I will survey a few topics in philosophy and history of QFT that are relevant to RQI, and then focus on a central topic: the Measurement Problem. In non-relativistic QM, one version of the Measurement Problem is that the measurement theory (i.e., the Born rule and state update rules) cannot be derived from the application of the dynamics (e.g., Schrodinger equation) to a measurement scenario....
Archimedes is an experiment designed to measure the discussed interaction between vacuum fluctuations and the gravitational field. It is based on the measurement of the weight variation of a suitable stack of Casimir cavities whose vacuum energy is varied thanks to a suitable superconducting phase transition. The experiment is currently being installed and commissioned at the Sos Enattos site...
The formalism of generalized quantum histories allows a symmetrical treatment of space and time correlations, by taking different traces of the same history density matrix. We characterize spatial and temporal entanglement in this framework. An operative protocol is presented, to map a history state into the ket of a static composite system. We show, by examples, how Leggett-Garg and temporal...
In this talk, I will discuss the ways in which philosophical work on causation and physics research in quantum foundations can usefully inform and influence each other. I will introduce some important philosophical ideas about causation, including the asymmetry of causation and its relation to time-symmetry in macroscopic and microscopic physics. I will also discuss the causal modelling...
"I will review the framework for measurement in QFT introduced in joint work with Rainer Verch [1], which provides a covariant and consistent description of measurements and state updates and (as an application) resolves the ""impossible measurement"" problems raised by Sorkin long ago [2]. The framework is also known to be comprehensive in the sense that there are classes of QFTs for which...
The harvesting of quantum resources from the vacuum state of a quantum field is a central topic in relativistic quantum information. While several proposals for the harvesting of entanglement from the quantum vacuum exist, less attention has been paid to other quantum resources, such as non-stabilizerness, commonly dubbed magic and quantified by the Stabilizer Rényi Entropy (SRE). In this...
Local quantum entropies are of utmost interest in characterizing quantum fields, many-body systems, and gravity. Despite their importance, being nonlinear functionals of the underlying quantum state hinders their theoretical as well as experimental accessibility. Here, we show that suitably chosen classical entropies of standard measurement distributions capture many features of their quantum...
To understand the fundamental nature of gravity, high-precision interferometers, namely, Holometer (Fermilab), QUEST (Cardiff) and GQuEST (CalTech), seek possible evidence of spacetime fluctuations. These spacetime fluctuations, a feature common to both quantum and semiclassical models of gravity, could be characterised by two-point correlation functions. A two-point correlation function of...
Recent work has shown that communication channels between Unruh–DeWitt detectors are sensitive not only to the initial particle content of a quantum field but also to the spacetime history prior to the communication protocol. In particular, a cosmological expansion occurring before the protocol begins reduces the channel’s capacity. This implies that the noise experienced by the receiver...
Spontaneous wavefunction collapse models, such as the Continuous Spontaneous Localization (CSL) model, provide a promising approach to address the quantum measurement problem by introducing stochastic, nonlinear modifications to the Schrödinger equation. We present new experimental constraints on the CSL model derived from recent high-precision measurements of optomechanical systems rotational...
A defining signature of classical systems is “in principle measurability” without disturbance: a feature manifestly violated by quantum systems. We describe a multi-interferometer experimental setup that can, in principle, reveal the nonclassicality of a spatial superposition-sourced gravitational field if an irreducible disturbance is caused by a measurement of gravity. While one...
The existence of zero-point modes, or the so-called vacuum fluctuations, is one of the fundamental predictions of quantum field theory. From an open quantum system perspective, they constitute an omnipresent and an unavoidable environment of a charged particle. In this talk I would like to discuss if such an environment can lead to observable decoherence and compare it with fundamental...
Gravitational-wave observatories such as LIGO and Virgo have enabled a new era in multimessenger astronomy. In recent years, predictions of quantum gravity signatures in interferometers by Craig Hogan, Tom Banks, Eric Verlinde, Frank Wilczek, and Kathryn Zurek have inspired multiple new experiments deploying precision laser interferometry at smaller scales to probe such phenomena, such as the...
Recent results on electron tunneling across a potential barrier, inferred from experimental observations or obtained from theoretical models, have suggested superluminal or instantaneous barrier traversal times. We will argue, by linking the QFT property of microcausality to the wave-packet second quantized state that the tunneling dynamics is fully causal, precluding instantaneous or...
We report on the 'QUantum-Enhanced Space-Time experiment' (QUEST), which consists of two co-located Michelson interferometers with the ultimate goal of searching for signatures from the quantization of space-time. We have performed a first engineering run with QUEST which already sets new upper limits for stochastic gravitational waves in the range 13 to 80 MHz, an auxiliary result from the...
It is believed that quantum fluctuations of various fields including electromagnetic and gravitational fields are generated during inflation. On top of those, quantum fluctuations of ultralight axion fields could be generated. These fields can be naturally mixed in the history of the universe. Moreover, because of the rapid expansion of the universe, the quantum fluctuations lead to the...
Studies of extraction of entanglement from quantum fields usually consider probes that couple to independent degrees of freedom of the field, in an attempt to harvest entanglement. These studies usually rely on the specific properties of the probes and perturbative results, resulting in a nearly negligible extraction of entanglement. In this talk we will first quantify the distillable...
How do quantum systems behave in a gravitational field, and what role does operator ordering play in their quantization? This work presents a consistent framework for relativistic quantization, tackling the longstanding operator ordering problem through the introduction of arbitrary constants and by coupling internal quantum and external gravitational degrees of freedom. A general,...
In this presentation we will discuss our work on the evolution of a quantum field subject to a time-dependent, confining potential well. In particular we focus on the entanglement dynamics in the process of the construction of a confined field in a finite region (that can be seen as the construction of an optical cavity) from the field vacuum in flat free space. Furthermore, we will discuss...
I will present the effects of changes in internal energy on gravity-induced entanglement in interference experiments, which in principle allows for faster-than-light communication. By including a change in internal mass-energy due to photon absorption, we show that previous solutions to the thought experiment are insufficient, and we propose new requirements to save causality and...
While there are many similarities between mechanics and field theory (both classical and quantum), there are also some fundamental conceptual differences. Examples include (i) the existence of derivatives in directions of 3-space (not to be confused with the configuration space directions), (ii) nonlocality of the evolution operator, (iii) different (and inequivalent) notions of "particle",...
Relativistic gravitational and many non-gravitational effects are intrinsically weak in their coupling to quantum systems and, therefore, require suitable amplification. To this end, we have identified coherent collections of quantum systems, such as atom arrays, as novel coupling interfaces between relativistic, gravitational, and quantum physics. To illustrate their potential, we shall...
In this talk, we define and characterize localized causal operations in a real scalar quantum field theory, and we will show that these operations exactly correspond to those satisfying various equivalent no-signalling conditions proposed in previous works. The simplicity of this characterization allows us to define a faithful quantifier of how much a map enables faster-than-light signalling...
The possibility of quantizing fields in neighborhood of arbitrary spacetime hypersurfaces, not necessarily of Cauchy nature, lies at the core of the so called General Boundary Formulation (GBF) of quantum theory. The GBF provides a novel perspective on quantum dynamics and offers the opportunity to address problems that are challenging (or even impossible) to solve within the standard...
Superpositions of spacetimes have received considerable attention from the Relativistic Quantum Information community. The standard RQI protocol involves calculating the response of an Unruh-DeWitt detector that is coupled to a quantum field whose background spacetime exists in a quantum superposition of geometries. In this work, we propose a method to simulate such a superposition of...
We present a novel approach for detecting the weak gravitational field generated at the Large Hadron Collider (LHC) using cascaded optomechanical cavities. Our methodology exploits coherent averaging to potentially reach Heisenberg-limited sensitivity without entangled resources. In this configuration, $N$ sequentially arranged optomechanical cavities interact with a single laser pulse in the...
The formalism of open quantum systems provides a way to derive evolution equations, called master equations, for a quantum system of interest that is coupled to an environment, without the need to solve the dynamics of the environment in detail. The starting point of this talk is a master equation for a scalar field as system of interest in an environment of quantised linearised gravity from...
Gravitationally Induced Entanglement (GIE) between two levitated objects in quantum states can investigates the quantum nature of the gravitational field in a tabletop experiment. To formally treat the entangling dynamics — both unitary and open — between superpositions of quantum states of matter entangled with a qubit, the Gaussian formalism of continuous-variable systems can be extended to...
Optical clocks based on atoms and ions probe relativistic effects with unprecedented sensitivity by resolving time dilation through frequency shifts. However, all measurements of time dilation so far are effectively classical, stemming from classical motion. Here we show that the first tests of time dilation where the proper time is no longer a single classical parameter can be achieved with...
The interplay between quantum mechanics and general relativity is one of the most profound open problems in fundamental physics. After decades of purely theoretical investigations, recent experimental advances turned the prospect of a phenomenological approach into a realistic possibility. On one hand, searches for quantum gravity effects in astrophysical signals constitute nowadays an...
In the ongoing work towards observing the circular motion Unruh effect in (2+1)-dimensional analogue spacetime systems, one challenge is that the effective temperature experienced by a local detector is much smaller than the linear acceleration prediction when the detector's energy gap is small and the interaction time is long. We show that an effective temperature of the order of the linear...
We study the exchange of energy between gravitational and electromagnetic waves in a Sagnac type geometry, in analogy to an ``optical Weber bar.'' In the presence of a gravitational wave (such as the ones measured by LIGO), we find that it should be possible to observe signatures of stimulated emission or absorption of gravitons with present day technology. Apart from marking the transition...
I will give a brief overview of proposals to test the quantization of the gravitational field, particularly in terrestrial experiments. This will include entanglement experiments and "single-graviton detection". As a particular example of a non-standard gravity model that could be tested, I will discuss a recent phenomenological model of "entropic gravity" and its experimental signatures.
"Atom interferometry has emerged as a powerful tool to probe gravitational physics with unprecedented precision. In this talk, I will present two distinct experimental efforts that, while targeting different fundamental questions, share this common methodology.
The first experiment, MEGANTE, addresses a long-standing challenge in metrology: the precise determination of the gravitational...
In this talk, I will give an overview of the state of the art and key open questions of this research programme and describe the related activities of the COST Action BridgeQG (Bridging high and low energies in search of quantum gravity).
The quantum nature of gravity remains an open question in fundamental physics, lacking experimental verification. Gravitational waves (GWs) provide a potential avenue for detecting gravitons, the hypothetical quantum carriers of gravity. However, by analogy with quantum optics, distinguishing gravitons from classical GWs requires the preservation of quantum coherence, which may be lost due to...
Candidate theories of quantum gravity are widely expected to resolve the singularities predicted by general relativity. In the absence of a complete theory, singularity-free models — often referred to as regular black holes — have emerged as a compelling alternative, sidestepping the problematic causal structure of their classical counterparts. A rather ubiquitous prediction across various...
Quantum field theory in curved spacetime famously predicts that information is lost as a black hole evaporates through Hawking radiation. While many resolutions have been proposed, we consider the role of singularities in black hole evaporation. This talk will present a general model of evaporating black holes in 2D dilaton gravity, with a focus on a Bardeen-like regular black hole model. The...
Aiming to explore quantum gravity, low-energy experiments have been proposed to test whether Newtonian gravity can generate quantum entanglement or not. However, the weakness of gravity hinders experimental realization. In this talk, we propose a novel optimal method to probe gravity-induced entanglement. We consider the gravitational interaction between a particle trapped in a shallow...
Understanding physical phenomena at the intersection of quantum mechanics and general relativity remains one of the major challenges in modern physics. Among various approaches, experimental tests have been proposed to investigate the dynamics of quantum systems in curved spacetime and to examine the quantum nature of gravity in the low-energy regime. However, most previous studies have...
In their seminal 1992 paper, Bañados, Teitelboim and Zanelli (BTZ) proposed a simple charged generalization of what is now known as the spinning BTZ black hole. However, it soon became clear that this spacetime does not satisfy Maxwell equations and was thus discarded. In this talk, we will see that this incorrect original BTZ metric can actually be redeemed - it can be interpreted as a...
Can we test the quantum mechanical nature of gravitational fields? Milligram-scale optomechanical experiments present a frontier for bridging quantum mechanics and gravitational physics by aiming to strike a balance between 1) making gravitational couplings of the controlled objects dominant and 2) making the motions of these objects quantum noise dominated. Required systems necessitate...
In this talk I will discuss how modelling local, nonperturvative measurements in relativistic field theories has traditionally led to a choice between mathematical untractability and frictions with covariance, locality and causality. In this context I will argue that there is a class of detector models in which nonperturbative, local and convariant, as well as mathematically tractable results...
We establish limitations and bounds on the transmission of quantum states between gravitationally interacting mechanical oscillators under different models of gravity. This provides benchmarks that can enable tests for quantum features of gravity. Our proposal does not require the measurement of gravitationally induced entanglement and only requires final measurements of a single subsystem. We...
Black holes provide a setting to test assumptions about the interplay of quantum theory and gravity. These tests have led to several puzzles, such as the xeroxing or firewall paradox. A common feature of these puzzles is that they combine the perspectives of an infalling observer and an exterior observer, who, for fundamental reasons, have access to different systems. In quantum foundations,...
The equivalence principle imposes stringent constraints on both kinematics and dynamics of the spacetime. In my talk, I discuss how these constraints manifest in the context of black hole thermodynamics. I introduce a thought experiment involving a small black hole which uncovers violations of the strong equivalence principle. I then explore its outcomes in several gravitational theories of...
The dynamics of quantum systems in indefinite spacetimes—such as superpositions of macroscopically distinct semiclassical geometries—have been studied extensively in the contexts of quantum reference frames and quantum field theory in curved spacetimes. These studies typically assume that quantum states associated with different spacetimes (i) form a complete orthonormal basis and (ii) possess...
We nonperturbatively examine the emission rate of acceleration-induced radiation from a uniformly accelerated gapless qudit-type Unruh-DeWitt detector. We find that the emission rate can be written as Larmor’s formula multiplied by a factor that depends on the detector’s initial state. In particular, certain initial states of integer-spin detectors do not produce radiation. Although the...
Entanglement entropy in dynamical and quantum‑corrected black hole spacetimes offers a key diagnostic of quantum correlations across horizons, motivating studies of its scaling and time evolution near these critical surfaces. We investigate the entanglement entropy scaling with the horizon area in two settings. In the first analysis, we consider a massive scalar field with nonminimal curvature...
I will review some recent progresses in the characterization of the properties of spacetimes with relativistic symmetries deformed at the Planck scale (DSR), relying on the exchange of signals between DSR relativisitc observers.
In recent years, extensive studies on quantum correlations in various scenarios, such as non-inertial frames, curved spacetime, and an expanding universe have been performed [1–7]. In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we investigate the time evolution of Gaussian quantum entanglement of two bosonic modes associated with a...
Unlike a classical charged bosonic field, a classical charged fermion field on a static charged black hole does not exhibit superradiant scattering. We demonstrate that the quantum analogue of this classical process is however present. We construct a vacuum state for the fermion field which has no incoming particles from past null infinity, but which contains, at future null infinity, a...
Computational quantum field theory (CQFT) has been successful in studying the pair production of electron-positron pairs resulting from colliding laser pulses—an effect yet to be observed. It has also been successful in studying the dynamics of Klein tunneling for fermions and bosons. We extend the framework of CQFT to curved spacetimes and use it to investigate the dynamics of fermionic and...
We present a general framework for understanding the finite-time operation of relativistic quantum thermal machines, focusing on their energy optimization. As an example, we introduce an Otto thermodynamic cycle where the working medium is a qubit Unruh-DeWitt detector interacting with a massless, conformally coupled scalar field in the Hartle-Hawking vacuum of a (2+1)-dimensional BTZ black...
We present an explicit construction of a relativistic quantum computing architecture using a variational quantum circuit approach that is shown to allow for universal quantum computing. The variational quantum circuit consists of tunable single-qubit rotations and entangling gates that are implemented successively. The single qubit rotations are parameterized by the proper time intervals of...
Hawking radiation is the most celebrated result of quantum field theory on a curved background. It completed the formulation of black hole thermodynamics and initiated the black hole information loss debate. Candidate theories of quantum gravity are required to demonstrate their way of entropy counting, indicate modifications to gravitational collapse, and take a stance on the issue of...
I will report on recent findings about the generation and distribution of entanglement in Quantum Electrodynamics (QED) scattering processes. The analysis takes advantage of the complete complementarity relations, which allow for a complete characterization of both local and nonlocal properties of these fundamental quantum processes. Remarkably, it is found that maximal entanglement is...
QFT models involving detectors are usually modelled perturbatively out of necessity, however, there are certain situations when non-perturbative methods can be used. When the detector is a finite dimensional qudit, non-perturbative modelling is possible if the detector interacts suddenly and very quickly ($\delta$-switching) or if the detector is degenerate (zero energy gap). When the detector...
We will discuss the notion of causal influence and compare it to signalling. We will then show the conditions on a theory of elementary systems for the two notions to coincide. After introducing quantifiers of signalling and causal influence, we will calculate them for special quantum channels. The discussion will proceed reviewing the main open problems related to the notion of causal...
What happens when one measures a quantum system in a relativistic setting? We will address the challenge of consistently updating quantum states after selective measurements in a relativistic spacetime. Standard updates along the future lightcones preserve causality but break correlations between causally disconnected parties, whereas updates along the past lightcone can either imply...
One of the most basic expectations of quantum gravity is that gravitational fields can be placed in a state of superposition, analogous to what can be done for electromagnetic fields. However in a relativistic context a gravitational field is equivalent to a particular spacetime, and so a superposed gravitational field is a superposed spacetime. Rather than consider how such a state might...
Models for gravitationally induced decoherence can be formulated in the framework of open quantum systems, where gravity is chosen as the environment and quantized together with the system under consideration. Existing phenomenological models often take the Lindblad equation as a starting point for the master equation, while from the perspective of quantum gravity approaches, an underlying...
I will introduce and motivate the Hopf-algebraic (quantum group) description of isometries in noncommutative spacetimes, emphasizing the quantum nature of transformations between reference frames. In this context, the notion of reference frame itself must acquire quantum properties. I will then overview recent work describing quantum reference frames via quantum groups of frame...
The idea of judicious selection of boundary conditions has been recently advanced to meaningfully enhance some low cross section quantum field theoretic events. In this talk, we will discuss some recent proposals of proper selection of mode functions to identify and amplify many interesting effects like acceleration radiation, Unruh thermality, Entanglement harvesting and Field-Field...
The Unruh effect, a fundamental prediction of quantum field theory, postulates that a uniformly accelerated observer perceives the vacuum as a thermal bath. Direct experimental verification remains a formidable challenge due to the minuscule magnitude of the effect under linear acceleration. We have previously proposed a tabletop experiment utilizing the circular motion of fluxon-antifluxon...
Causal modelling frameworks link observable correlations to causal explanations, which is a crucial aspect of science. These models represent causal relationships through directed graphs, with vertices and edges denoting systems and transformations within a theory. Most studies focus on acyclic causal graphs, where well-defined probability rules and powerful graph-theoretic properties like the...
More than a century after the birth of quantum theory, the question of which properties and phenomena are fundamentally quantum remains under active investigation. In this talk, I will discuss when and to what extent quantumness can be unambiguously associated with an open quantum system that is sequentially measured at different times. Central to our analysis are the quantum regression...
Analogue Hawking radiation from acoustic horizons is now a well-established phenomenon, both theoretically and experimentally. Its persistence, despite the modified dispersion relations characterizing phonons in analogue spacetimes, represents an evidence of the robustness of this effect against the ultraviolet non-relativistic modification of the particles' behavior. Previous theoretical...
Gravity simulators enable the study of black-hole quasinormal modes (QNMs) in controlled experimental settings. However, realistic laboratory setups introduce two key effects absent in traditional gravitational QNM analyses: dispersion and spatial confinement. The former introduces Lorentz-breaking terms in the wave equation, as encountered in modified gravity theories, whereas the latter...
The theory of relativity fundamentally reshaped our understanding of space and time, introducing conceptual shifts often illustrated explicitly through apparent paradoxes. Among these, the twin paradox stands out by clearly demonstrating how two observers following different spacetime trajectories can experience distinct elapsed times. Physically meaningful statements about elapsed time...
Gravitational wave studies and detection efforts have traditionally focused on their effects on test masses and geodesic deviation. In contrast, we show that gravitational waves can nontrivially influence spontaneous emission from point-like atoms, inducing directionality in the emission pattern and generating sidebands in the spectrum. We examine how much information about the gravitational...
Considering the problems to extract near-term testable predictions from theories of quantum gravity, a promising alternative is to instead start with phenomenological approaches. One such phenomenon, that might be rather generic, is indefinite causal structure: The dynamic causal structure of general relativity gets combined with quantum indeterminism. The most established framework to...
Experimental studies of information in continuous—variable quantum systems have thus far been highly limited due to the difficulty of accessing the full state of the system. Recently, novel reconstruction methods for Gaussian states — those fully characterised by mean and covariance — have been utilised, enabling the verification of the area-law scaling of mutual information in a...
We present a unified theoretical framework that combines a covariant Generalized Uncertainty Principle with a dynamical momentum‑space geometry. Using normal‑coordinate methods, we show that the extrinsic curvature of constant‑momentum hypersurfaces induces covariant deformations of the canonical commutators, yielding noncommutative position operators. Simultaneously, the momentum‑space metric...
In this talk, I will introduce a proposal for a quantum computing model that leverages a qubit's motion to suppress decoherence while enabling quantum gates. By treating the qubit as a moving Unruh-DeWitt detector interacting with a quantum field in a cavity, we use its trajectory to eliminate dominant decoherence channels—an effect known as acceleration-induced transparency. One-qubit gates...
Starting from operationally motivated principles, we derive a relational theory of local observables in Minkowski spacetime from which the notion of scalar quantum fields naturally emerges. We expand on quantum reference frames in spacetime and demonstrate that most properties of quantum fields arise as direct consequences of constraints on quantum reference frames -- that is, quantum fields...
Backaction plays a fundamental role in measurements made on quantum systems. In this talk I will discuss the role of backaction in quantum simulators on analogue spacetime, presenting both a non-perturbative treatment of backaction for an analogue realization of the circular Unruh effect and a general analogy incorporating perturbative backaction for Unruh-deWitt detectors in (2+1) dimensions....
Implementing RQI protocols such as entanglement harvesting in superconducting circuits requires moving beyond idealized UDW detector models. These implementations use superconducting qubits tunably coupled to transmission lines, which serve as one-dimensional quantum fields. We will present a series of upgrades to UDW detector models needed to capture such experimental implementations, and...
The Page-Wootters framework introduces a covariant observable for a physical system, allowing it to serve as a time reference—a clock—to describe the dynamics of a system of interest. Within this framework, standard Schrödinger dynamics is recovered when the clock and system do not interact. However, interactions generally lead to time-nonlocal and potentially nonunitary dynamics. We show that...
I review a number of theoretical results suggesting that gravitational (notably, cosmological) dynamics can be reproduced in the hydrodynamic regime of quantum many-body systems, and argue for a change in perspective (based on a relational understanding of spacetime physics and on these recent results) on what analogue simulations should strive for, to reproduce cosmology also in the lab. More...
Viewing frames of reference as physical systems, subject to the same laws as the systems they describe, is central to the relational approach in physics. Under the assumption that quantum mechanics universally governs all physical entities, this perspective naturally leads to the concept of quantum reference frames (QRFs). In this talk, I will discuss the perspective-dependence of position and...
One of the defining features of gauge theories is that they describe physics redundantly, in a way that is insensitive to certain local details. This redundancy is akin to how quantum error correcting codes (QECCs) protect quantum information from local errors by redundantly encoding logical states into a larger physical space. In this talk, I will show that this analogy is not merely a...
In sonic models of relativity, observers outside the sonic medium perceive the violation of ordinary Lorentz symmetry, while agents measuring distances and durations using sound pulses within the medium don't. Surprisingly, these "sonic observers" will interpret the physics of ordinary particles (like photons) as violating their own sonic Lorentz symmetries. In previous work, we argued that...
We propose a special relativistic framework for quantum mechanics. It is based on introducing a Hilbert space for events. Events are taken as primitive notions (as customary in relativity), whereas quantum systems (e.g. fields and particles) are emergent in the form of joint probability amplitudes for position and time of events. Textbook relativistic quantum mechanics and quantum field theory...
By describing the properties of one quantum system relative to another (treated as a quantum reference frame), we can construct a relational picture of physics that reduces or eliminates reliance on idealised background structures such as classical coordinates. When applied to time, this relational approach offers a compelling resolution of the "problem of time" in canonical approaches...
We model relativistic equations of motion, i.e. the physics of first quantization, using a port-based teleportation protocol. The entanglement resource is found in a quantum field's vacuum, and the measurement needed for a teleportation protocol is found in the interaction between a piece of matter and the vacuum of a quantum field. In this way, we find an interesting mapping between...
Causal set theory is an approach to quantum gravity that proposes that spacetime is fundamentally discrete and the causal relations among the discrete elements play a prominent role in the physics. Progress has been made in recognizing and understanding how some continuumlike features can emerge from causal sets at macroscopic scales, i.e., when the number of elements is large. An important...
Using the Feynman-Vernon influence functional approach, we study the effects of quantum noise of gravitons on particles. These effects manifest as a stochastic tensorial force whose correlator is given by the graviton noise kernel associated with the Hadamard function of the quantized gravitational field. We solve the corresponding Langevin equation to obtain the fluctuations of particle...
Exploring the dynamics of the early universe and black holes unveils profound insights into the interplay between general relativity and quantum fields. Important phenomena emerge when gravitational and/or field interactions are strong, and/or when quantum effects become prominent. Notable examples include Hawking's proposal on the evaporation of black holes, Penrose's conjecture on the...
A selection of 8 poster contributors give a "flash talk", i.e. a short talk of around 3 minutes, presenting their poster. The list is the following:
- "Cross-scale correlations and interactions in wavelet-based quantum field theory" by Dominic Lewis.
- "Kinematic and energy properties of dynamical regular black holes" by Sebastian Murk.
- "Inference and Fine-Tuning in Causal Explanations of...
"The Einstein Equivalence Principle (EEP), stating that all laws of physics take their special-relativistic form in any local inertial (classical) reference frame, lies at the core of general relativity.
Because of its fundamental status, this principle could be a very powerful guide in formulating physical laws at regimes where both gravitational and quantum effects are relevant. The...
Three foundational aspects will be discussed in which relational approaches offer insight into developing a background-independent description of quantum spacetime: the notions of events, diffeomorphisms and the assumption underlying quantum probability assignments. The first aspect concerns the notion of events and their localisation, which fundamentally differ in quantum theory and...
Quantum non-Markovianity—the influence of an external memory on a system’s dynamics—has posed longstanding technical and conceptual challenges. Recently, significant insight was transferred from the field of quantum causal structures, highlighting the role of interventions and multi-time correlations. In this talk, I will review the causal-structure approach to non-Markovian multi-time...
"Quantum position verification (QPV) plays a crucial role in secure quantum communication and nonlocal quantum computation. It ensures that a party involved in a communication protocol is at its claimed location, which is essential for secure communication, distributed computing, and location-based services.
In 2012, we established a tight connection between the security of QPV schemes and...
In the presence of symmetries, observables are defined as quantities that remain invariant under transformations of reference frames or coordinates. Recently, the concept of quantum reference frame (QRF) transformations has emerged, where reference frames themselves are treated as quantum systems subject to superposition and entanglement. This generalization extends the classical notion of...
I show that a manifold’s geometry can be reconstructed from its vibrational spectrum—provided one also measures the rates at which resonant modes nonlinearly excite one another under strong driving. Applied to spacetime, this yields a generalized Noether theorem: the specific pattern of energy-momentum non-conservation in quantum field theory on curved backgrounds, encoded in the scattering...
I will emphasise what I consider as the checkpoints on the road to quantum gravity as a part of my research program and ideology, the four points, viz., the prescription of gravity-matter interaction, observer dependence, resolution of issues and paradoxes in quantum fields in curved spacetimes (QFT in CST), and probes of quantum effects in gravity. QFT in CST has been very successful in...
Non-signalling conditions are usually understood to encode minimal requirements that any (quantum) systems put into spatial arrangements must satisfy in order to be consistent with special relativity. Recent works have argued that in scenarios involving more that two parties, conditions compatible with relativistic causality do not have to satisfy all possible non-signalling conditions but...
In this study, we explore a relativistic quantum Otto heat engine with a qutrit as the working substance interacting with a quantum scalar field in curved spacetime. Unlike qubits, which extract work by simply expanding or shrinking a single energy gap, qutrits allow multiple energy gaps to be adjusted independently, enabling more versatile work extraction in the quantum Otto cycle. We derive...
The localization problem in relativistic quantum theory has persisted for more than seven decades, yet it is largely unknown and continues to perplex even those well-versed in the subject. At the heart of this problem lies a fundamental conflict between localizability and relativistic causality, which can also be construed as part of the broader dichotomy between measurement and unitary...
A key prediction of quantum field theory that has yet to be tested experimentally is the existence of correlations between different regions in a quantum field. It is hypothesized that this phenomenon can be measured using the entanglement harvesting protocol, a process by which entanglement between detectors is induced due to their interaction with a quantum field in its vacuum state....
With the settings in JHEP04(2024)065, we calculate the quantum radiation emitted by relativistic single-electron wavepackets in Minkowski vacuum. We show that the quantum radiation of a single-electron wavepacket at rest is exactly zero. For a uniformly accelerated electron, the quantum radiated power grows in time exponentially. This indicates that our linear approximation which breaks the...
The Unruh effect asserts that the experience of uniformly linearly accelerated observer with proper acceleration a is indistinguishable from that of a static observer in a thermal bath whose temperature is given by T=a/(2π). This prediction of Minkowski quantum field theory continues to inspire both theoretical and experimental investigations. More generally, non-inertial trajectories—such as...
A quantum object in free fall is extended by virtue of quantum uncertainty, and therefore experiences tidal forces and other relativistic effects. As a result, entropy and purity affect geodesic motion and acquire weight, an observation that has broad implications from free-fall experiments to Hawking radiation. If the object's position is correlated in at least two directions, a complete...
Detector-based measurements in QFT describe how information about a quantum field's state can be extracted through a non-relativistic system moving in spacetime. This way, the standard quantum measurement postulate can be extended to QFT. The postulate consists of two parts: the Born rule, which relates outcomes to the probability of their occurrence, and the Lüders rule, which prescribes how...
In this talk, we consider the quantum Langevin equation for the Caldeira-Leggett model with an arbitrary time-dependent coupling constant. We solve this equation exactly by employing a train of Dirac-delta switchings. This method also enables us to visualize the memory effect in the environment. Furthermore, we compute the two-time correlation functions of the system's quadratures and show...
Particle detector models are widely used in quantum field theory as local probes of quantum fields. A common simplifying assumption is that the field-detector interaction is sufficiently weak that the detector's back-action on the field can be neglected. However, detectors necessarily perturb the systems they probe. In this talk, we explore the back-action of a pointlike Unruh–DeWitt detector...
In recent years, various frameworks have been proposed for the study of quantum processes with indefinite causal order. Beyond the standard quantum formalism, these processes do not only feature computational and communication advantages, but are also of foundational and philosophical interest regarding e.g. notions of physical events, quantum reference frames and potential theories of quantum...
The effect of black holes on entanglement harvesting has been of considerable interest over the past decade. Research involving stationary Unruh-DeWitt (UDW) detectors near a (2+1)-dimensional Bañados-Teitelboim-Zanelli (BTZ) black hole has uncovered phenomena such as entanglement shadows, entanglement amplification through black hole rotation, and differences between bipartite and tripartite...
Since 1970, the phenomena of particle production in curved/ flat spacetime has been of consistent interest to many physicists. This has led us to remarkable findings such as Unruh effect, Hawking radiation, cosmological particle production and many more. Subsequently, to investigate its experimental relevance, the Unruh DeWitt (UD) detector model, based on atom-field interaction, has been...
Cosmological particle creation is the phenomenon by which the expansion of spacetime results in the production of particles of a given quantum field in that spacetime. In this paper, we study this phenomenon by considering a multi-level quantum particle detector in de Sitter spacetime coupled to a massless real quantum scalar field. Rather than considering a fixed classical trajectory for the...
A well-established approach to enhance precision of quantum metrological protocols involves preparing multiple probes in an entangled state before interaction with the measured system. Fundamental precision limits for such entanglement-based protocols have been known for more than decade. Nevertheless, quantum mechanics permits more advanced strategies that employ quantum error correction,...
We generalize Pearl´s definition of causal influence from classical random variables and probability distributions to the quantum world. For two systems $A$, $B$, embedded in a common environment $C$ that might represent quantum fields and mediate an interaction between $A$ and $B$, we find the necessary and sufficient condition on a unitary U that jointly propagates $A,B,C$ for a causal...
I will discuss the existence conditions of stationary sonic black hole configurations in the presence of quantum fluctuations, assessed by computing the quantum depletion of the many-body system due to both interactions and Hawking radiation. Bogoliubov theory and the conventional neglect of backreaction in describing the analog Hawking process will thereby be validated, and the resulting...
