arXiv subjects

Nicola Pranzini

Publications and source records attributed to Nicola Pranzini.

12 recordsLinked to original sources

arXiv2026

Quantum Darwinism and the quality of Petz recovery

According to Quantum Darwinism, system-environment interactions both einselect particular system properties and encode them redundantly in many independent subsets of the environment, called fragments. This redundancy implies that an observer can recover the einselected information by accessing just one such fragment. However, the protocol by which such reconstruction should occur is often left unspecified. Considering a system $Γ$ interacting with a multipartite environment $Ξ$, we investigate whether, and under what conditions, the einselected state of $Γ$ can be recovered from environmental fragments using the Petz recovery map. We show that the fidelity between the system's initial state and the state reconstructed via Petz recovery develops a plateau as a function of the fragment size. Our results are supported by both analytical arguments and numerical simulations of large but tractable models.

quant-ph↗

arXiv2026

Induced Resource Theories and Harvesting via Quantum Probes

We consider scenarios in which a quantum system with a well-defined resource theory is used as a probe to interact with an environment, such as a quantum field, for which a resource-theoretic description is absent or incomplete. We clarify if and how the harvesting of a resource in the probe can tell us about the state of the environment. This is particularly ambiguous when the probe-environment interaction is not a free operation, or the concept of such free operations cannot be defined altogether. We propose a framework and precise conditions under which it becomes possible to interpret resource generation on the probe as evidence of resources in the environment, thereby introducing an effective notion of resources for the latter. Our results clarify in which sense resources can be said to be harvested from the environment and provide a systematic way to analyse such processes beyond fully controlled resource-theoretic settings. More generally, this work may provide a step towards a more general understanding of the interplay of different quantum resources.

quant-ph↗

arXiv2026

Detector-based measurement-induced state updates in AdS/CFT

Conventional understandings of quantum theory hold that measurements change the state of an observed system following the Lüders update rule. Textbooks describe the application of this idea to non-relativistic systems, but extensions to relativistic and gravitating systems encounter subtleties. One consistent approach is via detector-based measurements. We study the effects of such measurements in a CFT with a holographic dual. We work out the boundary space-time regions associated to a Lüders update and how the outcome extends to modifications of the bulk gravity state. We explore information-theoretic consequences of this picture, and relate the information extracted by a measurement to updates of the semiclassical parameters of the bulk state.

hep-th↗

arXiv2026

Quantum model for black holes and clocks

We consider a stationary quantum system consisting of two non-interacting yet entangled subsystems, $Ξ$ and $Γ$. We identify a quantum theory characterizing $Ξ$ such that, in the quantum-to-classical crossover of the composite system, $Γ$ behaves as a test particle within the gravitational field of a Schwarzschild Black Hole (SBH) near its event horizon. We then show that this same quantum theory naturally provides a representation of $Ξ$ in terms of bosonic modes, whose features match those of the Hawking radiation; this facilitates the establishment of precise relations between the phenomenological parameters of the SBH and the microscopic details of the quantum model for $Ξ$. Finally, we recognize that the conditions used to characterize $Γ$ and $Ξ$ coincide with those required by the Page and Wootters mechanism for identifying an evolving system and an associated clock. This leads us to discuss how the quantum model for $Ξ$ endows the SBH with all the characteristics of a "perfect" clock.

quant-ph↗

arXiv2024

Gravitational quantum speed limit

While playing an important role in the foundations of quantum theory, Quantum Speed Limits (QSL) have no role in discussions about the search for quantum gravity. We fill this gap by analysing what QSL arises when superposing spherically symmetric masses in canonical quantum gravity. By this procedure, we find that the quantum mechanical Mandelstam-Tamm and Margolus-Levitin bounds can be improved by superposing a spherically symmetric, static and asymptotically flat spacetime between states with different ADM energies and mass densities. We discuss the feasibility and significance of measuring times via these superpositions.

gr-qc↗

arXiv2024

Harvesting magic from the vacuum

Magic is the quantum resource allowing a quantum computer to perform operations that cannot be simulated efficiently by classical computation. As such, generating magic in a quantum system is crucial for achieving quantum advantage. This letter shows that magic can be harvested by a three-level Unruh-DeWitt detector (a qutrit) interacting with a quantum field in an initial vacuum state. While the idea of extracting resources from Quantum Field Theories (QFT) was born from the harvesting of entanglement, our result extends the protocol to evolve a qutrit from a non-magical state to a magical one, making it possible to generate magic from QFT.

quant-ph↗

arXiv2024

Quantum Time and the Time-Dilation induced Interaction Transfer mechanism

Given a bipartite quantum system in an energy eigenstate, the dynamical description for one component can be derived via entanglement using the other component as a clock. This is the essence of the Page and Wootters mechanism. Moreover, if the clock is subject to a gravitational-like interaction, relative time evolution is then described by a Time-Dilated Schrödinger equation, in which the so-called Redshift Operator describes a purely quantum effect, analogue to gravitational time-dilation. Here we adopt a non-perturbative approach and present a finite-dimensional generalisation of this mechanism, expressing the quantum time-dilation effect as an effective interaction involving previously non-interacting system components. We name this a Time-Dilation induced Interaction Transfer (TiDIT) mechanism and discuss an example using two coupled spins as a quantum clock model. Our approach is suitable for implementations in current quantum technology and provides a new tool for exploring gravity at the intersection with quantum physics.

quant-ph↗

arXiv2024

Repeated measurements on non-replicable systems and their consequences for Unruh-DeWitt detectors

The Born rule describes the probability of obtaining an outcome when measuring an observable of a quantum system. As it can only be tested by measuring many copies of the system under consideration, it does not hold for non-replicable systems. For these systems, we give a procedure to predict the future statistics of measurement outcomes through Repeated Measurements (RM). This is done by extending the validity of quantum mechanics to those systems admitting no replicas; we prove that if the statistics of the results acquired by performing RM on such systems is sufficiently similar to that obtained by the Born rule, the latter can be used effectively. We apply our framework to a repeatedly measured Unruh-DeWitt detector interacting with a massless scalar quantum field, which is an example of a system (detector) interacting with an uncontrollable environment (field) for which using RM is necessary. Analysing what an observer learns from the RM outcomes, we find a regime where history-dependent RM probabilities are close to the Born ones. Consequently, the latter can be used for all practical purposes. Finally, we numerically study inertial and accelerated detectors, showing that an observer can see the Unruh effect via RM.

quant-ph↗

arXiv2024

Detector-based measurements for QFT: two issues and an AQFT proposal

We present and investigate two issues within the measurement scheme for QFT presented by J. Polo-Gómez, L. J. Garay and E. Martín-Martínez in "A detector-based measurement theory for quantum field theory". We point out some discrepancies that arise when the measurement scheme is applied to contextual field states and show that $n$-point function assignments based on local processing regions sometimes lead to inconsistencies. To solve these issues, we modify the measurement scheme to use non-relativistic detectors to induce an update rule for algebraic states in the Haag-Kastler formulation of quantum field theory. In this way, $n$-point functions can be consistently evaluated across any region having a definite causal relation with measurements.

quant-ph↗

arXiv2024

A formula for the overlap between Generalized Coherent States of any rank one simple Lie algebra

We provide a formula for computing the overlap between two Generalized Coherent States of any rank one simple Lie algebra. Then, we apply our formula to spin coherent states (i.e. $\mathfrak{su}(2)$ algebra), pseudo-spin coherent states (i.e. $\mathfrak{su}(1,1)$ algebra), and the $\mathfrak{sl}(2,\mathbb{R})$ subalgebras of Virasoro. In all these examples, we show the emergence of a semi-classical behaviour from the set of coherent states and verify that it always happens when some parameter, depending on the algebra and its representation, becomes large.

quant-ph↗

arXiv2023

On the reliability and accessibility of quantum measurement apparatuses

We propose a classification of measurement apparatuses based on their reliability and accessibility. Our notion of reliability parameterises the possibility of getting unexpected wrong results when using the apparatus in a given time window, and the one of accessibility describes the energy cost required to make the apparatus interact with a measured system. The classification is obtained by relating an apparatus's reliability and accessibility to the time dependence of the overlap of its pointer states. As an example, we study a one-to-all qubit interaction in which all the qubits act as a measurement apparatus for the one. This model shows that using randomly selected couplings results in accessible but unpredictable measurement apparatuses. Conversely, apparatuses with uniform coupling exhibit higher reliability but are energetically more costly.

quant-ph↗

arXiv2022

Threshold size for the emergence of a classical-like behaviour

In this work we design a procedure to estimate the minimum size beyond which a system is amenable to a classical-like description, i.e. a description based on representative points in classical phase-spaces. This is obtained by relating quantum states to representative points via Generalized Coherent States (GCS), and designing a POVM for GCS discrimination. Conditions upon this discrimination are defined, such that the POVM results convey enough information to meet our needs for reliability and precision, as gauged by two parameters $ε$, of our arbitrary choice, and $δ$, set by the experimental apparatus, respectively. The procedure implies a definition of what is meant by "size" of the system, in terms of the number $N$ of elementary constituents that provide the global algebra leading to the phase-space for the emergent classical-like description. The above conditions on GCS discrimination can be thus turned into $N>N_{\rm t}(ε,δ)$, where $N_{\rm t}(ε,δ)$ is the threshold size mentioned in the title. The specific case of a magnetic system is considered, with details of a gedanken experiment presented and thoroughly commented. Results for pseudo-spin and bosonic systems are also given.

quant-ph↗