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:20260424T142515Z UID:3cqfs/1 DESCRIPTION:Title: Wavelets and Quantum Field Theory\nby Šimon Vedl (Macquarie Univ ersity) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstra ct\nIn this talk I will go through the wavelet-related topics investigated by the group at Macquarie University: Gavin Brennen\, Sukhwinder Singh (f ormer collaborator)\, Dan George\, Simon Vedl. These can be divided into t wo distinct categories\, applications of discrete wavelet transform\, and applications of continuous wavelet transform.\n\nOur main focus is to unde rstand and utilise the extra variable introduced in the wavelet transform that is often called the scale. The talk will begin with an introduction t o wavelet analysis and then proceed with discussion of state compression\, AdS/CFT correspondence and wavelet regularisation of QFT by a scale cutof f.\n LOCATION:https://master.researchseminars.org/talk/3cqfs/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Robert H. Jonsson (Nordic Institute for Theoretical Physics) DTSTART:20231121T070000Z DTEND:20231121T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/2 DESCRIPTION:Title: Gaussian states\, partner modes and an entanglement duality\nby R obert H. Jonsson (Nordic Institute for Theoretical Physics) as part of Tri continental Quantum Fundamentals Seminar\n\n\nAbstract\nGaussian states ap pear everywhere in quantum physics - from condensed matter\, to quantum op tics and quantum field theory in curved spacetimes. In this talk I aim for three objectives related to Gaussian states:\n\nFirst\, I discuss their p artner mode entanglement structure which is well known\, but maybe not wid ely known. This is the fact that a pure Gaussian state under any bipartiti on decomposes into a sum of two-mode squeezed states\, for example\, in th e Unruh effect or in Einstein-Bose condensates.\n\nSecond\, I review the p owerful Kähler structure formalism for Gaussian states. It captures the g eometry of Gaussian states\, it is very practical for applications\, and i t treats both bosons and fermions simultaneously.\n\nThird\, to showcase a n example connecting bosonic and fermionic systems\, I will present an ent anglement duality which arises in supersymmetric Gaussian states [1]. Here \, bosonic and fermionic partner subsystems\, canonically identified by th e supercharge construction\, exhibit an intriguing duality of their entang lement spectra.\n\n(Time permitting\, as a special application\, we consid er topological insulators and superconductors and their SUSY partners\, di scussing the recently derived classification of supercharges in this conte xt [2].)\n\n[1] Jonsson\, Robert H.\, Lucas Hackl\, and Krishanu Roychowdh ury. “Entanglement Dualities in Supersymmetry.” Physical Review Resear ch 3\, no. 2 (June 16\, 2021): 023213.\n\n[2] Gong\, Zongping\, Robert H. Jonsson\, and Daniel Malz. “Supersymmetric Free Fermions and Bosons: Loc ality\, Symmetry\, and Topology.” Physical Review B 105\, no. 8 (Februar y 24\, 2022): 085423.\n LOCATION:https://master.researchseminars.org/talk/3cqfs/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Joshua Foo (Stevens Institute of Technology) DTSTART:20230418T070000Z DTEND:20230418T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/3 DESCRIPTION:Title: Telefilters\, telemirrors\, and causality\nby Joshua Foo (Stevens Institute of Technology) as part of Tricontinental Quantum Fundamentals S eminar\n\n\nAbstract\nMode-selective interactions are ubiquitous in quantu m optics and interacting quantum field theories. Such unitaries take as in put a multi-mode field but uniquely affect a single mode\, compared with t hose orthogonal to it. Despite their wide application in theoretical and e xperimental physics\, the temporal dimension of such interactions are typi cally ignored.\n\nHere\, I demonstrate how the naïve treatment of a mode- selective unitaries leads to the possibility of acausal signalling\, due t o the tacit assumption that certain kinds of idealised measurements of qua ntum fields can be made. I achieve this by introducing new theoretical mod els for mode-selective mirrors using continuous-variable teleportation\, w hich is able to unveil the temporal aspects of the mode propagation.\n\nTh e main result is that mode-selective operations must generally enact a fun damental time-delay on input modes that are delocalised in time. This resu lt resolves Sorkin's long-standing "impossible measurement" problem in rel ativistic quantum field theory\, and thus has significant implications for experimental quantum optics and those working in quantum causality and fi eld theory.\n\nTalk not recorded\n LOCATION:https://master.researchseminars.org/talk/3cqfs/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Nicolas C. Menicucci (Royal Melbourne Institute of Technology) DTSTART:20230502T070000Z DTEND:20230502T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/4 DESCRIPTION:Title: Tachyonic media in sonic relativity\nby Nicolas C. Menicucci (Roy al Melbourne Institute of Technology) as part of Tricontinental Quantum Fu ndamentals Seminar\n\n\nAbstract\nIn sonic models of special relativity\, the fact that the sonic medium violates (ordinary) Lorentz symmetry is app arent to observers external to the sonic medium but not to a class of obse rvers existing within the medium itself. We show that the situation is sym metric: internal observers will judge physics in the external laboratory t o violate their own sonic Lorentz symmetries. We therefore treat all obser vers on an equal footing such that each is able to retain a commitment to their own Lorentz symmetries.\n\nWe then generalize beyond the case of sub system-environment decompositions to situations in which there exist multi ple phonon fields\, all obeying Lorentz symmetries but with different inva riant speeds. 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 choi ce is influenced -- but not determined -- by a desire for simplicity in th e description of physical laws.\n\nSending information faster than sound s erves as a model of tachyonic signalling to a distant receiver. Immutable causality of the laboratory setup when perceived externally to a sonic med ium manifests internally through the confinement of the tachyons to an app arent ether (with a rest frame)\, which we call a 'tachyonic medium\,' the reby preventing tachyonic exchange from emulating the scenario of a round- trip signal travelling into an observer's past causal cone. The assignment of sonic-Lorentz-violating effects to fields that obey 'photonic' Lorentz symmetries thus ensures that causality associated with the 'sonic' Lorent z symmetries is preserved.\n LOCATION:https://master.researchseminars.org/talk/3cqfs/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Dominic G. Lewis (Royal Melbourne Institute of Technology) DTSTART:20230516T070000Z DTEND:20230516T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/5 DESCRIPTION:Title: Bandlimitation\, wavelets\, and scaled QFT\nby Dominic G. Lewis ( Royal Melbourne Institute of Technology) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nThe likely presence of a fundamental minimum length scale to the universe (motivated by generalised uncertainty principles and UV divergences in quantum field theory to name a few) has led to the application of information theoretic techniques such as bandlim itation to quantum field theory\, allowing for field theories to be repres ented as simultaneously continuous and discrete through Shannon theory.\n\ nWe extend on this notion by showing that non-bandlimited quantum field th eories can be decomposed into bandlimited ones\, called scales\, using Sha nnon wavelets. Each scale of the wavelet decomposition gives a field theor y possessing an ultraviolet cut-off (and infrared cut-off) and\, as a resu lt\, an equivalent discrete theory. As such\, one can use wavelets to deco mpose an $N+1$ dimensional continuous field theory into a $2N+1$ dimension al discrete theory (where the scale of the wavelet decomposition is treate d as a spatial dimension).\n\nLinked paper only covers the first (bandlimi tation) part of the talk and not wavelets\, which will be included in a fu ture paper.\n LOCATION:https://master.researchseminars.org/talk/3cqfs/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Carolyn Wood (University of Queensland) DTSTART:20230530T070000Z DTEND:20230530T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/6 DESCRIPTION:Title: Journal club on 'Harvesting quantum coherence from axion dark matt er'\nby Carolyn Wood (University of Queensland) as part of Tricont inental Quantum Fundamentals Seminar\n\n\nAbstract\nIn this week's meeting \, Carolyn Wood will lead the discussion of the recent article 'Harvest ing quantum coherence from axion dark matter' by Sugumi Kanno\, Akira Matsumura\, and Jiro Soda.\n\nTalk not recorded\n LOCATION:https://master.researchseminars.org/talk/3cqfs/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Magdalena Zych (Stockholm University) DTSTART:20230620T070000Z DTEND:20230620T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/7 DESCRIPTION:Title: Relativity of quantum superpositions in the context of superpositions of gravitational sources\nby Magdalena Zych (Stockholm University) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nIt is anticipated that in a theory of quantum gravity\, there exist quantum supe rpositions of semiclassical states of spacetime geometry. It is often disc ussed how such states could arise from a source mass in a spatial superpos ition. In this talk I will discuss such spatial superposition scenarios fr om the perspective of relativity of the notion of location\, and thus of s uperposition itself. This perspective allows to show that for states in wh ich the superposed amplitudes differ by a coordinate transformation\, it i s always possible to re-express the scenario in terms of dynamics on a fix ed geometry albeit with adapted preparations and measurements on the invol ved degrees of freedom. The results unveil an ambiguity in the interpretat ion of such scenarios as genuinely quantum-gravitational\, and motivate fu rther research into loopholes and assumption behind such scenarios.\n\nTal k not recorded\n LOCATION:https://master.researchseminars.org/talk/3cqfs/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Nicholas Funai (Royal Melbourne Institute of Technology) DTSTART:20231107T070000Z DTEND:20231107T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/8 DESCRIPTION:Title: Covariant bandlimits and entanglement harvesting\nby Nicholas Fun ai (Royal Melbourne Institute of Technology) as part of Tricontinental Qua ntum Fundamentals Seminar\n\n\nAbstract\nIn QFT UV cutoffs are often used as renormalisation or calculational tools\, however sometimes these cutoff s can have a physical origin\, e.g. condensed matter systems. These UV cut offs also tend to overlook the need for Lorentz covariance in any notion o f minimum length.\n\nThis talk uses the covariant UV cutoff introduced by Kempf and Pye\; and investigates its effects on entanglement harvesting an d communication\, with particular attention on causality violations and an y non-local behaviour introduced by the cutoff.\n LOCATION:https://master.researchseminars.org/talk/3cqfs/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Evan Gale (University of Queensland) DTSTART:20230307T070000Z DTEND:20230307T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/9 DESCRIPTION:Title: Relativistic Unruh-DeWitt detectors with quantized center of mass \nby Evan Gale (University of Queensland) as part of Tricontinental Quantu m Fundamentals Seminar\n\n\nAbstract\nI examine the implications of partic le localisation in the Unruh-DeWitt model\, which provides a simple model of a two-level system (aka 'particle detector') coupled to a scalar quantu m field. By comparing the first- and second-quantised formulations of a de tector with a quantised centre of mass\, one is naturally led to two disti nct notions of localisation. I consider the consequences of these two loca lisation schemes in the context of spontaneous emission\, finding that the two localisations lead to distinguishable physical consequences\, which c an in principle be tested by future experiments.\n\nTalk not recorded\n LOCATION:https://master.researchseminars.org/talk/3cqfs/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Navdeep Arya (Stockholm University) DTSTART:20240305T080000Z DTEND:20240305T100000Z DTSTAMP:20260424T142515Z UID:3cqfs/12 DESCRIPTION:Title: Unruh effect inside a cylindrical cavity\nby Navdeep Arya (Stock holm University) as part of Tricontinental Quantum Fundamentals Seminar\n\ n\nAbstract\nThe Unruh effect states that the transition rates of a unifor mly accelerated detector in the inertial vacuum have a thermal character a t a temperature proportional to the detector's acceleration. Numerous prop osals studying different properties of the accelerated detector under vari ed settings still await fruition as the signal of interest is generally ve ry weak.\n\nWe will discuss the Unruh effect inside a cylindrical cavity\, with special emphasis on strategies that might help us resolve it better. We will discuss the transition rates and radiative energy shift of an ato m uniformly accelerated along the axis of the cavity. We will argue that t he requirement of large acceleration for an appreciable non-inertial contr ibution to these properties can be traded for a better precision in cavity design. We will conclude with a brief discussion on the possibility of se lective super-radiant enhancement of the Unruh signal.\n LOCATION:https://master.researchseminars.org/talk/3cqfs/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Flaminia Giacomini (ETH Zürich) DTSTART:20240319T080000Z DTEND:20240319T100000Z DTSTAMP:20260424T142515Z UID:3cqfs/13 DESCRIPTION:Title: Quantum effects in gravity beyond the Newton potential from a deloca lised quantum source\nby Flaminia Giacomini (ETH Zürich) as part of T ricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nUnderstanding th e fundamental nature of gravity at the interface with quantum theory is a major open question in theoretical physics. Recently\, the study of gravit ating quantum systems\, for instance a massive quantum system prepared in a quantum superposition of positions and sourcing a gravitational field\, has attracted a lot of attention: experiments are working towards realisin g such a scenario in the laboratory\, and measuring the gravitational fiel d associated to a quantum source is expected to give some information abou t quantum aspects of gravity. However\, there are still open questions con cerning the precise conclusions that these experiments could draw on the n ature of gravity\, such as whether experiments in this regime will be able to test more than the Newtonian part of the gravitational field.\n\nIn th is 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 kn own classical model of gravity. These effects can in principle be measured by performing an interference experiment\, and are independent of gravito n emission. Identifying stronger quantum aspects of gravity than those rep roducible with the Newton potential is crucial to prove the nonclassicalit y of the gravitational field and to plan a new generation of experiments t esting quantum aspects of gravity in a broader sense than what proposed so far.\n LOCATION:https://master.researchseminars.org/talk/3cqfs/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Robert B. Mann (University of Waterloo) DTSTART:20240402T080000Z DTEND:20240402T100000Z DTSTAMP:20260424T142515Z UID:3cqfs/14 DESCRIPTION:Title: The Holographic Chemistry of Black Holes\nby Robert B. Mann (Uni versity of Waterloo) as part of Tricontinental Quantum Fundamentals Semina r\n\n\nAbstract\nBlack Holes are amongst the strangest objects in the univ erse. They form from the collapse of matter into an object whose gravitati onal pull is so strong\, nothing can escape from them. Yet a black hole al so radiates heat like a blackbody\, with a temperature equal to its surfac e gravity\, 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 — as embodied by a cosmological constant — plays a pivotal role in t he thermodynamic behaviour of black holes. Mass becomes chemical enthalpy\ , the notion of a thermodynamic volume appears\, and black holes exhibit a broad range of chemical phenomena\, including liquid/gas phase transition s similar to a Van der Waals fluid\, triple points similar to that of wate r\, re-entrant phase transitions that appear in gels and heat engines. Und er certain conditions they can even behave like superfluid helium! Now kno wn as “Black Hole Chemistry”\, I will review this subject and then go on to describe new work that is providing a pathway toward understanding t hese phenomena from the perspective of Gauge-Gravity duality\, in which ph ase transitions in the (gravitational) bulk become dual to phase transitio ns in the dual gauge theory.\n LOCATION:https://master.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:20260424T142515Z UID:3cqfs/16 DESCRIPTION:Title: Incompleteness Theorems for Observables in General Relativity\nb y Aristotelis Panagiotopoulos (Kurt Gödel Research Center\, University of Vienna) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstr act\nOne of the biggest open problems in mathematical physics has been the problem of formulating a complete and consistent theory of quantum gravit y. Some of the core technical and epistemological difficulties come from t he fact that General Relativity (GR) is\, fundamentally\, a geometric theo ry and\, as such\, it oughts to be `generally covariant'\, i.e. invariant under change of coordinates by the arbitrary diffeomorphism of the ambient manifold. The Problem of Observables is a famous instance of the difficul ties that general covariance brings into quantization: no non-trivial diff eomorphism-invariant quantity has ever been reported on the collection of all spacetimes.\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 methods from Descriptive Set Theory (DST) in order to show that no comple te observables for full GR can be Borel definable. In other words\, the pr oblem of observables is to `analysis' what the Delian problem was to `stra ightedge and compass'. This talk will provide a gentle introduction to the main concepts of DST\, where they come from\, and how they connect to the problem of observables. We will then discuss the aforementioned Incomplet eness Theorem\, as well as the next steps in a research program that aims to further uncover this new connection between theoretical physics and DST .\n LOCATION:https://master.researchseminars.org/talk/3cqfs/16/ END:VEVENT BEGIN:VEVENT SUMMARY:Erickson Tjoa (Max Planck Institute for Quantum Optics) DTSTART:20240516T130000Z DTEND:20240516T150000Z DTSTAMP:20260424T142515Z UID:3cqfs/17 DESCRIPTION:Title: The Unruh-DeWitt model and its joint interacting Hilbert space\n by Erickson Tjoa (Max Planck Institute for Quantum Optics) as part of Tric ontinental Quantum Fundamentals Seminar\n\n\nAbstract\nIn this work we mak e the connection between the Unruh-DeWitt particle detector model applied to quantum 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 Unruh-DeWitt model. In the physically relevant setting involving mass less fields in $(3+1)$-dimensional spacetimes\, we argue that common choic es of the spacetime smearing functions regulate the ultraviolet behaviour of the model but can still exhibit infrared divergences. We discuss the co nditions under which this problem does not arise and the relevance of the operator-algebraic approach for better understanding of particle detector models and their applications.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Anne-Catherine de la Hamette (University of Vienna) DTSTART:20240611T070000Z DTEND:20240611T080000Z DTSTAMP:20260424T142515Z UID:3cqfs/19 DESCRIPTION:Title: Identification is pointless: Localisation of systems and events in s uperpositions of spacetimes\nby Anne-Catherine de la Hamette (Universi ty of Vienna) as part of Tricontinental Quantum Fundamentals Seminar\n\n\n Abstract\nA first step towards scenarios at the interface of quantum theor y and gravity is to consider a quantum superposition of semiclassical spac etimes\, such as the one\, arguably\, sourced by a gravitating object in s uperposition. But what does it mean that a gravitational source is in a su perposition of “different” locations? How can one compare points acros s the different manifolds? Due to the diffeomorphism invariance of general relativity\, there is a priori no notion of the “same” or “differen t” points across the branches. In fact\, there are multiple ways of rela ting points or events on the different spacetimes. Here\, we make this con crete by using coincidences of four scalar fields to construct a compariso n map between all spacetimes in superposition\, which allows us to determi ne whether a system or an event is located at the “same” or “differe nt” points across the branches. Different choices of scalar fields can b e understood as different instantiations of quantum reference frames (QRFs )\, connecting the construction to recent research in the field of quantum foundations. As an explicit application of this formalism\, we explore ho w the localisation of events is relative to the choice of QRF and formulat e a quantum generalisation of Einstein’s famous hole argument. The latte r calls into question the metaphysical meaning of not just spacetime point s but also the identification between spacetime points across manifolds in superposition. Finally\, we discuss the implications of QRF changes for i ndefinite causal order\, the locality of interaction\, and potential empir ical consequences in interference experiments.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Ioannis Soranidis (Macquarie University) DTSTART:20240625T230000Z DTEND:20240626T010000Z DTSTAMP:20260424T142515Z UID:3cqfs/21 DESCRIPTION:Title: Kinematic\, energetic\, and thermodynamic properties of regular blac k holes\nby Ioannis Soranidis (Macquarie University) as part of Tricon tinental Quantum Fundamentals Seminar\n\n\nAbstract\nRegular black holes h ave become a popular alternative to the singular mathematical black holes predicted by general relativity as they circumvent mathematical pathologie s associated with the singularity while preserving crucial black hole feat ures such as the trapping of light. Here\, we will analyze how to generate these geometries and study their thermodynamic properties within the fram ework of general relativity. Our study reveals that the regularization of the singularity\, through the introduction of a minimal length scale\, has a plethora of implications\, one of which is the absence of the Hawking-P age phase transition. We extend our study to the dynamical case\, showing that the internal energy in the first law of black hole thermodynamics is captured by the Misner-Sharp mass and demonstrating that the linear coeffi cient of the Misner-Sharp mass expansion near the outer apparent horizon s uffices for a complete thermodynamic description. Additionally\, we analyz e the behavior of the null energy condition and find that it is violated i n the vicinity of the outer horizon and satisfied in the vicinity of the i nner horizon\, which implies that the trapped spacetime region (as determi ned from the behavior of null geodesic congruences) is effectively separat ed into an NEC-violating and an NEC-non-violating domain. Moreover\, we sh ow that massive observers and particles can cross the inner and outer hori zon on an ingoing geodesic\, and thus entering and exiting the supposedly trapped spacetime region is possible. Lastly\, we comment on the connectio n between the singularity regularization and the entanglement entropy of m assless scalar fields living on the regular black hole background.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Julian De Vuyst (Okinawa Institute of Science and Technology) DTSTART:20240709T070000Z DTEND:20240709T080000Z DTSTAMP:20260424T142515Z UID:3cqfs/22 DESCRIPTION:Title: Gravitational entropy is observer-dependent\nby Julian De Vuyst (Okinawa Institute of Science and Technology) as part of Tricontinental Qu antum Fundamentals Seminar\n\n\nAbstract\nIn quantum gravity\, it has been argued that a proper accounting of the role played by an observer promote s the von Neumann algebra of observables in a given spacetime subregion fr om Type III to Type II. While this allows for a mathematically precise def inition of its entropy\, we show that this procedure depends on which obse rver is employed. We make this precise by considering a setup in which man y possible observers are present\; by generalising previous approaches\, w e derive density operators for the subregion relative to different observe rs (and relative to arbitrary collections of observers)\, and we compute t he associated entropies in a semiclassical regime\, as well as in some spe cific examples that go beyond this regime. We find that the entropies seen by distinct observers can drastically differ. Our work makes extensive us e of the formalism of quantum reference frames (QRF)\; indeed\, as we poin t out\, the 'observers' considered here and in the previous works are noth ing but QRFs. In the process\, we demonstrate that the description of phys ical states and observables invoked by Chandrasekaran et al. [arXiv:2206.10780] is equivalent to the Page-Wootters formalism\, leading to the informal slogan "PW=CLPW". It is our hope that this paper will help motivate a long overdue union between t he QRF and quantum gravity communities.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Daniel Terno (Macquarie University) DTSTART:20240730T070000Z DTEND:20240730T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/23 DESCRIPTION:Title: Spin\, localisation and uncertainty relations\nby Daniel Terno ( Macquarie University) as part of Tricontinental Quantum Fundamentals Semin ar\n\n\nAbstract\nDefining a relativistic position operator poses signific ant challenges\, even without considering particle creation and annihilati on. The solution involves using positive operator-valued measures (POVMs)\ , though they are not unique. This non-uniqueness also affects the relativ istic generalization of non-relativistic spin. In this talk\, I will descr ibe POVMs for scalar particles\, photons\, and spin-1/2 fermions\, focusin g on their properties and potential experimental relevance. Finally\, I wi ll highlight recent work addressing these (sloppily-defined) operators in a rigorous manner.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Guilherme Franzmann (Stockholm University) DTSTART:20241001T070000Z DTEND:20241001T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/27 DESCRIPTION:Title: Are quantum subsystems invariant?\nby Guilherme Franzmann (Stock holm University) as part of Tricontinental Quantum Fundamentals Seminar\n\ n\nAbstract\nWhat is a physical subsystem? How classical physical subsyste ms localized in spacetime (causally independent) are identified from quant um ones? Traditionally\, classical systems have been uniquely identified w ith quantum systems\, typically represented as factors in Hilbert space fo r finite-dimensional systems or associated with a local (microcausality) a lgebra of operators in QFT. Both representations aim to instantiate a spec ific prescription of subsystems' independence\, that they must be statisti cally independent for state preparations and measurements. Despite this pr escription\, it is easy to show that canonical linearized quantum gravity prevents us from obtaining a gauge-invariant local algebra\, thus undermin ing one of the conditions needed for statistical independence of subsystem s in QFT. Arguably\, this precludes most of the modeling associated with e arly universe cosmology as well as current attempts to model gravity-induc ed-entanglement table-top experiments. Nonetheless\, primarily it presents a major roadblock towards a theory of quantum gravity. In this talk\, aft er reviewing the aforementioned points\, I will propose that a way forward is that the unique identification between quantum and classical systems s hould be dropped\, and instead this mapping should be dynamical\, which op ens the possibility for a single-world unitary quantum mechanics.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Chris Mitsch (Bucknell University) DTSTART:20240919T130000Z DTEND:20240919T150000Z DTSTAMP:20260424T142515Z UID:3cqfs/28 DESCRIPTION:Title: Some Lessons from Haag's Theorem\nby Chris Mitsch (Bucknell Univ ersity) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstra ct\nHaag’s theorem is a classic no-go theorem: it rigorously demonstrate s that there is a conflict between the interaction picture and other basic \, intuitive-seeming assumptions in QFT. The precise significance of the t heorem continues to be debated\, however. I will focus on two big-picture questions in this talk. First\, why are there multiple\, distinct response s to Haag's theorem? Here I will compare and contrast these and\, in so do ing\, articulate the methodological choices motivating them. Second\, if o ur goal is building usable models of phenomena\, why should we care about esoteric results like Haag's theorem? Here I will draw on an analogous res ult in the social sciences to make the case that results like Haag's theor em help us organize models' varied applications and prioritize investigati ons in model development.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Fil Simovic (Macquarie University) DTSTART:20240820T070000Z DTEND:20240820T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/29 DESCRIPTION:Title: Understanding emergent geometry through symmetry breaking\nby Fi l Simovic (Macquarie University) as part of Tricontinental Quantum Fundame ntals Seminar\n\n\nAbstract\nQuantum field theory correlators allow for th e reconstruction of spacetime geometry from information-theoretic quantiti es\, leading to a viewpoint in which the fundamental role of spacetime is subsumed by different\, potentially abstract\, measures of correlation. Re cent work has demonstrated the emergence of higher-dimensional anti-de Sit ter geometries from this perspective\, with an emphasis on local measureme nts of CFTs using continuous wavelet transforms. In this talk\, I describe current efforts in understanding this emergence through the AdS/CFT corre spondence. The goal will be to establish a holographic map which can be us ed to demystify the scale-dependent features of the emergent geometries\, and to find new practical applications of holography.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Kasia Rejzner (University of York) DTSTART:20250204T080000Z DTEND:20250204T090000Z DTSTAMP:20260424T142515Z UID:3cqfs/30 DESCRIPTION:Title: Perturbative algebraic quantum field theory\nby Kasia Rejzner (U niversity of York) as part of Tricontinental Quantum Fundamentals Seminar\ n\n\nAbstract\nIn this talk\, I will present the motivation and brief hist ory of perturbative algebraic quantum field theory (pAQFT). It has its roo ts in the axiomatic framework of Haag and Kastler\, but uses the more prag matical approach of perturbative QFT for the construction of models. At th e same time\, the methods used in pAQFT are mathematically rigorous\, as r enormalization is treated using the Epstein-Glaser approach\, where physic al quantities can be constructed without the need of "subtracting infiniti es".\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Marta Maria Marchese (University of Siegen) DTSTART:20241029T080000Z DTEND:20241029T100000Z DTSTAMP:20260424T142515Z UID:3cqfs/31 DESCRIPTION:Title: Coherently Averaged Optmechanical Sensing\nby Marta Maria Marche se (University of Siegen) as part of Tricontinental Quantum Fundamentals S eminar\n\n\nAbstract\nCoherent averaging schemes have been introduced as a method to achieve the Heisenberg limit in parameter estimation. Typically \, these schemes involve multiple probes in a product state interacting wi th a quantum bus\, with parameter estimation performed via measurements on the bus. We propose a novel coherent averaging scheme for force sensing u sing an array of optomechanical detectors. Our setup consists of $N$ optom echanical cavities\, unidirectionally coupled via an input laser pulse in the stroboscopic regime. The goal is to detect some weak unknown force tha t couples with all the mechanical elements within the cavities. Before bei ng read out\, the pulse sequentially passes through all the cavities\, acc umulating phase shifts\, which encode information about the force. Potenti al applications of this approach include the sensing of gravitational fiel ds at the Large Hadron Collider (LHC)\, the detection of dark matter signa tures\, and the measurement of effects predicted by potential collapse mod els.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Thiago Guerreiro (Pontifical Catholic University of Rio de Janeiro ) DTSTART:20241114T150000Z DTEND:20241114T160000Z DTSTAMP:20260424T142515Z UID:3cqfs/32 DESCRIPTION:Title: Nonclassical gravitational waves and the quantum nature of gravity\nby Thiago Guerreiro (Pontifical Catholic University of Rio de Janeiro) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nEin stein's theory of gravity admits a low energy effective quantum field desc ription from which predictions beyond classical general relativity can be made. As gravitational wave detectors improve\, we may ask whether nonclas sical features of such theory can be experimentally verified? In this talk \, I will discuss three aspects of this question: First\, what kinds of si gnals would nonclassical gravitational waves impart on a detector? Next\, what would we need to measure in order to certify the quantum nature of gr avity? And finally\, do nonclassical gravitational wave states get produce d in Nature\, and if yes\, what are the sources?\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:José Polo-Gómez (University of Waterloo) DTSTART:20250121T160000Z DTEND:20250121T170000Z DTSTAMP:20260424T142515Z UID:3cqfs/33 DESCRIPTION:Title: No Black Holes from Light\nby José Polo-Gómez (University of W aterloo) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstr act\nWe show that it is not possible to concentrate enough light to precip itate the formation of an event horizon. We argue that the dissipative qua ntum effects coming from the self-interaction of light (such as vacuum pol arization) are enough to prevent any meaningful buildup of energy that cou ld create a black hole in any realistic scenario.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Doreen Fraser (University of Waterloo) and Maria Papageorgiou (IQO QI-Vienna) DTSTART:20250225T160000Z DTEND:20250225T170000Z DTSTAMP:20260424T142515Z UID:3cqfs/34 DESCRIPTION:Title: The role of dynamics in the relativistic quantum measurement problem \nby Doreen Fraser (University of Waterloo) and Maria Papageorgiou (IQ OQI-Vienna) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAb stract\nRecent developments in local measurement theory for relativistic q uantum field theory offer new perspectives on relativistic causality. One important feature is that the representation of relativistic dynamics in s uch theories imposes crucial constraints on relativistic quantum measureme nts. In this talk\, we will consider two different approaches to imposing dynamical constraints: 1. abstractly within the Fewster-Verch framework fo r algebraic quantum field theory and 2. for a concrete model of time-exten ded field measurements. These considerations also have implications for th e form of the measurement problem in quantum field theory.\n LOCATION:https://master.researchseminars.org/talk/3cqfs/34/ END:VEVENT BEGIN:VEVENT SUMMARY:Linda van Manen (University of Jena) DTSTART:20250429T140000Z DTEND:20250429T150000Z DTSTAMP:20260424T142515Z UID:3cqfs/35 DESCRIPTION:Title: Environmental gravitational decoherence with a higher derivative the ory\nby Linda van Manen (University of Jena) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nWe discuss the decoherence in a quantum system induced by interaction with gravitational degrees of fre edom that are part of a higher derivative theory. The deformation of a mas s distribution due to gravitational waves acquires naturally a mass quadru pole moment. This adds higher derivative dynamics of the quadrupole moment to the unitary evolution of the system\, where the quadrupole moment osci llates with the gravitational frequencies following a higher derivative th eory. The consequence of higher derivatives in the dynamics is that four c anonical variables describe the system. This departure from the usual part icle position and momentum operators gives an entirely different interpret ation of the decoherence basis. This model focuses on the open dynamics of the quadrupole moment\, rather than on individual particles. As such\, a short example is given to utilize quadrupole measurements to probe gravita tional decoherence and noise. We first derive a Langevin equation for a lo wer derivative model and show how higher derivatives naturally emerge on t he boundary. A quantum master equation is derived for the emerging quadrup ole moment\, considering that the environment is a higher derivative theor y of gravity.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Germain Tobar (Stockholm University) DTSTART:20260127T080000Z DTEND:20260127T093000Z DTSTAMP:20260424T142515Z UID:3cqfs/36 DESCRIPTION:Title: Quantum metasurfaces as probes of vacuum particle content\nby Ge rmain Tobar (Stockholm University) as part of Tricontinental Quantum Funda mentals Seminar\n\n\nAbstract\nThe quantum vacuum of the electromagnetic f ield is inherently entangled across distinct spatial sub-regions\, resulti ng in entangled particle content across these sub-regions. However\, acces sing this particle content in a controlled laboratory experiment has remai ned 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 that divides a photonic cavity. The array's response to light is tun able between transmissive and reflective states by a control atom that is excited to a Rydberg state. We find that vacuum photon content from non-pe rturbative changes of the boundary conditions and therefore distinct spati al sub-regions of the vacuum causes subtle frequency shifts that are acces sible to sub-wavelength atom array platforms. This novel approach for prob ing vacuum particle content stems from the system’s unique ability to cr eate coherent dynamics of superpositions of transmissive and reflective st ates\, providing a quantum-enhanced platform for observing vacuum particle creation from highly non-perturbative boundary condition changes of the e lectromagnetic field vacuum.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Chris Fewster (University of York) DTSTART:20250603T070000Z DTEND:20250603T080000Z DTSTAMP:20260424T142515Z UID:3cqfs/38 DESCRIPTION:Title: Exact measurement schemes for local observables and the preparation of physical local product states\nby Chris Fewster (University of York ) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nTh is talk describes further developments in the framework for measurement in quantum field theory introduced by myself and Verch [Commun. Math. Phys. 378 (2020) 851-889 arXiv:1810.06512]. In particular\, it will be sho wn in a class of theories that any local observable can be measured\, and that two observers in spacelike separated laboratories can independently p repare desired physical states\, which amounts to a constructive proof of the existence of physical local product states. I will aim to introduce th e relevant background.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Laura Ruetsche (University of Michigan) DTSTART:20250715T150000Z DTEND:20250715T160000Z DTSTAMP:20260424T142515Z UID:3cqfs/39 DESCRIPTION:Title: Scale invaders and the ascent of pessimism\nby Laura Ruetsche (U niversity of Michigan) as part of Tricontinental Quantum Fundamentals Semi nar\n\n\nAbstract\n21st century philosophy of physics has been enriched by a developing alliance between (i) a broad effective field theory philosop hy\, embracing a range of effective field theory techniques\, and (ii) a s pecies of scientific realism educated by that philosophy and those techniq ues. Key to the alliance is the idea that\, for a healthy variety of quant um field theories understood as effective theories\, a separation of scale s enables the aspirant realist to identify "the right variables" for effec tive physics\, and frame her realism in their terms. In this talk\, I'll e xplicate the alliance between physicists' effective theory technologies an d philosophers'—specifically\, scientific realists'—aspirations to und erstand 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 ho ping for\, despite the trouble they make for scientific realism.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Rainer Verch (University of Leipzig) DTSTART:20250513T150000Z DTEND:20250513T160000Z DTSTAMP:20260424T142515Z UID:3cqfs/40 DESCRIPTION:Title: Causality violations in quantum field theory? A ping-pong ball test< /a>\nby Rainer Verch (University of Leipzig) as part of Tricontinental Qua ntum Fundamentals Seminar\n\n\nAbstract\nIt has been pointed out that ther e are local operations in quantum field theory which can lead to superlumi nal effects. A prominent example is the "impossible measurements scenario" put forward by Sorkin. In this presentation\, it will be explained that s uch apparent difficulties are not a specific defect or pathology of quantu m 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 local interactions\, then there are no superluminal effects. If time al lows\, it will also be explained that the time-travel analogue scenario in quantum circuits proposed by Deutsch (D-CTC) is\, on one hand\, not relat ed to closed timelike curves in the sense of general relativity\, and on t he other hand\, can be realized also in classical statistical theories and is therefore not based on quantum mechanics.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Jan Mandrysch (IQOQI-Vienna) DTSTART:20260312T090000Z DTEND:20260312T103000Z DTSTAMP:20260424T142515Z UID:3cqfs/41 DESCRIPTION:Title: How to measure quantum fields? Implementing a causal measurement sch eme\nby Jan Mandrysch (IQOQI-Vienna) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstract\nWhile measurement processes in standa rd quantum mechanics are well understood\, the extension of these ideas to quantum field theory (QFT) remains a key challenge. In particular\, ensur ing that measurements respect fundamental principles such as relativistic causality is crucial. A persistent issue concerning measurements in QFT is \, though\, that microcausality alone is insufficient to prevent superlumi nal signaling. In this talk\, I will present a concrete scheme for measuri ng real linear scalar fields\, grounded in the Fewster-Verch measurement f ramework\, which allows to model projective and Gaussian measurements and more. The approach fully respects the principles of relativistic covarianc e\, locality\, and causality\, offering a robust solution to the challenge s of measurement in QFT.\n\nTalk has been rescheduled for 12 March 2026 at 10:00 CET.\n LOCATION: END:VEVENT BEGIN:VEVENT SUMMARY:Antoine Soulas (Choups) (University of Vienna) DTSTART:20260505T070000Z DTEND:20260505T083000Z DTSTAMP:20260424T142515Z UID:3cqfs/42 DESCRIPTION:Title: A proof that no-signalling implies microcausality in quantum field t heory\nby Antoine Soulas (Choups) (University of Vienna) as part of Tr icontinental Quantum Fundamentals Seminar\n\n\nAbstract\nMicrocausality co unts among the basic requirements that ensure the consistency of quantum f ield theories (QFT). In the literature on the foundations of QFT\, however \, an elementary derivation of microcausality from the relativistic constr aints seemed to be missing. Authors generally proceed the other way round\ , justifying the axiom as a sufficient condition to guarantee some desired properties\, typically involving properties like no-signalling\, separabi lity\, independence of operations\, tensor product structure... The aim of this work [1] is to study some logical interrelationships between fundame ntal properties in (relativistic) quantum theories\, and in particular to provide an elementary but important proof concerning microcausality that w as apparently missing in the literature.\n\nTo do so\, an operational no-s ignalling condition is first introduced in the context of quantum mechanic s\, where we prove its equivalence to an apparently weaker version (CPTP v ersion equivalent to PVM version)\, and to a property of factorisation of the evolution unitary operator\, generalising some results of [2]. We then translate this condition in QFT and prove that it implies both microcausa lity and the spin-statistics theorem\, in the ideal case of pointwise meas urements implemented in the projection postulate sense. This provides an a rgument (often invoked but apparently missing in the literature) to see mi crocausality as a necessary condition for the compatibility of spacelike s eparated operations.\n\n[1] Soulas\, Antoine. "A proof that no-signalling implies microcausality in quantum field theory." Foundations of Physics 55.2 (2025): 22.\n\n[ 2] Beckman\, David\, et al. "Causal and localizable quantum operations." Physical Review A 64 .5 (2001): 052309.\n LOCATION:https://master.researchseminars.org/talk/3cqfs/42/ END:VEVENT END:VCALENDAR