arXiv subjects

Manuel Gessner

Publications and source records attributed to Manuel Gessner.

At least 19 recordsLinked to original sources

arXiv2026

Quantum Barankin bounds beyond local unbiasedness: Analytic results for Gaussian states via a right-division framework

We propose a quantum version of the Barankin bound as an alternative to the quantum Cram\'er-Rao bound for quantum parameter estimation. The quantum Barankin bound provides a lower bound on the mean squared error of estimators satisfying arbitrarily chosen bias constraints at arbitrarily chosen parameter points. In particular, unbiasedness over the entire parameter space can be imposed, yielding precision limits for globally unbiased quantum parameter estimation. In contrast to the recently derived quantum Barankin bound, which is based on a symmetric division superoperator, our bound is based on a nonsymmetric right-division superoperator. This formulation enables us to find analytic expressions for the Barankin matrix for Gaussian states, which allows for an efficient calculation of the bound. We demonstrate the usefulness of our results by applying them to various examples that exhibit the threshold effect in the few-shot regime, which is invisible to the standard quantum Cram\'er-Rao bound approach.

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arXiv2026

Irreducible Architectures of Multipartite Entanglement

Multipartite entanglement is commonly characterized by scalar notions such as separability and entanglement depth, which do not resolve the distribution of entangled cluster sizes. For mixed states, we introduce formation profiles that assign weights to the entanglement architectures appearing in pure-state decompositions. We show that after discarding every profile that admits a strictly weaker feasible replacement, the remaining irreducible structure need not be unique: a four-qubit example exhibits a continuous family of incomparable irreducible profiles. Monotone functions of the architectures recover widely used scalar quantifiers as special cases, whereas the full profile geometry retains additional information, including the minimum weight that every decomposition must assign outside a chosen architectural class. Finally, we derive experimentally accessible bounds on these weights from convex witnesses, including the quantum Fisher information, thereby connecting detailed formation structure with practical entanglement certification.

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arXiv2025

Metrological Sensitivity beyond Gaussian Limits with Cubic Phase States

Cubic phase states provide the essential non-Gaussian resource for continuous-variable quantum computing. We show that they also offer significant potential for quantum metrology, surpassing the phase-sensing sensitivity of all Gaussian states at equal average photon number. Optimal sensitivity requires only moderate initial squeezing, and the non-Gaussian advantage remains robust against loss and detection noise. We identify optimal measurement strategies and show that several experimentally relevant preparation schemes surpass Gaussian limits, in some cases reaching the sensitivity of cubic phase states. Our results establish cubic phase states as a promising resource for quantum-enhanced precision measurements beyond Gaussian limits.

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arXiv2025

Differential magnetometry with partially flipped Dicke states

We study magnetometry of gradients and homogeneous background fields along the three orthogonal directions using two spatially separated spin ensembles. We derive trade-off relations for the achievable estimation precision of these parameters. Dicke states, optimal for homogeneous field estimation, can be locally rotated into states sensitive to magnetic gradients by rotating the spins in one subensemble. We determine bounds for the precision for gradient metrology in the three orthogonal directions as a function of the sensitivities to the homogenous field in those directions. The resulting partially flipped Dicke state saturates the bounds above, showing similar sensitivity in two directions but significantly reduced sensitivity in the third. Exploiting entanglement between the two ensembles, this state achieves roughly twice the precision attainable by the best bipartite separable state, which is a product of local Dicke states. For small ensembles, we explicitly identify measurement operators saturating the quantum Cram\'er-Rao bound, while for larger ensembles, we propose simpler but suboptimal schemes. In both cases, the gradient is estimated from second moments and correlations of angular momentum operators. Our results demonstrate how the metrological properties of Dicke states can be exploited for quantum-enhanced multiparameter estimation.

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arXiv2025

Complete characterisation of state conversions by work extraction

We introduce a thermodynamic work extraction task that describes the energy storage enhancement of quantum systems. This task induces majorisation-like conditions that provide a necessary and sufficient characterisation of state conversions in general quantum resource theories. When applied to specific resources, these conditions reduce to the majorisation conditions under unital channels and provide a thermodynamic version of Nielsen's theorem in entanglement theory. We show how this result establishes the first universal resource certification class based on thermodynamics, and how it can be employed to quantify general quantum resources based on work extraction.

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arXiv2025

Ultimate resolution limits in coherent anti-Stokes Raman scattering imaging

Coherent anti-Stokes Raman scattering is a widely used imaging technique that provides chemical contrast without the need for labels, making it an extremely valuable tool in physics, chemistry, and biology. In this work, we explore its fundamental precision limits by applying tools from quantum information theory. We identify optimal measurement strategies and show that spatial mode demultiplexing--a technique already accessible in current experimental setups--can achieve these quantum limits and in many situations improve the sensitivity of conventional intensity measurements. Building on this, we introduce an advanced imaging scheme based on vortex beams, which we predict to enhance the image information in the final quantum state of light and thereby lead to even higher resolution and sensitivity. These findings establish a clear path for enhancing nonlinear imaging techniques using concepts from quantum science, bridging the gap between established microscopy methods and the emerging capabilities of quantum technologies.

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arXiv2025

Spinor Bose-Einstein condensate as an analog simulator of molecular bending vibrations

We demonstrate that spinor Bose-Einstein condensates (BEC) can be operated as an analog simulator of the two-dimensional vibron model. This algebraic model for the description of bending and stretching vibrations of molecules, in the case of a triatomic molecules, exhibits two phases where linear and bent configurations are stabilised. Spinor BECs can be engineered to simulate states that correspond to linear or bent triatomic molecules, with the BEC's Wigner function encoding information about the molecular configuration. We show how quantum simulations of the bending dynamics of linear molecules can be realized, and how the straightening of a bent molecule leads to a dynamical instability. In the dynamics triggered by the corresponding instability, a significant amount of entanglement is generated, and we characterise the dynamics with the squeezing parameter and the quantum Fisher information (QFI). The scaling of the non-Gaussian sensitivity, described by the difference between squeezing and QFI, grows with the system size once the spinor system crosses from the linear to the bent phase, thus serving as a dynamical witness for the quantum phase transition.

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arXiv2025

Estimation of multiple parameters encoded in the modal structure of light

We investigate the problem of estimating simultaneously multiple parameters encoded in the shape of the modes on which the light is expanded. For this, we generalize the mode-encoded parameter estimation theory as introduced in Ref.[1] to a multi-parameter scenario. We derive the general expression for the Quantum Fisher information matrix and establish the conditions under which the multi-parameter Quantum Cram\'er-Rao bound is attainable. In specific scenarios, we find that each parameter can be associated with a mode -- the detection mode -- that is proportional to the derivative of either a single non-vacuum mode or the mean-field mode. For a single non-vacuum mode, the correlation between parameters is determined by the real part of the overlap of these detection modes, while in the case of a strong mean-field by the covariance of the quadrature operators of the derivative modes. In both cases, the attainability of the Quantum Cram\'er-Rao bound is determined by the imaginary part of the overlap of the detection modes. Our findings provide clear criteria for optimal joint estimation of parameters encoded in the modal structure of light, and can be used to benchmark experimental multi-parameter estimations and find optimal measurement strategies by carefully shaping the modes and populating them with non-classical light.

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arXiv2025

Theory of Quantum-Enhanced Stimulated Raman Scattering

Stimulated Raman scattering (SRS) is a powerful method for label-free imaging and spectroscopy of materials. Recent experiments have shown that quantum-enhanced Raman scattering can surpass the shot noise limit and improve the sensitivity substantially. Here, we introduce a full theory of quantum-enhanced SRS based on the framework of quantum metrology. Our results enable the assessment of quantum-enhancements of arbitrary measurement strategies and identify optimal measurement observables that extract maximal information about the signal. We use this to identify the optimal employment of squeezed states in SRS, highlighting the potential to improve quantum gains beyond those observed in recent experiments. Our work establishes the theoretical foundation for understanding and approaching the quantum limits of precision in SRS, and provide a tool to discuss nonlinear spectroscopy and imaging more broadly.

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arXiv2024

Quantum metrology with a continuous-variable system

As one of the main pillars of quantum technologies, quantum metrology aims to improve measurement precision using techniques from quantum information. The two main strategies to achieve this are the preparation of nonclassical states and the design of optimized measurement observables. We discuss precision limits and optimal strategies in quantum metrology and sensing with a single mode of quantum continuous variables. We focus on the practically most relevant cases of estimating displacements and rotations and provide the sensitivities of the most important classes of states that includes Gaussian states and superpositions of Fock states or coherent states. Fundamental precision limits that are obtained from the quantum Fisher information are compared to the precision of a simple moment-based estimation strategy based on the data obtained from possibly sub-optimal measurement observables, including homodyne, photon number, parity and higher moments. Finally, we summarize some of the main experimental achievements and present emerging platforms for continuous-variable sensing. These results are of particular interest for experiments with quantum light, trapped ions, mechanical oscillators, and microwave resonators.

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arXiv2024

Characterizing the Multipartite Entanglement Structure of Non-Gaussian Continuous-Variable States with a Single Evolution Operator

Multipartite entanglement is an essential resource for quantum information tasks, but characterizing entanglement structures in continuous variable systems remains challenging, especially in multimode non-Gaussian scenarios. In this work, we introduce an efficient method for detecting multipartite entanglement structures in continuous-variable states. Based on the quantum Fisher information, we propose a systematic approach to identify an optimal encoding operator that can capture the quantum correlations in multimode non-Gaussian states. We demonstrate the effectiveness of our method on over $10^5$ randomly generated multimode-entangled quantum states, achieving a very high success rate in entanglement detection. Additionally, the robustness of our method can be considerably enhanced against losses by expanding the set of accessible operators. This work provides a general framework for characterizing entanglement structures in diverse continuous variable systems, enabling a number of experimentally relevant applications.

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arXiv2024

General quantum resources providing advantages in work-extraction tasks

In developing quantum science and technologies, it is essential to demonstrate so-called quantum advantages, which are performances that can be achieved only with the assistance of quantum resources. Most of the time, different quantum features lead to different advantages. Interestingly, there are certain classes of tasks where quantum advantages are achievable by general quantum resources. This work reports such a class of tasks in thermodynamics---we provide a work-extraction task that certifies general quantum resources of both states and channels, suggesting general quantum effects can provide non-classical advantages in work extraction. We also show that such work-extraction tasks can be applied to certify quantum entanglement in a one-sided device-independent way. As an application, we report a novel type of anomalous energy flow---a type of locally extractable energy that is attributed to the globally distributed entanglement. Finally, we show that the existence of this novel anomalous energy flow is equivalent to measurement incompatibility.

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arXiv2024

Fundamental bounds for parameter estimation with few measurements

Bounding the optimal precision in parameter estimation tasks is of central importance for technological applications. In the regime of a small number of measurements, or that of low signal-to-noise ratios, the meaning of common frequentist bounds such as the Cram\'er-Rao bound (CRB) become questionable. Here, we discuss different linear (Barankin-like) conditions that can be imposed on estimators and analyze when these conditions admit an optimal estimator with finite variance, for any number of measurement repetitions. We show that, if the number of imposed conditions is larger than the number of measurement outcomes, there generally does not exist a corresponding estimator with finite variance. We analyze this result from different viewpoints and examples and elaborate on connections to the shot-noise limit and the Kitaev phase estimation algorithm. We then derive an extended Cram\'er-Rao bound that is compatible with a finite variance in situations where the Barankin bound is undefined. Finally, we show an exemplary numerical confrontation between frequentist and Bayesian approaches to parameter estimation.

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arXiv2024

Breaking local quantum speed limits with steering

We show how quantum correlations allow us to break the local speed limits of physical processes using only local measurements and classical communication between two parties that share an entangled state. Inequalities that bound the minimal time of evolution of a quantum state by energy fluctuations can be violated in the presence of steering by conditioning on the measurement outcomes of a remote system. Our results open up new pathways for studying how quantum correlations influence the dynamical properties of states and observables.

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arXiv2023

Application range of crosstalk-affected spatial demultiplexing for resolving separations between unbalanced sources

Superresolution is one of the key issues at the crossroads of contemporary quantum optics and metrology. Recently, it was shown that for an idealized case of two balanced sources, spatial mode demultiplexing (SPADE) achieves resolution better than direct imaging even in the presence of measurement crosstalk [Phys. Rev. Lett. 125, 100501 (2020)]. In this work, we consider arbitrarily unbalanced sources and provide a systematic analysis of the impact of crosstalk on the resolution obtained from SPADE. As we dissect, in this generalized scenario, SPADE's effectiveness depends non-trivially on the strength of crosstalk, relative brightness and the separation between the sources. In particular, for any source imbalance, SPADE performs worse than ideal direct imaging in the asymptotic limit of vanishing source separations. Nonetheless, for realistic values of crosstalk strength, SPADE is still the superior method for several orders of magnitude of source separations.

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arXiv2023

Estimation of a parameter encoded in the modal structure of a light beam: a quantum theory

Quantum light is described not only by a quantum state but also by the shape of the electromagnetic modes on which the state is defined. Optical precision measurements often estimate a ``mode parameter'' that determines properties such as frequency, temporal shape and the spatial distribution of the light field. By deriving quantum precision limits, we establish the fundamental bounds for mode parameter estimation. Our results reveal explicit mode-design recipes that enable the estimation of any mode parameter with quantum enhanced precision. Our approach provides practical methods for optimizing mode parameter estimation with relevant applications, including spatial and temporal positioning, spectroscopy, phase estimation, and superresolution imaging.

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arXiv2023

Gaussian quantum metrology for mode-encoded parameters

Quantum optical metrology aims to identify ultimate sensitivity bounds for the estimation of parameters encoded into quantum states of the electromagnetic field. In many practical applications, including imaging, microscopy, and remote sensing, the parameter of interest is not only encoded in the quantum state of the field, but also in its spatio-temporal distribution, i.e. in its mode structure. In this mode-encoded parameter estimation setting, we derive an analytical expression for the quantum Fisher information valid for arbitrary multimode Gaussian fields. To illustrate the power of our approach, we apply our results to the estimation of the transverse displacement of a beam and to the temporal separation between two pulses. For these examples, we show how the estimation sensitivity can be enhanced by adding squeezing into specific modes.

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arXiv2023

Metrological detection of entanglement generated by non-Gaussian operations

Entanglement and non-Gaussianity are physical resources that are essential for a large number of quantum-optics protocols. Non-Gaussian entanglement is indispensable for quantum-computing advantage and outperforms its Gaussian counterparts in a number of quantum-information protocols. The characterization of non-Gaussian entanglement is a critical matter as it is in general highly demanding in terms of resources. We propose a simple protocol based on the Fisher information for witnessing entanglement in an important class of non-Gaussian entangled states: photon-subtracted states. We demonstrate that our protocol is relevant for the detection of non-Gaussian entanglement generated by multiple photon-subtraction and that it is experimentally feasible through homodyne detection.

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