arXiv subjects

Luca Pezzè

Publications and source records attributed to Luca Pezzè.

At least 19 recordsLinked to original sources

arXiv2026

Many-body gravitating quantum systems with Bose-Einstein condensates and dipolar analogue

Quantum probes of gravity in the Newtonian regime, based on mass-energy equivalence in clocks or spatial superpositions in interferometers, share a common description in terms of an effective qubit-qubit coupling. Here we extend this framework to atomic ensembles, regarded as interacting collective qudits. The many-body enhancement boosts the signal-to-noise and increases the effective interaction rate, facilitating the observation of gravitationally-induced entanglement and decoherence, certified by metrological witnesses based on local and collective spin squeezing. We further identify trapped bimodal Bose-Einstein condensates with long-range interactions, including dipolar couplings, as a programmable analogue platform for simulating gravitating quantum dynamics at accessible time and energy scales. Extending the protocol to a sensor network broadens the entanglement-detection window.

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arXiv2026

Programmable Cavity Squeezing for Distributed Sensing in a Tweezer Array

Field sensing with state-of-the-art atom interferometers is restricted to the use of uncorrelated devices op- erating in parallel. We can overcome this limitation by using distributed sensing protocols where quantum correlations among spatially-separated devices are engineered in the spatial mode carrying the signal. We show that a tweezer array in a cavity offers an ideal testbed to engineer quantum states for distributed sensing, with the possibility to generate entanglement both within and between the clouds. The competition between local and intercloud cavity-mediated exchange allows the sign and spatial pattern of the intercloud couplings to select the squeezed mode. For two ensembles, positive coupling produces uniform collective squeezing, whereas negative coupling generates strong staggered, nonlocal squeezing. A semiclassical analysis reveals a counter-twisting- like phase-space flow, qualitatively distinct from standard one-axis twisting. The analysis and results can be further generalized to a larger number of ensembles. We apply the scheme to differential Ramsey interferometry with common phase noise spanning the full 2 πrange, the resulting staggered states reduce the phase uncertainty below the standard quantum limit, with an ellipse estimator approaching the Cramèr-Rao bound. These results establish programmable cavity interactions as a scalable route to entanglement tailored to distributed signals.

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arXiv2026

Rotation Sensing via Josephson-frequency Splitting in a Toroidal Superfluid

We show that a toroidal superfluid interrupted by $n$ tunneling barriers realizes a compact Josephson gyroscope with an $n$-enhanced response to rotation. In the small-amplitude regime, we derive analytically the normal mode spectrum of the coupled population-phase oscillations. In the absence of rotation, pairs of modes are degenerate: a finite angular velocity $Ω$ lifts this degeneracy through a Doppler shift, producing a frequency splitting that grows linearly with both $Ω$ and $n$. Full numerical simulations confirm this prediction and reveal long-lived two-frequency beatings, in sharp contrast with the monochromatic Josephson oscillations of the nonrotating system. These beatings provide a direct rotation signal with estimation uncertainty scaling as $ΔΩ\sim n^{-3/2}$, while remaining robust against imperfections and dynamical excitations. These results identify multi-junction toroidal superfluids as scalable, micrometer-size rotation sensors compatible with current experimental platforms.

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arXiv2026

Increasing the stability of a superfluid in a rotating necklace potential

Recent experiments have probed the stability of ring superfluids in the presence of Josephson barriers or Gaussian impurities. Here we present a theoretical analysis that extends beyond the regimes explored so far. We study the onset of dynamical instabilities in a ring superfluid, addressing both tunneling and hydrodynamic regimes. The stability of the system is controlled by the effective rotation frequency $ω$, given by the difference between the initial quantized circulation and the frequency of barrier rotation. The instability occurs when $ω$ overcomes a critical value $ω_c$. We show that $ω_c$ increases approximately linearly with the number of barriers, with a slope set by the barrier height and width. When the system is quenched into the dynamically unstable regime, it emits multiple solitons, which can switch or even reverse the direction of circulation. The stabilization mechanism is robust against imperfections of the potential and does not require a perfectly periodic array of barriers. In particular, we find that adding a disordered speckle potential to an ordered array of barriers can further increase $ω_c$: disorder can therefore make a ring superfluid more resilient to dynamical instabilities.

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arXiv2026

Finite-Shot Sensitivity for Moment Estimation in Quantum Metrology

The quantum Cramér-Rao bound can be saturated only asymptotically and does not specify how many measurements are needed for a concrete estimator to approach it. We develop a finite-measurement theory for method-of-moments estimation, where the parameter is inferred from the sample mean of a calibrating observable rather than from the full likelihood. For general quantum statistical models, the expansion is written in terms of the calibration curve and the central moments of the measured observable. Nonlinear calibration curves make the usual moment estimator biased at finite measurement number; we construct a bias-corrected estimator with bias $O(ν^{-3})$. This gives sensitivity corrections beyond the leading error-propagation term of the chosen moment protocol. We identify a general density-matrix condition under which the full $1/ν^2$ correction vanishes. In unitary examples, the leading residual correction appears at order $1/ν^3$, is governed by calibration curvature, and can be reduced or cancelled by higher-rank components of the same measured observable. The resulting thresholds quantify how many measurements are needed before the asymptotic sensitivity of a moment-estimation protocol is operationally visible.

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arXiv2026

Hierarchy of saturation conditions for multiparameter quantum metrology bounds

The quantum Cramér-Rao (QCR) bound sets the ultimate local precision limit for unbiased multiparameter estimation. Unlike in the single-parameter case, however, its saturability is not generally guaranteed and is often analyzed through a hierarchy of commutativity-based conditions. Here, we resolve the logical structure of these conditions for unitary parameter-encoding transformations. We identify strict separations among the conditions, reveal previously overlooked gaps in their implications, and construct explicit counterintuitive examples that expose the boundaries among distinct classes. In particular, we show that commutativity of the parameter-encoding generators alone does not guarantee saturation of the QCR bound when realistic noise leads to mixed probe states. Our results provide a systematic classification of saturation conditions in multiparameter quantum metrology and clarify fundamental precision limits of noisy distributed quantum sensing beyond idealized pure-state regimes.

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arXiv2026

Hong-Ou-Mandel interference of more than 10 indistinguishable atoms

When two indistinguishable bosons interfere at a beam splitter, they both exit through the same output port. This foundational quantum-mechanical phenomenon, known as the Hong-Ou-Mandel (HOM) effect, has become a cornerstone in the field of quantum information. It also extends to many indistinguishable particles, resulting in complex interference patterns. However, despite of its fundamental and applied interest, the many-particle effect has only been observed in notoriously lossy photonic systems, but a realization with atomic systems has remained elusive until now. Here, we demonstrate HOM interference with up to 12 indistinguishable neutral atoms in a system with negligible loss. Our single-particle counting clearly reveals parity oscillations, a bunching envelope and genuine multi-partite entanglement, defining features of the multi-particle HOM effect. Our technique offers the potential for scaling to much larger numbers, presenting promising applications in quantum information with indistinguishable particles and Heisenberg-limited atom interferometry.

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arXiv2026

Robust multipartite entanglement in dirty topological wires

Identifying and characterizing quantum phases of matter in the presence of long range correlations and/or spatial disorder is, generally, a challenging and relevant task. Here, we study a generalization of the Kiteav chain with variable-range pairing and different site-dependence of the chemical potential, addressing commensurable and incommensurable modulations as well as Anderson disorder. In particular, we analyze multipartite entanglement (ME) in the ground state of the dirty topological wires by studying the scaling of the quantum Fisher information (QFI) with the system's size. For nearest-neighbour pairing the Heisenberg scaling of the QFI is found in one-to-one correspondence with topological phases hosting Majorana modes. For finite-range pairing, we recognize long-range phases by the super-extensive scaling of the QFI and characterize complex lobe-structured phase diagrams. Overall, we observe that ME is robust against finite strengths of spatial inhomogeneity. This work contributes to establish ME as a central quantity to study intriguing aspects of topological systems.

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arXiv2026

Semi-classical geometric tensor in multiparameter quantum information

The discrepancy between quantum distinguishability in Hilbert space and classical distinguishability in probability space is expressed by the gap between the quantum and classical Fisher information matrices (QFIM and CFIM, respectively). This intrinsic quantum obstruction is generally not saturable and plays a central role in both fundamental insights and practical applications in modern quantum physics. Here, we develop a geometrical framework for this gap by introducing the notion of semi-classical geometric tensor (SCGT). We relate this quantity to the quantum geometric tensor (QGT), whose real part equals the QFIM. We prove the matrix inequality between QGT and SCGT, which sharpens the standard inequality between QFIM and CFIM and provides novel multiparameter information bounds: the real part of the SCGT reproduces the CFIM plus an additional nonnegative contribution capturing quantum obstruction. This further motivates a natural extension of the Berry phase to the semi-classical setting.

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arXiv2026

A geometric criterion for optimal measurements in multiparameter quantum metrology

Determining when the multiparameter quantum Cramér--Rao bound (QCRB) is saturable with experimentally relevant single-copy measurements is a central open problem in quantum metrology. Here we establish an equivalence between QCRB saturation and the simultaneous hollowization of a set of traceless operators associated with the estimation model, i.e., the existence of complete (generally nonorthogonal) bases in which all corresponding diagonal matrix elements vanish. This formulation yields a geometric characterization: optimal rank-one measurement vectors are confined to a subspace orthogonal to a state-determined Hermitian span. This provides a direct criterion to construct optimal Positive Operator-Valued Measures(POVMs). We then identify conditions under which the partial commutativity condition proposed in [Phys. Rev. A 100, 032104(2019)] becomes necessary and sufficient for the saturation of the QCRB, demonstrate that this condition is not always sufficient, and prove the counter-intuitive uselessness of informationally-complete POVMs.

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arXiv2025

Quantum Chaos, Randomness and Universal Scaling of Entanglement in Various Krylov Spaces

Multipartite entanglement is a crucial resource for advancing quantum technologies, with considerable research efforts directed toward achieving its rapid and scalable generation. In this work, we derive an analytical expression for the time-averaged quantum Fisher information (QFI), enabling the detection of scalable multipartite entanglement dynamically generated by all quantum chaotic systems governed by Dyson's ensembles. Our approach integrates concepts of randomness and quantum chaos, demonstrating that the QFI is universally determined by the structure and dimension of the Krylov space that confines the chaotic dynamics. In particular, the QFI ranges from $N^2/3$ for $N$ qubits in the permutation-symmetric subspace (e.g. for chaotic kicked top models with long-range interactions), to $N$ when the dynamics extend over the full Hilbert space with or without bit reversal symmetry or parity symmetry (e.g. in chaotic models with short-range Ising-like interactions). In the former case, the QFI reveals multipartite entanglement among $N/3$ qubits and highlights the power of chaotic collective spin systems in generating scalable multipartite entanglement. Interestingly this result can be related to isotropic substructures in the Wigner distribution of chaotic states and demonstrates the efficacy of quantum chaos for Heisenberg-scaling quantum metrology. Finally, our general expression for the QFI agrees with that obtained for random states and, differently from out-of-time-order-correlators, it can also distinguish chaotic from integrable unstable spin dynamics.

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arXiv2025

Joint estimation of phase and uncorrelated dephasing in a differential quantum interferometer

Precise measurements in optical and atomic systems often rely on differential interferometry. This method allows to handle large and correlated phase noise contributions -- such as environmental vibrations, thermal fluctuations, or instrumental drifts -- preventing them from blurring the signal. To date, this approach has primarily focused on extracting the differential phase shift. However, valuable information about the system is also contained in the width of uncorrelated phase fluctuations. In this work, we present a maximum likelihood approach for the simultaneous estimation of both the differential phase shift and the width of uncorrelated phase noise. Unlike conventional methods, our technique explicitly accounts for the data spreading and outperforms traditional ellipse fitting in terms of both precision and accuracy. We demonstrate our methodology using a quantum mechanical model of coupled interferometers, where uncorrelated dephasing arises from projection noise and interparticle interactions. Our results establish a novel approach to data analysis in differential interferometry that is readily applicable to current experiments.

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arXiv2025

Metrological usefulness of entanglement and nonlinear Hamiltonians

A central task in quantum metrology is to exploit quantum correlations to outperform classical sensitivity limits. Metrologically useful entanglement is identified when the quantum Fisher information (QFI) exceeds a separability bound for a given parameter-encoding Hamiltonian. However, so far, only results for linear Hamiltonians are well-established. Here, we characterize metrologically useful entanglement for nonlinear Hamiltonians, presenting separability bounds for collective angular momenta. Also, we provide a general expression for entangled states maximizing the QFI, which can be written as the superposition between the GHZ-like and singlet states. Finally, we compare the metrological usefulness of linear and nonlinear cases, in terms of entanglement detection and random symmetric states.

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arXiv2025

Advances in multiparameter quantum sensing and metrology

Recent years have witnessed a growing interest in understating the limitations imposed by quantum noise in precision measurements and devising techniques to reduce it. The attention is currently turning to the simultaneously estimation of several parameters of interest, driven by its promising potential across a wide range of sensing applications as well as fueled by experimental progress in various optical and atomic platforms. Here, we provide a comprehensive overview of key research directions in multiparameter quantum sensing and metrology, highlighting both opportunities and challenges. We introduce the basic framework, discuss ultimate sensitivity bounds, optimal measurement strategies, and the role of quantum incompatibility, showing important differences with respect to single-parameter estimation. Additionally, we discuss emerging experimental implementations in distributed quantum sensing, including cutting-edge optimization techniques. This review aims to bridge the gap between theory and experiments, paving the way for the next-generation of quantum sensors and their integration with other quantum technologies.

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arXiv2025

Self-induced Josephson oscillations and self-trapping in a supersolid dipolar quantum gas

The Josephson effect characterizes superfluids and superconductors separated by a weak link, the so-called Josephson junction. A recent experiment has shown that Josephson oscillations can be observed also in a supersolid, where the weak link is not due to an external barrier, but is self-induced by interparticle interactions. Here we show theoretically that supersolids -- despite their self-induced character -- feature all the standard properties of bosonic Josephson junction arrays, including macroscopic quantum self-trapping. We focus on the harmonically trapped dipolar supersolids of interest for current experiments, and show that they can be described with a generalized Josephson model that takes into account spatial inhomogeneities. Our work shades new light on the dynamics of supersolids and opens the way to the study of a novel class of Josephson junctions.

cond-mat.quant-gas↗

arXiv2025

Squeezing-enhanced accurate differential sensing under large phase noise

Atom interferometers are reaching sensitivities fundamentally constrained by quantum fluctuations. A main challenge is to integrate entanglement into quantum sensing protocols to enhance precision while ensuring robustness against noise and systematics. Here, we theoretically investigate differential phase measurements with two atom interferometers using spin-squeezed states, accounting for common-mode phase noise spanning the full $2π$ range. We estimate the differential signal using model-free ellipse fitting, a robust method requiring no device calibration and resilient to additional noise sources. Our results show that spin-squeezing enables sensitivities below the standard quantum limit. Specifically, we identify optimal squeezed states that minimize the differential phase variance, scaling as $N^{-2/3}$, while eliminating bias inherent in ellipse fitting methods. We benchmark our protocol against the Cramér-Rao bound and compare it with hybrid methods that incorporate auxiliary classical sensors. Our findings provide a pathway to robust and high-precision atom interferometry, in realistic noisy environments and using readily available states and estimation methods.

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arXiv2024

Distributed quantum multiparameter estimation with optimal local measurements

We study the multiparameter sensitivity bounds of a sensor made by an array of $d$ spatially-distributed Mach-Zehnder interferometers (MZIs). A generic single non-classical state is mixed with $d-1$ vacuums to create a $d$-modes entangled state, each mode entering one input port of a MZI, while a coherent state enters its second port. We show that local measurements, independently performed on each MZI, are sufficient to provide a sensitivity saturating the quantum Cramér-Rao bound. The sensor can overcome the shot noise limit for the estimation of arbitrary linear combinations of the $d$ phase shifts, provided that the non-classical probe state has an anti-squeezed quadrature variance. We compare the sensitivity bounds of this sensor with that achievable with $d$ independent MZIs, each probed with a nonclassical state and a coherent state. We find that the $d$ independent interferometers can achieve the same sensitivity of the entangled protocol but at the cost of using additional $d$ non-classical states rather than a single one. When using in the two protocols the same average number of particles per shot $\bar{n}_T$, we find analytically a sensitivity scaling $1/\bar{n}_T^2$ for the entangled case which provides a gain factor $d$ with respect to the separable case where the sensitivity scales as $d/\bar{n}_T^2$. We have numerical evidences that the gain factor $d$ is also obtained when fixing the total average number of particles, namely when optimizing with respect to the number of repeated measurements.

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arXiv2024

Tomography of a single-atom-resolved detector in the presence of shot-to-shot number fluctuations

Tomography of single-particle-resolved detectors is of primary importance for characterizing particle correlations with applications in quantum metrology, quantum simulation and quantum computing. However, it is a non-trivial task in practice due to the unavoidable presence of noise that affects the measurement but does not originate from the detector. In this work, we address this problem for a three-dimensional single-atom-resolved detector where shot-to-shot atom number fluctuations are a central issue to perform a quantum detector tomography. We overcome this difficulty by exploiting the parallel measurement of counting statistics in sub-volumes of the detector, from which we evaluate the effect of shot-to-shot fluctuations and perform a local tomography of the detector. In addition, we illustrate the validity of our method from applying it to Gaussian quantum states with different number statistics. Finally, we show that the response of Micro-Channel Plate detectors is well-described from using a binomial distribution with the detection efficiency as a single parameter.

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