Degree Of Entanglement Research Articles

Two-Photon Excitation Sets Limit to Entangled Photon Pair Generation from Quantum Emitters.

Entangled photon pairs are key to many novel applications in quantum technologies. Semiconductor quantum dots can be used as sources of on-demand, highly entangled photons. The fidelity to a fixed maximally entangled state is limited by the excitonic fine-structure splitting. This work demonstrates that, even if this splitting is absent, the degree of entanglement cannot reach unity when the excitation pulse in a two-photon resonance scheme has a finite duration. The degradation of the entanglement has its origin in a dynamically induced splitting of the exciton states caused by the laser pulse itself. Hence, in the setting explored here, the excitation process limits the achievable concurrence for entangled photons generated in an optically excited four-level quantum emitter.

Strong coupling in the entanglement dynamics of two qubits interacting with a graphene nanodisk

We investigate the entanglement dynamics of two qubits interacting with a graphene nanodisk using the macroscopic quantum electrodynamics method. By modifying the free-space decay rate of each qubit, we study the coupling strength between the nanoparticle and the qubits. We find that as the free-space decay rate increases, the decaying Rabi oscillations featured in the qubit population dynamics change to complex non-Markovian dynamical population evolution. This is also reflected on the concurrence, which at weak or moderate light–matter coupling conditions, attains values up to 0.5, while as the coupling conditions become stronger, larger values are also transiently observed. Our findings indicate that graphene nanostructures can provide a platform for the realization of high degree of entanglement in the strong coupling regime at the nanoscale, essential for quantum technology applications.

Molecular Dynamics Study on the Microscopic Mechanism of Mechanical Properties of Nafion Membrane

As the core component of new energy vehicles, the safe operation of polymer electrolyte fuel cells has become more important with the rapid development of the new energy field. Since polymer electrolyte membrane (PEM) works at a hydrated environment, the mechanical properties of its hydrated state must remain stable. At present, studies have shown that the increase of water content will reduce the mechanical properties of materials, such as the decrease of Young's modulus, but the microscopic mechanism has not been elucidated. This presents a challenge to the work to develop novel PEMs. We tried to use the method of coarse-grained (CG) molecular dynamics (MD) simulation to study the microscopic mechanism of the mechanical properties of basic PEM Nafion membrane under different water content conditions. The purpose of this study is to seek to demonstrate the microscopic mechanism by which macroscopic mechanical properties are determined from the MD perspective, thereby providing general guidance for the future development of novel PEMs. More specifically, we tested the Nafion membrane (CG model with 4 beads on the main chain and 2 beads on the side chain) under tensile and compressive stress (strain 0-0.5) at different water contents (2-14). Quantified micro-parameters make it possible to establish macro-micro relationships. Considering that our chosen Nafion is the basic model, it may have good generality to other complex models.At the macroscopic level, our results show that increasing the water content reduces Young's modulus of the material. The decreasing rate of Young's modulus shows a slowing trend. This is in good agreement with previous research. At the microscopic level, our results show that the coordination number between any two types of atoms except water molecules within the same volume decreases with increasing water content, suggesting that the increase in water molecules forces other atoms to away from each other, thereby increasing the spacing between molecules. Therefore, the dominant force on this distance scale, that is, the electrostatic attraction between positive and negative ions is reduced. We have a reason to think that this is the main micromechanical factor to change macroscopic mechanical properties.In addition, the results of polymer chain entanglement parameters show that the degree of entanglement of polymer chains deepened with the increase of water content. The complex entangled structure will increase the difficulty of the polymer deformation. We believe that this is one of the micromechanical factors to decrease the Young's modulus. The study of these mechanisms may help in the development of new Nafion materials.

Nonlinear dynamics of a heterogeneous quantum Commons’ tragedy

This paper first builds a nonlinear dynamic system of the Commons’ tragedy with quantum strategies in discrete time. There are two heterogeneous expectations in the game, namely, one of the two players is boundedly rational and the other is of adaptive expectation. Secondly, we obtain a sufficient and necessary condition for quantum Nash equilibria to be stable equilibria. Finally, we investigate the impacts of quantum entanglement on the stable region of systems and analyze the behaviors of complex dynamical systems. The results show that quantum Nash equilibria are stable points of nonlinear dynamics for quantum Commons’ tragedy if both quantum entanglement and quantum strategy adjustment speed satisfy certain conditions. In addition, numerical simulations discuss the features of nonlinear dynamics, such as bifurcation, the largest Lyapunov exponent, fractal dimension, strange attractor, and sensitivity to initial conditions. The numerical results show that nonlinear dynamics appear chaotic if the adjustment speed of quantum strategy or the quantum entanglement degree is larger.

Geometrical and dynamical description of two interacting spins under the XXZ-type Heisenberg model

We consider a physical system consisting of two interacting spins governed by the [Formula: see text]-type Heisenberg Hamiltonian in an external magnetic field. We investigate the quantum evolution and the Riemannian geometry of the two-spin state space by means of the relevant Fubini–Study metric. The geometrical phase accumulated by the two-spin state is also examined under arbitrary and cyclic evolutions. By computing the evolution speed and the corresponding geodesic distance, we solve the quantum brachistochrone problem. The entanglement between the two spins is also studied via two approaches: the first one deals with the entanglement effect on the Fubini–Study metric and the geometrical phase, while the second one treats the entanglement effect on the evolution speed and the corresponding geodesic distance. Finally, we solve the quantum brachistochrone problem using the entanglement degree.

Lattice connectivity and entanglement in quantum spin-glasses

I have studied the role of lattice connectivity and coupling weights distribution on the entanglement of quantum spin-glasses. It's found in this work that the connectivity of the lattice weakly influence the degree of entanglement in the spin-glass compared to the distribution of the coupling constants between the spins. This suggest important implications for machine learning models such as Boltzmann machines and the study of complex quantum systems.

Superresolution of two unbalanced point sources assisted by the entangled partner

Sub-diffraction-limit resolution, or superresolution, has been successfully demonstrated in recent theoretical and experimental studies for two equal-brightness and incoherent point sources. However, practical situations of either nonequal brightness (i.e., unbalancedness) or partial coherence are shown to have fatal effects on such superresolution. As a step towards resolving such issues, we consider the effects of both unbalancedness and a form of partial coherence (i.e., quantum state coherence) together by including an entangled degree of freedom of the two point sources. Unexpectedly, it is found that the two negative effects can counteraffect each other, thus permitting credible superresolution, when the measurement is analyzed in the entangled partner's rotated basis. The least resolvable non-zero two-source separation is also identified analytically. Our result represents useful guidance towards the realization of superresolution for practical point sources. The vector-structure analog of quantum and classical light sources also suggests that our analysis applies to both contexts.

Multiparticle quantum walk–based error correction algorithm with two-lattice Bose–Hubbard model

When the evolution of discrete time quantum walk is carried out for particles, the ramble state is prone to error due to the influence of system noise. A multiparticle quantum walk error correction algorithm based on the two-lattice Bose–Hubbard model is proposed in this study. First, two point Bose–Hubbard models are constructed according to the local Euclidean generator, and it is proved that the two elements in the model can be replaced arbitrarily. Second, the relationship between the transition intensity and entanglement degree of the particles in the model is obtained by using the Bethe hypothesis method. Third, the position of the quantum lattice is coded and the quantum state exchange gate is constructed. Finally, the state replacement of quantum walk on the lattice point is carried out by switching the walker to the lattice point of quantum error correction code, and the replacement is carried out again. The entanglement of quantum particles in the double-lattice Bose–Hubbard model is simulated numerically. When the ratio of the interaction between particles and the transition intensity of particles is close to 0, the entanglement operation of quantum particles in the model can be realized by using this algorithm. According to the properties of the Bose–Hubbard model, quantum walking error correction can be realized after particle entanglement. This study introduces the popular restnet network as a training model, which increases the decoding speed of the error correction circuit by about 33%. More importantly, the lower threshold limit of the convolutional neural network (CNN) decoder is increased from 0.0058 under the traditional minimum weight perfect matching (MWPM) to 0.0085, which realizes the stable progress of quantum walk with high fault tolerance rate.

Long-time protection of thermal correlations in a hybrid-spin system under random telegraph noise.

The engineering features of transmitting mediums and their impact on different characteristics of a quantum system play a significant role in the efficient performance of nonlocal protocols. For this purpose, the dynamics of open quantum systems and coupling mediums remain a pathway. In this work, we investigate the dynamics of quantum correlations using negativity, uncertainty-induced nonlocality, and local quantum Fisher information in a hybrid qubit-qutrit thermal state when coupled with a magnetic field and influenced by random telegraph noise. Different features of the system parameters are taken into account while designing longer preservation of qubit-qutrit correlations. We show that the temperature has an inverse impact on the initial values of negativity, uncertainty-induced nonlocality, and local quantum Fisher information. When the magnetic field is characterized by different features, the entanglement, nonlocality, and Fisher information show a variety of dynamical maps, assuring their distinct nature. In addition, the qubit-qutrit correlations undergo repeated revivals when the configuration is restricted to the non-Markovian regime. On the other hand, an exponential drop with a single minimum is observed in the Markovian regime of the coupled field. Most importantly, our findings reveal that the present coupled fields have several advantages that can be leveraged to generate the optimal degree of entanglement, nonlocality, and local quantum Fisher information preservation in quantum dynamical maps.

Implementation of the entanglement measure in quantum gates language

Entanglement is an important resource for quantum technologies that allow us to go beyond the classical world. Quantum systems can be entangled in various ways. Also, the degree of entanglement between the subsystems of a quantum system can be calculated in different ways. In our recent paper [Prog. Theor. Exp. Phys. (2022)], we directly measure the three-tangle of a pure three-qubit quantum state. In this paper, we extend this method to pure N-qubit quantum states (N is any odd number greater than 1) by considering polynomial invariant of degree 4 as a measure of entanglement. In this algorithm, we use quantum gates and output probabilities to calculate polynomial invariant of degree 4. The importance of this method lies in the possibility of experimental implementation of quantum calculations in the language of quantum gates.

Microstructure and barrier properties of reactive compatibilized PLA/PA11 blends investigated by positron annihilation lifetime spectroscopy

Poly(lactic acid)/polyamide11 (PLA/PA11) blends were prepared by reactive blending with multifunctional epoxy oligomer as compatibilizer, and the compatibility of PLA and PA11 was improved. The compatibilization, toughness mechanisms, and rheological behavior of PLA/PA11 blends were studied. Positron annihilation lifetime spectroscopy (PALS) was used to study the free volume and interfacial compatibility of the compatibilized blends. Moreover, the influence of free volume and void volume on the barrier properties of the blend films was discussed. The glass-transition temperature and storage modulus of PLA in the compatibilized PLA/PA11 blends decreased, and the rheological behavior in the blends changed from liquid-like to solid-like at low-frequency. This finding showed that the interfacial compatibility between PLA and PA11 improved, and the material properties underwent a rigid-to-tough transition. PALS analysis further showed the improved interfacial compatibility of the multifunctional epoxy reactive compatibilizer reduced the free-volume pores and increased the number of free-volume pores. The entanglement degree of the molecular-chain segment in the compatibilized blend system increased, and the volume of free-volume pore decreased. The reactively compatibilized PLA/PA11 blend had excellent oxygen and water barrier properties, and its oxygen transmissibility and water-vapor diffusion coefficient greatly decreased. Therefore the reactive compatible PLA/PA11 blends had potential application and research value as packaging-barrier film materials.

Monolithically Programmed Stretchable Conductor by Laser‐Induced Entanglement of Liquid Metal and Metallic Nanowire Backbone (Small 37/2022)

Biphasic Metallic Composites In article number 2202841, Sukjoon Hong, Seung Hwan Ko, and co-workers report a laser-irradiated biphasic metallic composite stretchable conductor. The conductor is composed of silver nanowires and liquid metal particles, exhibiting different degrees of entanglement depending on the laser intensity. The conductor has monolithically varying electrical properties according to the laser intensity.

Kerr nonlinearity hinders symmetry-breaking states of coupled quantum oscillators.

We study the effect of Kerr anharmonicity on the symmetry-breaking phenomena of coupled quantum oscillators. Two types of symmetry-breaking processes are studied, namely, the inhomogeneous steady state (or quantum oscillation death state) and quantum chimera state. Remarkably, it is found that Kerr nonlinearity hinders the process of symmetry breaking in both the cases. We establish our results using direct simulation of the quantum master equationand analysis of the stochastic semiclassical model. Interestingly, in the case of quantum oscillation death, an increase in the strength of Kerr nonlinearity tends to favor the symmetry and at the same time decreases the degree of quantum mechanical entanglement. This paper presents a useful mean to control and engineer symmetry-breaking states for quantum technology.

How gravitational fluctuations degrade the high-dimensional spatial entanglement

Twisted photons carrying orbital angular momentum (OAM) are competent candidates for future interstellar communications. However, the gravitational fluctuations are ubiquitous in spacetime. Thus a fundamental question arises naturally as to how the gravitational fluctuations affect the coherence and the degree of high-dimensional OAM entanglement when twisted photons travel across the textures of curved spacetime. Here, we consider the covariant scalar Helmholtz equations and the Minkowski metric with fluctuations of Gaussian distribution and formulate analytically the equations describing the motion for twisted light in the Laguerre-Gaussian mode space. It is seen that the OAM cannot remain conserved in the presence of gravitational fluctuations. Furthermore, two-photon density matrices are derived for interstellar OAM quantum entanglement distribution, and the degree of entanglement degradation is characterized by purity and negativity. It is revealed that the higher-dimensional OAM entanglement is more susceptible to spacetime fluctuations. We believe that our findings will be of fundamental importance for the future interstellar quantum communications with twisted photons.

Tomographic entanglement indicators in frequency combs and Talbot carpets

Recent theoretical investigations on tomographic entanglement indicators have showcased the advantages of the tomographic approach in the context of continuous-variable (CV), spin and hybrid quantum systems. Direct estimation of entanglement using experimental data from the IBM quantum computing platform and NMR experiments has also been carried out in earlier work. A similar investigation in the context of CV systems is necessary to assess fully the utility of the tomographic approach. In this paper, we highlight the advantages of this approach in the context of experiments reported in the literature on two CV systems, namely, entangled Talbot carpets and entangled biphoton frequency combs. We use the tomographic entanglement indicator to estimate the degree of entanglement between a pair of Talbot carpets, and demonstrate that this provides a simpler and more direct procedure as compared to the one suggested in the experiment. We also establish that the tomograms corresponding to two biphoton frequency combs carry clear entanglement signatures that distinguish between the two states.

Implementation of Photonic Phase Gate and Squeezed States via a Two-Level Atom and Bimodal Cavity

We propose a theoretical model for realizing a photonic two-qubit phase gate in cavity QED using a one-step process. The fidelity and probability of success of the conditional quantum phase gate is very high in the presence of cavity decay. Our scheme only employs one two-level atom, and thus is much simpler than other schemes involving multi-level atoms. This proposal can also be applied to generate two-mode squeezed states; therefore, we give three examples, i.e., the two-mode squeezed vacuum state, two-mode squeezed odd coherent state, and two-mode squeezed even coherent state, to estimate the variance of Duan’s criterion when taking into account cavity decay. It is shown that the variance is smaller than 2 for the three squeezed states in most cases. Furthermore, we utilize logarithmic negativity to measure the entanglement, and find that these squeezed states have very high degrees of entanglement.

Manipulating the mechanical properties of cis-polyisoprene nanocomposites via molecular dynamics simulation

Attributed to the reinforcing effect of the NPs, filled natural rubber (NR) exhibits more excellent mechanical properties compared to pure natural rubber and has been attracting considerable scientific and technological attention. However, only a few studies have shown a systematical understanding of the structure-mechanics relation of filled natural rubber. Herein, a common strategy used to study the effects of the critical structural factors on strain-induced crystallization (SIC) and mechanical properties at the molecular level is to adopt molecular dynamic simulation (MD). Increasing the cross-linkage of the polymer matrix improves the entanglement degree, and the mechanical properties are reinforced by the high orientation of the polymer chains due to the high entanglement degree and the dissipation of energy due to the unentangling. Surprisingly, we find that the stress-strain behaviour of filled natural rubber is significantly manipulated by nanoparticle (NP) content, size and strength of interfacial interaction, evidenced by the increase of the chain orientation, SIC, and energy dissipated by NPs and polymer matrix, compared with the case of pure natural rubber. The underlying mechanism is the adsorption of the polymer by NPs, which leads to the orientation and crystallization of the polymer chains induced by NPs during the deformation process and energy dissipation through the slip of NPs and polymer chains. In general, this work demonstrates a detailed molecular-level structure-mechanics relation of filled natural rubber and provides some rational guidelines for experimentally designing and fabricating high-performance elastomer nanocomposites.

Tensor network approach to electromagnetic duality in (3+1)d topological gauge models

Given the Hamiltonian realisation of a topological (3+1)d gauge theory with finite group G, we consider a family of tensor network representations of its ground state subspace. This family is indexed by gapped boundary conditions encoded into module 2-categories over the input spherical fusion 2-category. Individual tensors are characterised by symmetry conditions with respect to non-local operators acting on entanglement degrees of freedom. In the case of Dirichlet and Neumann boundary conditions, we show that the symmetry operators form the fusion 2-categories 2VecG of G-graded 2-vector spaces and 2Rep(G) of 2-representations of G, respectively. In virtue of the Morita equivalence between 2VecG and 2Rep(G) — which we explicitly establish — the topological order can be realised as the Drinfel’d centre of either 2-category of operators; this is a realisation of the electromagnetic duality of the theory. Specialising to the case G = ℤ2, we recover tensor network representations that were recently introduced, as well as the relation between the electromagnetic duality of a pure ℤ2 gauge theory and the Kramers-Wannier duality of a boundary Ising model.

Entropy fluctuation and correlation transfer in tunable discrete-time quantum walk with fractional Gaussian noise.

We study the time correlation in the von Neumann entropy fluctuation of the tunable discrete-time quantum walk in one dimension, induced by the coin disorder arising from the temporal fractional Gaussian noise (fGn). The fGn is characterized by the Hurst exponent H, which provides three different correlation scenarios, namely antipersistent (0<H<0.5), memoryless (H=0.5), and persistent (0.5<H<1). We show the correlation of fGn is transferred to the coin's degree of entanglement and eventually transpires in the time correlation of the von Neumann entropy fluctuation. This study hints at the potential of using noise correlation as a resource to sustain information backflow via the interaction of quantum system with the noisy environment.

Social e-leaders in Frontline Service Industries: A Sociomaterial Analysis

Deskless workforces comprise more than 80% of the global workforce and many of these are found in customer facing service industries (e.g., retail, hospitality and healthcare). These frontline industries are often characterised by workforces lacking access to corporate email and in attempting to fill this communication gap, organisations are increasingly employing mobile technologies – including enterprise social media – to enable leaders to communicate with their teams. The consequence has been an increase in e-leadership via web 2.0 technology, about which little is currently known. Adopting a sociomateriality perspective and drawing on qualitative findings of 33 interviews with senior, mid-level and frontline leaders, we reveal how the entanglement of web 2.0 technology with formal leaders culminates in the emergence of three social e-leader types (avoidant, pragmatic, intrepid), and how their different configurations have implications for fulfilling a service-oriented leadership strategy. In doing so, we highlight the distinctive ways in which leadership in this context is enacted. We further identify conditions under which these social e-leadership practices are likely to emerge, highlighting factors affecting the degree of entanglement between the human and material.