Generation Of Multipartite Entanglement Research Articles

Quantum Delocalization on Correlation Landscape: The Key to Exponentially Fast Multipartite Entanglement Generation.

Entanglement, a hallmark of quantum mechanics, is a vital resource for quantum technologies. Generating highly entangled multipartite states is a key goal in current quantum experiments. We unveil a novel framework for understanding entanglement generation dynamics in Hamiltonian systems by quantum delocalization of an effective operator wave function on a correlation landscape. Our framework establishes a profound connection between the exponentially fast generation of multipartite entanglement, witnessed by the quantum Fisher information, and the linearly increasing asymptotics of hopping amplitudes governing the delocalization dynamics in Krylov space. We illustrate this connection using the paradigmatic Lipkin-Meshkov-Glick model and highlight potential signatures in chaotic Feingold-Peres tops. Our results provide a transformative tool for understanding and harnessing rapid entanglement production in complex quantum systems, providing a pathway for quantum enhanced technologies by large-scale entanglement.

Multipartite entanglement generation and dynamics of three giant atoms coupling to a one-dimensional waveguide

Multipartite entanglement generation and dynamics of three giant atoms coupling to a one-dimensional waveguide

All-photonic quantum repeater for multipartite entanglement generation.

Quantum network applications such as distributed quantum computing and quantum secret sharing represent a promising future network equipped with quantum resources. Entanglement generation and distribution over long distances are critical and unavoidable when utilizing quantum technology in a fully connected network. The distribution of bipartite entanglement over long distances has seen some progress, while the distribution of multipartite entanglement over long distances remains unsolved. Here we report a two-dimensional quantum repeater protocol for the generation of multipartite entanglement over long distances with an all-photonic framework to fill this gap. The entanglement generation yield remains proportional to the transmission efficiency regardless of the number of network users and shows long transmission distance under various numbers of network users. With the improved efficiency and flexibility of extending the number of users, we anticipate that our protocol can work as a significant building block for quantum networks in the future.

Atomic-coherence-assisted multipartite entanglement generation with dressing-energy-level-cascaded four-wave mixing

Multipartite entanglement plays an important role in quantum information processing and quantum metrology. Here, the dressing-energy-level-cascaded four-wave mixing (FWM) processes are proposed to generate all-optical controlled multipartite entanglement within a single device. The entanglement characteristics of the produced states of light are characterized by applying the Duan criterion and the positivity under partial transposition criterion. Moreover, by using an internal dressing field to modulate atomic coherence, multiple quantum coherent channels of FWM are simultaneously constructed, which result in a great extension of entanglement mode number and quantum information capacity. We find that the violation of the entanglement criteria inequalities is coherent-channel dependent, and the produced states can be directly modulated via atomic coherence. Our system can integrate the generation and modulation of the entangled states in one process. It may help provide a compact method for realizing large-scale quantum networks.

Generation of multipartite entanglement between spin-1 particles with bifurcation-based quantum annealing

Quantum annealing is a way to solve a combinational optimization problem where quantum fluctuation is induced by transverse fields. Recently, a bifurcation-based quantum annealing with spin-1 particles was suggested as another mechanism to implement the quantum annealing. In the bifurcation-based quantum annealing, each spin is initially prepared in |0rangle, let this state evolve by a time-dependent Hamiltonian in an adiabatic way, and we find a state spanned by |pm 1rangle at the end of the evolution. Here, we propose a scheme to generate multipartite entanglement, namely GHZ states, between spin-1 particles by using the bifurcation-based quantum annealing. We gradually decrease the detuning of the spin-1 particles while we adiabatically change the amplitude of the external driving fields. Due to the dipole-dipole interactions between the spin-1 particles, we can prepare the GHZ state after performing this protocol. We discuss possible implementations of our scheme by using nitrogen vacancy centers in diamond.

Generation of twelve-partite entanglement from two symmetric four-wave mixing processes

Entanglement shared by multipartite is an important resource for quantum technologies. Recently, the hexapartite entanglement generated from the four-wave mixing (FWM) process with a spatially structured pump (SSP) has been experimentally demonstrated (Zhang et al., 2020). To further increase the number of entangled beams, we theoretically propose a scheme for generating twelve-partite entanglement based on two independent symmetric FWM processes with a SSP and one linear beam splitter (BS). The entanglement properties are analyzed by utilizing the positivity under partial transposition criterion, and we find that there is twelve-partite entanglement in the whole interaction region and the degree of entanglement increases as the interaction time increases. In addition, we investigate the dependence of entanglement characteristics of the system on transmissivity of BS and eigenmode structure embedded within the system as well to further study the underlying entanglement structure. Our results pave the way for the experimental generation of multipartite entanglement from the SSP-based FWM process.

Fusing atomic W states with Rydberg superatom

Quantum entanglement is the basic resource of quantum information processing and quantum computation, especially multi-partite entanglement. The simple and efficient generation of multi-partite entanglement has always been one of the hot topics of scholars. In this paper, we propose a qubit-loss-free fusion scheme for generation of large-scale entangled W states with Rydberg superatom. By sending two superatoms belonging to a k-atom W states and a l-atom W states, respectively, into a cavity, we may obtain a (k + l)-atom W states via detecting the cavity state after interaction. The numerical simulation analysis shows that the fidelity is robust against both spontaneous emission of superatoms and decay of the cavity. In addition, the feasibility analysis indicates this scheme can also be realized in experiment.

Locally optimal measurement-based quantum feedback with application to multiqubit entanglement generation

We present a general approach to measurement-based quantum feedback that employs proportional and quantum state-based (PaQS) feedback components to obtain locally optimal protocols. To demonstrate the power of the method, we first show that it reproduces many known feedback protocols, and then apply it to generation of multipartite entanglement with an emphasis on remote entanglement, which requires spatially local feedback Hamiltonians. The symmetry of both measurement and feedback operators is found to be essential for construction of effective protocols. We show that under perfect measurement efficiency, entangled states can be reached with fidelity approaching unity under non-Markovian feedback control protocols, while Markovian protocols resulting from optimizing the feedback unitaries on ensemble averaged states still yield fidelities above 94%. Application of the PaQS approach to generation of N-qubit W, general Dicke and GHZ states shows that such entangled states can be efficiently generated with high fidelity, for up to N = 100 in some cases.

Silicon-based photonic quantum information technologies

Silicon quantum photonics is a promising platform for the development of advanced quantum information technologies, offering a high level of stability, controllability, scalability and integration density. Silicon quantum photonics has enabled a range of key demonstrations including the development of a versatile toolbox for controlling single-photon’s different degrees of freedom, the generation of multipartite entanglement and high-dimensional entanglement, and realization of large-scale programmable quantum devices. The progress has unlocked the unprecedented power of chip-scale quantum photonic technologies for advanced applications in quantum communication, computing and simulation.

Non-resonant interactions and multipartite entanglement in a system of coupled cavities

We study quantum state transfer and multipartite entanglement generation in the ensembles of qubits enclosed by a one-dimensional system of coupled optical cavities. Each cavity contains N qubits whose interaction with the quantum field of their respective cavity is governed by the Dicke Lipkin–Meshkov–Glick model. An excitation initially seeded in the ensemble at the end of the one-dimensional chain of coupled cavities transfers to the corresponding ensemble of the last cavity with success that depends on the mode-ensemble coupling χ , ensemble-mode detuning δ , photon hopping rate λ , and size of a given ensemble N . Suitable choices of such parameters enable overcoming the freezing effect induced by the choice of a far-off detuning regime. We identify working points at which three-ensemble W states and two-ensemble maximally entangled states emerge in the multipartite entanglement dynamics. This study provides a basis for manipulation of quantum states in a multipartite coupled cavity arrangement that may be useful in understanding very complex systems in the field of quantum information processing.

Multipartite Entanglement Generation in a Structured Environment.

In this paper, we investigate the entanglement generation of n-qubit states in a model consisting of n independent qubits, each coupled to a harmonic oscillator which is in turn coupled to a bath of N additional harmonic oscillators with nearest-neighbor coupling. With analysis, we can find that the steady multipartite entanglement with different values can be generated after a long-time evolution for different sizes of the quantum system. Under weak coupling between the system and the harmonic oscillator, multipartite entanglement can monotonically increase from zero to a stable value. Under strong coupling, multipartite entanglement generation shows a speed-up increase accompanied by some oscillations as non-Markovian behavior. Our results imply that the strong coupling between the harmonic oscillator and the N additional harmonic oscillators, and the large size of the additional oscillators will enhance non-Markovian dynamics and make it take a very long time for the entanglement to reach a stable value. Meanwhile, the couplings between the additional harmonic oscillators and the decay rate of additional harmonic oscillators have almost no effect on the multipartite entanglement generation. Finally, the entanglement generation of the additional harmonic oscillators is also discussed.

Generation of quadripartite entanglement based on four-wave mixing process and linear beam splitter

As a crucial quantum resource in quantum information processing, multipartite entanglement plays an important role not only in the field of testing basic quantum effects, but also in the applications of quantum network, quantum communication and quantum computing. The generation of multipartite entanglement usually involves many complex linear processes and nonlinear processes. In this paper, we theoretically propose a scheme for generating genuine quadripartite entanglement by linking two independent four-wave mixing (FWM) processes with one linear beam splitter (BS). Here, we use one linear BS to mix the probe beams amplified by two independent FWM processes. We first set the transmissivity of the linear BS to be 0.5 and study the effect of the intensity gain of the system on quadripartite entanglement by applying the positivity under partial transposition (PPT) criterion. The results show that there exists genuine quadripartite entanglement in all gain regions, and the degree of entanglement increases with intensity gain increasing. And then, the dependence of quadripartite entanglement on the transmissivity of the linear BS is studied when the intensity gains of two independent FWM processes are both set to be 3. We find that the transmissivity of the linear BS can affect the entanglement properties of the system. At the same time, we also find that the system can generate genuine quadripartite entanglement when the transmissivity of the linear BS is not equal to 0 or 1. Finally, in order to reveal the entanglement structure of the system, we further investigate the dependence of the possible tripartite entanglement and bipartite entanglement on the intensity gain of the system by using the PPT criterion. The results show that there exists the genuine tripartite entanglement in this system, and the degree of entanglement increases as the intensity gain increases. However, there exists no genuine bipartite entanglement in this system, some of bipartite states are always separable, and the entanglement of the other bipartite states gradually become weak and eventually disappear with the increase of the intensity gain. Our theoretical result provides a simple and reliable scheme for generating genuine quadripartite entanglement by using FWM process in atomic ensemble and linear BS.

Effect of long-range interactions on multipartite entanglement in Heisenberg chains

It is well known that the notions of spatial locality are often lost in quantum systems with long-range interactions, as exhibited by the emergence of phases with exotic long-range order and faster propagation of quantum correlations. We demonstrate here that such induced ``quasinonlocal'' effects do not necessarily translate to growth of global entanglement in the quantum system. By investigating the ground and quenched states of the variable-range, spin-1/2 Heisenberg Hamiltonian, we observe that the genuine multiparty entanglement in the system can either increase or counterintuitively diminish with a growing range of interactions. The behavior is reflective of the underlying phase structure of the quantum system and provides key insights for generation of multipartite entanglement in experimental atomic, molecular, and optical physics where such variable-range interactions have been implemented.

Controlled generation of genuine multipartite entanglement in Floquet Ising spin models

We propose a method for generation of genuine multipartite entangled states in a short-range Ising spin chain with periodic global pulses of magnetic field. We consider an integrable and a non-integrable Floquet system that are periodic in time and have constant quasi-energy gaps with degeneracies. We start with all spins polarized along one direction and show that they evolve into states with high entanglement by calculating the average entanglement entropy and geometric measure of entanglement. We show that some of these states have a high number of parties involved in the entanglement by calculating the quantum Fisher information. Such controlled generation of multipartite entanglement has potential applications in quantum information processing.

Generation of Different Classes of Multipartite Entanglement Using Cavity-QED

Using a system of cavity quantum electrodynamics (QED) we present two schemes for multipartite entanglement generation. In the first scheme, a three-level atom is interacting with three cavities successively. In the second one, two three-level atoms are interacted with a coherent optical cavity. These protocols allow us to generate the six classes of tripartite entanglement (GHZ, W, A-B-C, AB-C, C-AB, and B-AC class states) by controling the interaction time between atoms and cavities. Moreover, they allow us to generate entanglement between the cavity fields degrees of freedom (from the first scheme), and a mixed entanglement between the cavity field degrees of freedom and the atomic degrees of freedom.

Multipartite entanglement generation with dipole induced transparency effect in indirectly coupled dipole-microcavity systems

We propose a feasible scheme of generating multipartite entanglement with the dipole induced transparency (DIT) effect in indirectly coupled dipole-microcavity systems. It is shown that the transmission spectrum is closely related with the interference of dipole-microcavity systems, and we can generate different classes of multipartite entanglement, e.g., the Greenberger–Horne–Zeilinger state, the W state, and the Dicke state, of the dipole emitters just by choosing an appropriate frequency of the incident photon. Benefiting from the DIT effect, the schemes may work in the bad or low-Q cavity regime only if the large Purcell factor of the dipole-microcavity system is fulfilled, and they are also insensitive to experimental noise, which may be feasible with present accessible technology.

Scalable Creation of Long-Lived Multipartite Entanglement.

We demonstrate the deterministic generation of multipartite entanglement based on scalable methods. Four qubits are encoded in ^{40}Ca^{+}, stored in a microstructured segmented Paul trap. These qubits are sequentially entangled by laser-driven pairwise gate operations. Between these, the qubit register is dynamically reconfigured via ion shuttling operations, where ion crystals are separated and merged, and ions are moved in and out of a fixed laser interaction zone. A sequence consisting of three pairwise entangling gates yields a four-ion Greenberger-Horne-Zeilinger state |ψ⟩=(1/sqrt[2])(|0000⟩+|1111⟩), and full quantum state tomography reveals a state fidelity of 94.4(3)%. We analyze the decoherence of this state and employ dynamic decoupling on the spatially distributed constituents to maintain 69(5)% coherence at a storage time of 1.1sec.

Polarization map of correlated sideband generation in vectorial four-wave mixing

Polarization analysis of vectorial four-wave mixing (FWM) in birefringent photonic-crystal fibers reveals physically significant tendencies in the behavior of FWM sideband correlations as a function of fiber birefringence, dispersion, and nonlinearity, as well as the pump intensity and bandwidth. Scanning over this parameter space is shown to steer vectorial FWM from largely decoupled sideband generation by individual polarization modes of the pump to FWM scenarios enabling multipartite entanglement generation.

Direct generation of spatial quadripartite continuous variable entanglement in an optical parametric oscillator.

Multipartite entanglement is used for quantum information applications, such as building multipartite quantum communications. Generally, generation of multipartite entanglement is based on a complex beam-splitter network. Here, based on the spatial freedom of light, we experimentally demonstrated spatial quadripartite continuous variable entanglement among first-order Hermite-Gaussian modes using a single type II optical parametric oscillator operating below threshold with an HG0245° pump beam. The entanglement can be scalable for larger numbers of spatial modes by changing the spatial profile of the pump beam. In addition, spatial multipartite entanglement will be useful for future spatial multichannel quantum information applications.

Measurement-induced long-distance entanglement of superconducting qubits using optomechanical transducers

Although superconducting systems provide a promising platform for quantum computing, their networking poses a challenge because they cannot be interfaced to light, the medium used to send quantum signals through channels at room temperature. We show that mechanical oscillators can mediate such coupling and light can be used to measure the joint state of two distant qubits. The measurement provides information on the total spin of the two qubits such that entangled qubit states can be postselected. Entanglement generation is possible without ground-state cooling of the mechanical oscillators for systems with optomechanical cooperativity moderately larger than unity; in addition, our setup tolerates a substantial transmission loss. The approach is scalable to the generation of multipartite entanglement and represents a crucial step towards quantum networks with superconducting circuits.