles allow insig
hts into quantum causal structures by allowing us to construct quantum spa
cetimes and quantify non-classical features of their causal structures. Su
rprisingly\, this approach also shows that operational means may fail to d
istinguish a genuine superposition of different (non-diffeomorphic) spacet
imes from a single classical spacetime. This opens a question: under what
conditions non-classical spacetimes can be operationally distinguished fro
m the classical ones?\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sougato Bose (University College London)
DTSTART:20210602T130000Z
DTEND:20210602T133000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/15
DESCRIPTION:Title: Quantum Nature of Gravity in the Lab: Assumptions\, Implementation a
nd Applications on the Way\nby Sougato Bose (University College London
) as part of BIRS workshop : Quantum Foundations\, Gravity\, and Causal Or
der\n\n\nAbstract\nThere is no empirical evidence yet as to “whether”
gravity has a quantum mechanical origin. Motivated by this\, I will presen
t a feasible idea for testing the quantum origin of the Newtonian interact
ion based on the simple fact that two objects cannot be entangled without
a quantum mediator. I will show that despite its weakness\, gravity can de
tectably entangle two adjacent micron sized test masses held in quantum su
perpositions even when they are placed far apart enough to keep Casimir-Po
lder forces at bay. A prescription for witnessing this entanglement throug
h spin correlations is also provided. Further\, I clarify the assumptions
underpinning the above proposal such as our reasonable definition of “cl
assicality”\, as well as relativistic causality. We note a few ways to a
ddress principal practical challenges: Decoherence\, Screening EM forces a
nd Inertial noise reduction. I will also describe how unprecedented compac
t sensors for classical gravity (including meter scale sensors for low fre
quency gravitational waves) will arise on the way to the above grand goal.
\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anupam Mazumdar (University of Groeningen)
DTSTART:20210602T133000Z
DTEND:20210602T140000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/16
DESCRIPTION:Title: Quantum test of gravity by colliding Schrödinger's kittens\nby
Anupam Mazumdar (University of Groeningen) as part of BIRS workshop : Quan
tum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nQuantum gravit
y is yet to be tested in a laboratory. I will provide criteria for testing
the quantum fluctuation of a graviton in a laboratory by colliding two no
n-relativistically Schrödinger’s kittens and study how the final states
would be entangled in this process. Realising such an experiment will be
filled with various challenges\, from developing new technologies to logis
tics to financial costs. I will motivate the community\, despite all these
challenges\, why doing such an experiment is necessary to understand both
the foundations of quantum mechanics and gravity.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alessio Belenchia (Universitaet Tuebingen)
DTSTART:20210602T141000Z
DTEND:20210602T144000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/17
DESCRIPTION:Title: Quantum Superposition of Massive Objects and the Quantization of Gra
vity\nby Alessio Belenchia (Universitaet Tuebingen) as part of BIRS wo
rkshop : Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nW
hen a massive quantum body is put into a spatial superposition\, it is of
interest to consider the quantum aspects of the gravitational field source
d by the body. In this talk\, I will discuss a Gedankenexperiment where Al
ice and Bob control masses in quantum superposition. I will show that the
analysis of this experiment does not lead to any inconsistency provided th
e gravitational radiation is quantized and that vacuum fluctuations limit
the localization of a particle to no better than a Planck length. This pro
vides support for the view that (linearized) gravity should have a quantum
field description and that table-top experiments testing entanglement of
systems interacting via gravity do probe the quantum nature of gravity\, e
ven if no ``gravitons'' are emitted during the experiment.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Caslav Brukner (Institute for Quantum Optics and Quantum Informati
on - Vienna (IQOQI-Vienna) and Faculty fo Physics)
DTSTART:20210602T144000Z
DTEND:20210602T151000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/18
DESCRIPTION:Title: Quantum reference frames and the weak and Einstein equivalence princ
iples\nby Caslav Brukner (Institute for Quantum Optics and Quantum Inf
ormation - Vienna (IQOQI-Vienna) and Faculty fo Physics) as part of BIRS w
orkshop : Quantum Foundations\, Gravity\, and Causal Order\n\nAbstract: TB
A\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dan Carney (Berkeley National Lab)
DTSTART:20210602T220000Z
DTEND:20210602T223000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/19
DESCRIPTION:Title: Tests and implications of gravitational entanglement\nby Dan Car
ney (Berkeley National Lab) as part of BIRS workshop : Quantum Foundations
\, Gravity\, and Causal Order\n\n\nAbstract\nI'll briefly overview the bas
ic notion that one can look for entanglement generation via gravity in exp
eriments. In particular I will present a recent proposal (joint with H. Mu
ller and J. M. Taylor) using an atom interferometer coupled to a high-Q me
chanical mass. The central idea relies on a new method of entanglement ver
ification in time-dependent systems. Time permitting\, I'll also make some
comments about the interpretation of these entanglement experiments more
broadly\, particularly the relation to gravitons.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Achim Kempf (University of Waterloo)
DTSTART:20210602T223000Z
DTEND:20210602T230000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/20
DESCRIPTION:Title: Spacetime and causality when the notion of distance is replaced by t
he notion of correlation\nby Achim Kempf (University of Waterloo) as p
art of BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n\
n\nAbstract\nQuantum field fluctuations are the more strongly correlated t
he smaller their spacetime distance. As a consequence\, the very notion of
distance can be replaced by the notion of correlation strength. This sugg
ests a picture in which all degrees of freedom are described by the same a
bstract structure\, namely (multi-point) correlators\, a picture which is
essentially information theoretic. At low energies\, these abstract correl
ators possess a mathematical representation as the correlation functions o
f matter fields that live on a curved spacetime with a definite causal str
ucture. As one approaches the Planck scale\, the abstract correlators may
no longer possess such a representation\, thereby superseding the notions
of matter and of spacetime\, but the abstract correlators can still be exa
mined information theoretically\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Thomas Galley (Perimeter Institute)
DTSTART:20210602T231000Z
DTEND:20210602T234000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/21
DESCRIPTION:Title: Quantum Relativity of Subsystems\nby Thomas Galley (Perimeter In
stitute) as part of BIRS workshop : Quantum Foundations\, Gravity\, and Ca
usal Order\n\n\nAbstract\nOne of the most basic notions in physics is the
partitioning of a system into subsystems\, and the study of correlations a
mong its parts. In this talk\, we will explore these notions in the contex
t of quantum reference frame (QRF) covariance\, in which this partitioning
is subject to a symmetry constraint. We will see that different reference
frame perspectives induce different sets of subsystem observable algebras
\, which leads to a gauge-invariant\, frame-dependent notion of subsystems
and entanglement. We will then see that subalgebras which commute before
imposing the symmetry constraint can translate into non-commuting algebras
in a given QRF perspective after symmetry imposition. Such a QRF perspect
ive does not inherit the distinction between subsystems in terms of the co
rresponding tensor factorizability of the kinematical Hilbert space and ob
servable algebra. Since the condition for this to occur is contingent on t
he choice of QRF\, the notion of subsystem locality is frame-dependent. Fi
nally I will comment on the relevance of these results for existing progra
ms in quantum gravity\, as well as relate them to existing results on the
relativity of quantum systems within approaches in quantum information. Th
is talk is based on joint work with Philipp A. Hoehn\, Maximilian P. E. Lo
ck\, Shadi Ali Ahmad and Alexander R. H. Smith which can be found at https
://arxiv.org/abs/2103.01232\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sumati Surya (Raman Research Institute)
DTSTART:20210603T130000Z
DTEND:20210603T133000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/22
DESCRIPTION:Title: Growing a Quantum Discrete Universe\, Causally\nby Sumati Surya
(Raman Research Institute) as part of BIRS workshop : Quantum Foundations\
, Gravity\, and Causal Order\n\n\nAbstract\nIn this talk I will discuss th
e criteria for constructing a covariant quantum dynamics for causal sets u
sing the Rideout-Sorkin sequential growth paradigm. In the histories-formu
lation\, the growth process determines the complex weight or quantum measu
re\, with the covariant observables or be-ables given by the covariant mea
surable sets. The existence of covariant observables in turn puts constrai
nts on the allowed growth dynamics. I will present some recent results wi
th Stav Zalel on a simplified “abelian” model which demonstrates the
existence of classes of covariant quantum dynamics. I will end the talk w
ith a broad discussion of this observer independent formulation of quantum
gravity.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Helen Dowker (Imperial College London)
DTSTART:20210603T133000Z
DTEND:20210603T140000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/23
DESCRIPTION:Title: Recovering General Relativity from a Planck scale discrete theory of
quantum gravity\nby Helen Dowker (Imperial College London) as part of
BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbs
tract\nI will present an argument that if a theory of quantum gravity is p
hysically discrete at the Planck scale and the theory recovers General Re
lativity as an approximation\, then\, at the current stage of our knowledg
e\, causal sets must arise within the theory\, even if they are not its ba
sis.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ivette Fuentes (University of Southampton)
DTSTART:20210603T141000Z
DTEND:20210603T144000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/24
DESCRIPTION:Title: Quantum Frequency Interferometry: with applications ranging from gra
vitational wave detection to dark matter searches\nby Ivette Fuentes (
University of Southampton) as part of BIRS workshop : Quantum Foundations\
, Gravity\, and Causal Order\n\n\nAbstract\nWe introduce a quantum interfe
rometric scheme that uses states that are sharp in frequency and delocaliz
ed in position. The states are frequency modes of a quantum field that is
trapped at all times in a finite volume potential\, such as a small box po
tential. This allows for significant miniaturization of interferometric de
vices. Since the modes are in contact at all times\, it is possible to est
imate physical parameters of global multi-mode channels. As an example\, w
e introduce a three-mode scheme and calculate precision bounds in the esti
mation of parameters of two-mode Gaussian channels. This scheme can be imp
lemented in several systems\, including superconducting circuits\, cavity-
QED and cold atoms. We consider a concrete implementation using the ground
state and two phononic modes of a trapped Bose-Einstein condensate. We ap
ply this to show that frequency interferometry can improve the sensitivity
of phononic gravitational waves detectors by several orders of magnitude\
, even in the case that squeezing is much smaller than assumed previously
and that the system suffers from short phononic lifetimes. Other applicati
ons range from magnetometry\, gravimetry and gradiometry to dark matter/en
ergy searches.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jorma Louko (University of Nottingham)
DTSTART:20210603T144000Z
DTEND:20210603T151000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/25
DESCRIPTION:Title: Thermality of circular motion\nby Jorma Louko (University of Not
tingham) as part of BIRS workshop : Quantum Foundations\, Gravity\, and Ca
usal Order\n\n\nAbstract\nAn observer in uniform linear acceleration respo
nds to the Minkowski vacuum thermally\, in the Unruh temperature $T_U =\\f
rac{proper\\\, acceleration}{2 \\pi}$. An observer in uniform circular mot
ion experiences a similar Unruh-type temperature $T_c$\, with better prosp
ects of detection in analogue spacetime laboratory experiments\, but $T_c$
depends not just on the proper acceleration but also on the orbital radiu
s and on the excitation energy. We establish a range of analytic and numer
ical results for $T_c$ for a massless scalar field in $3+1$ and $2+1$ spac
etime dimensions\, the latter being motivated by proposed condensed matter
experiments. In particular\, we find that the circular motion analogue Un
ruh temperature grows arbitrarily large in the near-sonic limit\, encourag
ingly for the experimental prospects\, but less quickly in effective space
time dimension $2+1$ than in $3+1$. [Based on Biermann et al\, Phys. Rev.
D 102\, 085006 (2020)]\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Terno (Macquarie University)
DTSTART:20210603T220000Z
DTEND:20210603T223000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/26
DESCRIPTION:Title: Why astrophysical black holes do not have horizons\, and what it mea
ns if they do\nby Daniel Terno (Macquarie University) as part of BIRS
workshop : Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\
nDo astrophysical black holes observed by LIGO and EHT actually trap light
? We argue that properties of the near-horizon regions\, such as an atmosp
here of exotic matter violating the null energy condition or a firewall pr
oduced by an accreting black hole\, combined with our current understandin
g of physics make this unlikely. If\, however\, a distant observer does de
tect an apparent horizons this will indicate the onset of radically new ph
ysics.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Valentina Baccetti (RMIT)
DTSTART:20210603T223000Z
DTEND:20210603T230000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/27
DESCRIPTION:Title: Vacuum entanglement harvesting with delocalized matter\nby Valen
tina Baccetti (RMIT) as part of BIRS workshop : Quantum Foundations\, Grav
ity\, and Causal Order\n\n\nAbstract\nEntanglement harvesting has been stu
died extensively using the Unruh-deWitt (UdW) detector. In this detector t
he matter systems are modelled as two-level quantum detector systems while
the classical centre of mass degrees of freedom are described using a sme
aring profile function. As has been extensively shown\, entanglement harve
sting depends very sensitively on the detector details. In this talk we co
nsider two quantum delocalized detectors in their respective\nground state
s [1]\, and we ask how their ability to become entangled with each other i
s affected by their mass and their initial centre of mass delocalization.
For comparison we consider entanglement harvesting from two UdW detectors
with classical centre of mass and Gaussian smearing profile. We will show
that the process of entanglement harvesting is affected by the coherent de
localization of matter and\, in particular\, that delocalized detectors ha
rvest less entanglement than detectors whose centre of mass degrees of fre
edom are assumed to behave classically. We will also identify the limit in
which the results for entanglement harvesting for coherently delocalized
detectors reduce to the results for detectors with classical external degr
ees of freedom [2].\n[1] N. Stritzelberger and A. Kempf\, “Coherent delo
calization in the light-matter interaction”\, Phys. Rev. D\, 101\, 03600
7\, 2020.\n[2] Nadine Stritzelberger\, Laura J. Henderson\, Valentina Bacc
etti\, Nicolas C. Menicucci\, and Achim Kempf\, “Entanglement harvesting
with coherently delocalized matter”\, Phys. Rev. D 103\, 016007\, 2021.
\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hui Wang (Dartmouth College)
DTSTART:20210603T231000Z
DTEND:20210603T234000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/28
DESCRIPTION:Title: Coherently amplifying photon production from vacuum with a dense clo
ud of accelerating photodetectors\nby Hui Wang (Dartmouth College) as
part of BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n
\n\nAbstract\nAn accelerating photodetector is predicted to see photons in
the electromagnetic vacuum. However\, the extreme accelerations required
have prevented the direct experimental verification\n of this quantum vacu
um effect. In this work\, we consider many accelerating photodetectors tha
t are contained within an electromagnetic cavity. We show that the resulti
ng photon production from the cavity vacuum can be collectively enhanced s
uch as to be measurable. The combined cavity-photodetectors system maps on
to a parametrically driven Dicke-type model\; when the detector number exc
eeds a\ncertain critical value\, the vacuum photon production undergoes a
phase transition from a normal phase to an enhanced superradiant-like\, in
verted lasing phase. Such a model may be realized as a mechanical membrane
with a dense concentration of optically active defects undergoing gigaher
tz flexural motion within a superconducting microwave cavity. We provide e
stimates suggesting that recent related experimental devices are close to
demonstrating this inverted\, vacuum photon lasing\nphase.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Markus Aspelmeyer (University of Vienna & Austrian Academy of Scie
nces)
DTSTART:20210604T130000Z
DTEND:20210604T133000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/29
DESCRIPTION:Title: Quantum tests of (quantum) gravity\nby Markus Aspelmeyer (Univer
sity of Vienna & Austrian Academy of Sciences) as part of BIRS workshop :
Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nNo experim
ent today provides evidence that gravity requires a quantum description. T
wo type of table-top searches have been suggested to provide answers: expe
riments that test low-energy consequences of quantum theories of gravity\,
and experiments that directly probe the phenomenology of superposition st
ates of gravitational source masses (in the spirit of a quantum-Cavendish
experiment). The latter requires to bridge the gap between two different r
ealms: precision measurements of gravity with microscopic source masses (c
urrently 10^21 atoms) and quantum state preparations of massive solid stat
e objects (currently 10^9 atoms). I will review the current status in the
lab and the challenges to be overcome for future experiments.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fabio Sciarrino (Sapienza Università di Roma)
DTSTART:20210604T133000Z
DTEND:20210604T140000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/30
DESCRIPTION:Title: Experimental tests on quantum causality\nby Fabio Sciarrino (Sap
ienza Università di Roma) as part of BIRS workshop : Quantum Foundations\
, Gravity\, and Causal Order\n\n\nAbstract\nThe fields of quantum non-loca
lity\, in physics\, and causal discovery\, in machine learning\, both face
the problem of deciding whether observed data are compatible with a presu
med causal relationship between the variables. Bell’s theorem shows that
quantum mechanical correlations can violate the causal constraints impose
d on any classical explanation of experiments performed by space-like sepa
rated parties\, the phenomenon of non-locality. Recently\, it has been rea
lized that many of the concepts and tools from the field of causal inferen
ce\, such as Bayesian networks\, are useful not only to reinterpret known
results but most importantly to provide generalizations of Bell’s theore
m. We will report several experiments aimed at developing a deep understan
ding of the departure between classical and quantum causality by starting
from elementary but fundamental causal structures. We will then briefly di
scuss applications to quantum information processinng [1-8]. \n\n[1] G. Ca
rvacho\, F. Andreoli\, L. Santodonato\, M. Bentivegna\, R. Chaves\, F. Sci
arrino. “Experimental violation of local causality in a quantum network
”\, Nature Communications 8\, 14775 (2017).\n[2] F. Andreoli\, G. Carvac
ho\, L. Santodonato\, R. Chaves\, F. Sciarrino\, “Maximal qubit violatio
n of n-locality inequalities in a star-shaped quantum network”\, New J.
Phys. 19\, 113020 (2017).\n[3] F. Andreoli\, G. Carvacho\, L. Santodonato\
, M. Bentivegna\, R. Chaves\, F. Sciarrino\, “Experimental bilocality vi
olation without shared reference frames”\, Phys. Rev. A 95\, 062315 (201
7).\n[4] R. Chaves\, G. Carvacho\, I. Agresti\, V. Di Giulio\, L. Aolita\,
S. Giacomini\, F. Sciarrino\, “Quantum violation of an instrumental tes
t”\, Nature Physics (2017). doi:10.1038/s41567-017-0008-5.\n[5] E. Polin
o\, I. Agresti\, D. Poderini\, G. Carvacho\, G. Milani\, G. Barreto Lemos\
, R. Chaves\, F Sciarrino\, “Device independent certification of a quant
um delayed choice experiment”\, Phys. Rev. A 100\, 022111 (2019)\n[6] I.
Agresti\, D. Poderini\, L. Guerini\, M. Mancusi\, G. Carvacho\, L. Aolita
\, D. Cavalcanti\, R. Chaves\, F. Sciarrino\, “Experimental device-indep
endent certified randomness generation with an instrumental causal structu
re”\, Communications Physics 3\, 110 (2020)\n[7] D. Poderini\, I. Agres
ti\, G. Marchese\, E. Polino\, T. Giordani\, A. Suprano\, M. Valeri\, G. M
ilani\, N. Spagnolo\, G. Carvacho\, R. Chaves and F. Sciarrino\, “Experi
mental violation of n-locality in a star quantum network”\, Nature Commu
nications 11\, 2467 (2020).\n[8] D. Poderini\, S. Brito\, R. Nery\, F. Sci
arrino\, R. Chaves\, “Criteria for nonclassicality in the prepare-and-me
asure scenario”\, Phys. Rev. Research 2\, 043106 (2020)\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Silke Weinfurtner (The University of Nottingham)
DTSTART:20210604T141000Z
DTEND:20210604T144000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/31
DESCRIPTION:Title: Quantum simulators for fundamental physics\nby Silke Weinfurtner
(The University of Nottingham) as part of BIRS workshop : Quantum Foundat
ions\, Gravity\, and Causal Order\n\n\nAbstract\nThe dynamics of the early
universe and black holes are fundamental reflections of the interplay bet
ween general relativity and quantum fields. The essential physical process
es occur in situations that are difficult to observe and impossible to exp
eriment with: when gravitational interactions are strong\, quantum effects
are important\, and theoretical predictions for these regimes are based o
n major extrapolations of laboratory-tested physics. \n\nWe will discuss t
he possibility to study these processes in experiments by employing analog
ue classical/quantum simulators. Their high degree of tunability\, in term
s of dynamics\, effective geometry\, and field theoretical description\, a
llows one to emulate a wide range of elusive physical phenomena in a contr
olled laboratory setting. We will discuss recent developments in this area
of research.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Christopher Wilson (University of Waterloo)
DTSTART:20210604T144000Z
DTEND:20210604T151000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/32
DESCRIPTION:Title: Analog Quantum Simulation of Strongly-Coupled Field Theories with a
Parametric Cavity\nby Christopher Wilson (University of Waterloo) as p
art of BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n\
nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Philippe Allard Guerin (Perimeter Institute)
DTSTART:20210604T223000Z
DTEND:20210604T230000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/33
DESCRIPTION:Title: A no-go theorem for the persistent reality of Wigner's friend's perc
eption\nby Philippe Allard Guerin (Perimeter Institute) as part of BIR
S workshop : Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbstrac
t\nThe notorious Wigner's friend thought experiment has in recent years re
ceived renewed interest especially due to new arguments that force us to q
uestion some of the fundamental assumptions of quantum theory. In this wor
k we formulate a no-go theorem for the persistent reality of Wigner's frie
nd's perception\, which allows us to conclude that the perceptions that th
e friend has of her own measurement outcomes at different times cannot "sh
are the same reality"\, if seemingly natural quantum mechanical assumption
s are met. We show that there is no joint probability distribution for the
friend's perceived measurement outcomes at two different times\, that dep
ends linearly on the initial state of the measured system and whose margin
als reproduce the predictions of unitary quantum theory. This theorem enta
ils that one must either (1) propose a nonlinear modification of the Born
rule for two-time predictions\, (2) sometimes prohibit the use of present
information to predict the future --thereby reducing the predictive power
of quantum theory-- or (3) deny that unitary quantum mechanics makes valid
single-time predictions for all observers. We briefly discuss which of th
e theorem's assumptions are more likely to be dropped within various popul
ar interpretations of quantum mechanics.\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Timothy Ralph (University of Queensland)
DTSTART:20210604T231000Z
DTEND:20210604T234000Z
DTSTAMP:20260422T185742Z
UID:BIRS_21w5104/34
DESCRIPTION:Title: Weak value Bohmian Trajectories of Relativistic particles\nby Ti
mothy Ralph (University of Queensland) as part of BIRS workshop : Quantum
Foundations\, Gravity\, and Causal Order\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/BIRS_21w5104/34/
END:VEVENT
END:VCALENDAR