arXiv subjects

Victor Montenegro

Publications and source records attributed to Victor Montenegro.

At least 19 recordsLinked to original sources

arXiv2026

Squeezed Phonon Lasing via Floquet-Controlled Solid-State Defects

We propose a general Floquet-engineered scheme for squeezed phonon lasing that enables a continuous crossover from conventional phase-diffused phonon lasing to phase-locked squeezed phonon lasing. Our system consists of two pairs of periodically driven spins--a primary pair and an ancilla pair--coupled to a single mechanical mode. While the underlying mechanism applies generally to such spin-mechanical systems, we focus on a solid-state implementation based on color centers embedded in a circular hexagonal boron nitride (hBN) membrane. We show that the primary spins provide mechanical gain, whereas the ancilla pair engineer a dissipative channel for the Bogoliubov mode, thereby stabilizing robust steady-state squeezed phonon lasing. We support these findings through a comprehensive steady-state analysis of the lasing threshold, mechanical occupation, emission spectrum, and second-order correlations. Remarkably, we demonstrate that Floquet engineering intrinsically induces phase locking while enabling controllable quadrature squeezing, providing a simple and versatile route toward squeezed lasing in solid-state spin-mechanical platforms.

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arXiv2026

Scalable phonon-laser arrays with self-organized synchronization

Quantum mechanical oscillators operating at frequencies up to the GHz regime have been predicted to support phonon lasing -- self-sustained coherent vibrational motion emerging when the effective gain exceeds intrinsic losses. Current phonon-laser proposals face two key limitations, namely: they lack scalability and rely on coupling all oscillators to a common field, which significantly restricts flexibility and prevents selective, on-demand phonon lasing at specific locations. Given that numerous applications and theoretical insights naturally emerge from scalable many-body systems, addressing these limitations is timely. In this Letter, we demonstrate how scalable arrays of individually addressable phonon lasers can be generated through local driving in a quantum many-body Ising-like spin chain. We rigorously establish the resonance conditions under which mechanical oscillators transition from thermal motion to sustained coherent self-oscillation. Unlike previous approaches that rely on a common coupling bus, our proposal employs purely local driving, resulting in an inherently modular and scalable architecture ideally suited for integration into large-scale quantum systems. Additionally, our approach enables on-demand lasing of individual mechanical oscillators at specific sites by simply switching the spin-mechanical coupling interaction on and off, provided specific resonance conditions are satisfied. Notably, our phonon laser array is robust against resonance mismatches and naturally exhibits both pairwise self-organized synchronization and global phase locking near resonance. Finally, we outline an experimental implementation within current experimental capabilities.

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arXiv2025

Quantum error correction for multiparameter metrology

For single-parameter sensing, Greenberger-Horne-Zeilinger (GHZ) probes achieve optimal quantum-enhanced precision across the unknown parameter range, solely relying on parameter-independent separable measurement strategies for all values of the unknown parameter. However, in the multiparameter setting, a single GHZ probe not only fails to achieve quantum advantage but also the corresponding optimal measurement becomes complex and dependent on the unknown parameters. Here, we provide a recipe for multiparameter sensing with GHZ probes using quantum error correction techniques by treating all but one unknown parameters as noise, whose effects can be corrected. This strategy restores the core advantage of single parameter GHZ-based quantum sensing, namely reaching optimally quantum-enhanced precision for all unknown parameter values while keeping the measurements separable and fixed. Specifically, given one shielded ancilla qubit per GHZ probe, our protocol extracts optimal possible precision for any probe size. While this optimal precision is shot-noise limited for a single GHZ probe, we recover the Heisenberg scaling through use of multiple complementary GHZ probes. We demonstrate the effectiveness of the protocol with Bayesian estimation.

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arXiv2025

Stroboscopic Saturation of Multiparameter Quantum Limits in Distributed Quantum Sensing

High-precision sensors that exploit uniquely quantum phenomena have been shown to surpass the standard quantum limit of measurement precision. However, in the general scenario where multiple parameters are simultaneously encoded in a quantum probe, while surpassing the standard quantum limit is possible, its practical attainability is severely hindered. This difficulty arises due to the fundamental incompatibility among the optimal measurements required for estimating different parameters. A naturally multiparameter sensing scenario emerges when a network of quantum sensors is spatially distributed, with each individual sensor probing a distinct parameter of interest. The central goal in such a setting is twofold: first, to surpass the standard quantum limit in estimating global properties of the system -- thereby achieving quantum-enhanced sensitivity for a given network size -- and second, to explicitly identify the optimal measurement strategies necessary to practically attain this quantum advantage. Here, we analytically demonstrate quantum-enhanced sensitivity for a broad class of distributed quantum probes, including cases where the precision scales quadratically or quartically with the sensing resources. We construct the corresponding optimal measurement strategies that achieve the ultimate precision limits -- namely, saturation of both the Holevo and quantum Cram\'{e}r-Rao bounds. We then apply our framework to two concrete scenarios: the simultaneous estimation of multiple gravitational accelerations (gravimetry) and coupling strengths across spatially separated locations. Feasibility analyses indicate that the proposed distributed quantum-enhanced sensing schemes are within reach of current experimental capabilities.

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arXiv2025

Near-Ultimate Quantum-Enhanced Sensitivity in Dissipative Critical Sensing with Partial Access

Quantum sensors are powerful devices that exploit quantum effects to detect minute quantities with extremely high precision. Two obstacles to harnessing the full capacity of quantum probes are the resource-intensive preparation of the probe and the need for sophisticated measurements that typically require full access to the entire probe. Here, we address these challenges by investigating the driven Jaynes-Cummings system undergoing a dissipative quantum phase transition as a quantum sensor. We show that detuning the system off resonance significantly improves sensing performance by adequately selecting a preferred bistable state in phase space. Our dissipative sensor, independent of the initial probe preparation, exhibits a super-linear enhancement in sensitivity with respect to a specific sensing resource -- the strong-coupling regime ratio -- which manifests in both the full system and partial subsystem. Hence, quantum-enhanced sensitivity persists even when only partial system accessibility is available. Remarkably, we show that a homodyne detection of the field state, combined with Bayesian estimation, nearly saturates the ultimate sensitivity limit of the entire system.

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arXiv2025

Attaining Quantum Sensing Enhancement from Monitored Dissipative Time Crystals

This study investigates quantum-enhanced parameter estimation through continuous monitoring in open quantum systems that exhibit a dissipative time crystal phase. We first analytically derive the global quantum Fisher information (QFI) rate for boundary time crystals (BTCs), demonstrating that within the time-crystal phase, the ultimate precision exhibits a cubic scaling with the system size, $f_{\mathrm{global}}\sim N^3$. We then generalize this finding to a broader class of dynamics, including the transverse collective dephasing (TCD) model, which achieves a time-crystal phase through a closing Liouvillian gap without requiring a dissipative phase transition. We proceed to numerically demonstrate that this maximal global QFI rate is experimentally attainable for both the BTC and TCD models, even at finite system sizes, via continuous homodyne and photodetection. Moving towards practical implementations, we analyze the precision limits under inefficient detection, revealing a critical difference: for BTC dynamics, inefficiencies asymptotically restore a classical scaling, and only a constant-factor quantum advantage remains possible. In contrast, for TCD dynamics, a super-classical scaling is still in principle observable, and our numerical simulations confirm its presence, even under inefficient measurement conditions, establishing the TCD model as a highly robust platform for quantum metrology.

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arXiv2025

Probing the Limits of Dispersive Quantum Thermometry with a Nonlinear Mach-Zehnder-Based Quantum Simulator

Temperature estimation, known as thermometry, is a critical sensing task for physical systems operating in the quantum regime. Indeed, thermal fluctuations can significantly degrade quantum coherence. Therefore, accurately determining the system's operating temperature is a crucial first step toward distinguishing thermal noise from other sources of decoherence. In this work, we estimate the unknown temperature of a collection of identical and independent two-level atoms dispersively probed by a single-mode quantized electromagnetic field. In contrast to previous works, we present an analytical sensing analysis demonstrating that the joint atom-field evolution -- without any assumptions or approximations -- can achieve, at best, the standard quantum limit of precision concerning the number of field excitations. To investigate our analysis further, we propose and implement a quantum thermometer based on a nonlinear Mach-Zehnder interferometer, which we realize through quantum digital simulation. Our simulation is highly flexible regarding atomic state preparation, allowing the initialization of atomic ensembles with positive and effective negative temperatures. This makes our platform a promising and versatile testbed for benchmarking thermometric capabilities in current quantum simulators.

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arXiv2025

Beating joint quantum estimation limits with stepwise multiparameter metrology

Conventional multiparameter quantum sensing relies on joint estimation, but this approach faces two key limitations: theoretical bounds may be unattainable due to measurement incompatibility, and sensing may fail due to parameter interdependencies. We propose stepwise estimation and identify regimes where it outperforms joint estimation. For multiple quantum sensors, this scheme achieves far lower error bounds than joint estimation. With many-body probes, stepwise sensing retains a quantum-enhanced scaling advantage often lost in joint estimation due to parameter correlations. We demonstrate its concrete advantages through Bayesian implementations across diverse examples.

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arXiv2025

Enhanced quantum frequency estimation by nonlinear scrambling

Frequency estimation, a cornerstone of basic and applied sciences, has been significantly enhanced by quantum sensing strategies. Despite breakthroughs in quantum-enhanced frequency estimation, key challenges remain: static probes limit flexibility, and the interplay between resource efficiency, sensing precision, and potential enhancements from nonlinear probes remains not fully understood. In this work, we show that dynamically encoding an unknown frequency in a nonlinear quantum electromagnetic field can significantly improve frequency estimation. To provide a fair comparison of resources, we define the energy cost as the figure of merit for our sensing strategy. We further show that specific higher-order nonlinear processes lead to nonlinear-enhanced frequency estimation. This enhancement results from quantum scrambling, where local quantum information spreads across a larger portion of the Hilbert space. We quantify this effect using the Wigner-Yanase skew information, which measures the degree of noncommutativity in the Hamiltonian structure. Our work sheds light on the connection between Wigner-Yanase skew information and quantum sensing, providing a direct method to optimize nonlinear quantum probes.

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arXiv2025

Overcoming Quantum Metrology Singularity through Sequential Measurements

The simultaneous estimation of multiple unknown parameters is the most general scenario in quantum sensing. Quantum multi-parameter estimation theory provides fundamental bounds on the achievable precision of simultaneous estimation. However, these bounds can become singular (no finite bound exists) in multi-parameter sensing due to parameter interdependencies, limited probe accessibility, and insufficient measurement outcomes. Here, we address the singularity issue in quantum sensing through a simple mechanism based on a sequential measurement strategy. This sensing scheme overcomes the singularity constraint and enables the simultaneous estimation of multiple parameters with a local and fixed measurement throughout the sensing protocol. This is because sequential measurements, involving consecutive steps of local measurements followed by probe evolution, inherently produce correlated measurement data that grows exponentially with the number of sequential measurements. Finally, through two different examples, namely a strongly correlated probe and a light-matter system, we demonstrate how such singularities are reflected when inferring the unknown parameters through Bayesian estimation.

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arXiv2024

Current Trends in Global Quantum Metrology

Quantum sensors are now universally acknowledged as one of the most promising near-term quantum technologies. The traditional formulation of quantum sensing introduces a concrete bound on ultimate precision through the so-called local sensing framework, in which a significant knowledge of prior information about the unknown parameter value is implicitly assumed. Moreover, the framework provides a systematic approach for optimizing the sensing protocol. In contrast, the paradigm of global sensing aims to find a precision bound for parameter estimation in the absence of such prior information. In recent years, vigorous research has been pursued to describe the contours of global quantum estimation. Here, we review some of these emerging developments. These developments are both in the realm of finding ultimate precision bounds with respect to appropriate figures of merit in the global sensing paradigm, as well as in the search for algorithms that achieve these bounds. We categorize these developments into two largely mutually exclusive camps; one employing Bayesian updating and the other seeking to generalize the frequentist picture of local sensing towards the global paradigm. In the first approach, in order to achieve the best performance, one has to optimize the measurement settings adaptively. In the second approach, the measurement setting is fixed, however the challenge is to identify this fixed measurement optimally.

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arXiv2024

Heisenberg-Limited Spin-Mechanical Gravimetry

Precision measurements of gravitational acceleration, or gravimetry, enable the testing of physical theories and find numerous applications in geodesy and space exploration. By harnessing quantum effects, high-precision sensors can achieve sensitivity and accuracy far beyond their classical counterparts when using the same number of sensing resources. Therefore, developing gravimeters with quantum-enhanced sensitivity is essential for advancing theoretical and applied physics. While novel quantum gravimeters have already been proposed for this purpose, the ultimate sensing precision, known as the Heisenberg limit, remains largely elusive. Here, we demonstrate that the gravimetry precision of a conditional displacement spin-mechanical system increases quadratically with the number of spins: a Heisenberg-limited spin-mechanical gravimeter. In general, the gravitational parameter is dynamically encoded into the entire entangled spin-mechanical probe. However, at some specific times, the mechanical degree of freedom disentangles from the spin subsystem, transferring all the information about the gravitational acceleration to the spin subsystem. Hence, we prove that a feasible spin magnetization measurement can reveal the ultimate gravimetry precision at such disentangling times. We predict an absolute gravimetry uncertainty of $10^{-11}\text{m/s}^2$ to $10^{-6}\text{m/s}^2$, without relying on free-fall methodologies, ground-state cooling of the mechanical object, and robust against spin-mechanical coupling anisotropies.

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arXiv2024

Review: Quantum Metrology and Sensing with Many-Body Systems

The main power of quantum sensors is achieved when the probe is composed of several particles. In this situation, quantum features such as entanglement contribute to enhancing the precision of quantum sensors beyond the capacity of classical sensors. Originally, quantum sensing was formulated for non-interacting particles that are prepared in a special form of maximally entangled states. These probes are extremely sensitive to decoherence, and any interaction between particles is detrimental to their performance. An alternative framework for quantum sensing has been developed exploiting quantum many-body systems, where the interaction between particles plays a crucial role. In this review, we investigate different aspects of the latter approach for quantum metrology and sensing. Many-body probes have been used in both equilibrium and non-equilibrium scenarios. Quantum criticality has been identified as a resource for achieving quantum-enhanced sensitivity in both scenarios. In equilibrium, various types of criticalities, such as first-order, second-order, topological, and localization phase transitions, have been exploited for sensing purposes. In non-equilibrium scenarios, quantum-enhanced sensitivity has been discovered for Floquet, dissipative, and time crystal phase transitions. While each type of these criticalities has its own characteristics, the presence of one feature is crucial for achieving quantum-enhanced sensitivity: the energy/quasi-energy gap closing. In non-equilibrium quantum sensing, time is another parameter that can affect the sensitivity of the probe. Typically, the sensitivity enhances as the probe evolves in time. In general, a more complete understanding of resources for non-equilibrium quantum sensors is now rapidly evolving. In this review, we provide an overview of recent progress in quantum metrology and sensing using many-body systems.

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arXiv2024

Sequential measurements thermometry with quantum many-body probes

Measuring the temperature of a quantum system is an essential task in almost all aspects of quantum technologies. Theoretically, an optimal strategy for thermometry requires measuring energy which demands full accessibility over the entire system as well as complex entangled measurement basis. In this paper, we take a different approach and show that single qubit sequential measurements in the computational basis not only allows precise thermometry of a many-body system but may also achieve precision beyond the theoretical bound, avoiding demanding energy measurements at equilibrium. To obtain such precision, the time between the two subsequent measurements should be smaller than the thermalization time so that the probe never thermalizes. Therefore, the non-equilibrium dynamics of the system continuously imprint information about temperature in the state of the probe. This allows the sequential measurement scheme to reach precision beyond the accuracy achievable by complex energy measurements on equilibrium probes.

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arXiv2023

Extractable Information Capacity in Sequential Measurements Metrology

The conventional formulation of quantum sensing is based on the assumption that the probe is reset to its initial state after each measurement. In a very distinct approach, one can also pursue a sequential measurement scheme in which time-consuming resetting is avoided. In this situation, every measurement outcome effectively comes from a different probe, yet correlated with other data samples. Finding a proper description for the precision of sequential measurement sensing is very challenging as it requires the analysis of long sequences with exponentially large outcomes. Here, we develop a recursive formula and an efficient Monte-Carlo approach to calculate the Fisher information, as a figure of merit for sensing precision, for arbitrary lengths of sequential measurements. Our results show that Fisher information initially scales non-linearly with the number of measurements and then asymptotically saturates to linear scaling. Such transition, which fundamentally constrains the extractable information about the parameter of interest, is directly linked to the finite memory of the probe when undergoes multiple sequential measurements. Based on these, we establish a figure of merit to determine the optimal measurement sequence length and exemplify our results in three different physical systems.

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arXiv2022

Sequential measurements for quantum-enhanced magnetometry in spin chain probes

Quantum sensors outperform their classical counterparts in their estimation precision, given the same amount of resources. So far, quantum-enhanced sensitivity has been achieved by exploiting the superposition principle. This enhancement has been obtained for particular forms of entangled states, adaptive measurement basis change, critical many-body systems, and steady-state of periodically driven systems. Here, we introduce a different approach to obtain quantum-enhanced sensitivity in a many-body probe through utilizing the nature of quantum measurement and its subsequent wave-function collapse without demanding prior entanglement. Our protocol consists of a sequence of local measurements, without re-initialization, performed regularly during the evolution of a many-body probe. As the number of sequences increases, the sensing precision is enhanced beyond the standard limit, reaching the Heisenberg bound asymptotically. The benefits of the protocol are multi-fold as it uses a product initial state and avoids complex initialization (e.g. prior entangled states or critical ground states) and allows for remote quantum sensing.

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arXiv2022

Dissipative optomechanical preparation of non-Gaussian mechanical entanglement

Entanglement had played a crucial role in developing frontier technologies as a critical resource, for instance, in quantum teleportation and quantum sensing schemes. Notably, thanks to the ability to cool down the vibrational modes of mechanical oscillators to its quantum regime, entanglement between mechanical modes and the production of nonclassical mechanical states have emerged as central resources for quantum technological applications. Thus, proposing deterministic schemes to achieve those tasks is of paramount importance. While the dominant scheme for bipartite mechanical entanglement involves Gaussian optomechanical interactions (linearized regime) to generate two-mode squeezed vacuum states, entangling two-modes exploiting the bare non-Gaussian optomechanical interaction (nonlinear strong single-photon regime) remains less covered. This work proposes an on-demand scheme to engineer phononic non-Gaussian bipartite entanglement in the nonlinear regime by exploiting cavity dissipation. Interestingly, our protocol (operating in the resolved sideband and photon blockade regime) renders the possibility of achieving a high degree of steady-state entanglement. We further show that our deterministic scheme is robust in the presence of decoherence and temperature within state-of-the-art optomechanics, along with the required conditions to obtain non-Gaussianity of the achieved bipartite mechanical steady-state.

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arXiv2021

Global sensing and its impact for quantum many-body probes with criticality

Quantum sensing is one of the key areas which exemplifies the superiority of quantum technologies. Nonetheless, most quantum sensing protocols operate efficiently only when the unknown parameters vary within a very narrow region, i.e., local sensing. Here, we provide a systematic formulation for quantifying the precision of a probe for multi-parameter global sensing when there is no prior information about the parameters. In many-body probes, in which extra tunable parameters exist, our protocol can tune the performance for harnessing the quantum criticality over arbitrarily large sensing intervals. For the single-parameter sensing, our protocol optimizes a control field such that an Ising probe is tuned to always operate around its criticality. This significantly enhances the performance of the probe even when the interval of interest is so large that the precision is bounded by the standard limit. For the multi-parameter case, our protocol optimizes the control fields such that the probe operates at the most efficient point along its critical line. Interestingly, for an Ising probe, it is predominantly determined by the longitudinal field. Finally, we show that even a simple magnetization measurement significantly benefits from our optimization and moderately delivers the theoretical precision.

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