Field Entanglement Research Articles

Compact source for quadripartite deterministically entangled optical fields

Since entangled multiple optical fields were identified as the building blocks of quantum networks, the quadripartite entangled optical fields have been produced by using four degenerate optical parametric amplifiers or two nondegenerate optical parametric amplifiers (NOPAs). However, realizing an efficient and compact source for multiple quantum users has remained an outstanding challenge, hindering their practical applications. Here, we proposed a compact and feasible scheme to deterministically entangle four spatially separated optical fields, employing only a single NOPA. Accordingly, two-sided output NOPA-based optical fields were coupled on a beam splitter network to form the quadripartite entangled state, causing the deterministic generation of both the Greenberger–Horne–Zeilinger (GHZ) and the linear cluster states in this compact entanglement source. We also obtained the optimal experimental parameters based on the simulation results, thereby providing a direct reference for experimental implementation. Our findings propose that the resultant GHZ and linear cluster states can be potentially applied in quantum-enhanced information science, specifically in quantum secret sharing, controlled quantum teleportation networks, and quantum-entangled atomic ensemble networks.

Entanglement and quantum correlations in the XX spin-1/2 honeycomb lattice

The ground state phase diagram of the dimerized spin-1/2 XX honeycomb model in presence of a transverse magnetic field (TF) is known. With the absence of the magnetic field, two quantum phases, namely, the Néel and the dimerized phases have been identified. Moreover, canted Néel and the paramagnetic (PM) phases also emerge by applying the magnetic field. In this paper, using two powerful numerical exact techniques, Lanczos exact diagonalization, and Density matrix renormalization group (DMRG) methods, we study this model by focusing on the quantum correlations, the concurrence, and the quantum discord (QD) among nearest-neighbor spins. We show that the quantum correlations can capture the position of the quantum critical points in the whole range of the ground state phase diagram consistent with previous results. Although the concurrence and the QD are short-range, informative about long-ranged critical correlations. In addition, we address a ”magnetic-entanglement” behavior that starts from an entangled field around the saturation field.

How can quantum field operators encode entanglement?

We present techniques to construct the Deutsch–Hayden representation for quantum field operators and apply them to an entangled state of identical nonrelativistic spin-1/2 fermions localized in well-separated spatial regions. Using these entangled field operators we construct operators measuring spin in localized spatial regions, and verify that matrix elements of the spin-measurement operators in the information-free Deutsch–Hayden state yield the expected correlations between pairs of both entangled and unentangled particles. The entangled Deutsch–Hayden representation field operators furnish an explicitly separable description of the entangled system.

The Electrophoretic Revolution in the 1960s: Historical Epistemology Meets the Global History of Science and Technology.

This paper uses zone electrophoresis, one of the most frequently used tools in molecular biology, to explore two ideas derived from Hans‐Jörg Rheinberger's reflections on experiments. First, the constraining role played by technical objects—instrumentation and material conditions—in the production of knowledge or epistemic things. Second, the production of interconnected experimental systems by such technical objects, which results in the unexpected entanglement of research fields and experimental cultures. By the beginning of the 1960s, the inception of zone electrophoresis in laboratories around the world transformed—some say, revolutionized—the study of proteins. Even today, electrophoresis continues to open research venues and questions in biomedicine, molecular biology, human genetics, and in the field of molecular evolution. In my essay, I seek to look at the interconnected lives of zone electrophoresis and address the broader social, and even global context, in which this apparently humble technique became a salient tool in the production of biological knowledge. In so doing, I aim to take the past and present of the history and historiography of experimental systems to the future, where experiments and technologies are interrogated as they are used in different geographies and contexts, including contexts of poverty.

Gain Saturation Modified Quantum Noise Effect on Preparing a Continuous-Variable Entanglement

We examine the gain saturation effect in non-Hermitian systems of coupled gain–loss waveguides and whispering-gallery-mode microresonators, through which a continuous-variable (CV) entanglement of light fields is generated. Here, we consider squeezed vacuum inputs for coupled waveguide setup and coherent drive for coupled microresonators, and study the influence from the saturation of the used optical gain. Unlike the ideal situation without gain saturation, it is possible to generate stabilized entanglement measured by logarithmic negativity under gain saturation. Both types of setups realize steady CV entanglement, provided that the gain saturation is sufficiently quick. Particularly, with the coupled microresonators which are pumped by coherent drive, the created CV entanglement is actually out of the gain noise with a squeezing characteristic, under the condition of fast saturation of the initial optical gain.

Generation of a polygonal perfect optical vortex array by optical pen

The perfect optical vortex (POV) has generated a large number of applications in classical to quantum physics because its diameter is independent of its topological charge (TC). Previous reported POVs still show a lack of controllable size, shape, and amplitude, which may hinder their applications. In this paper, a combined phase is used to create complex polygonal perfect optical vortex (PPOV) arrays. The size, number, position, shape, and amplitude of the PPOVs in the array are controllable, where the shape can be an arbitrary symmetric polygon. We investigate the transmission characteristics of the PPOV arrays. The generation of PPOV arrays further provides more flexibility in optical micro-manipulation, quantum entanglement, optical communication, and other fields.

Enhanced entanglement and quantum steering of directly and indirectly coupled modes in a magnomechanical system

This study is based on a theoretical proposal for quantum steering, non-locality, and entanglement in a two microwave cavities based magnomechanical system. The system is composed of two microwave (MW) cavity mode photons, phonons associated with mechanical mode and a magnon mode. We have employed a standard damping approach and found that steerability and entanglements among different bipartite subsystems strongly depend upon the detuning of indirectly coupled cavity mode and effective magnon detuning. One/two-way quantum Steering and non-local correlation have been found in the system for different choices of bipartitions. In addition, entanglement generated in the system enhances and has shown to be more robust against the thermal effects, as compared with the earlier studies. Interestingly, we have shown that the magnomechanical entanglements among different bipartitions have a complementary relation due to the transfer entanglement. This shows an additional insight into the system dynamics which shows that there exists a ‘tie-up’ relationship among these bipartitions. The present magnomechanical system will open new perspectives in quantum tasks that demand the entanglement of microwave cavity fields.

Entanglement entropy across the lattice-continuum correspondence

This paper revisits the standard calculations of free field entanglement entropy in light of the newly developed lattice-continuum correspondence. This correspondence prescribes an explicit method to extract an approximately continuum quantum field theory out of a fully regularized lattice theory. This prescription will here be extended to subregion algebras, and it will be shown how entropies of continuum boson and fermion theories can be computed by working purely with lattice quantities. This gives a clear picture of the origin of divergences in entanglement entropy while also presenting a concise and detailed recipe for calculating this important quantity in continuum theories.

Generation of multiple entangled fields via mechanical oscillator displacement

We present a convenient and efficient scheme to generate arbitrarily multipartite continuous-variable entanglement via mechanical oscillator displacement induced by two strong input pump fields in the conventional single-cavity optomechanical system. It is shown that multipartite entanglement among the outputs of the two pump fields and any number of relatively weak probe fields can be realized and optimized when the two pump fields with suitable amplitude ratio and relative initial phase are, respectively, tuned to the red and blue mechanical sidebands of a single cavity mode and each probe field is red-detuned by the mechanical frequency with respect to a different neighboring cavity mode. This method can, in principle, be extended to flexibly and conveniently generate arbitrarily multiple nondegenerate bright entangled fields by using only coherent laser fields, and may find promising applications in realistic quantum communication and networks.

Entangled Vacuum State for Accelerated Observers

Entanglement of Dirac fields has been studied and it is known to decrease with increasing acceleration when a quantum state is shared between users in non-inertial frames. A new form of an entangled vacuum state observed by the accelerated observer is postulated in which it is assumed that entanglement is present between the modes of the quantum field with sharp and opposite momenta defined in two causally disconnected regions of space-time. We find that this assumption does not affect the entanglement of the system.

Entanglement harvesting with a twist

One consequence of the cosmic censorship conjecture is that any topological structure will ultimately collapse to within the horizons of a set of black holes, and as a result, an external classical observer will be unable to probe it. However, a single two-level quantum system [Unruh–DeWitt (UDW) detector] that remains outside of the horizon has been shown to distinguish between a black hole and its associated geon counterpart via its different response rates. Here, we extend this investigation of the quantum vacuum outside of an ℝP2 geon by considering the entanglement structure of the vacuum state of a quantum scalar field in this spacetime, and how this differs from its Banados–Teitelboim–Zanelli (BTZ) black hole counterpart. Employing the entanglement harvesting protocol, where field entanglement is swapped to a pair of UDW detectors, we find that the classically hidden topology of the geon can have an appreciable difference in the amount of entanglement harvested in the two spacetimes for sufficiently small mass. In this regime, we find that detectors with a small energy gap harvest more entanglement in the BTZ spacetime; however, as the energy gap increases, the detectors harvest more entanglement in a geon spacetime. The energy gap at the crossover is dependent on the black hole mass, occurring at lower values for lower masses. This also impacts the size of the entanglement shadow, the region near the horizon where the detectors cannot harvest entanglement. Small gap detectors experience a larger entanglement shadow in a geon spacetime, whereas for large gap detectors, the shadow is larger in a BTZ spacetime.

Quantum treatment of cavity-assisted entanglement of three-level atoms and two fields in an electromagnetically-induced-transparency configuration

We examine the field-field and field-atom entanglements generated by \ensuremath{\Lambda}-type three-level atoms placed in an optical cavity driven above threshold by two coherent input optical fields. It is shown that under realistic experimental conditions entanglement between the two output cavity fields as well as between the fields and the atoms can be achieved when the two cavity fields are both one- and two-photon (Raman) resonant with the atomic transitions, as in the configuration for electromagnetically induced transparency (EIT). The entanglement has similar features to pump-signal-idler three-color entanglement in an above-threshold optical parametric oscillator [Villar et al., Phys. Rev. Lett. 97, 140504 (2006)]. This cavity-enhanced atom-field cooperative coupling could enable convenient and efficient generation of bright, nondegenerate, narrow-band entangled fields, which may find potential applications in realistic quantum communications and networking protocols.

Entanglement robustness of continuous variable Einstein-Podolsky-Rosen-entangled state distributed over optical fiber channel

Einstein-Podolsky-Rosen (EPR)-entangled state light field at a telecommunication wavelength of 1.5 μm is an important quantum source for realizing the continuous variable quantum information processing and some quantum protocols over optical fiber channel. When the EPR-entangled state light field is distributed over the optical fiber channel, the disentanglement is always present because the the EPR entangled state interacts with the fiber channel. It affects the performance of quantum information processing. In this paper, we theoretically calculate the positive partial transposition (PPT) of the entangled state distributed over the optical fiber channel in the single-channel and dual-channel distribution scheme, respectively. Three types of initial entangled light field are considered and analyzed, they being an initial EPR entangled state, an EPR entangled state with asymmetric quadratures, and an EPR entangled state with asymmetric modes. Furthermore, the influence of the extra noise in the optical fiber on the transmission distance of EPR entangled state over the optical fiber channel is investigated. In the single-channel scheme or dual-channel scheme, the extra noise in the optical fiber channel leads the entangled state light field to be disentangled, and the transmission distance of EPR entangled state over the optical fiber channel to decrease rapidly with the increase of the extra noise. For maintaining the robustness of EPR entangled states in lossy optical fiber channels, the dual-channel scheme has more stringent requirements for the correlation quadrature symmetry and purity of the initial entangled state than the single-channel scheme. In the single fiber noise channel scheme, the maximum transmission distance and the robustness of the EPR entangled states with asymmetric modes are not sensitive to the asymmetry between modes. The change of asymmetry between modes does not lead to being disentangled. The maximum transmission distance does not change either. However, the decrease of asymmetry between modes results in the disentanglement in the double fiber noise channels’ scheme. The maximum transmission distance is reduced and the sudden death occurs to the entanglement. The present results will lay a foundation for continuous variables quantum information processing based on optical fiber, such as realizing continuous variables quantum communication over optical fiber and constructing metropolitan quantum network over optical fiber.

Quantum entanglement between two antiferromagnets in the microcavities

Magnons are being currently developed as qubits for quantum storage and information processing. Here, in this work, we focus on a hybrid quantum system containing two antiferromagnets, and entanglement between magnons in the antiferromagnets can be generated through strong coupling mediated by the same microwave mode. Moreover, we numerically simulate the process with feasible parameters. The influence of the system parameters, such as the magnon-photon coupling rate, detuning, bias magnetic field and dissipation of entanglement, are discussed. By adjusting some of the experimental parameters, we show that two antiferromagnets can produce a large entanglement, which is a result that has not been previously found in other quantum systems. Our findings may provide a potential platform for the completion of related quantum tasks in the future.

Genuine tripartite nonlocality and entanglement in curved spacetime

We study the genuine tripartite nonlocality (GTN) and the genuine tripartite entanglement (GTE) of Dirac fields in the background of a Schwarzschild black hole. We find that the Hawking radiation degrades both the physically accessible GTN and the physically accessible GTE. The former suffers from “sudden death” at some critical Hawking temperature, and the latter approaches to the nonzero asymptotic value in the limit of infinite Hawking temperature. We also find that the Hawking effect cannot generate the physically inaccessible GTN, but can generate the physically inaccessible GTE for fermion fields in curved spacetime. These results show that on the one hand the GTN cannot pass through the event horizon of black hole, but the GTE do can, and on the other hand the surviving physically accessible GTE and the generated physically inaccessible GTE for fermions in curved spacetime are all not nonlocal. Some monogamy relations between the physically accessible GTE and the physically inaccessible GTE are found.

The foundation of the hyperunified field theory I — Fundamental building block and symmetry

Starting from the motional property of functional field based on the action principle of path integral formulation while proposing maximum coherence motion principle and maximum locally entangled-qubits motion principle as guiding principles, we show that such a functional field as fundamental building block appears naturally as an entangled qubit-spinor field expressed by a locally entangled state of qubits. Its motion brings about the appearance of Minkowski space–time with dimension determined by the motion-correlation [Formula: see text]-spin charge and the emergence of [Formula: see text]-spin/hyperspin symmetry as fundamental symmetry. Intrinsic [Formula: see text]-spin charge displays a periodic feature as the mod 4 qubit number, which enables us to classify all entangled qubit-spinor fields and space–time dimensions into four categories with respect to four [Formula: see text]-spin charges [Formula: see text]. An entangled decaqubit-spinor field in 19-dimensional hyper-space–time is found to be a hyperunified qubit-spinor field which unifies all discovered leptons and quarks and brings on the existence of mirror lepton–quark states. The inhomogeneous hyperspin symmetry [Formula: see text] as hyperunified symmetry in association with inhomogeneous Lorentz-type symmetry [Formula: see text] and global scaling symmetry provides a unified fundamental symmetry. The maximum locally entangled-qubits motion principle is shown to lay the foundation of hyperunified field theory, which enables us to comprehend long-standing questions raised in particle physics and quantum field theory.

Crossing-symmetric twist field correlators and entanglement negativity in minimal CFTs

We study conformal twist field four-point functions on a ℤN orbifold. We examine in detail the case N = 3 and analyze theories obtained by replicated N-times a minimal model with central charge c < 1. A fastly convergent expansion of the twist field correlation function in terms of sphere conformal blocks with central charge Nc is obtained by exploiting covering map techniques. We discuss extensive applications of the formalism to the entanglement of two disjoint intervals in CFT, in particular we propose a conformal block expansion for the partially transposed reduced density matrix. Finally, we refine the bounds on the structure constants of unitary CFTs determined previously by the genus two modular bootstrap.

Who are the dominant players in the experimental field of quantum entanglement? A bibliometric analysis

Quantum entanglement is a major research resource in quantum information science, which has obtained increasing attention and has been intensively studied experimentally in recent years. Based on 7089 research papers in the experimental field of quantum entanglement obtained from the Web of Science Core Collection database, this study investigates the 400 top-cited papers which were written by 498 first or corresponding authors from188 institutions in 32 countries/territories. This study not only relies on traditional methods with first author full counting and corresponding author full counting to present the critical authors, institutions, and countries as designers or executors but also uses distinctive methods with first/corresponding author full counting and first/corresponding author fractional counting to find the dominant players in the experimental field of quantum entanglement. Considering authors, A. Zeilinger and J.W. Pan are the most dominant scientists in this field. The University of Vienna has the best institutional performance in this field, and other institutions such as the University of Science and Technology of China also do fairly well. The results show that the USA, Germany, Austria, the UK, and mainland China fit their reputations as dominant players in the field.

Nonclassical atomic system dynamics time-dependently interacts with finite entangled pair coherent parametric converter cavity fields

We consider a time-dependent model that describes a qubit time-dependently interacting with a cavity containing finite entangled pair coherent parametric converter fields. The dynamics of some quantum phenomena, as: phase space information, quantum entanglement and squeezing, are explored by atomic Husimi function, atomic Wehrl entropy, variance, and entropy squeezing. The influences of the unitary qubit-cavity interaction, the difference between the two-mode photon numbers, the initial atomic coherence, and the time-dependent qubit location are investigated. It is found that the regularity, the amplitudes and the frequency of the quantum phenomena can be controlled by the physical parameters. For the initial atomic pure state, the qubit-cavity entanglement, the qubit phase space information, and atomic squeezing can be generated strongly compared to those of the initial atomic mixed state. The time-dependent location parameters enhance the generated quantum phenomena, and their effect can be enhanced by the parameters of the two-mode photon numbers and the initial atomic coherence.

Dynamics of quantum effects of a qubit time-dependently interacting with finite entangled coherent cavity fields

Dynamics of quantum effects of a qubit time-dependently interacting with finite entangled coherent cavity fields