BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Šimon Vedl (Macquarie University) DTSTART:20231205T070000Z DTEND:20231205T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/1 DESCRIPTION:Title: Wa velets and Quantum Field Theory\nby Šimon Vedl (Macquarie University) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nIn this talk I will go through the wavelet-related topics investigated by the group at Macquarie University: Gavin Brennen\, Sukhwinder Singh (former c ollaborator)\, Dan George\, Simon Vedl. These can be divided into two dist inct categories\, applications of discrete wavelet transform\, and applica tions of continuous wavelet transform.\n\nOur main focus is to understand and utilise the extra variable introduced in the wavelet transform that is often called the scale. The talk will begin with an introduction to wavel et analysis and then proceed with discussion of state compression\, AdS/CF T correspondence and wavelet regularisation of QFT by a scale cutoff.\n LOCATION:https://researchseminars.org/talk/3cqfs/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Robert H. Jonsson (Nordic Institute for Theoretical Physics) DTSTART:20231121T070000Z DTEND:20231121T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/2 DESCRIPTION:Title: Ga ussian states\, partner modes and an entanglement duality\nby Robert H . Jonsson (Nordic Institute for Theoretical Physics) as part of Tricontine ntal Quantum Fundamentals Seminar\n\n\nAbstract\nGaussian states appear ev erywhere in quantum physics - from condensed matter\, to quantum optics an d quantum field theory in curved spacetimes. In this talk I aim for three objectives related to Gaussian states:\n\nFirst\, I discuss their partner mode entanglement structure which is well known\, but maybe not widely kno wn. This is the fact that a pure Gaussian state under any bipartition deco mposes into a sum of two-mode squeezed states\, for example\, in the Unruh effect or in Einstein-Bose condensates.\n\nSecond\, I review the powerful Kähler structure formalism for Gaussian states. It captures the geometry of Gaussian states\, it is very practical for applications\, and it treat s both bosons and fermions simultaneously.\n\nThird\, to showcase an examp le connecting bosonic and fermionic systems\, I will present an entangleme nt duality which arises in supersymmetric Gaussian states [1]. Here\, boso nic and fermionic partner subsystems\, canonically identified by the super charge construction\, exhibit an intriguing duality of their entanglement spectra.\n\n(Time permitting\, as a special application\, we consider topo logical insulators and superconductors and their SUSY partners\, discussin g the recently derived classification of supercharges in this context [2]. )\n\n[1] Jonsson\, Robert H.\, Lucas Hackl\, and Krishanu Roychowdhury. “Entanglement Dualities in Supersymmetry.” Physical Review Research 3\ , no. 2 (June 16\, 2021): 023213.\n\n[2] Gong\, Zongping\, Robert H. Jonss on\, and Daniel Malz. “Supersymmetric Free Fermions and Bosons: Locality \, Symmetry\, and Topology.” Physical Review B 105\, no. 8 (February 24\ , 2022): 085423.\n LOCATION:https://researchseminars.org/talk/3cqfs/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Joshua Foo (Stevens Institute of Technology) DTSTART:20230418T070000Z DTEND:20230418T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/3 DESCRIPTION:Title: Te lefilters\, telemirrors\, and causality\nby Joshua Foo (Stevens Instit ute of Technology) as part of Tricontinental Quantum Fundamentals Seminar\ n\n\nAbstract\nMode-selective interactions are ubiquitous in quantum optic s and interacting quantum field theories. Such unitaries take as input a m ulti-mode field but uniquely affect a single mode\, compared with those or thogonal to it. Despite their wide application in theoretical and experime ntal physics\, the temporal dimension of such interactions are typically i gnored.\n\nHere\, I demonstrate how the naïve treatment of a mode-selecti ve unitaries leads to the possibility of acausal signalling\, due to the t acit assumption that certain kinds of idealised measurements of quantum fi elds can be made. I achieve this by introducing new theoretical models for mode-selective mirrors using continuous-variable teleportation\, which is able to unveil the temporal aspects of the mode propagation.\n\nThe main result is that mode-selective operations must generally enact a fundamenta l time-delay on input modes that are delocalised in time. This result reso lves Sorkin's long-standing "impossible measurement" problem in relativist ic quantum field theory\, and thus has significant implications for experi mental quantum optics and those working in quantum causality and field the ory.\n\nTalk not recorded\n LOCATION:https://researchseminars.org/talk/3cqfs/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Nicolas C. Menicucci (Royal Melbourne Institute of Technology) DTSTART:20230502T070000Z DTEND:20230502T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/4 DESCRIPTION:Title: Ta chyonic media in sonic relativity\nby Nicolas C. Menicucci (Royal Melb ourne Institute of Technology) as part of Tricontinental Quantum Fundament als Seminar\n\n\nAbstract\nIn sonic models of special relativity\, the fac t that the sonic medium violates (ordinary) Lorentz symmetry is apparent t o observers external to the sonic medium but not to a class of observers e xisting within the medium itself. We show that the situation is symmetric: internal observers will judge physics in the external laboratory to viola te their own sonic Lorentz symmetries. We therefore treat all observers on an equal footing such that each is able to retain a commitment to their o wn Lorentz symmetries.\n\nWe then generalize beyond the case of subsystem- environment decompositions to situations in which there exist multiple pho non fields\, all obeying Lorentz symmetries but with different invariant s peeds. In such cases\, we argue that all observers have freedom to choose which field is symmetry preserving\, and so -- in a certain precise sense -- which other fields are perceived as having an 'ether.' This choice is i nfluenced -- but not determined -- by a desire for simplicity in the descr iption of physical laws.\n\nSending information faster than sound serves a s a model of tachyonic signalling to a distant receiver. Immutable causali ty of the laboratory setup when perceived externally to a sonic medium man ifests internally through the confinement of the tachyons to an apparent e ther (with a rest frame)\, which we call a 'tachyonic medium\,' thereby pr eventing tachyonic exchange from emulating the scenario of a round-trip si gnal travelling into an observer's past causal cone. The assignment of son ic-Lorentz-violating effects to fields that obey 'photonic' Lorentz symmet ries thus ensures that causality associated with the 'sonic' Lorentz symme tries is preserved.\n LOCATION:https://researchseminars.org/talk/3cqfs/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Dominic G. Lewis (Royal Melbourne Institute of Technology) DTSTART:20230516T070000Z DTEND:20230516T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/5 DESCRIPTION:Title: Ba ndlimitation\, wavelets\, and scaled QFT\nby Dominic G. Lewis (Royal M elbourne Institute of Technology) as part of Tricontinental Quantum Fundam entals Seminar\n\n\nAbstract\nThe likely presence of a fundamental minimum length scale to the universe (motivated by generalised uncertainty princi ples and UV divergences in quantum field theory to name a few) has led to the application of information theoretic techniques such as bandlimitation to quantum field theory\, allowing for field theories to be represented a s simultaneously continuous and discrete through Shannon theory.\n\nWe ext end on this notion by showing that non-bandlimited quantum field theories can be decomposed into bandlimited ones\, called scales\, using Shannon wa velets. Each scale of the wavelet decomposition gives a field theory posse ssing an ultraviolet cut-off (and infrared cut-off) and\, as a result\, an equivalent discrete theory. As such\, one can use wavelets to decompose a n $N+1$ dimensional continuous field theory into a $2N+1$ dimensional disc rete theory (where the scale of the wavelet decomposition is treated as a spatial dimension).\n\nLinked paper only covers the first (bandlimitation) part of the talk and not wavelets\, which will be included in a future pa per.\n LOCATION:https://researchseminars.org/talk/3cqfs/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Carolyn Wood (University of Queensland) DTSTART:20230530T070000Z DTEND:20230530T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/6 DESCRIPTION:Title: Jo urnal club on 'Harvesting quantum coherence from axion dark matter' \nby Carolyn Wood (University of Queensland) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nIn this week's meeting\, Caro lyn Wood will lead the discussion of the recent article 'Harvesting qua ntum coherence from axion dark matter' by Sugumi Kanno\, Akira Matsumu ra\, and Jiro Soda.\n\nTalk not recorded\n LOCATION:https://researchseminars.org/talk/3cqfs/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Magdalena Zych (Stockholm University) DTSTART:20230620T070000Z DTEND:20230620T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/7 DESCRIPTION:Title: Re lativity of quantum superpositions in the context of superpositions of gra vitational sources\nby Magdalena Zych (Stockholm University) as part o f Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nIt is anticip ated that in a theory of quantum gravity\, there exist quantum superpositi ons of semiclassical states of spacetime geometry. It is often discussed h ow such states could arise from a source mass in a spatial superposition. In this talk I will discuss such spatial superposition scenarios from the perspective of relativity of the notion of location\, and thus of superpos ition itself. This perspective allows to show that for states in which the superposed amplitudes differ by a coordinate transformation\, it is alway s possible to re-express the scenario in terms of dynamics on a fixed geom etry albeit with adapted preparations and measurements on the involved deg rees of freedom. The results unveil an ambiguity in the interpretation of such scenarios as genuinely quantum-gravitational\, and motivate further r esearch into loopholes and assumption behind such scenarios.\n\nTalk not r ecorded\n LOCATION:https://researchseminars.org/talk/3cqfs/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Nicholas Funai (Royal Melbourne Institute of Technology) DTSTART:20231107T070000Z DTEND:20231107T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/8 DESCRIPTION:Title: Co variant bandlimits and entanglement harvesting\nby Nicholas Funai (Roy al Melbourne Institute of Technology) as part of Tricontinental Quantum Fu ndamentals Seminar\n\n\nAbstract\nIn QFT UV cutoffs are often used as reno rmalisation or calculational tools\, however sometimes these cutoffs can h ave a physical origin\, e.g. condensed matter systems. These UV cutoffs al so tend to overlook the need for Lorentz covariance in any notion of minim um length.\n\nThis talk uses the covariant UV cutoff introduced by Kempf a nd Pye\; and investigates its effects on entanglement harvesting and commu nication\, with particular attention on causality violations and any non-l ocal behaviour introduced by the cutoff.\n LOCATION:https://researchseminars.org/talk/3cqfs/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Evan Gale (University of Queensland) DTSTART:20230307T070000Z DTEND:20230307T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/9 DESCRIPTION:Title: Re lativistic Unruh-DeWitt detectors with quantized center of mass\nby Ev an Gale (University of Queensland) as part of Tricontinental Quantum Funda mentals Seminar\n\n\nAbstract\nI examine the implications of particle loca lisation in the Unruh-DeWitt model\, which provides a simple model of a tw o-level system (aka 'particle detector') coupled to a scalar quantum field . By comparing the first- and second-quantised formulations of a detector with a quantised centre of mass\, one is naturally led to two distinct not ions of localisation. I consider the consequences of these two localisatio n schemes in the context of spontaneous emission\, finding that the two lo calisations lead to distinguishable physical consequences\, which can in p rinciple be tested by future experiments.\n\nTalk not recorded\n LOCATION:https://researchseminars.org/talk/3cqfs/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Navdeep Arya (Stockholm University) DTSTART:20240305T080000Z DTEND:20240305T100000Z DTSTAMP:20260417T041311Z UID:3cqfs/12 DESCRIPTION:Title: U nruh effect inside a cylindrical cavity\nby Navdeep Arya (Stockholm Un iversity) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbst ract\nThe Unruh effect states that the transition rates of a uniformly acc elerated detector in the inertial vacuum have a thermal character at a tem perature proportional to the detector's acceleration. Numerous proposals s tudying different properties of the accelerated detector under varied sett ings still await fruition as the signal of interest is generally very weak .\n\nWe will discuss the Unruh effect inside a cylindrical cavity\, with s pecial emphasis on strategies that might help us resolve it better. We wil l discuss the transition rates and radiative energy shift of an atom unifo rmly accelerated along the axis of the cavity. We will argue that the requ irement of large acceleration for an appreciable non-inertial contribution to these properties can be traded for a better precision in cavity design . We will conclude with a brief discussion on the possibility of selective super-radiant enhancement of the Unruh signal.\n LOCATION:https://researchseminars.org/talk/3cqfs/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Flaminia Giacomini (ETH Zürich) DTSTART:20240319T080000Z DTEND:20240319T100000Z DTSTAMP:20260417T041311Z UID:3cqfs/13 DESCRIPTION:Title: Q uantum effects in gravity beyond the Newton potential from a delocalised q uantum source\nby Flaminia Giacomini (ETH Zürich) as part of Triconti nental Quantum Fundamentals Seminar\n\n\nAbstract\nUnderstanding the funda mental nature of gravity at the interface with quantum theory is a major o pen question in theoretical physics. Recently\, the study of gravitating q uantum systems\, for instance a massive quantum system prepared in a quant um superposition of positions and sourcing a gravitational field\, has att racted a lot of attention: experiments are working towards realising such a scenario in the laboratory\, and measuring the gravitational field assoc iated to a quantum source is expected to give some information about quant um aspects of gravity. However\, there are still open questions concerning the precise conclusions that these experiments could draw on the nature o f gravity\, such as whether experiments in this regime will be able to tes t more than the Newtonian part of the gravitational field.\n\nIn this talk \, I will show that a static mass in a quantum state gives rise to effects that cannot be reproduced using the Newton potential nor with a known cla ssical model of gravity. These effects can in principle be measured by per forming an interference experiment\, and are independent of graviton emiss ion. Identifying stronger quantum aspects of gravity than those reproducib le with the Newton potential is crucial to prove the nonclassicality of th e gravitational field and to plan a new generation of experiments testing quantum aspects of gravity in a broader sense than what proposed so far.\n LOCATION:https://researchseminars.org/talk/3cqfs/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Robert B. Mann (University of Waterloo) DTSTART:20240402T080000Z DTEND:20240402T100000Z DTSTAMP:20260417T041311Z UID:3cqfs/14 DESCRIPTION:Title: T he Holographic Chemistry of Black Holes\nby Robert B. Mann (University of Waterloo) as part of Tricontinental Quantum Fundamentals Seminar\n\n\n Abstract\nBlack Holes are amongst the strangest objects in the universe. T hey form from the collapse of matter into an object whose gravitational pu ll is so strong\, nothing can escape from them. Yet a black hole also radi ates heat like a blackbody\, with a temperature equal to its surface gravi ty\, an entropy equal to its area\, and an energy equal to its mass. Over the past 15 years we have come to understand that the vacuum energy — a s embodied by a cosmological constant — plays a pivotal role in the ther modynamic behaviour of black holes. Mass becomes chemical enthalpy\, the n otion of a thermodynamic volume appears\, and black holes exhibit a broad range of chemical phenomena\, including liquid/gas phase transitions simil ar to a Van der Waals fluid\, triple points similar to that of water\, re- entrant phase transitions that appear in gels and heat engines. Under cert ain conditions they can even behave like superfluid helium! Now known as “Black Hole Chemistry”\, I will review this subject and then go on to describe new work that is providing a pathway toward understanding these p henomena from the perspective of Gauge-Gravity duality\, in which phase tr ansitions in the (gravitational) bulk become dual to phase transitions in the dual gauge theory.\n LOCATION:https://researchseminars.org/talk/3cqfs/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Aristotelis Panagiotopoulos (Kurt Gödel Research Center\, Univers ity of Vienna) DTSTART:20240430T080000Z DTEND:20240430T100000Z DTSTAMP:20260417T041311Z UID:3cqfs/16 DESCRIPTION:Title: I ncompleteness Theorems for Observables in General Relativity\nby Arist otelis Panagiotopoulos (Kurt Gödel Research Center\, University of Vienna ) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nOn e of the biggest open problems in mathematical physics has been the proble m of formulating a complete and consistent theory of quantum gravity. Some of the core technical and epistemological difficulties come from the fact that General Relativity (GR) is\, fundamentally\, a geometric theory and\ , as such\, it oughts to be `generally covariant'\, i.e. invariant under c hange of coordinates by the arbitrary diffeomorphism of the ambient manifo ld. The Problem of Observables is a famous instance of the difficulties th at general covariance brings into quantization: no non-trivial diffeomorph ism-invariant quantity has ever been reported on the collection of all spa cetimes.\n\nIt turns out that there is a good reason for this! In a recent joint work with Marios Christodoulou and George Sparling we employ method s from Descriptive Set Theory (DST) in order to show that no complete obse rvables for full GR can be Borel definable. In other words\, the problem o f observables is to `analysis' what the Delian problem was to `straightedg e and compass'. This talk will provide a gentle introduction to the main c oncepts of DST\, where they come from\, and how they connect to the proble m of observables. We will then discuss the aforementioned Incompleteness T heorem\, as well as the next steps in a research program that aims to furt her uncover this new connection between theoretical physics and DST.\n LOCATION:https://researchseminars.org/talk/3cqfs/16/ END:VEVENT BEGIN:VEVENT SUMMARY:Erickson Tjoa (Max Planck Institute for Quantum Optics) DTSTART:20240516T130000Z DTEND:20240516T150000Z DTSTAMP:20260417T041311Z UID:3cqfs/17 DESCRIPTION:Title: T he Unruh-DeWitt model and its joint interacting Hilbert space\nby Eric kson Tjoa (Max Planck Institute for Quantum Optics) as part of Tricontinen tal Quantum Fundamentals Seminar\n\n\nAbstract\nIn this work we make the c onnection between the Unruh-DeWitt particle detector model applied to quan tum field theory in curved spacetimes and the rigorous construction of the spin-boson model. With some modifications\, we show that existing results about the existence of a spin-boson ground state can be adapted to the Un ruh-DeWitt model. In the physically relevant setting involving massless fi elds in $(3+1)$-dimensional spacetimes\, we argue that common choices of t he spacetime smearing functions regulate the ultraviolet behaviour of the model but can still exhibit infrared divergences. We discuss the condition s under which this problem does not arise and the relevance of the operato r-algebraic approach for better understanding of particle detector models and their applications.\n LOCATION:https://researchseminars.org/talk/3cqfs/17/ END:VEVENT BEGIN:VEVENT SUMMARY:Anne-Catherine de la Hamette (University of Vienna) DTSTART:20240611T070000Z DTEND:20240611T080000Z DTSTAMP:20260417T041311Z UID:3cqfs/19 DESCRIPTION:Title: I dentification is pointless: Localisation of systems and events in superpos itions of spacetimes\nby Anne-Catherine de la Hamette (University of V ienna) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstrac t\nA first step towards scenarios at the interface of quantum theory and g ravity is to consider a quantum superposition of semiclassical spacetimes\ , such as the one\, arguably\, sourced by a gravitating object in superpos ition. But what does it mean that a gravitational source is in a superposi tion of “different” locations? How can one compare points across the d ifferent manifolds? Due to the diffeomorphism invariance of general relati vity\, there is a priori no notion of the “same” or “different” po ints across the branches. In fact\, there are multiple ways of relating po ints or events on the different spacetimes. Here\, we make this concrete b y using coincidences of four scalar fields to construct a comparison map b etween all spacetimes in superposition\, which allows us to determine whet her a system or an event is located at the “same” or “different” p oints across the branches. Different choices of scalar fields can be under stood as different instantiations of quantum reference frames (QRFs)\, con necting the construction to recent research in the field of quantum founda tions. As an explicit application of this formalism\, we explore how the l ocalisation of events is relative to the choice of QRF and formulate a qua ntum generalisation of Einstein’s famous hole argument. The latter calls into question the metaphysical meaning of not just spacetime points but a lso the identification between spacetime points across manifolds in superp osition. Finally\, we discuss the implications of QRF changes for indefini te causal order\, the locality of interaction\, and potential empirical co nsequences in interference experiments.\n LOCATION:https://researchseminars.org/talk/3cqfs/19/ END:VEVENT BEGIN:VEVENT SUMMARY:Ioannis Soranidis (Macquarie University) DTSTART:20240625T230000Z DTEND:20240626T010000Z DTSTAMP:20260417T041311Z UID:3cqfs/21 DESCRIPTION:Title: K inematic\, energetic\, and thermodynamic properties of regular black holes \nby Ioannis Soranidis (Macquarie University) as part of Tricontinenta l Quantum Fundamentals Seminar\n\n\nAbstract\nRegular black holes have bec ome a popular alternative to the singular mathematical black holes predict ed by general relativity as they circumvent mathematical pathologies assoc iated with the singularity while preserving crucial black hole features su ch as the trapping of light. Here\, we will analyze how to generate these geometries and study their thermodynamic properties within the framework o f general relativity. Our study reveals that the regularization of the sin gularity\, through the introduction of a minimal length scale\, has a plet hora of implications\, one of which is the absence of the Hawking-Page pha se transition. We extend our study to the dynamical case\, showing that th e internal energy in the first law of black hole thermodynamics is capture d by the Misner-Sharp mass and demonstrating that the linear coefficient o f the Misner-Sharp mass expansion near the outer apparent horizon suffices for a complete thermodynamic description. Additionally\, we analyze the b ehavior of the null energy condition and find that it is violated in the v icinity of the outer horizon and satisfied in the vicinity of the inner ho rizon\, which implies that the trapped spacetime region (as determined fro m the behavior of null geodesic congruences) is effectively separated into an NEC-violating and an NEC-non-violating domain. Moreover\, we show that massive observers and particles can cross the inner and outer horizon on an ingoing geodesic\, and thus entering and exiting the supposedly trapped spacetime region is possible. Lastly\, we comment on the connection betwe en the singularity regularization and the entanglement entropy of massless scalar fields living on the regular black hole background.\n LOCATION:https://researchseminars.org/talk/3cqfs/21/ END:VEVENT BEGIN:VEVENT SUMMARY:Julian De Vuyst (Okinawa Institute of Science and Technology) DTSTART:20240709T070000Z DTEND:20240709T080000Z DTSTAMP:20260417T041311Z UID:3cqfs/22 DESCRIPTION:Title: G ravitational entropy is observer-dependent\nby Julian De Vuyst (Okinaw a Institute of Science and Technology) as part of Tricontinental Quantum F undamentals Seminar\n\n\nAbstract\nIn quantum gravity\, it has been argued that a proper accounting of the role played by an observer promotes the v on Neumann algebra of observables in a given spacetime subregion from Type III to Type II. While this allows for a mathematically precise definition of its entropy\, we show that this procedure depends on which observer is employed. We make this precise by considering a setup in which many possi ble observers are present\; by generalising previous approaches\, we deriv e density operators for the subregion relative to different observers (and relative to arbitrary collections of observers)\, and we compute the asso ciated entropies in a semiclassical regime\, as well as in some specific e xamples that go beyond this regime. We find that the entropies seen by dis tinct observers can drastically differ. Our work makes extensive use of th e formalism of quantum reference frames (QRF)\; indeed\, as we point out\, the 'observers' considered here and in the previous works are nothing but QRFs. In the process\, we demonstrate that the description of physical st ates and observables invoked by Chandrasekaran et al. [arXiv:2206.10780] is equivalent to the Page-Wo otters formalism\, leading to the informal slogan "PW=CLPW". It is our hop e that this paper will help motivate a long overdue union between the QRF and quantum gravity communities.\n LOCATION:https://researchseminars.org/talk/3cqfs/22/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniel Terno (Macquarie University) DTSTART:20240730T070000Z DTEND:20240730T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/23 DESCRIPTION:Title: S pin\, localisation and uncertainty relations\nby Daniel Terno (Macquar ie University) as part of Tricontinental Quantum Fundamentals Seminar\n\n\ nAbstract\nDefining a relativistic position operator poses significant cha llenges\, even without considering particle creation and annihilation. The solution involves using positive operator-valued measures (POVMs)\, thoug h they are not unique. This non-uniqueness also affects the relativistic g eneralization of non-relativistic spin. In this talk\, I will describe POV Ms for scalar particles\, photons\, and spin-1/2 fermions\, focusing on th eir properties and potential experimental relevance. Finally\, I will high light recent work addressing these (sloppily-defined) operators in a rigor ous manner.\n LOCATION:https://researchseminars.org/talk/3cqfs/23/ END:VEVENT BEGIN:VEVENT SUMMARY:Guilherme Franzmann (Stockholm University) DTSTART:20241001T070000Z DTEND:20241001T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/27 DESCRIPTION:Title: A re quantum subsystems invariant?\nby Guilherme Franzmann (Stockholm Un iversity) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbst ract\nWhat is a physical subsystem? How classical physical subsystems loca lized in spacetime (causally independent) are identified from quantum ones ? Traditionally\, classical systems have been uniquely identified with qua ntum systems\, typically represented as factors in Hilbert space for finit e-dimensional systems or associated with a local (microcausality) algebra of operators in QFT. Both representations aim to instantiate a specific pr escription of subsystems' independence\, that they must be statistically i ndependent for state preparations and measurements. Despite this prescript ion\, it is easy to show that canonical linearized quantum gravity prevent s us from obtaining a gauge-invariant local algebra\, thus undermining one of the conditions needed for statistical independence of subsystems in QF T. Arguably\, this precludes most of the modeling associated with early un iverse cosmology as well as current attempts to model gravity-induced-enta nglement table-top experiments. Nonetheless\, primarily it presents a majo r roadblock towards a theory of quantum gravity. In this talk\, after revi ewing the aforementioned points\, I will propose that a way forward is tha t the unique identification between quantum and classical systems should b e dropped\, and instead this mapping should be dynamical\, which opens the possibility for a single-world unitary quantum mechanics.\n LOCATION:https://researchseminars.org/talk/3cqfs/27/ END:VEVENT BEGIN:VEVENT SUMMARY:Chris Mitsch (Bucknell University) DTSTART:20240919T130000Z DTEND:20240919T150000Z DTSTAMP:20260417T041311Z UID:3cqfs/28 DESCRIPTION:Title: S ome Lessons from Haag's Theorem\nby Chris Mitsch (Bucknell University) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nHaa g’s theorem is a classic no-go theorem: it rigorously demonstrates that there is a conflict between the interaction picture and other basic\, intu itive-seeming assumptions in QFT. The precise significance of the theorem continues to be debated\, however. I will focus on two big-picture questio ns in this talk. First\, why are there multiple\, distinct responses to Ha ag's theorem? Here I will compare and contrast these and\, in so doing\, a rticulate the methodological choices motivating them. Second\, if our goal is building usable models of phenomena\, why should we care about esoteri c results like Haag's theorem? Here I will draw on an analogous result in the social sciences to make the case that results like Haag's theorem help us organize models' varied applications and prioritize investigations in model development.\n LOCATION:https://researchseminars.org/talk/3cqfs/28/ END:VEVENT BEGIN:VEVENT SUMMARY:Fil Simovic (Macquarie University) DTSTART:20240820T070000Z DTEND:20240820T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/29 DESCRIPTION:Title: U nderstanding emergent geometry through symmetry breaking\nby Fil Simov ic (Macquarie University) as part of Tricontinental Quantum Fundamentals S eminar\n\n\nAbstract\nQuantum field theory correlators allow for the recon struction of spacetime geometry from information-theoretic quantities\, le ading to a viewpoint in which the fundamental role of spacetime is subsume d by different\, potentially abstract\, measures of correlation. Recent wo rk has demonstrated the emergence of higher-dimensional anti-de Sitter geo metries from this perspective\, with an emphasis on local measurements of CFTs using continuous wavelet transforms. In this talk\, I describe curren t efforts in understanding this emergence through the AdS/CFT corresponden ce. The goal will be to establish a holographic map which can be used to d emystify the scale-dependent features of the emergent geometries\, and to find new practical applications of holography.\n LOCATION:https://researchseminars.org/talk/3cqfs/29/ END:VEVENT BEGIN:VEVENT SUMMARY:Kasia Rejzner (University of York) DTSTART:20250204T080000Z DTEND:20250204T090000Z DTSTAMP:20260417T041311Z UID:3cqfs/30 DESCRIPTION:Title: P erturbative algebraic quantum field theory\nby Kasia Rejzner (Universi ty of York) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAb stract\nIn this talk\, I will present the motivation and brief history of perturbative algebraic quantum field theory (pAQFT). It has its roots in t he axiomatic framework of Haag and Kastler\, but uses the more pragmatical approach of perturbative QFT for the construction of models. At the same time\, the methods used in pAQFT are mathematically rigorous\, as renormal ization is treated using the Epstein-Glaser approach\, where physical quan tities can be constructed without the need of "subtracting infinities".\n LOCATION:https://researchseminars.org/talk/3cqfs/30/ END:VEVENT BEGIN:VEVENT SUMMARY:Marta Maria Marchese (University of Siegen) DTSTART:20241029T080000Z DTEND:20241029T100000Z DTSTAMP:20260417T041311Z UID:3cqfs/31 DESCRIPTION:Title: C oherently Averaged Optmechanical Sensing\nby Marta Maria Marchese (Uni versity of Siegen) as part of Tricontinental Quantum Fundamentals Seminar\ n\n\nAbstract\nCoherent averaging schemes have been introduced as a method to achieve the Heisenberg limit in parameter estimation. Typically\, thes e schemes involve multiple probes in a product state interacting with a qu antum bus\, with parameter estimation performed via measurements on the bu s. We propose a novel coherent averaging scheme for force sensing using an array of optomechanical detectors. Our setup consists of $N$ optomechanic al cavities\, unidirectionally coupled via an input laser pulse in the str oboscopic regime. The goal is to detect some weak unknown force that coupl es with all the mechanical elements within the cavities. Before being read out\, the pulse sequentially passes through all the cavities\, accumulati ng phase shifts\, which encode information about the force. Potential appl ications of this approach include the sensing of gravitational fields at t he Large Hadron Collider (LHC)\, the detection of dark matter signatures\, and the measurement of effects predicted by potential collapse models.\n LOCATION:https://researchseminars.org/talk/3cqfs/31/ END:VEVENT BEGIN:VEVENT SUMMARY:Thiago Guerreiro (Pontifical Catholic University of Rio de Janeiro ) DTSTART:20241114T150000Z DTEND:20241114T160000Z DTSTAMP:20260417T041311Z UID:3cqfs/32 DESCRIPTION:Title: N onclassical gravitational waves and the quantum nature of gravity\nby Thiago Guerreiro (Pontifical Catholic University of Rio de Janeiro) as par t of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nEinstein's theory of gravity admits a low energy effective quantum field description from which predictions beyond classical general relativity can be made. A s gravitational wave detectors improve\, we may ask whether nonclassical f eatures of such theory can be experimentally verified? In this talk\, I wi ll discuss three aspects of this question: First\, what kinds of signals w ould nonclassical gravitational waves impart on a detector? Next\, what wo uld we need to measure in order to certify the quantum nature of gravity? And finally\, do nonclassical gravitational wave states get produced in Na ture\, and if yes\, what are the sources?\n LOCATION:https://researchseminars.org/talk/3cqfs/32/ END:VEVENT BEGIN:VEVENT SUMMARY:José Polo-Gómez (University of Waterloo) DTSTART:20250121T160000Z DTEND:20250121T170000Z DTSTAMP:20260417T041311Z UID:3cqfs/33 DESCRIPTION:Title: N o Black Holes from Light\nby José Polo-Gómez (University of Waterloo ) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nWe show that it is not possible to concentrate enough light to precipitate t he formation of an event horizon. We argue that the dissipative quantum ef fects coming from the self-interaction of light (such as vacuum polarizati on) are enough to prevent any meaningful buildup of energy that could crea te a black hole in any realistic scenario.\n LOCATION:https://researchseminars.org/talk/3cqfs/33/ END:VEVENT BEGIN:VEVENT SUMMARY:Doreen Fraser (University of Waterloo) and Maria Papageorgiou (IQO QI-Vienna) DTSTART:20250225T160000Z DTEND:20250225T170000Z DTSTAMP:20260417T041311Z UID:3cqfs/34 DESCRIPTION:Title: T he role of dynamics in the relativistic quantum measurement problem\nb y Doreen Fraser (University of Waterloo) and Maria Papageorgiou (IQOQI-Vie nna) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\ nRecent developments in local measurement theory for relativistic quantum field theory offer new perspectives on relativistic causality. One importa nt feature is that the representation of relativistic dynamics in such the ories imposes crucial constraints on relativistic quantum measurements. In this talk\, we will consider two different approaches to imposing dynamic al constraints: 1. abstractly within the Fewster-Verch framework for algeb raic quantum field theory and 2. for a concrete model of time-extended fie ld measurements. These considerations also have implications for the form of the measurement problem in quantum field theory.\n LOCATION:https://researchseminars.org/talk/3cqfs/34/ END:VEVENT BEGIN:VEVENT SUMMARY:Linda van Manen (University of Jena) DTSTART:20250429T140000Z DTEND:20250429T150000Z DTSTAMP:20260417T041311Z UID:3cqfs/35 DESCRIPTION:Title: E nvironmental gravitational decoherence with a higher derivative theory \nby Linda van Manen (University of Jena) as part of Tricontinental Quantu m Fundamentals Seminar\n\n\nAbstract\nWe discuss the decoherence in a quan tum system induced by interaction with gravitational degrees of freedom th at are part of a higher derivative theory. The deformation of a mass distr ibution due to gravitational waves acquires naturally a mass quadrupole mo ment. This adds higher derivative dynamics of the quadrupole moment to the unitary evolution of the system\, where the quadrupole moment oscillates with the gravitational frequencies following a higher derivative theory. T he consequence of higher derivatives in the dynamics is that four canonica l variables describe the system. This departure from the usual particle po sition and momentum operators gives an entirely different interpretation o f the decoherence basis. This model focuses on the open dynamics of the qu adrupole moment\, rather than on individual particles. As such\, a short e xample is given to utilize quadrupole measurements to probe gravitational decoherence and noise. We first derive a Langevin equation for a lower der ivative model and show how higher derivatives naturally emerge on the boun dary. A quantum master equation is derived for the emerging quadrupole mom ent\, considering that the environment is a higher derivative theory of gr avity.\n LOCATION:https://researchseminars.org/talk/3cqfs/35/ END:VEVENT BEGIN:VEVENT SUMMARY:Germain Tobar (Stockholm University) DTSTART:20260127T080000Z DTEND:20260127T093000Z DTSTAMP:20260417T041311Z UID:3cqfs/36 DESCRIPTION:Title: Q uantum metasurfaces as probes of vacuum particle content\nby Germain T obar (Stockholm University) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nThe quantum vacuum of the electromagnetic field is inherently entangled across distinct spatial sub-regions\, resulting in e ntangled particle content across these sub-regions. However\, accessing th is particle content in a controlled laboratory experiment has remained out of experimental reach. Here we propose to overcome this challenge with a quantum mirror made from a two-dimensional sub-wavelength array of atoms t hat divides a photonic cavity. The array's response to light is tunable be tween transmissive and reflective states by a control atom that is excited to a Rydberg state. We find that vacuum photon content from non-perturbat ive changes of the boundary conditions and therefore distinct spatial sub- regions of the vacuum causes subtle frequency shifts that are accessible t o sub-wavelength atom array platforms. This novel approach for probing vac uum particle content stems from the system’s unique ability to create co herent dynamics of superpositions of transmissive and reflective states\, providing a quantum-enhanced platform for observing vacuum particle creati on from highly non-perturbative boundary condition changes of the electrom agnetic field vacuum.\n LOCATION:https://researchseminars.org/talk/3cqfs/36/ END:VEVENT BEGIN:VEVENT SUMMARY:Chris Fewster (University of York) DTSTART:20250603T070000Z DTEND:20250603T080000Z DTSTAMP:20260417T041311Z UID:3cqfs/38 DESCRIPTION:Title: E xact measurement schemes for local observables and the preparation of phys ical local product states\nby Chris Fewster (University of York) as pa rt of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nThis talk describes further developments in the framework for measurement in quantu m field theory introduced by myself and Verch [Commun. Math. Phys. 378 (2020) 851-889 arXiv:1810.06512]. In particular\, it will be shown in a class of theories that any local observable can be measured\, and that tw o observers in spacelike separated laboratories can independently prepare desired physical states\, which amounts to a constructive proof of the exi stence of physical local product states. I will aim to introduce the relev ant background.\n LOCATION:https://researchseminars.org/talk/3cqfs/38/ END:VEVENT BEGIN:VEVENT SUMMARY:Laura Ruetsche (University of Michigan) DTSTART:20250715T150000Z DTEND:20250715T160000Z DTSTAMP:20260417T041311Z UID:3cqfs/39 DESCRIPTION:Title: S cale invaders and the ascent of pessimism\nby Laura Ruetsche (Universi ty of Michigan) as part of Tricontinental Quantum Fundamentals Seminar\n\n \nAbstract\n21st century philosophy of physics has been enriched by a deve loping alliance between (i) a broad effective field theory philosophy\, em bracing a range of effective field theory techniques\, and (ii) a species of scientific realism educated by that philosophy and those techniques. Ke y to the alliance is the idea that\, for a healthy variety of quantum fiel d theories understood as effective theories\, a separation of scales enabl es the aspirant realist to identify "the right variables" for effective ph ysics\, and frame her realism in their terms. In this talk\, I'll explicat e the alliance between physicists' effective theory technologies and philo sophers'—specifically\, scientific realists'—aspirations to understand our best physics as revealing deep truths about the physical world. Then I'll develop a challenge to the alliance in the form of what I call scale invaders—something\, I'll argue\, working physicists should be hoping fo r\, despite the trouble they make for scientific realism.\n LOCATION:https://researchseminars.org/talk/3cqfs/39/ END:VEVENT BEGIN:VEVENT SUMMARY:Rainer Verch (University of Leipzig) DTSTART:20250513T150000Z DTEND:20250513T160000Z DTSTAMP:20260417T041311Z UID:3cqfs/40 DESCRIPTION:Title: C ausality violations in quantum field theory? A ping-pong ball test\nby Rainer Verch (University of Leipzig) as part of Tricontinental Quantum Fu ndamentals Seminar\n\n\nAbstract\nIt has been pointed out that there are l ocal operations in quantum field theory which can lead to superluminal eff ects. A prominent example is the "impossible measurements scenario" put fo rward by Sorkin. In this presentation\, it will be explained that such app arent difficulties are not a specific defect or pathology of quantum field theory\, but that they also occur in classical relativistic field theory. On the other hand\, if the operations are required to be mediated by loca l interactions\, then there are no superluminal effects. If time allows\, it will also be explained that the time-travel analogue scenario in quantu m circuits proposed by Deutsch (D-CTC) is\, on one hand\, not related to c losed timelike curves in the sense of general relativity\, and on the othe r hand\, can be realized also in classical statistical theories and is the refore not based on quantum mechanics.\n LOCATION:https://researchseminars.org/talk/3cqfs/40/ END:VEVENT BEGIN:VEVENT SUMMARY:Jan Mandrysch (IQOQI-Vienna) DTSTART:20260312T090000Z DTEND:20260312T103000Z DTSTAMP:20260417T041311Z UID:3cqfs/41 DESCRIPTION:Title: H ow to measure quantum fields? Implementing a causal measurement scheme \nby Jan Mandrysch (IQOQI-Vienna) as part of Tricontinental Quantum Fundam entals Seminar\n\n\nAbstract\nWhile measurement processes in standard quan tum mechanics are well understood\, the extension of these ideas to quantu m field theory (QFT) remains a key challenge. In particular\, ensuring tha t measurements respect fundamental principles such as relativistic causali ty is crucial. A persistent issue concerning measurements in QFT is\, thou gh\, that microcausality alone is insufficient to prevent superluminal sig naling. In this talk\, I will present a concrete scheme for measuring real linear scalar fields\, grounded in the Fewster-Verch measurement framewor k\, which allows to model projective and Gaussian measurements and more. T he approach fully respects the principles of relativistic covariance\, loc ality\, and causality\, offering a robust solution to the challenges of me asurement in QFT.\n\nTalk has been rescheduled for 12 March 2026 at 10:00 CET.\n LOCATION:https://researchseminars.org/talk/3cqfs/41/ END:VEVENT BEGIN:VEVENT SUMMARY:Antoine Soulas (Choups) (University of Vienna) DTSTART:20260505T070000Z DTEND:20260505T083000Z DTSTAMP:20260417T041311Z UID:3cqfs/42 DESCRIPTION:Title: A proof that no-signalling implies microcausality in quantum field theory\nby Antoine Soulas (Choups) (University of Vienna) as part of Tricontin ental Quantum Fundamentals Seminar\n\n\nAbstract\nMicrocausality counts am ong the basic requirements that ensure the consistency of quantum field th eories (QFT). In the literature on the foundations of QFT\, however\, an e lementary derivation of microcausality from the relativistic constraints s eemed to be missing. Authors generally proceed the other way round\, justi fying the axiom as a sufficient condition to guarantee some desired proper ties\, typically involving properties like no-signalling\, separability\, independence of operations\, tensor product structure... The aim of this w ork [1] is to study some logical interrelationships between fundamental pr operties in (relativistic) quantum theories\, and in particular to provide an elementary but important proof concerning microcausality that was appa rently missing in the literature.\n\nTo do so\, an operational no-signalli ng condition is first introduced in the context of quantum mechanics\, whe re we prove its equivalence to an apparently weaker version (CPTP version equivalent to PVM version)\, and to a property of factorisation of the evo lution unitary operator\, generalising some results of [2]. We then transl ate this condition in QFT and prove that it implies both microcausality an d the spin-statistics theorem\, in the ideal case of pointwise measurement s implemented in the projection postulate sense. This provides an argument (often invoked but apparently missing in the literature) to see microcaus ality as a necessary condition for the compatibility of spacelike separate d operations.\n\n[1] Soulas\, Antoine. "A proof that no-signalling implies microcausality in quan tum field theory." Foundations of Physics 55.2 (2025): 22.\n\n[2] Beck man\, David\, et al. "C ausal and localizable quantum operations." Physical Review A 64.5 (200 1): 052309.\n LOCATION:https://researchseminars.org/talk/3cqfs/42/ END:VEVENT END:VCALENDAR