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BEGIN:VEVENT
SUMMARY:Giulio Chiribella (The University of Hong Kong)
DTSTART:20210531T130000Z
DTEND:20210531T133000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/1
DESCRIPTION:Title: Quantum operations with indefinite direction of time: the quan
tum time flip\nby Giulio Chiribella (The University of Hong Kong) as p
art of BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n\
n\nAbstract\nThe standard operational framework of quantum theory is time-
asymmetric. 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 measur
ements. However\, the fundamental dynamics of quantum particles is time-sy
mmetric\, and is compatible with a broader class of operations where pre-s
elections and post-selections are combined in general ways that do not pre
suppose a definite direction of time. In this talk I introduce a framework
for quantum operations with indefinite time direction\, providing an exam
ple\, called the quantum time flip\, where an unknown\, time-symmetric pro
cess is accessed in a coherent superposition of two alternative time direc
tions. In certain information-theoretic tasks\, a hypothetical agent with
access to the quantum flip can in principle outperform all agents who oper
ate 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://stable.researchseminars.org/talk/BIRS_21w5104/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Aleks Kissinger (University of Oxford)
DTSTART:20210531T133000Z
DTEND:20210531T140000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/2
DESCRIPTION:Title: The Logic of Influence and Causation\nby Aleks Kissinger (
University of Oxford) as part of BIRS workshop : Quantum Foundations\, Gra
vity\, and Causal Order\n\n\nAbstract\nI will talk about some recent devel
opments in the framework of "black box causal reasoning". In this minimal
setting\, we assume access to some abstract process and attempt to describ
e\, quantify\, or prove properties about the causal relationships between
its inputs and outputs. This works both for first-order processes\, which
can capture e.g. a device shared by multiple agents\, or higher-order proc
esses\, which capture the environment in which those agents live. This hig
her-order picture leads naturally to a particular categorical structure th
at has long been studied in theoretical computer science called a *-autono
mous category. Whereas first order processes (e.g. quantum gates) only hav
e two natural notions of composition (in series and in parallel)\, higher-
order processes have an extremely rich and multi-faceted notion of composi
tion guided by the "internal logic" of a *-autonomous category. In this ta
lk\, I will highlight some aspects of this logic\, show how they can be us
ed for causal reasoning\, and discuss some recent extensions and open prob
lems.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gavin Morley (University of Warwick)
DTSTART:20210531T141000Z
DTEND:20210531T144000Z
DTSTAMP:20260424T222111Z
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 works
hop : Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nWe a
re building an experiment in which a nitrogen-vacancy-centre electron spin
would be used to put a levitated nanodiamond into a spatial quantum super
position [1-3]. This would be able to test theories of spontaneous wavefun
ction collapse and is the first step of a much more ambitious experiment t
o test if gravitational effects can be in a quantum superposition [4\, 5].
This talk 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
. Frangeskou\, P. F. Barker & G. W. Morley\, RSI 89\, 023109 (2018).\n[3]
A. C. Frangeskou\, A. T. M. A. Rahman\, L. Gines\, S. Mandal\, O. A. Willi
ams\, P. F. Barker & G. W. Morley\, NJP 20\, 043016 (2018).\n[4] S. Bose\,
A. Mazumdar\, G. W. Morley\, H. Ulbricht\, M. Toroš\, M. Paternostro\, A
. A. Geraci\, P. F. Barker\, M. S. Kim & G. Milburn\, PRL 119\, 240401 (20
17).\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
. Morley\, P. F. Barker & S. Bose\, PRL 111\, 180403 (2013).\n[8] C. Wan\,
M. Scala\, 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.
Pedernales\, G. W. Morley & M. B. Plenio\, PRL 125\, 023602 (2020).\n[10]
R. J. Marshman\, A. Mazumdar\, G. W. Morley\, P. F. Barker\, S. Hoekstra &
S. Bose\, NJP 22\, 083012 (2020).\n[11] Z.-q. Yin\, T. Li\, X. Zhang & L.
M. Duan\, PRA 88\, 033614 (2013).\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Philip Walther (University of Vienna)
DTSTART:20210531T144000Z
DTEND:20210531T151000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/4
DESCRIPTION:Title: Shining light on the interface of gravity and quantum physics:
precision measurements using photonic quantum interferometry\nby Phil
ip Walther (University of Vienna) as part of BIRS workshop : Quantum Found
ations\, Gravity\, and Causal Order\n\n\nAbstract\nQuantum mechanics and g
eneral relativity are two fundamentally different theories and have both b
een tested independently with very high precision. However\, even after a
century of research\, the interplay of those two very different theories h
as never been tested experimentally. Within this talk I will present the
experimental research aiming to explore this interface between quantum mec
hanics and general relativity by performing high-precision experiments at
the level of single quanta of light\, the photons. Such quantum systems al
low one to examine the influence of gravity on interference effects. For t
his purpose\, a high-precision interferometer whose paths are subject to d
ifferent gravitational potentials will be used.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fabio Costa (University of Queensland)
DTSTART:20210531T220000Z
DTEND:20210531T223000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/5
DESCRIPTION:Title: Background independent quantum causal structures\nby Fabio
Costa (University of Queensland) as part of BIRS workshop : Quantum Found
ations\, Gravity\, and Causal Order\n\n\nAbstract\nThe process matrix form
alism formalises non-classical causal structures\, which are expected to e
merge in a theory that combines quantum indeterminacy with the dynamical c
ausal structure of general relativity. The framework relies on the notion
of local laboratories—an abstraction of spacetime events or regions—wh
ere local operations and measurements can be performed. In a theory of qua
ntum gravity\, we expect that it should not be possible to label laborator
ies a priori: this requires a background reference frame (although possibl
y non-classical)\, while general relativity is background independent. I w
ill present a background independent formulation of the process matrix for
malism that incorporates a discrete version of background independence: in
variance under permutations. Although the formalism abandons an absolute n
otion of “local operation”\, such a notion re-emerges as relative to a
physical reference frame. Permutation symmetry also implies some type of
superselection rule\, although\, for quantum processes\, this cannot be in
terpreted as implying the existence of a conserved charge with a definite
value. Finally\, I will comment on the possibility to extend the approach
to include quantum coordinate transformations.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Laura Henderson (University of Waterloo)
DTSTART:20210531T223000Z
DTEND:20210531T230000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/6
DESCRIPTION:Title: Entanglement Harvesting with a Twist\nby Laura Henderson (
University of Waterloo) as part of BIRS workshop : Quantum Foundations\, G
ravity\, and Causal Order\n\n\nAbstract\nPrevious work has shown that a si
ngle Unruh-DeWitt (UDW) detector can distinguish between a black hole and
geon even through the topological differences are hidden behind a horizon.
We extend this work to two detectors to study the effects of topology on
the entanglement harvesting protocol by placing a pair of UDW detectors ou
tside of an RP2 geon and comparing resulting entanglement to a similar pai
r placed outside of a BTZ black hole. The detectors are stationary\, locat
ed at different radii from the horizon the interact with the Hartle-Hawkin
g vacuum of a conformally coupled massless scalar field. We find that the
two spacetimes are distinguishable by this protocol only when the black ho
le has a small mass. We also find the difference in the amount entanglemen
t harvested is highly dependent on the energy gap of the detector: detecto
rs with a large gap harvest more entanglement outside of a geon\, while de
tectors with a small energy gap harvest more entanglement outside of a bla
ck hole. This may suggest a frequency dependent difference in the entangle
ment structure of quantum field.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrew White (University of Queensland)
DTSTART:20210531T231000Z
DTEND:20210531T234000Z
DTSTAMP:20260424T222111Z
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://stable.researchseminars.org/talk/BIRS_21w5104/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Markus Müller (Austrian Academy of Sciences)
DTSTART:20210601T130000Z
DTEND:20210601T133000Z
DTSTAMP:20260424T222111Z
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
Sciences) as part of BIRS workshop : Quantum Foundations\, Gravity\, and C
ausal Order\n\n\nAbstract\nIn a quantum world\, reference frames are ultim
ately quantum systems too -- but what does it mean to "jump into the persp
ective of a quantum particle"? In this work\, we show that quantum referen
ce frame (QRF) transformations appear naturally as symmetries of simple ph
ysical systems. This allows us to rederive and generalize known QRF transf
ormations within an alternative\, operationally transparent framework\, an
d to shed new light on their structure and interpretation. We give an expl
icit description of the observables that are measurable by agents constrai
ned by such quantum symmetries\, and apply our results to a puzzle known a
s the `paradox of the third particle'. We argue that it can be reduced to
the question of how to relationally embed fewer into more particles\, and
give a thorough physical and algebraic analysis of this question. This lea
ds us to a generalization of the partial trace (`relational trace') which
arguably resolves the paradox\, and it uncovers important structures of co
nstraint quantization within a simple quantum information setting\, such a
s relational observables which are key in this resolution. While we restri
ct our attention to finite Abelian groups for transparency and mathematica
l rigor\, the intuitive physical appeal of our results makes us expect tha
t they remain valid in more general situations.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marios Christodoulou (University of Vienna)
DTSTART:20210601T133000Z
DTEND:20210601T140000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/9
DESCRIPTION:Title: Quantum Superpositions of Graphs\nby Marios Christodoulou
(University of Vienna) as part of BIRS workshop : Quantum Foundations\, Gr
avity\, and Causal Order\n\n\nAbstract\nGraphs are a discrete topological
canvas that in many applications can completely replace a continuous manif
old. Nevertheless\, invariance of dynamics defined on graphs under change
s of reference frames is typically attempted by embedding the graph in an
ambient manifold. This seems superfluous as node names already label point
s similarly to a choice of coordinates in continuous space. As node names
are fiducial\, graph renamings can be seen as a change of coordinates on
the graph. Thus\, graph renamings correspond to a natively discrete analo
gue of diffeomorphisms. In quantum theory\, node names become even more im
portant. We first provide a robust notion of quantum superpositions of gra
phs and argue with a simple example that in quantum theory in order to avo
id instantaneous signalling it is necessary to use node names to define th
e ‘localisation’ of a node\, rather than values of a physical field. W
e propose renaming invariance as a symmetry principle of similar weight to
diffeomorphism invariance and show how to impose it at the level of quant
um superpositions of graphs.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Esteban Castro Ruiz (ETH Zurich)
DTSTART:20210601T141000Z
DTEND:20210601T144000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/10
DESCRIPTION:Title: Relative subsystems and quantum reference frame transformatio
ns\nby Esteban Castro Ruiz (ETH Zurich) as part of BIRS workshop : Qua
ntum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nTransformatio
ns between reference frames play a crucial role in our understanding of ph
ysical processes. In practice\, reference frames are realised by physical
systems\, which are standardly treated as classical. However\, assuming th
at every physical system is ultimately quantum\, it is interesting to ask
how a theory of transformations wrt quantum reference frames would look li
ke\, and what implications it would have for our description of spacetime.
Recently\, there has been a lot of effort towards developing a quantum ge
neralisation of reference frame transformations\, unveiling novel phenomen
a that are absent in the classical treatment of reference frames. Here\, w
e develop a first-principles framework for quantum reference frame transfo
rmations which clarifies important conceptual issues of previous treatment
s. Based on the algebra of relative observables between a system and a re
ference frame\, our operational perspective leads naturally to a mixed-sta
te approach (incoherent twirling)\, in contrast to current pure-state appr
oaches (coherent twirling). Within our framework\, the full invariant quan
tum subsystem contains not only the algebra of relative observables betwee
n the system and the reference frame but also an “extra particle\,” re
lated to the invariant degrees of freedom of the reference frame itself. I
mportantly\, this extra particle contains information about the “quantum
ness” of the reference frame and is essential to the unitarity of quantu
m reference 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 a
nalysing quantum reference frame transformations with respect to the (cent
rally extended) Galilei group.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ognyan Oreshkov (Université libre de Bruxelles)
DTSTART:20210601T144000Z
DTEND:20210601T151000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/11
DESCRIPTION:Title: Quantum processes on time-delocalised systems\nby Ognyan
Oreshkov (Université libre de Bruxelles) as part of BIRS workshop : Quant
um Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nTransformations
between reference frames play a crucial role in our understanding of phys
ical processes. In practice\, reference frames are realised by physical sy
stems\, which are standardly treated as classical. However\, assuming that
every physical system is ultimately quantum\, it is interesting to ask ho
w a theory of transformations wrt quantum reference frames would look like
\, and what implications it would have for our description of spacetime. R
ecently\, there has been a lot of effort towards developing a quantum gene
ralisation of reference frame transformations\, unveiling novel phenomena
that are absent in the classical treatment of reference frames. Here\, we
develop a first-principles framework for quantum reference frame transform
ations which clarifies important conceptual issues of previous treatments.
Based on the algebra of relative observables between a system and a refe
rence frame\, our operational perspective leads naturally to a mixed-state
approach (incoherent twirling)\, in contrast to current pure-state approa
ches (coherent twirling). Within our framework\, the full invariant quantu
m subsystem contains not only the algebra of relative observables between
the system and the reference frame but also an “extra particle\,” rela
ted to the invariant degrees of freedom of the reference frame itself. Imp
ortantly\, this extra particle contains information about the “quantumne
ss” of the reference frame and is essential to the unitarity of quantum
reference frame transformations. Our approach is general\, in the sense th
at it can be applied to a vast set of symmetry groups and to any type of s
ystem. We illustrate the physical meaning of the concepts developed by ana
lysing quantum reference frame transformations with respect to the (centra
lly extended) Galilei group.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexander Smith (Saint Anselm College)
DTSTART:20210601T220000Z
DTEND:20210601T223000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/12
DESCRIPTION:Title: Relational dynamics and quantum time dilation\nby Alexand
er Smith (Saint Anselm College) as part of BIRS workshop : Quantum Foundat
ions\, Gravity\, and Causal Order\n\n\nAbstract\nThe lesson of general rel
ativity is background independence\, which results in a Hamiltonian constr
aint. This presents a challenge for quantum gravity because the quantizati
on of this constraint demands that physical states of geometry and matter
are frozen\, leading to the problem of time. We must then explain how the
conventional notion of time evolution emerges\, which motivates the need f
or a relational description of quantum dynamics. Using quantum clocks and
covariant time observables\, I will introduce a formulation of relational
quantum dynamics that allows for a probabilistic notion of relativistic ti
me dilation. This framework will then be used to describe a quantum time d
ilation effect that occurs when a clock moves in a superposition of differ
ent relativistic momenta. I will argue that this time dilation effect may
be observable with present-day technology and offers a new test of relativ
istic quantum mechanics. Implications for causal structure will be discuss
ed.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eduardo Martin-Martinez (University of Waterloo)
DTSTART:20210601T223000Z
DTEND:20210601T230000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/13
DESCRIPTION:Title: A tale of two detector models: Causal structure and measureme
nts in quantum field\nby Eduardo Martin-Martinez (University of Waterl
oo) as part of BIRS workshop : Quantum Foundations\, Gravity\, and Causal
Order\n\n\nAbstract\nWe will discuss how relativistic causality and covari
ance play a role in the measurement problem in quantum fields and even in
our ability to put information into a quantum field. We will compare the F
ewster-Verch formalism with the Unruh-DeWitt-like (UDW) particle detector
models. We will discuss the limitations of both measurement frameworks as
well as the typical abuses that are often made with Unruh-DeWitt-like det
ector models and how they matter in general relativistic scenarios. Final
ly we will discuss the claim in [arXiv:2103.13400] that weakly coupled det
ectors cannot harvest entanglement and show what is the effect of that cla
im\, if any\, on the feasibility of entanglement harvesting with particle
detectors.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Magdalena Zych (University of Queensland)
DTSTART:20210601T231000Z
DTEND:20210601T234000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/14
DESCRIPTION:Title: Clocks and detectors for characterising quantum causal struct
ures\nby Magdalena Zych (University of Queensland) as part of BIRS wor
kshop : Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nUn
derstanding and characterising causal structures which posses provably non
-classical features is of direct relevance for the research on quantum the
ory with indefinite causal order as well as for quantum gravity. Due to di
ffeomorphism invariance of general relativity (GR)\, causal structure of s
pacetime in GR requires an operational description — in terms of physica
l systems and their ability to exchange information. In quantum theory suc
h systems can be taken as composite quantum particles\, modelling ideal cl
ocks as well as particle detectors. I will discuss how such particles allo
w insights into quantum causal structures by allowing us to construct quan
tum spacetimes and quantify non-classical features of their causal structu
res. Surprisingly\, this approach also shows that operational means may fa
il to distinguish a genuine superposition of different (non-diffeomorphic)
spacetimes from a single classical spacetime. This opens a question: unde
r what conditions non-classical spacetimes can be operationally distinguis
hed from the classical ones?\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sougato Bose (University College London)
DTSTART:20210602T130000Z
DTEND:20210602T133000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/15
DESCRIPTION:Title: Quantum Nature of Gravity in the Lab: Assumptions\, Implement
ation and Applications on the Way\nby Sougato Bose (University College
London) as part of BIRS workshop : Quantum Foundations\, Gravity\, and Ca
usal Order\n\n\nAbstract\nThere is no empirical evidence yet as to “whet
her” gravity has a quantum mechanical origin. Motivated by this\, I will
present a feasible idea for testing the quantum origin of the Newtonian i
nteraction based on the simple fact that two objects cannot be entangled w
ithout a quantum mediator. I will show that despite its weakness\, gravity
can detectably entangle two adjacent micron sized test masses held in qua
ntum superpositions even when they are placed far apart enough to keep Cas
imir-Polder forces at bay. A prescription for witnessing this entanglement
through spin correlations is also provided. Further\, I clarify the assum
ptions underpinning the above proposal such as our reasonable definition o
f “classicality”\, as well as relativistic causality. We note a few wa
ys to address principal practical challenges: Decoherence\, Screening EM f
orces and Inertial noise reduction. I will also describe how unprecedented
compact sensors for classical gravity (including meter scale sensors for
low frequency gravitational waves) will arise on the way to the above gran
d goal.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anupam Mazumdar (University of Groeningen)
DTSTART:20210602T133000Z
DTEND:20210602T140000Z
DTSTAMP:20260424T222111Z
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
: Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nQuantum
gravity 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 non-relativistically Schrödinger’s kittens and study how the final
states would be entangled in this process. Realising such an experiment w
ill be filled with various challenges\, from developing new technologies t
o logistics to financial costs. I will motivate the community\, despite al
l these challenges\, why doing such an experiment is necessary to understa
nd both the foundations of quantum mechanics and gravity.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alessio Belenchia (Universitaet Tuebingen)
DTSTART:20210602T141000Z
DTEND:20210602T144000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/17
DESCRIPTION:Title: Quantum Superposition of Massive Objects and the Quantization
of Gravity\nby Alessio Belenchia (Universitaet Tuebingen) as part of
BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbst
ract\nWhen a massive quantum body is put into a spatial superposition\, it
is of interest to consider the quantum aspects of the gravitational field
sourced by the body. In this talk\, I will discuss a Gedankenexperiment w
here Alice and Bob control masses in quantum superposition. I will show th
at the analysis of this experiment does not lead to any inconsistency prov
ided the gravitational radiation is quantized and that vacuum fluctuations
limit the localization of a particle to no better than a Planck length. T
his provides support for the view that (linearized) gravity should have a
quantum field description and that table-top experiments testing entanglem
ent of systems interacting via gravity do probe the quantum nature of grav
ity\, even if no ``gravitons'' are emitted during the experiment.\n
LOCATION:https://stable.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:20260424T222111Z
UID:BIRS_21w5104/18
DESCRIPTION:Title: Quantum reference frames and the weak and Einstein equivalenc
e principles\nby Caslav Brukner (Institute for Quantum Optics and Quan
tum Information - Vienna (IQOQI-Vienna) and Faculty fo Physics) as part of
BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n\nAbstr
act: TBA\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dan Carney (Berkeley National Lab)
DTSTART:20210602T220000Z
DTEND:20210602T223000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/19
DESCRIPTION:Title: Tests and implications of gravitational entanglement\nby
Dan Carney (Berkeley National Lab) as part of BIRS workshop : Quantum Foun
dations\, Gravity\, and Causal Order\n\n\nAbstract\nI'll briefly overview
the basic notion that one can look for entanglement generation via gravity
in experiments. In particular I will present a recent proposal (joint wit
h H. Muller and J. M. Taylor) using an atom interferometer coupled to a hi
gh-Q mechanical mass. The central idea relies on a new method of entanglem
ent verification in time-dependent systems. Time permitting\, I'll also ma
ke some comments about the interpretation of these entanglement experiment
s more broadly\, particularly the relation to gravitons.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Achim Kempf (University of Waterloo)
DTSTART:20210602T223000Z
DTEND:20210602T230000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/20
DESCRIPTION:Title: Spacetime and causality when the notion of distance is replac
ed by the notion of correlation\nby Achim Kempf (University of Waterlo
o) as part of BIRS workshop : Quantum Foundations\, Gravity\, and Causal O
rder\n\n\nAbstract\nQuantum field fluctuations are the more strongly corre
lated the smaller their spacetime distance. As a consequence\, the very no
tion of distance can be replaced by the notion of correlation strength. Th
is suggests a picture in which all degrees of freedom are described by the
same abstract structure\, namely (multi-point) correlators\, a picture wh
ich is essentially information theoretic. At low energies\, these abstract
correlators possess a mathematical representation as the correlation func
tions of matter fields that live on a curved spacetime with a definite cau
sal structure. As one approaches the Planck scale\, the abstract correlato
rs may no longer possess such a representation\, thereby superseding the n
otions of matter and of spacetime\, but the abstract correlators can still
be examined information theoretically\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Thomas Galley (Perimeter Institute)
DTSTART:20210602T231000Z
DTEND:20210602T234000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/21
DESCRIPTION:Title: Quantum Relativity of Subsystems\nby Thomas Galley (Perim
eter Institute) as part of BIRS workshop : Quantum Foundations\, Gravity\,
and Causal Order\n\n\nAbstract\nOne of the most basic notions in physics
is the partitioning of a system into subsystems\, and the study of correla
tions among its parts. In this talk\, we will explore these notions in the
context of quantum reference frame (QRF) covariance\, in which this parti
tioning is subject to a symmetry constraint. We will see that different re
ference frame perspectives induce different sets of subsystem observable a
lgebras\, which leads to a gauge-invariant\, frame-dependent notion of sub
systems and entanglement. We will then see that subalgebras which commute
before imposing the symmetry constraint can translate into non-commuting a
lgebras in a given QRF perspective after symmetry imposition. Such a QRF p
erspective does not inherit the distinction between subsystems in terms of
the corresponding tensor factorizability of the kinematical Hilbert space
and observable algebra. Since the condition for this to occur is continge
nt on the choice of QRF\, the notion of subsystem locality is frame-depend
ent. Finally I will comment on the relevance of these results for existing
programs in quantum gravity\, as well as relate them to existing results
on the relativity of quantum systems within approaches in quantum informat
ion. This talk is based on joint work with Philipp A. Hoehn\, Maximilian P
. E. Lock\, Shadi Ali Ahmad and Alexander R. H. Smith which can be found a
t https://arxiv.org/abs/2103.01232\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sumati Surya (Raman Research Institute)
DTSTART:20210603T130000Z
DTEND:20210603T133000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/22
DESCRIPTION:Title: Growing a Quantum Discrete Universe\, Causally\nby Sumati
Surya (Raman Research Institute) as part of BIRS workshop : Quantum Found
ations\, Gravity\, and Causal Order\n\n\nAbstract\nIn this talk I will dis
cuss the criteria for constructing a covariant quantum dynamics for causal
sets using the Rideout-Sorkin sequential growth paradigm. In the historie
s-formulation\, the growth process determines the complex weight or quantu
m measure\, with the covariant observables or be-ables given by the covari
ant measurable sets. The existence of covariant observables in turn puts c
onstraints on the allowed growth dynamics. I will present some recent res
ults with Stav Zalel on a simplified “abelian” model which demonstrat
es the existence of classes of covariant quantum dynamics. I will end the
talk with a broad discussion of this observer independent formulation of
quantum gravity.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Helen Dowker (Imperial College London)
DTSTART:20210603T133000Z
DTEND:20210603T140000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/23
DESCRIPTION:Title: Recovering General Relativity from a Planck scale discrete th
eory of quantum gravity\nby Helen Dowker (Imperial College London) as
part of BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n
\n\nAbstract\nI will present an argument that if a theory of quantum gravi
ty is physically discrete at the Planck scale and the theory recovers Gen
eral Relativity as an approximation\, then\, at the current stage of our k
nowledge\, causal sets must arise within the theory\, even if they are not
its basis.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ivette Fuentes (University of Southampton)
DTSTART:20210603T141000Z
DTEND:20210603T144000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/24
DESCRIPTION:Title: Quantum Frequency Interferometry: with applications ranging f
rom gravitational wave detection to dark matter searches\nby Ivette Fu
entes (University of Southampton) as part of BIRS workshop : Quantum Found
ations\, Gravity\, and Causal Order\n\n\nAbstract\nWe introduce a quantum
interferometric scheme that uses states that are sharp in frequency and de
localized in position. The states are frequency modes of a quantum field t
hat is trapped at all times in a finite volume potential\, such as a small
box potential. This allows for significant miniaturization of interferome
tric devices. Since the modes are in contact at all times\, it is possible
to estimate physical parameters of global multi-mode channels. As an exam
ple\, we introduce a three-mode scheme and calculate precision bounds in t
he estimation of parameters of two-mode Gaussian channels. This scheme can
be implemented 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 apply this to show that frequency interferometry can improve the sens
itivity of phononic gravitational waves detectors by several orders of mag
nitude\, even in the case that squeezing is much smaller than assumed prev
iously and that the system suffers from short phononic lifetimes. Other ap
plications range from magnetometry\, gravimetry and gradiometry to dark ma
tter/energy searches.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jorma Louko (University of Nottingham)
DTSTART:20210603T144000Z
DTEND:20210603T151000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/25
DESCRIPTION:Title: Thermality of circular motion\nby Jorma Louko (University
of Nottingham) as part of BIRS workshop : Quantum Foundations\, Gravity\,
and Causal Order\n\n\nAbstract\nAn observer in uniform linear acceleratio
n responds to the Minkowski vacuum thermally\, in the Unruh temperature $T
_U =\\frac{proper\\\, acceleration}{2 \\pi}$. An observer in uniform circu
lar motion experiences a similar Unruh-type temperature $T_c$\, with bette
r prospects of detection in analogue spacetime laboratory experiments\, bu
t $T_c$ depends not just on the proper acceleration but also on the orbita
l radius and on the excitation energy. We establish a range of analytic an
d numerical results for $T_c$ for a massless scalar field in $3+1$ and $2+
1$ spacetime dimensions\, the latter being motivated by proposed condensed
matter experiments. In particular\, we find that the circular motion anal
ogue Unruh temperature grows arbitrarily large in the near-sonic limit\, e
ncouragingly for the experimental prospects\, but less quickly in effectiv
e spacetime dimension $2+1$ than in $3+1$. [Based on Biermann et al\, Phys
. Rev. D 102\, 085006 (2020)]\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Terno (Macquarie University)
DTSTART:20210603T220000Z
DTEND:20210603T223000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/26
DESCRIPTION:Title: Why astrophysical black holes do not have horizons\, and what
it means if they do\nby Daniel Terno (Macquarie University) as part o
f BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n\n\nAb
stract\nDo astrophysical black holes observed by LIGO and EHT actually tra
p light? We argue that properties of the near-horizon regions\, such as an
atmosphere of exotic matter violating the null energy condition or a fire
wall produced by an accreting black hole\, combined with our current under
standing of physics make this unlikely. If\, however\, a distant observer
does detect an apparent horizons this will indicate the onset of radically
new physics.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Valentina Baccetti (RMIT)
DTSTART:20210603T223000Z
DTEND:20210603T230000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/27
DESCRIPTION:Title: Vacuum entanglement harvesting with delocalized matter\nb
y Valentina Baccetti (RMIT) as part of BIRS workshop : Quantum Foundations
\, Gravity\, and Causal Order\n\n\nAbstract\nEntanglement harvesting has b
een studied extensively using the Unruh-deWitt (UdW) detector. In this det
ector the matter systems are modelled as two-level quantum detector system
s while the classical centre of mass degrees of freedom are described usin
g a smearing profile function. As has been extensively shown\, entanglemen
t harvesting depends very sensitively on the detector details. In this tal
k we consider two quantum delocalized detectors in their respective\ngroun
d states [1]\, and we ask how their ability to become entangled with each
other is affected by their mass and their initial centre of mass delocaliz
ation. For comparison we consider entanglement harvesting from two UdW det
ectors with classical centre of mass and Gaussian smearing profile. We wil
l show that the process of entanglement harvesting is affected by the cohe
rent delocalization of matter and\, in particular\, that delocalized detec
tors harvest less entanglement than detectors whose centre of mass degrees
of freedom are assumed to behave classically. We will also identify the l
imit in which the results for entanglement harvesting for coherently deloc
alized detectors reduce to the results for detectors with classical extern
al degrees of freedom [2].\n[1] N. Stritzelberger and A. Kempf\, “Cohere
nt delocalization in the light-matter interaction”\, Phys. Rev. D\, 101\
, 036007\, 2020.\n[2] Nadine Stritzelberger\, Laura J. Henderson\, Valenti
na Baccetti\, Nicolas C. Menicucci\, and Achim Kempf\, “Entanglement har
vesting with coherently delocalized matter”\, Phys. Rev. D 103\, 016007\
, 2021.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hui Wang (Dartmouth College)
DTSTART:20210603T231000Z
DTEND:20210603T234000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/28
DESCRIPTION:Title: Coherently amplifying photon production from vacuum with a de
nse cloud of accelerating photodetectors\nby Hui Wang (Dartmouth Colle
ge) as part of BIRS workshop : Quantum Foundations\, Gravity\, and Causal
Order\n\n\nAbstract\nAn accelerating photodetector is predicted to see pho
tons in the electromagnetic vacuum. However\, the extreme accelerations re
quired have prevented the direct experimental verification\n of this quant
um vacuum effect. In this work\, we consider many accelerating photodetect
ors that are contained within an electromagnetic cavity. We show that the
resulting photon production from the cavity vacuum can be collectively enh
anced such as to be measurable. The combined cavity-photodetectors system
maps onto a parametrically driven Dicke-type model\; when the detector num
ber exceeds a\ncertain critical value\, the vacuum photon production under
goes a phase transition from a normal phase to an enhanced superradiant-li
ke\, inverted lasing phase. Such a model may be realized as a mechanical m
embrane with a dense concentration of optically active defects undergoing
gigahertz flexural motion within a superconducting microwave cavity. We pr
ovide estimates suggesting that recent related experimental devices are cl
ose to demonstrating this inverted\, vacuum photon lasing\nphase.\n
LOCATION:https://stable.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:20260424T222111Z
UID:BIRS_21w5104/29
DESCRIPTION:Title: Quantum tests of (quantum) gravity\nby Markus Aspelmeyer
(University of Vienna & Austrian Academy of Sciences) as part of BIRS work
shop : Quantum Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nNo
experiment today provides evidence that gravity requires a quantum descrip
tion. Two type of table-top searches have been suggested to provide answer
s: experiments that test low-energy consequences of quantum theories of gr
avity\, and experiments that directly probe the phenomenology of superposi
tion states of gravitational source masses (in the spirit of a quantum-Cav
endish experiment). The latter requires to bridge the gap between two diff
erent realms: precision measurements of gravity with microscopic source ma
sses (currently 10^21 atoms) and quantum state preparations of massive sol
id state 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://stable.researchseminars.org/talk/BIRS_21w5104/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fabio Sciarrino (Sapienza Università di Roma)
DTSTART:20210604T133000Z
DTEND:20210604T140000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/30
DESCRIPTION:Title: Experimental tests on quantum causality\nby Fabio Sciarri
no (Sapienza Università di Roma) as part of BIRS workshop : Quantum Found
ations\, Gravity\, and Causal Order\n\n\nAbstract\nThe fields of quantum n
on-locality\, in physics\, and causal discovery\, in machine learning\, bo
th face the problem of deciding whether observed data are compatible with
a presumed causal relationship between the variables. Bell’s theorem sho
ws that quantum mechanical correlations can violate the causal constraints
imposed on any classical explanation of experiments performed by space-li
ke separated parties\, the phenomenon of non-locality. Recently\, it has b
een realized that many of the concepts and tools from the field of causal
inference\, such as Bayesian networks\, are useful not only to reinterpret
known results but most importantly to provide generalizations of Bell’s
theorem. We will report several experiments aimed at developing a deep un
derstanding of the departure between classical and quantum causality by st
arting from elementary but fundamental causal structures. We will then bri
efly discuss applications to quantum information processinng [1-8]. \n\n[1
] G. Carvacho\, F. Andreoli\, L. Santodonato\, M. Bentivegna\, R. Chaves\,
F. Sciarrino. “Experimental violation of local causality in a quantum n
etwork”\, Nature Communications 8\, 14775 (2017).\n[2] F. Andreoli\, G.
Carvacho\, L. Santodonato\, R. Chaves\, F. Sciarrino\, “Maximal qubit vi
olation of n-locality inequalities in a star-shaped quantum network”\, N
ew J. Phys. 19\, 113020 (2017).\n[3] F. Andreoli\, G. Carvacho\, L. Santod
onato\, M. Bentivegna\, R. Chaves\, F. Sciarrino\, “Experimental bilocal
ity violation without shared reference frames”\, Phys. Rev. A 95\, 06231
5 (2017).\n[4] R. Chaves\, G. Carvacho\, I. Agresti\, V. Di Giulio\, L. Ao
lita\, S. Giacomini\, F. Sciarrino\, “Quantum violation of an instrument
al test”\, Nature Physics (2017). doi:10.1038/s41567-017-0008-5.\n[5] E.
Polino\, I. Agresti\, D. Poderini\, G. Carvacho\, G. Milani\, G. Barreto
Lemos\, R. Chaves\, F Sciarrino\, “Device independent certification of a
quantum 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
-independent certified randomness generation with an instrumental causal s
tructure”\, Communications Physics 3\, 110 (2020)\n[7] D. Poderini\, I.
Agresti\, G. Marchese\, E. Polino\, T. Giordani\, A. Suprano\, M. Valeri\
, G. Milani\, N. Spagnolo\, G. Carvacho\, R. Chaves and F. Sciarrino\, “
Experimental violation of n-locality in a star quantum network”\, Nature
Communications 11\, 2467 (2020).\n[8] D. Poderini\, S. Brito\, R. Nery\,
F. Sciarrino\, R. Chaves\, “Criteria for nonclassicality in the prepare-
and-measure scenario”\, Phys. Rev. Research 2\, 043106 (2020)\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Silke Weinfurtner (The University of Nottingham)
DTSTART:20210604T141000Z
DTEND:20210604T144000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/31
DESCRIPTION:Title: Quantum simulators for fundamental physics\nby Silke Wein
furtner (The University of Nottingham) as part of BIRS workshop : Quantum
Foundations\, Gravity\, and Causal Order\n\n\nAbstract\nThe dynamics of th
e early universe and black holes are fundamental reflections of the interp
lay between general relativity and quantum fields. The essential physical
processes occur in situations that are difficult to observe and impossible
to experiment with: when gravitational interactions are strong\, quantum
effects are important\, and theoretical predictions for these regimes are
based on major extrapolations of laboratory-tested physics. \n\nWe will di
scuss the possibility to study these processes in experiments by employing
analogue classical/quantum simulators. Their high degree of tunability\,
in terms of dynamics\, effective geometry\, and field theoretical descript
ion\, allows one to emulate a wide range of elusive physical phenomena in
a controlled laboratory setting. We will discuss recent developments in th
is area of research.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Christopher Wilson (University of Waterloo)
DTSTART:20210604T144000Z
DTEND:20210604T151000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/32
DESCRIPTION:Title: Analog Quantum Simulation of Strongly-Coupled Field Theories
with a Parametric Cavity\nby Christopher Wilson (University of Waterlo
o) as part of BIRS workshop : Quantum Foundations\, Gravity\, and Causal O
rder\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Philippe Allard Guerin (Perimeter Institute)
DTSTART:20210604T223000Z
DTEND:20210604T230000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/33
DESCRIPTION:Title: A no-go theorem for the persistent reality of Wigner's friend
's perception\nby Philippe Allard Guerin (Perimeter Institute) as part
of BIRS workshop : Quantum Foundations\, Gravity\, and Causal Order\n\n\n
Abstract\nThe notorious Wigner's friend thought experiment has in recent y
ears received renewed interest especially due to new arguments that force
us to question some of the fundamental assumptions of quantum theory. In t
his work we formulate a no-go theorem for the persistent reality of Wigner
's friend's perception\, which allows us to conclude that the perceptions
that the friend has of her own measurement outcomes at different times can
not "share the same reality"\, if seemingly natural quantum mechanical ass
umptions are met. We show that there is no joint probability distribution
for the friend's perceived measurement outcomes at two different times\, t
hat depends linearly on the initial state of the measured system and whose
marginals reproduce the predictions of unitary quantum theory. This theor
em entails that one must either (1) propose a nonlinear modification of th
e Born rule for two-time predictions\, (2) sometimes prohibit the use of p
resent information to predict the future --thereby reducing the predictive
power of quantum theory-- or (3) deny that unitary quantum mechanics make
s valid single-time predictions for all observers. We briefly discuss whic
h of the theorem's assumptions are more likely to be dropped within variou
s popular interpretations of quantum mechanics.\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Timothy Ralph (University of Queensland)
DTSTART:20210604T231000Z
DTEND:20210604T234000Z
DTSTAMP:20260424T222111Z
UID:BIRS_21w5104/34
DESCRIPTION:Title: Weak value Bohmian Trajectories of Relativistic particles
\nby Timothy Ralph (University of Queensland) as part of BIRS workshop : Q
uantum Foundations\, Gravity\, and Causal Order\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/BIRS_21w5104/34/
END:VEVENT
END:VCALENDAR