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In this article, we investigate quantum entanglement (QE) filtering to address the challenges in multi-isotope positron emission tomography (PET) or in PET studies utilizing radiotracers with dual- positron and prompt gamma emissions. Via GATE simulation, we demonstrate the efficacy of QE filtering using a one-of-a-kind cadmium zinc telluride (CZT) PET system - establishing its viability as a multimodal scanner and ability to perform QE filtering. We show the high Compton scattering probability in this CZT-based scanner with 44.2% of gammas undergoing a single scatter prior to absorption. Additionally, the overall system sensitivity as a standard PET scanner (11.29%), QE-PET scanner (6.81%), and Compton Camera (11.29%) is quantified. Further, we find a 23% decrease in the double Compton scatter (DCSc) frequency needed for QE filtering for each mm decrease in crystal resolution and an increase in mean absolute error (MAE) of their Δϕs from 6.8° for 1 mm resolution to 9.5° , 12.2° , and 15.3° for 2, 4, and 8 mm resolution, respectively. These results reinforce the potential of CZT detectors to lead next generation PET systems taking full advantage of the QE information of positron annihilation photons.

We investigate the entanglement between the spins of two quantum dots that are not simultaneously connected to the same system. Quantum entanglement among localized spins is a crucial property for the advancement of quantum computing and quantum information. Generating and controlling an entangled state between quantum dots have garnered significant attention in recent years for this reason. In this study, we demonstrate that information about the spin orientation of a quantum dot can be preserved, utilizing Kondo entanglement, within a reservoir of electrons. Subsequently, this information can be transmitted to another dot after the initial dot has been decoupled from the reservoirs. We employ a double quantum dot system in a parallel geometry to establish the initial state, where each dot interacts with reservoirs of different symmetries. A specific phase in the couplings is chosen to induce antiferromagnetic spin correlation between the dots. The time evolution of the initial state is analyzed using the time-dependent density matrix renormalization group method. Our findings reveal that a partially entangled state between the dots can be achieved, even when they are not simultaneously connected. This entangled state arises transiently and dissipates in the stationary state. The stability of the state observed during the transient phase is demonstrated. To comprehend the details of these phenomena, we employ a canonical transformation of real space. [ABSTRACT FROM AUTHOR]

The operations of current quantum computers are still significantly affected by decoherence caused by interaction with the environment. In this work, we employ the non-perturbative hierarchical equations of motion (HEOM) method to simulate the operation of model quantum computers and reveal the effects of dissipation on the entangled quantum states and on the performance of well-known quantum algorithms. Multi-qubit entangled states in Shor's factorizing algorithm are first generated and propagated using the HEOM. It is found that the failure of factorization is accompanied by a loss of fidelity and mutual information. An important challenge in using the HEOM to simulate quantum computers in a dissipative environment is how to efficiently treat systems with many qubits. We propose a two-dimensional tensor network scheme for this problem and demonstrate its capability by simulating a one-dimensional random circuit model with 21 qubits. [ABSTRACT FROM AUTHOR]

Scaffolded molecular networks are important building blocks in biological pigment–protein complexes, and DNA nanotechnology allows analogous systems to be designed and synthesized. System–environment interactions in these systems are responsible for important processes, such as the dissipation of heat and quantum information. This study investigates the role of nanoscale molecular parameters in tuning these vibronic system–environment dynamics. Here, genetic algorithm methods are used to obtain nanoscale parameters for a DNA-scaffolded chromophore network based on comparisons between its calculated and measured optical spectra. These parameters include the positions, orientations, and energy level characteristics within the network. This information is then used to compute the dynamics, including the vibronic population dynamics and system–environment heat currents, using the hierarchical equations of motion. The dissipation of quantum information is identified by the system's transient change in entropy, which is proportional to the heat currents according to the second law of thermodynamics. These results indicate that the dissipation of quantum information is highly dependent on the particular nanoscale characteristics of the molecular network, which is a necessary first step before gleaning the systematic optimization rules. Subsequently, the I-concurrence dynamics are calculated to understand the evolution of the vibronic system's quantum entanglement, which are found to be long-lived compared to these system–bath dissipation processes. [ABSTRACT FROM AUTHOR]

A quantum homomorphic aggregation signature scheme is proposed based on GHZ states, combined with homomorphic aggregation techniques. The scheme has the following features: Firstly, by changing the existing quantum homomorphic signature scheme which generally uses Bell state as the signature particle, and choosing GHZ state as the signature particle, it can realize the signature of the multi-bit messages by preparing fewer quantum resources; Secondly, the idea of classical aggregated signature is introduced, where multiple message signatures are aggregated into a single signature by quantum entanglement swapping technique, and the verifier can determine the validity of all signatures by only one verification; At the same time, the verification of individual signatures by the aggregator is realized, and dishonest behaviors among the signature members can be detected in time; Finally, the whole signature process satisfies the basic homomorphic property. Compared with the existing quantum homomorphic signature scheme, this scheme can effectively reduce the consumption of quantum resources, improving the efficiency of signature verification and enhancing the reliability of the signature. The security analysis shows that the scheme has the verifiability, unforgeability and non-repudiation. [ABSTRACT FROM AUTHOR]

Bell-network states are a class of entangled states of the geometry that satisfy an area-law for the entanglement entropy in a limit of large spins and are automorphism-invariant, for arbitrary graphs. We present a comprehensive analysis of the effective geometry of Bell-network states on a dipole graph. Our main goal is to provide a detailed characterization of the quantum geometry of a class of diffeomorphism-invariant, area-law states representing homogeneous and isotropic configurations in loop quantum gravity, which may be explored as boundary states for the dynamics of the theory. We found that the average geometry at each node in the dipole graph does not match that of a flat tetrahedron. Instead, the expected values of the geometric observables satisfy relations that are characteristic of spherical tetrahedra. The mean geometry is accompanied by fluctuations with considerable relative dispersion for the dihedral angle, and perfectly correlated for the two nodes. [ABSTRACT FROM AUTHOR]

Quantum correlation and quantum measurement are core issues in understanding the quantum world. Revealing quantum correlations in microphysical systems through proper quantum measurements became an important research topic in the last century and gave rise to the birth of quantum information technologies. However, quantum correlations, quantum measurements, and their relationship are not yet fully understood and require further clarification. The development of generalized quantum measurement and non-destructive measurement provides new possibilities for studying these issues. In the past decade, a series of studies on quantum correlation sharing through sequential generalized measurements have unveiled a new avenue for exploring quantum correlations. These studies not only have important fundamental significance, but also involve the unexplored issue of quantum resource recycling. This review thoroughly examines recent advancements in quantum correlation sharing. It begins by elucidating the fundamental reasons for quantum correlation sharing based on the interpretation of joint probabilities, and discussing the basic definitions and concepts. Next, the sharing of Bell nonlocality under different measurement strategies and scenarios is carefully examined, especially pointing out the impact of these strategies on the maximum number of parties that can exhibit Bell nonlocality. The subsequent chapters provide an overview of other forms of quantum correlation sharing, including quantum steering, network nonlocality, quantum entanglement, and quantum contextuality. Furthermore, we summarize the advancements in the application of quantum correlation sharing across various quantum tasks, highlighting examples such as quantum random access codes, random number generation, and self-testing tasks. Finally, we discuss and enumerate some key unresolved issues in this research area, concluding this review. [ABSTRACT FROM AUTHOR]

In this paper, we analyzed the influence of transition between nontrivial and trivial topological phases on tight binding Haldane-like model in both monolayer and bilayer depleted Lieb lattices. We obtained the behavior of the entanglement negativity as a function of the temperature for different couplings of the system with aim to verify the influence of topological phase transition on entanglement. We got that the effect of gap opening of the spectrum generates a small change in the behavior of the quantum correlation and entanglement. The topological properties of the Haldane-like model on a depleted Lieb lattice, both in monolayer and bilayer configurations, are interesting for exploring topological phases of matter, especially with regard to quantum Hall effects and the role of lattice symmetries. [ABSTRACT FROM AUTHOR]

This study aims to investigates the impact of thermal effects on quantum correlations and entanglement in a two-qubit bipartite system modeled by the Heisenberg XXZ spin chain with Dzyaloshinskii-Moriya (DM) interaction along the Y-axis ( D y ). Using both analytical and numerical methods, our study examines how temperature, the DM interaction parameter D y , and the coupling coefficient J (which represents isotropy of the spin-spin interaction along the X and Y axes) influence entanglement, measured by concurrence, and general quantum correlations, quantified by quantum discord. The results reveal that entanglement and quantum discord are affected by temperature, although quantum discord persists beyond the critical temperature T c where entanglement vanishes. Furthermore, the DM interaction mitigates thermal decoherence, with higher values of D y slowing the decay of quantum correlations as temperature increases. These results are significant for developing thermally resilient quantum systems and advancing quantum information processing. [ABSTRACT FROM AUTHOR]

It's not your grandfather's quantum mechanics. Today, researchers treat entanglement as a physical resource: Quantum information can now be measured, mixed, distilled, concentrated, and diluted. [ABSTRACT FROM AUTHOR]

This paper investigates the significant role of Rashba coupling in controlling entanglement within graphene systems. We demonstrate that tuning Rashba coupling allows for effective enhancement or suppression of entanglement, with higher values providing increased robustness against thermal fluctuations. Our results indicate that achieving substantial entanglement may require external factors, such as enhanced Rashba interactions. Notably, while elevated temperatures typically degrade quantum coherence, we find that significant Rashba coupling can preserve quantum correlations, maintaining coherence under challenging thermal conditions. This preservation is essential for improving the fidelity of quantum teleportation processes, which depend on the availability of robust entangled states. Overall, the interplay between Rashba coupling, temperature, and entanglement in graphene carries significant implications for future advancements in quantum technology. The potential to develop stable and efficient quantum information systems utilizing graphene may lead to transformative breakthroughs in quantum computing and communication, underscoring the necessity for continued exploration in this promising area. [ABSTRACT FROM AUTHOR]

The article "Explaining Quanta with Optical Illusions" proposes a new way to help high school students and the general population understand quantum concepts by using optical illusions. The author introduces the concept of bistable drawings, which create ambiguity between two distinct shapes, to represent quantum objects and explain quantum superposition, collapse, complementarity, entanglement, and quantum teleportation. Additionally, the article discusses the limitations of the analogy and suggests using other optical illusions, such as spinning illusions and hybrid drawings, to overcome these limitations and further explain quantum concepts. [Extracted from the article]

The article provides an introduction to quantum computing, focusing on key concepts such as qubits, superposition, and entanglement. It explains the principles of quantum mechanics, introduces quantum gates and circuits, and discusses the implementation of quantum teleportation using the IBM Quantum Platform. The paper emphasizes the importance of quantum mechanics in modern technology and highlights the potential applications of quantum computing in various industries. The authors, Azar Khosravani and Constantin Rasinariu, provide a comprehensive overview of quantum computation and its practical implications. [Extracted from the article]

Quantum key distribution (QKD) has become an essential technology in the realm of secure communication, with applications ranging from secure data transmission to quantum networks. This paper presents a simple, compact, and cost-effective setup for undergraduate tutorial demonstrations of QKD. It relies on using weak coherent pulses, which can be readily produced using an attenuated laser. The system employs the simplified three-state BB84 protocol in free space, with states encoded using linear polarization. Polarization encoding can be done passively or actively, depending on the budget available. Time multiplexing is implemented at the receiver to reduce the number of required detectors. Only two detectors are used to implement measurements on two bases, with a total of four outcomes. The result demonstrates the practicality of the system for free-space quantum communication, and its compact and portable nature makes it particularly suitable for pedagogical demonstrations. This work paves the way for engaging undergraduate students in the field of quantum communication through hands-on laboratory projects. Editor's note: Quantum cryptography is not only a major application of quantum technologies but also an easy gateway to entanglement and modern quantum mechanics in the classroom. Several protocols based upon the exchange of single photons can easily be demonstrated with faint laser pulses. This paper presents a simple and cost-effective quantum key distribution setup based on the BB84 protocol that can be used for science outreach, in the undergraduate laboratory, or in class demonstrations. [ABSTRACT FROM AUTHOR]

We determine the asymptotics of the block Toeplitz determinants detTn(ϕ)$\det T_n(\phi)$ as n→∞$n\rightarrow \infty$ for N×N$N\times N$ matrix‐valued piecewise continuous functions ϕ$\phi$ with a finitely many jumps under mild additional conditions. In particular, we prove that detTn(ϕ)∼GnnΩEasn→∞,$$\begin{equation*} \hspace*{50pt}\det T_n(\phi) \sim G^n n^\Omega E\quad {\rm as}\ n\rightarrow \infty,\hspace*{-50pt} \end{equation*}$$where G$G$, E$E$, and Ω$\Omega$ are constants that depend on the matrix symbol ϕ$\phi$ and are described in our main results. Our approach is based on a new localization theorem for Toeplitz determinants, a new method of computing the Fredholm index of Toeplitz operators with piecewise continuous matrix‐valued symbols, and other operator theoretic methods. As an application of our results, we consider piecewise continuous symbols that arise in the study of entanglement entropy in quantum spin chain models. [ABSTRACT FROM AUTHOR]

In this work, we investigate effect of parity-time ( PT ) symmetric operation on the dynamic behavior of entanglement for two qubits system in Markovian and non-Markovian regimes with the resonant and off-resonant cases. First we derive the explicit expressions of concurrence quantifying entanglement for an exactly solving model consisting of two qubits interacting with independent structured reservoir. Then, we give two schemes, i.e. pre- and post- PT symmetric operations, to show the performance of PT symmetric operation on entanglement dynamics of two qubits. By investigation, we find that the lower the absolute value of the PT operation strength, the better the enhancement of entanglement. In addition, we show that the entanglement can be obviously enhanced by means of the pre- PT symmetric operation in different regimes. [ABSTRACT FROM AUTHOR]

As 'Internet+' technology and e-commerce third-party platforms evolve, consumer options for purchasing fresh products now include both offline and online channels, giving rise to a mixed dual-channel supply chain. We examine this dual-channel supply chain, constructing a market demand function influenced by fresh produce pricing and preservation efforts.Optimal strategies for each stakeholder and the supply chain's maximum profit are analyzed through both classical and quantum game theory. The results indicate that under centralized decision-making, the equilibrium solutions are identical for classical and quantum games, with the quantum entanglement degree $ \gamma = 0 $. In scenarios where market demand exhibits low sensitivity to freshness preservation efforts, the entanglement degree between suppliers and retailers can be elevated by implementing a 'freshness preservation cost-sharing + revenue-sharing contract, ' thereby enhancing supply chain efficiency and profit. This study contributes to the literature by offering new theoretical insights into mitigating free-riding behavior in fresh food retail and explores the potential applications of quantum games in economics. [ABSTRACT FROM AUTHOR]

Microwave‐optics entanglement plays a crucial role in building hybrid quantum networks with quantum nodes working in the microwave and optical frequency bands. However, there are limited efficient ways to produce such entanglement due to the large frequency mismatch between the two regimes. Here, a new mechanism is presented to prepare microwave‐optics entanglement based on a hybrid system of two coupled opto‐ and magnomechanical microspheres, i.e., an yttrium‐iron‐garnet (YIG) sphere and a silica sphere. The YIG sphere holds a magnon mode and a vibration mode induced by magnetostriction, while the silica sphere supports an optical whispering‐gallery mode and a mechanical mode coupled via an optomechanical interaction. The two mechanical modes are close in frequency and directly coupled via physical contact of the two microspheres. It is shown that by simultaneously activating the magnomechanical (optomechanical) Stokes (anti‐Stokes) scattering, stationary entanglement can be established between the magnon and optical modes via mechanics‐mechanics coupling. This leads to stationary microwave‐optics entanglement by further coupling the YIG sphere to a microwave cavity and utilizing the magnon‐microwave state swapping. The protocol is within reach of current technology and may become a promising new approach for preparing microwave‐optics entanglement, which finds unique applications in hybrid quantum networks and quantum information processing with hybrid quantum systems. [ABSTRACT FROM AUTHOR]

In this paper, we extend a holographic construction for the entanglement negativity of two disjoint subsystems in the literature to CFTds with a conserved charge dual to bulk AdSd+1 geometries. This involves an algebraic sum of the areas of bulk RT surfaces for certain appropriate combinations of subsystems. In this context, we compute the holographic entanglement negativity for two disjoint subsystems with long rectangular strip geometries in CFTds dual to bulk RN-AdSd+1 black holes in a perturbative framework. Our results at the leading order reproduce significant features observed earlier in the literature and conform to quantum information theory, which constitute strong substantiation of our construction. [ABSTRACT FROM AUTHOR]

The controlled SWAP test for detecting and quantifying entanglement applied to pure qubit states is robust to small errors in the states and efficient for large multi-qubit states (Foulds et al. 2021 Quantum Sci. Technol. 6, 035002 (doi:10.1088/2058-9565/abe458)). We extend this, and the related measure concentratable entanglement (CE), to enable important practical applications in quantum information processing. We investigate the lower bound of concentratable entanglement given in (Beckey et al. 2023 Phys. Rev. A107, 062425 (doi:10.1103/physreva.107.062425)) and conjecture an upper bound of the mixed-state concentratable entanglement that is robust to c-SWAP test errors. Since experimental states are always slightly mixed, our work makes the c-SWAP test and CE measure suitable for application in experiments to characterize entanglement. We further present the CE of some key higher-dimensional states such as qudit states and entangled optical states to validate the CE as a higher-dimensional measure of entanglement. This article is part of the theme issue 'The quantum theory of light'. [ABSTRACT FROM AUTHOR]

Quantum entanglement describes superposition states in multi-dimensional systems—at least two partite—which cannot be factorized and are thus non-separable. Non-separable states also exist in classical theories involving vector spaces. In both cases, it is possible to violate a Bell-like inequality. This has led to controversial discussions, which we resolve by identifying an operational distinction between the classical and quantum cases. This article is part of the theme issue 'The quantum theory of light'. [ABSTRACT FROM AUTHOR]

Establishing quantum mechanically entangled states between spatially separated 2D heterostructure offers a way to tailor novel energy transfer mechanisms at the precision of atomic level. Here, strongly coupled systems formed by monolayer WS2, spatially separated monolayer MoS2, and Ag nanoholes (Ag‐NHs) with square lattice are investigated by using an ultrafast pump‐probe approach. From transient absorption spectra of the prototypical Ag‐NHs/WS2/SiO2 (10 nm)/MoS2 heterostructures, a Rabi splitting up to 80 meV is observed, which is almost 21/2 times larger than that of each individual component. The result is as expected since Rabi splitting depends on the square root of the layer number involved, thus suggesting that the A exciton of WS2 and spatially separated B exciton of MoS2 are entangled by the Bloch‐surface plasmon polariton mode. Additionally, whether the donor or the acceptor is excited, the bleaching signals in the heterostructures all appear instantaneously and exhibit exactly the same dynamic process, further clearly highlighting the presence of quantum mechanically entangled states. From another perspective, such entangled states assist remarkably efficient energy transfer, which is also demonstrated by significantly enhanced fluorescence emission from MoS2, with an enhancement factor of 25. This research establishes the scientific foundation for developing related heterostructure optoelectronic devices. [ABSTRACT FROM AUTHOR]

Optical quantum communication technologies are making the prospect of unconditionally secure and efficient information transfer a reality. The possibility of generating and reliably detecting quantum states of light, with the further need of increasing the private data-rate is where most research efforts are focusing. The physical concept of entanglement is a solution guaranteeing the highest degree of security in device-independent schemes, yet its implementation and preservation over long communication links is hard to achieve. Lithium niobate-on-insulator has emerged as a revolutionising platform for high-speed classical telecommunication and is equally suited for quantum information applications owing to the large second-order nonlinearities that can efficiently produce entangled photon pairs. In this work, we generate maximally entangled quantum states in the time-bin basis using lithium niobate-on-insulator photonics at the fibre optics telecommunication wavelength, and reconstruct the density matrix by quantum tomography on a single photonic integrated circuit. We use on-chip periodically-poled lithium niobate as source of entangled qubits with a brightness of 242 MHz/mW and perform quantum tomography with a fidelity of 91.9 ± 1.0 %. Our results, combined with the established large electro-optic bandwidth of lithium niobate, showcase the platform as perfect candidate to realise fibre-coupled, high-speed time-bin quantum communication modules that exploit entanglement to achieve information security. [ABSTRACT FROM AUTHOR]

Quantum correlations between a pair of spin-1/2 represented by an XYZ-Heisenberg chain are investigated under symmetric, anti-symmetric and long-range dipolar interactions. Entanglement, steering, and nonlocality are quantified through concurrence, 3-steering functions, and normalized Bell functions, respectively. By modulating interaction directions, effects on quantum correlations are elucidated for two scenarios: dipolar coupling along x or z, with symmetric and anti-symmetric terms oriented perpendicular or parallel. The results indicate that quantum correlations are enhanced when dipolar coupling aligns with the z-direction versus the x-direction. Moreover, increasing long-range dipolar interaction strength degrades the quantum correlations for weaker Heisenberg chain coupling. Positioning symmetric and anti-symmetric couplings along the z-direction affect quantum correlation dissipation at a critical point. Furthermore, with symmetric and anti-symmetric terms oriented along x, quantum correlations diminish for x-direction dipolar coupling. [ABSTRACT FROM AUTHOR]

This article introduces new neutrosophic principles aiming to extend and generalize the concepts of locality and nonlocality by addressing scenarios involving indeterminacy, together with partiality and multitude, in physics, mechanics, cosmology, biology, medicine, chemistry, economics, ecology, sociology. Locality refers to interactions or processes confined within a limited region of space or time. But there may be a Total (100%) Locality, or a Partial Locality (less than 100% and greater than 0%). The effects are constrained to the immediate environment. Contrariwise, NonLocality refers to interactions or connections between entities separated by space or time. The changes in one location have instantaneous effects on another. Similarly, there may be a Total (100%) NonLocality, or a Partial NonLocality (less than 100% and greater than 0%). Total (100%) or Partial (less than 100% and greater than 0%) Indeterminacy may arise from hidden variables and from environment. For instance, it may involve nonlocal connections between objects that are only partially entangled or influence each other in limited ways, rather than exhibiting complete freedom. The Principle of Partial Locality, Partial Indeterminacy, and Partial NonLocality implies an interplay of locality, indeterminacy, and nonlocality acting in a dynamic neutrosophic system. A generalization of (Locality, Indeterminacy, NonLocality) is the (MultiLocality, MultiIndeterminacy, MultiNonLocality). Practical examples from different fields are provided. [ABSTRACT FROM AUTHOR]

Open quantum systems are a subject of immense interest as their understanding is crucial in the implementation of modern quantum technologies. In the study of their dynamics, the role of the initial system–environment correlations is commonly ignored. In this work, to gain insights into the role of these correlations, we solve an exactly solvable model of a single two-level system interacting with a spin environment, with the initial system state prepared by a suitable unitary operation. By solving the dynamics exactly for arbitrary system–environment coupling strength while taking into account the initial system–environment correlations, we show that the effect of the initial correlations is, in general, very significant and nontrivial. To further highlight the importance of the initial system–environment correlations, we also extend our study to investigate the dynamics of the entanglement between two two-level systems interacting with a common spin environment. [ABSTRACT FROM AUTHOR]

The growth of quantum technologies is attracting the interest of many students eager to learn concepts such as quantum entanglement or quantum superposition. However, the non-intuitive nature of these concepts poses a challenge to understanding them. Here, we present an entangled photon system which can perform a Bell test, i.e. the CHSH inequality, and can obtain the complete tomography of the two-photon state. The proposed setup is versatile, cost-effective and allows for multiple classroom operating modes. We present two variants, both facilitating the measurement of Bell inequalities and quantum state tomography. Experimental results showcase successful manipulation of the quantum state of the photons, achieving high-fidelity entangled states and significant violations of Bell's inequalities. Our setup's simplicity and affordability enhances accessibility for less specialized laboratories, allowing students to familiarize themselves with quantum physics concepts. [ABSTRACT FROM AUTHOR]

In this paper, we provide a structure theorem and various characterizations of degradable strong entanglement breaking maps on separable Hilbert spaces. In the finite-dimensional case, we prove that unital degradable entanglement breaking maps are precisely the C ⁎ -extreme points of the convex set of unital entanglement breaking maps on matrix algebras. Consequently, we get a structure for unital degradable positive partial transpose (PPT) maps. [ABSTRACT FROM AUTHOR]

This study reevaluates criticism of the Korean government's R&D investment strategy, which was considered an 'R&D cartel' and was cited as a reason for the Korean government's R&D cuts in 2023, through an advanced framework of quantum game theory. By modeling the interaction between the government and researchers as a quantum information strategy game, it redefines the dynamics of R&D investment as a quantum game involving two key players: the R&D manager (Alice) and the research performer (Bob). This quantum game, akin to the Prisoner's Dilemma but focused on responsibility and sincerity, allows for the exploration of strategic complexities and decision-making dynamics not possible in classical models. It introduces quantum entanglement and superposition as innovative strategies to shift the paradigm of R&D investment, suggesting that terms like 'R&D bureaucracy' and 'R&D monopoly' more accurately describe the moral hazards in this sector than 'R&D cartel'. Through simulations, the paper demonstrates how quantum strategies can significantly alter outcomes, providing fresh insights and policy alternatives for R&D innovation. This research not only challenges conventional investment frameworks but also proposes a novel approach for achieving Pareto optimal outcomes in government R&D investments, emphasizing the transformative potential of quantum game theory in strategic decision-making and policy development. [ABSTRACT FROM AUTHOR]

Polarization entanglement holds significant importance for photonic quantum technologies. Recently emerging subwavelength nonlinear quantum light sources, e.g., GaP and LiNbO3 thin films, benefiting from the relaxed phase-matching constraints and volume confinement, have shown intriguing properties, such as high-dimensional hyperentanglement and robust entanglement anti-degradation. Van der Waals (vdW) NbOCl2 crystal, with strong optical nonlinearities, has emerged as a potential candidate for ultrathin quantum light sources. However, polarization entanglement is inaccessible in the NbOCl2 crystal due to its unfavorable nonlinear susceptibility tensor. Here, by leveraging the twist-stacking degree of freedom inherently in vdW systems, we showcase the preparation of polarization entanglement and quantum Bell states. Van der Waals NbOCl2 crystal is a candidate platform for subwavelength thin film photon-pair sources. Here, the authors demonstrate generation of polarization entangled states from a two-layer stack of orthogonally oriented van der Waals crystal. [ABSTRACT FROM AUTHOR]

The quantum properties of superradiant pulses generated at the radiative recombination of an electron–hole condensate in semiconductor heterostructures at room temperature have been studied using optical homodyne tomography. Signatures of the quantum entanglement of superradiant states, which are superpositions of two coherent states, have been revealed. It has been demonstrated that reconstructed Wigner functions under certain conditions are very similar to the Wigner functions of the Schrödinger cat states. [ABSTRACT FROM AUTHOR]

Parrondo's paradox refers to an unexpected effect when some combination of biased quantum walks shows a counterintuitive inversion of the bias direction. To date this effect was studied in the case of one-dimensional discrete-time quantum walks with deterministic sequences of two or more quantum coins and one shift operator. In the present work, we show that Parrondo's paradox may also occur for one coin and two different shift operators which create deterministic periodic or aperiodic sequences. Moreover, we demonstrate how Parrondo's paradox affects the time evolution of the walker-coin quantum entanglement for this kind of quantum walks. [ABSTRACT FROM AUTHOR]

The Schmidt number characterizes the quantum entanglement of a bipartite mixed state and plays a significant role in certifying entanglement of quantum states. We derive a Schmidt number criterion based on the trace norm of the correlation matrix obtained from the general symmetric informationally complete measurements. The criterion gives an effective way to quantify the entanglement dimension of a bipartite state with arbitrary local dimensions. We show that this Schmidt number criterion is more effective and superior than other criteria such as fidelity, CCNR (computable cross-norm or realignment), MUB (mutually unbiased bases) and EAM (equiangular measurements) criteria in certifying the Schmidt numbers by detailed examples. [ABSTRACT FROM AUTHOR]

Quantum entanglement plays a pivotal role in quantum information processing. Quantifying quantum entanglement is a challenging and essential research area within the field. This manuscript explores the relationships between bipartite entanglement concurrence, multipartite entanglement concurrence, and genuine multipartite entanglement (GME) concurrence. We derive lower bounds on GME concurrence from these relationships, demonstrating their superiority over existing results through rigorous proofs and numerical examples. Additionally, we investigate the connections between GME concurrence and other entanglement measures, such as tangle and global negativity, in multipartite quantum systems. [ABSTRACT FROM AUTHOR]

The existence of quantum entanglement implies a non-vanishing thermodynamic quantity termed an ergotropic gap (EG). Our goal in this work is to characterize entanglement from the perspective of the ergotropic gap. We firstly define the passive-state energy of the marginals as an entanglement monotone named EG entanglement, additionally, we derive an analytical formula for two-qubit entangled systems. Another interesting result is the monogamy relation for the EG entanglement, which indicates that the shareability of bipartite entanglement in multipartite entangled systems is bounded by the amount of entanglement. Finally, we show that a necessary condition for an n-qubit pure state is that all marginal EG entanglements should satisfy polygon inequalities. These results reveal a new understanding of entanglement from the view of thermodynamics. [ABSTRACT FROM AUTHOR]

We study the polygamy property in tripartite and multipartite quantum systems. In tripartite system, we build a solution set for polygamy in tripartite system and find a sufficient and necessary condition of the set for continuous measure of quantum correlation Q to be polygamous. In multipartite system, we provide generalized definitions for polygamy in n-qubit systems with n ≥ 4 , and then, we build polygamy inequalities with a polygamy power β . Next we also describe that any entanglement of assistance can be polygamy according to our new definition in multipartite systems. For better understanding, we use right triangle and tetrahedron to explain our new polygamy relations. Moreover, the polygamy relations between each single qubit and its remaining partners are also investigated to enrich our results. [ABSTRACT FROM AUTHOR]

Correlations may arise in quantum systems through various means, of which the most remarkable one is quantum entanglement. Additionally, there are systems that exhibit nonclassical correlations even in the absence of entanglement. Quantum dissonance refers to how Quantum Discord (QD) — the difference between the total correlation and the classical correlation in a given quantum state — appears as a nonclassical correlation in a system without entanglement. It could be said that QD has the potential to provide a more inclusive viewpoint for discerning the nonclassical correlations. In this paper, we address the problem of manipulating the QD between two subsystems through local operations. We propose two explicit procedures for obtaining separable Werner states, a type of mixed state with nonzero QD. Both approaches involve performing local operations on classically correlated states and offers a step-by-step method for obtaining separable Werner states with nonzero discord, providing an alternative (explicit and user-friendly) to existing methods. [ABSTRACT FROM AUTHOR]

In this paper, we analyze, under realistic experimental conditions, entanglement and quantum discord in a two-mode Gaussian state ρ A B coupled to a thermal reservoir. The mode A (B) is generated during the first(second) transition of a nondegenerate three-level laser. The gain medium of the laser is a set of three-level atoms in a cascade configuration. The atoms are prepared initially in a superposition of the upper and lower levels. In the good cavity-limit, applying the master equation we obtain the covariance matrix of the state ρ A B at steady-state. We use the entanglement of formation and the Gaussian quantum discord to quantify entanglement and quantum correlations beyond entanglement, respectively. The two indicators of nonclassicality are defined by means of the von Neumann entropy, and obtained as functions of the parameters characterizing the physical and environmental parameters of the state ρ A B , i.e. atomic coherence, dissipation and thermal photon number. As results, we find that maximum entanglement and discord could be achieved by adjusting the degree of atomic coherence. In contrary to the expectation based on the assumption that entanglement is a part of quantum discord, it is found that the latter can be less than the former. Under thermal noise effect, we find that quantum discord measured when the state ρ A B exhibits entanglement diminishes drastically, while that measured when the ρ A B is separable displays a relatively robust behavior seeming to be captured over a wide range of temperature. Our results assert that nondegenerate three-level lasers may play a crucial role in the implementation of quantum processing tasks, particularly those who do not need entangled states. [ABSTRACT FROM AUTHOR]

Effective schemes are proposed for the generation of bipartite Bell states and theoretically scaling up to arbitrary multiparticle Greenberger–Horne–Zeilinger, cluster, and W states among quantum-dot (QD) spins. They are realized based on the interaction between an single incident photon and single QD spin. Errors from system nonuniformity and defective photon scattering are transformed into detectable photon losses. In the event of a failed experiment, the system allows for the reinjection of a single photon and the reinitiation of the quantum circuit, until a successful outcome is achieved. This loss-prediction and experiment-repeatability approach ensures that the schemes are implemented with uniform and robust fidelity. Compared with the previous methods, these schemes significantly simplify experimental procedures and analysis processes. Furthermore, upon successful execution of the experiment, the use of single-photon detector can faithfully differentiate between various types of entangled states, depending on the initial states of the QD spins. An analysis of the feasibility of the schemes under current experimental parameters suggests high efficiency even in the weak coupling region. [ABSTRACT FROM AUTHOR]

In this paper, a quantum secure multi-party summation scheme with a third party based on quantum Fourier transform (QFT) is put forward, where the third party cannot be permitted to cooperate with others but is allowed for all kinds of attacks. Under the help of third party, N users can calculate the addition modulo d of their private integer strings. The third party generates two-level single qubit and its product state as the initial quantum resource, produces the traveling particles with QFT and the controlled-not (CNOT) operations, and sends the traveling particles out to the first users; then, N users encode their private integer sequences by performing the phase shifting operations on the travelling particles one after another; and finally, the third party decodes out the summation of the private integer sequences from N users through CNOT operations and inverse quantum Fourier transform (IQFT). This protocol only adopts two-level single particle state and its product state as initial quantum resource, only needs d -level single particle measurement and does not need to perform quantum entanglement swapping. Security analysis indicates that this protocol can overcome not only the outside attack but also the participant attack. [ABSTRACT FROM AUTHOR]

In this paper, by using eleven entangled quantum states as a quantum channel, we propose a cyclic and asymmetric novel protocol for four participants in which both Alice and Bob can transmit two-qubit states, and Charlie can transmit three-qubit states with the assistance of the supervisor David, who provides a guarantee for communication security. This protocol is based on GHZ state measurement (GHZ), single-qubit measurement (SM), and unitary operations (UO) to implement the communication task. The analysis demonstrates that the success probability of the proposed protocol can reach 100%. Furthermore, considering that in actual production environments, it is difficult to avoid the occurrence of noise in quantum channels, this paper also analyzes the changes in fidelity in four types of noisy scenarios: bit-flip noise, phase-flip noise, bit-phase-flip noise, and depolarizing noise. Showing that communication quality only depends on the amplitude parameters of the initial state and decoherence rate. Additionally, we give a comparison with previous similar schemes in terms of achieved method and intrinsic efficiency, which illustrates the superiority of our protocol. Finally, in response to the vulnerability of quantum channels to external attacks, a security analysis was conducted, and corresponding defensive measures were proposed. [ABSTRACT FROM AUTHOR]

We discuss a family of W-class states describing three-qubit systems. For such systems, we analyze the relations between the entanglement measures and the nonlocality parameter for a two-mode mixed state related to the two-qubit subsystem. We find the conditions determining the boundary values of the negativity, parameterized by concurrence, for violating the Bell-CHSH inequality. Additionally, we derive the value ranges of the mixedness measure, parameterized by concurrence and negativity for the qubit–qubit mixed state, guaranteeing the violation and non-violation of the Bell-CHSH inequality. [ABSTRACT FROM AUTHOR]

In this paper, we analyzed the influence of the spin Nernst effect on quantum correlation in a layered ferrimagnetic model. In the study of three-dimensional ferrimagnets, the focus is on materials with a specific arrangement of spins, where the neighboring spins are parallel and the others are antiparallel. The anisotropic nature of these materials means that the interactions between spins depend on their relative orientations in different directions. We analyzed the effect of magnon bands induced by the coupling parameters on entanglement negativity. The influence of the coupling parameters of the topologic phase transition on quantum entanglement is investigated as well. Numerical simulations using the Lanczos algorithm and exact diagonalization for different lattice sizes are compared with the results of spin wave theory. [ABSTRACT FROM AUTHOR]

Machine learning has demonstrated tremendous potential in solving real-world problems. However, with the exponential growth of data amount and the increase of model complexity, the processing efficiency of machine learning declines rapidly. Meanwhile, the emergence of quantum computing has given rise to quantum machine learning, which relies on superposition and entanglement, exhibiting exponential optimisation compared to traditional machine learning. Therefore, in the paper, we survey the basic concepts, algorithms, applications and challenges of quantum machine learning. Concretely, we first review the basic concepts of quantum computing including qubit, quantum gates, quantum entanglement, etc.. Secondly, we in-depth discuss 5 quantum machine learning algorithms of quantum support vector machine, quantum neural network, quantum k-nearest neighbour, quantum principal component analysis and quantum k-Means algorithm. Thirdly, we conduct discussions on the applications of quantum machine learning in image recognition, drug efficacy prediction and cybersecurity. Finally, we summarise the challenges of quantum machine learning consisting of algorithm design, hardware limitations, data encoding, quantum landscapes, noise and decoherence. [ABSTRACT FROM AUTHOR]

Quantum heat engines (QHEs) are established by applying the principles of quantum thermodynamics to small−scale systems, which leverage quantum effects to gain certain advantages. In this study, we investigate the quantum Otto cycle by employing the dipole−dipole coupled polar molecules as the working substance of QHE. Here, the molecules are considered to be trapped within an optical lattice and located in an external electric field. We analyze the work output and the efficiency of the quantum Otto heat engine (QOHE) as a function of various physical parameters, including electric field strength, dipole−dipole interaction and temperatures of heat baths. It is found that by adjusting these physical parameters the performance of the QOHE can be optimized effectively. Moreover, we also examine the influences of the entanglement and relative entropy of coherence for the polar molecules in thermal equilibrium states on the QOHE. Our results demonstrate the potential of polar molecules in achieving QHEs. [ABSTRACT FROM AUTHOR]

In this paper we investigate the quantum correlation(geometric quantum discord and quantum entanglement) in two-qubit Heisenberg XYZ Hamiltonian with Dzyaloshinskii-Moriya interaction and Kaplan–Shekhtman–Entin-Wohlman–Aharony interaction under the effect of nonuniform external magnetic field. Here, we calculate the effect of nonuniform magnetic field, exchange interaction J x , J y , J z , Dzyaloshinskii –Moriya interaction D and Kaplan–Shekhtman–Entin-Wohlman–Aharony interaction Γ on the quantum correlation`dynamics in case of the antiferromagnetism. The results obtained reveal that the nonuniform part of the external magnetic field plays the important role in the preservation of quantum correlation. Also, it is shown that the geometric quantum discord is more robust than the quantum entanglement and the effect of the different parameters on the quantum correlation` dynamic depend noticeably on choice of initial state. In Fig. 13, we indicate the time evolution of GQD and QE for various b = 1 , 1.5 , 2 , 4 with = 0.99 , γ = 1 , J x = 2 , J y = 1.5 , , J z = 1 , D = 0.5 , Γ = 0.2 , B = 1 . [ABSTRACT FROM AUTHOR]