Projective Measurements Research Articles

Fast alternating minimization algorithm for coded aperture snapshot spectral imaging based on sparsity and deep image priors

Coded aperture snapshot spectral imaging is a computational imaging technique used to reconstruct three-dimensional hyperspectral images from one or several two-dimensional projection measurements. However, fewer projection measurements or more spectral channels lead to a severely ill-posed problem, in which case regularization methods have to be applied. In order to significantly improve the accuracy of reconstruction, this paper proposes a fast alternating minimization algorithm based on the sparsity and deep image priors of natural images. By integrating deep image prior into the principle of compressive sensing reconstruction, the proposed algorithm can achieve state-of-the-art results without any training dataset. Extensive experiments show that the Fama-SDIP method significantly outperforms prevailing methods on simulation and real HSI datasets.

Measurement-driven transitions between area law phases

Abstract In recent years, quantum circuits consisting of unitary gates and projective measurements have become valuable tools for stimulating or preparing quantum many-body states with non-trivial properties. Here, we introduce and examine a measurement-only circuit (the projective quantum Ising model with three-spin interactions) that involves three non-commuting projective measurements. This model features three distinct phases, separated by two critical lines. We utilize two entanglement measures (topological entanglement entropy and mutual information) to identify the phase boundaries and derive various critical exponents through scaling analysis. We establish a relationship between our model and a two-dimensional statistical model (bond percolation) within certain limits. We hope that our results will shed light on further studies using other measurement-only models.

Information versus physicality: on the nature of the wavefunctions of quantum mechanics

The physical states of matter and fields are represented in the quantum theory with complex valued wavefunctions, or more generally by quantum states in an abstract linear vector space. Determining the physical nature of wavefunctions remains an open problem that is at the very core of quantum mechanics, About a decade ago, Pusey, Barret and Rudolf (PBR) claimed to prove an ontologically real status of wavefunctions by ruling out ψ -epistemic models. The result was obtained by associating wavefunctions to hypothetical distributions of notional physical states, and by examining whether some physical states were associated with more than one wavefunction, a criterion they chose for defining a wavefunction as ‘epistemic’. I show that the starting assumption in the PBR argument, of associating a wavefunction with a distribution of physical states, is flawed and contradictory to the linear structure of quantum mechanics coupled with its quadratic Born’s rule. Since none of the axioms or calculations of observable statistical results in the standard quantum theory depends on specifying the physical nature of a ψ -function, the considerations in the PBR paper, involving a standard process of the preparation and projective measurements of quantum states, cannot address the ontological status of the wavefunctions in space and time.

Freiflächen-Photovoltaikanlagen bieten der Feldlerche Alauda arvensis keinen (Ersatz-)Lebensraum

Natura 2000: Project or area management measure? // The article deals with new decisions of the European Court of Justice (ECJ) and the Federal Administrative Court (BVerwG) regarding habitat protection law (key word: Abolition of hunting closed seasons) and describes their practical implications. It addresses the question of what requirements must be met for an administrative measure in the area to exist that is not subject to the obligation of an impact assessment under the Habitats Directive (HD).

Integrating Clinical and Digital Measures in the AMP SCZ Project

Integrating Clinical and Digital Measures in the AMP SCZ Project

Thermodynamic phases in first detected return times of quantum many-body systems

We study the probability distribution of the first return time to the initial state of a quantum many-body system subject to global projective measurements at stroboscopic times. We show that this distribution can be mapped to a continuation of the canonical partition function of a classical spin chain with noninteracting domains at equilibrium, which is entirely characterized by the Loschmidt amplitude of the quantum many-body system. This allows us to conclude that this probability may decay either algebraically or exponentially at long times, depending on whether the spin chain displays a ferromagnetic or a paramagnetic phase. We illustrate this idea on the example of the return time of N adjacent fermions in a tight-binding model, revealing a rich phase behavior, which can be tuned by scaling the probing time as a function of N. The analysis presented here provides an overarching understanding of many-body quantum first detection problems in terms of equilibrium thermodynamic phases. Our theoretical predictions are in excellent agreement with exact numerical computations. Published by the American Physical Society 2025

Measurement and teleportation in the cSYK/JT correspondence

We consider two complex SYK models entangled in a thermofield double (TFD) state and investigate the effect of one-sided projective measurements. As measurement operator we choose single site charge operators. Performing a measurement results in a non-zero U(1) charge. The entropy curve differs from the previously studied SYK model due to a thermodynamic phase transition that takes place after a certain charge is reached. We also match our results to a dual bulk description. Finally, a teleportation protocol is provided to support the notion of a traversable wormhole being formed.

Incorporação de Critérios de Sustentabilidade nos Empreendimentos do Programa Minha Casa, Minha Vida em São Gonçalo/RJ

Objective – To analyze the incorporation of environmental sustainability criteria in housing projects of the Minha Casa Minha Vida Program (PMCMV) in the municipality of São Gonçalo (RJ), between 2012 and 2022, focusing on its relationship with the construction industry and the principles of bioclimatic architecture, thermal comfort, and energy efficiency. Methodology – The study is based on a literature review on sustainability in civil construction, analysis of legal and regulatory instruments related to the PMCMV, and document analysis of Neighborhood Impact Reports (RIV) and Neighborhood Impact Studies (EIV) submitted by the developments to the municipal authorities. The investigation focused on five variables representative of environmental impact in the construction sector: (i) planned disposal of solid waste; (ii) adequacy of disposal methods when provided; (iii) proposed measures to mitigate air pollution; (iv) adequacy of these measures; and (v) planned actions to mitigate the increase in local temperature. Originality/relevance – This work contributes to the discussion on environmental sustainability in large-scale housing programs, highlighting the importance of regulations in ensuring the effectiveness of mitigation measures in social housing projects. Results – The data indicate that the developments analyzed are more compliant with environmental mitigation measures when these are clearly established in legal and regulatory frameworks. In contrast, in the absence of specific guidelines, companies tend to be less proactive in identifying and implementing sustainable actions. Theoretical/methodological contributions – The research proposes a critical approach to evaluate the effectiveness of normative frameworks in promoting environmental sustainability in social housing. It also presents a replicable methodology for analyzing EIVs and RIVs in the urban context. Social and environmental contributions – By discussing the effectiveness of sustainable practices in the PMCMV, the study offers insights for the improvement of public housing policies and the promotion of more resilient and environmentally responsible cities.

Identification and assessment of quantitative metrics for measuring emergency healthcare facility project performance in China

PurposeWhen facing major emergencies, emergency healthcare facilities (EHFs) are vital in mitigating the medical pressures of traditional hospitals by providing immediate and flexible healthcare services. Performance measurement of EHF projects is crucial to ensuring that emergency medical services can respond effectively and efficiently to health demands. However, there is a lack of comprehensive understanding regarding the appropriate performance metrics that can measure the performance of these projects. This study aims to bridge this gap by identifying and assessing the quantitative metrics (QMs) for measuring the performance of EHF projects throughout their lifecycle, with a focus on their application in China.Design/methodology/approachA four-stage multi-criteria decision-making framework was employed to carry out this study. Initially, preliminary QMs for EHF projects were identified through in-depth expert interviews in China. Three rounds of Delphi surveys and statistical analysis were then conducted in China to determine the QMs most appropriate for EHF projects. Lastly, the priority of the shortlisted QMs was evaluated using the C-OWA (Combination Ordered Weighted Averaging) operator, considering three evaluation dimensions: importance, data availability, and overall suitability.FindingsTwenty QMs that are most appropriate for measuring the performance of EHF projects in China are identified. Among these QMs, “schedule deviation”, “deconstruction casualty rate”, “engineering quality qualification rate”, “cost deviation”, “schedule efficiency”, and “bed density”, are deemed as the top six QMs in the overall suitability. In the overall ranking of top metrics, those related to scheduling are prominently positioned, highlighting the time-sensitivity of EHFs.Originality/valueThis study provides a framework for measuring emergency healthcare facility project performance, thereby addressing the theoretical void in the fields of performance measurement and emergency management. It also enables healthcare administrators, emergency management staff, and project managers to quantitatively measure the performance of EHF projects, facilitating the rapid deployment and provision of effective emergency medical care under major crises.

Ptychographic estimation of qudit states encoded in the angular position and orbital angular momentum of single photons

Ptychography is a computational imaging technique mainly used in optical and electron microscopy. Its quantum analog was recently introduced as a simple method for estimating unknown pure quantum states through projections onto partially overlapping subspaces, each one followed by a projective measurement in the Fourier basis. In the end, an iterative algorithm estimates the state from the collected data. Here, we theoretically describe how to implement this method for D-dimensional qudit states encoded in the angular position and orbital angular momentum (OAM) of single photons. For this purpose, we define the qudit by discretizing the spatial profile of a photon in cylindrical coordinates, using an array of D angular slits symmetrically distributed in the transverse plane. To apply ptychography to this encoding, we show that the intermediate projections will be carried out by simple binary spatial filters in the angular paths, while the measurement in the Fourier basis will be performed by postselecting D OAM modes compatible with the quantum Fourier transform of the path basis. We illustrate the effectiveness of this scheme through simulations and discuss its experimental feasibility.

Nonclassical states of light induced via measurement in a bimodal system

Abstract We investigate generation of nonclassical photon states via conditional measurement process in a two mode coupled waveguide. Interaction of the fields takes place in a waveguide beamsplitter due to the overlap between normal modes supported therein. A quadratic Hamiltonian of two degrees of freedom describes the hopping interaction. An initial two mode squeezed state undergoes a unitary evolution governed by the interaction Hamiltonian for a specified time. Following this the bipartite state is subjected to a projective measurement that detects nth Fock state in one subsystem. The post-measurement excitation rendered in the residual subsystem depends on the prior time of interaction between the modes as well as the interaction strength. The Wigner quasiprobability distribution of an arbitrary post-selection state is computed. Its nonclassicality is examined via the negativity of the Wigner distribution. The sub-Poissonian nature of the photon statistics is revealed by the Mandel parameter. The dynamically generated squeezing is evidenced in the post-measurement state. In the ultrastrong coupling regime the parity even and odd states display markedly different nonclassical properties. The nonclassicality of the post-measurement states obtained here may be controlled by varying the interaction strength and the time span of interaction between the modes.

Frequency-bin entanglement-based Quantum Key Distribution

Entanglement is an essential ingredient in many quantum communication protocols. In particular, entanglement can be exploited in quantum key distribution (QKD) to generate two correlated random bit strings whose randomness is guaranteed by the nonlocal property of quantum mechanics. Most of QKD protocols tested to date rely on polarization and/or time-bin encoding. Despite compatibility with existing fiber-optic infrastructure and ease of manipulation with standard components, frequency-bin QKD have not yet been fully explored. Here we report a demonstration of entanglement-based QKD using frequency-bin encoding. We implement the BBM92 protocol using photon pairs generated by two independent, high-finesse, ring resonators on a silicon photonic chip. We perform a passive basis selection scheme and simultaneously record sixteen projective measurements. A key finding is that frequency-bin encoding is sensitive to the random phase noise induced by thermal fluctuations of the environment. To correct for this effect, we developed a real-time adaptive phase rotation of the measurement basis, achieving stable transmission over a 26 km fiber spool with a secure key rate ≥ 4.5 bit/s. Our work introduces a new degree of freedom for the realization of entangled based QKD protocols in telecom networks.

Coherence analysis of local randomness and nonlocal correlation through polarization-basis projections of entangled photon pairs

Polarization-entangled photon pairs generated from second-order nonlinear optical media have been extensively studied for both fundamental research and potential applications of quantum information. In a spontaneous parametric down-conversion process, quantum entanglement between paired photons, often regarded as ‘mysterious,’ has been demonstrated for local randomness and nonlocal correlation through polarization-basis projections using linear optics (Phys. Rev. A 60, R773 (1999)). Unlike the conventional particle nature-based perspective, this paper presents a coherence analysis rooted in the wave nature of quantum mechanics to examine these well-established quantum phenomena, incorporating polarization control of the paired photons and their projection measurements. First, we analyze the quantum superposition of photon pairs generated randomly from cross-sandwiched nonlinear media, focusing on local randomness, which depends on the incoherence among measured events. Second, we investigate coincidence detection between paired photons to understand the nonlocal correlation arising from independently controlled remote parameters, resulting in an inseparable product-basis relationship. This coherence-based approach sheds light on a deterministic perspective on quantum features, emphasizing the significance of phase information intrinsic to the wave nature of photons, which is incompatible with the particle nature.

Artificially intelligent Maxwell’s demon for optimal control of open quantum systems

Abstract Feedback control of open quantum systems is of fundamental importance for practical applications in various contexts, ranging from quantum computation to quantum error correction and quantum metrology. Its use in the context of thermodynamics further enables the study of the interplay between information and energy. However, deriving optimal feedback control strategies is highly challenging, as it involves the optimal control of open quantum systems, the stochastic nature of quantum measurement, and the inclusion of policies that maximize a long-term time- and trajectory-averaged goal. In this work, we employ a reinforcement learning approach to automate and capture the role of a quantum Maxwell’s demon: the agent takes the literal role of discovering optimal feedback control strategies in qubit-based systems that maximize a trade-off between measurement-powered cooling and measurement efficiency. Considering weak or projective quantum measurements, we explore different regimes based on the ordering between the thermalization, the measurement, and the unitary feedback timescales, finding different and highly non-intuitive, yet interpretable, strategies. In the thermalization - dominated regime, we find strategies with elaborate finite-time thermalization protocols conditioned on measurement outcomes. In the measurement-dominated regime, we find that optimal strategies involve adaptively measuring different qubit observables reflecting the acquired information, and repeating multiple weak measurements until the quantum state is “sufficiently pure”, leading to random walks in state space. Finally, we study the case when all timescales are comparable, finding new feedback control strategies that considerably outperform more intuitive ones. We discuss a two-qubit example where we explore the role of entanglement and conclude discussing the scaling of our results to quantum many-body systems.

Transformer neural networks and quantum simulators: a hybrid approach for simulating strongly correlated systems

Owing to their great expressivity and versatility, neural networks have gained attention for simulating large two-dimensional quantum many-body systems. However, their expressivity comes with the cost of a challenging optimization due to the in general rugged and complicated loss landscape. Here, we present a hybrid optimization scheme for neural quantum states (NQS), involving a data-driven pretraining with numerical or experimental data and a second, Hamiltonian-driven optimization stage. By using both projective measurements from the computational basis as well as expectation values from other measurement configurations such as spin-spin correlations, our pretraining gives access to the sign structure of the state, yielding improved and faster convergence that is robust w.r.t. experimental imperfections and limited datasets. We apply the hybrid scheme to the ground state search for the 2D transverse field Ising model and dipolar XY model on 6×6 and 10×10 square lattices with a patched transformer wave function, using numerical data as well as experimental data from a programmable Rydberg quantum simulator [Chen et al., Nature 616 (2023)], and show that the information from a second measurement basis highly improves the performance. Our work paves the way for a reliable and efficient optimization of neural quantum states.

Controlled Double-Direction Cyclic Quantum Communication of Arbitrary Two-Particle States.

With the rapid development of quantum communication technologies, controlled double-direction cyclic (CDDC) quantum communication has become an important research direction. However, how to choose an appropriate quantum state as a channel to achieve double-direction cyclic (DDC) quantum communication for multi-particle entangled states remains an unresolved challenge. This study aims to address this issue by constructing a suitable quantum channel and investigating the DDC quantum communication of two-particle states. Initially, we create a 25-particle entangled state using Hadamard and controlled-NOT (CNOT) gates, and provide its corresponding quantum circuit implementation. Based on this entangled state as a quantum channel, we propose two new four-party CDDC schemes, applied to quantum teleportation (QT) and remote state preparation (RSP), respectively. In both schemes, each communicating party can synchronously transmit two different arbitrary two-particle states to the other parties under supervisory control, achieving controlled quantum cyclic communication in both clockwise and counterclockwise directions. Additionally, the presented two schemes of four-party CDDC quantum communication are extended to situations where n>3 communicating parties. In each proposed scheme, we provide universal analytical formulas for the local operations of the sender, supervisor, and receiver, demonstrating that the success probability of each scheme can reach 100%. These schemes only require specific two-particle projective measurements, single-particle von Neumann measurements, and Pauli gate operations, all of which can be implemented with current technologies. We have also evaluated the inherent efficiency, security, and control capabilities of the proposed schemes. In comparison to earlier methods, the results demonstrate that our schemes perform exceptionally well. This study provides a theoretical foundation for bidirectional controlled quantum communication of multi-particle states, aiming to enhance security and capacity while meeting the diverse needs of future network scenarios.

Boosted Bell-state measurements for photonic quantum computation

Fault-tolerant fusion-based photonic quantum computing (FBQC) greatly relies on entangling two-photon measurements, called fusions. These fusions can be realized using linear-optical projective Bell-state measurements (BSMs). These linear-optical BSMs are limited to a success probability of 50%, greatly reducing the performance of FBQC schemes. The performance of FBQC can be improved using boosting, thus achieving higher success probabilities by adding additional resources. Here, we realize a boosted BSM using a 4 × 4 multiport splitter and an additional entangled photon pair, allowing for a success probability of up to 75%. In our experiment, we obtain a success probability for our boosted BSM of (69.3 ± 0.3)%, clearly exceeding the 50% limit. We further demonstrate the significance of our boosted BSM for FBQC, showing a threefold increase in robustness to photon loss and a significant reduction of the logical error rates.

Randomness-free detection of non-projective measurements: qubits & beyond

Abstract Non-projective measurements play a crucial role in various information-processing protocols. In this work, we propose an operational task to identify measurements that are neither projective nor classical post-processing of data obtained from projective measurements. Our setup involves space-like separated parties with access to a shared state with bounded local dimensions. Specifically, in the case of qubits, we focus on a bipartite scenario with different sets of target correlations. While some of these correlations can be obtained through non-projective measurements on a shared two-qubit state, it is impossible to generate these correlations using projective simulable measurements on bipartite qubit states, or equivalently, by using one bit of shared randomness and local post-processing. For certain target correlations, we show that detecting qubit non-projective measurements is robust under arbitrary depolarizing noise, except in the limiting case. We extend this task for qutrits and demonstrate that some correlations achievable via local non-projective measurements cannot be reproduced by both parties performing the same qutrit projective simulable measurements on their pre-shared state. We provide numerical evidence for the robustness of this scheme under arbitrary depolarizing noise. For a more generic consideration (bipartite and tripartite scenario), we provide numerical evidence for a projective-simulable bound on the reward function for our task. We also show a violation of this bound by using qutrit positive operator valued measures. From a foundational perspective, we extend the notion of non-projective measurements to general probabilistic theories (GPTs) and use a randomness-free test to demonstrate that a class of GPTs, called square-bits or box-world are unphysical.

Optimal local measurements in single-parameter quantum metrology

Quantum measurement plays a crucial role in quantum metrology. Due to the limitations of experimental capabilities, collectively measuring multiple copies of probing systems can present significant challenges. Therefore, the concept of locality in quantum measurements must be considered. In this work, we investigate the possibility of achieving the quantum Cramér-Rao bound (QCRB) through local measurements (LMs). We first demonstrate that if there exists a LM to saturate the QCRB for qubit systems, then we can construct another rank-1 local projective measurement to saturate the QCRB. In this sense, rank-1 local projective measurements are sufficient to analyze the problem of saturating the QCRB. For pure qubits, we propose two necessary and sufficient methods to determine whether and how a given parameter estimation model can achieve the QCRB through LMs. The first method, dubbed the iterative matrix partition method and based on unitary transformations that render the diagonal entries of a traceless matrix vanish, elucidates the underlying mathematical structure of LMs as well as the local measurements with classical communications (LMCC), generalizing the result by Zhou . [], which only holds for the later case. We clarify that the saturation of the QCRB through LMs for the Greenberger–Horne–Zeilinger-encoded states is actually due to the self-similar structure in this approach. The second method, dubbed the hierarchy of orthogonality conditions and based on the parametrization of rank-1 measurements for qubit systems, allows us to construct several examples of saturating QCRBs, including the three-qubit W states and the N-qubit W states (N≥3). Our findings offer insights into achieving optimal performance in quantum metrology when measurement resources are limited. Published by the American Physical Society 2025

Impact of Ecological Restoration on Carbon Sink Function in Coastal Wetlands: A Review

Reducing carbon emissions and increasing carbon sinks have become the core issues of the international community. Although coastal blue carbon ecosystems (such as mangroves, seagrass beds, coastal salt marshes and large algae) account for less than 0.5% of the seafloor area, they contain more than 50% of marine carbon reserves, occupying an important position in the global carbon cycle. However, with the rapid development of the economy and the continuous expansion of human activities, coastal wetlands have suffered serious damage, and their carbon sequestration capacity has been greatly limited. Ecological restoration has emerged as a key measure to reverse this trend. Through a series of measures, including restoring the hydrological conditions of damaged wetlands, cultivating suitable plant species, effectively managing invasive species and rebuilding habitats, ecological restoration is committed to restoring the ecological functions of wetlands and increasing their ecological service value. Therefore, this paper first reviews the research status and influencing factors of coastal wetland carbon sinks, discusses the objectives, types and measures of various coastal wetland ecological restoration projects, analyzes the impact of these ecological restoration projects on wetland carbon sink function, and proposes suggestions for incorporating carbon sink enhancement into wetland ecological restoration.