Einstein-Podolsky-Rosen Steering Research Articles

Mode-selective photon-added two-mode squeezed vacuum state and its entanglement properties

A class of non-Gaussian entangled states is introduced by applying the nonlocal single-photon addition to two-mode squeezed vacuum state and the properties of entanglement are numerically investigated according to linear entropy and Einstein–Podolsky–Rosen (EPR) steering. After the nonlocal single-photon addition operation, Wigner function of the generated state appears some negative region and loses its Gaussian property in phase space. In essence, non-Gaussian entangled states are generated after applying nonlocal single-photon addition. Additionally, by studying the linear entropy and EPR steering, we find that single-photon addition can enhance their entanglement degree and non-Gaussian steering can be witnessed in a large range of squeezing parameter for the second-order quadratures, which may provide a well application in the fields of quantum information processing.

Quantum correlations in a chain-type quantum network

A quantum network concerns several independent entangled resources and can create strong quantum correlations by performing joint measurements on some observers. In this paper, we discuss an n-partite chain network with each of two neighboring observers sharing an arbitrary Bell state and all intermediate observers performing some positive-operator-valued measurements with parameter λ. The expressions of all post-measurement states between any two observers are obtained, and their quantifications of Bell nonlocality, Einstein–Podolsky–Rosen steering and entanglement with different ranges of λ are respectively detected and analyzed.

Quantum synchronization and controllable Einstein-Podolsky-Rosen steering of a dynamical Casimir waveguide system composed of giant atoms

We obtain the quantum synchronization and controllable Einstein-Podolsky-Rosen (EPR) steering through theoretical research in a Dynamical Casimir array (DCA) composed of two giant atoms. We achieve one-way or two-way EPR steering between giant atoms, as well as the reversal and exchange of monogamy relations by adjusting system parameters. Remarkably, we find that the system temperature can serve as a switch for regulating different types of EPR steering. By adjusting this switch, we obtain the sudden death of EPR steering between giant atoms and the resurrection of two-way EPR steering between Casimir photons and giant atoms. Most importantly, the resurrection of EPR steering generated by the temperature shows the synchronicity and shareability of multipartite EPR steering. Contrary to the monogamy relations, the shareability of EPR steering allows the state of one party to be steered by two or more observers. The emergence of quantum synchronization and shareability of EPR steering provides an innovative perspective and approach for studying multipartite EPR steering and has potential applications in many quantum information protocols.

All-optical Einstein-Podolsky-Rosen steering swapping.

Einstein-Podolsky-Rosen (EPR) steering, an important resource in quantum information, describes the ability of one party to influence the state of another party through local measurements. It differs from Bell nonlocality and entanglement due to its asymmetric property. EPR steering swapping allows two spatially independent parties to present EPR steering without direct interaction. Here, we theoretically propose an all-optical EPR steering swapping (AOSS) scheme based on low-noise high-broadband optical parametric amplifiers (OPAs). A low-noise high-broadband OPA is utilized to implement the function of Bell-state measurement without detection, avoiding the optic-electro and electro-optic conversions. After AOSS, one-way and two-way EPR steering between two independent optical modes can be obtained. Our scheme provides a guidance for the construction of a measurement-free, all-optical broadband quantum network utilizing EPR steering swapping.

Maxwell Demon and Einstein–Podolsky–Rosen Steering

Research of Maxwell demon and quantum entanglement is important because of its foundational significance in physics and its potential applications in quantum information. Previous studies on the Maxwell demon have primarily focused on thermodynamics, taking into account quantum correlations. Here we consider from another perspective and ask whether quantum non-locality correlations can be simulated by performing work. The Maxwell demon-assisted Einstein–Podolsky–Rosen (EPR) steering is thus proposed, which implies a new type of loophole. The application of Landauer’s erasure principle suggests that the only way to close this loophole during a steering task is by continuously monitoring the heat fluctuation of the local environment by the participant. We construct a quantum circuit model of Maxwell demon-assisted EPR steering, which can be demonstrated by current programmable quantum processors, such as superconducting quantum computers. Based on this quantum circuit model, we obtain a quantitative formula describing the relationship between energy dissipation due to the work of the demon and quantum non-locality correlation. The result is of great physical interest because it provides a new way to explore and understand the relationship between quantum non-locality, information, and thermodynamics.

Experimental distillation of tripartite quantum steering with an optimal local filtering operation

Multipartite Einstein-Podolsky-Rosen (EPR) steering admits multipartite entanglement in the presence of uncharacterized verifiers, enabling practical applications in semi-device-independent protocols. Such applications generally require stronger steerability, while the unavoidable noise weakens steerability and consequently degrades the performance of quantum information processing. Here, we propose the local filtering operation that can maximally distill genuine tripartite EPR steering from N copies of three-qubit generalized Greenberger-Horne-Zeilinger states, in the context of two semi-device-independent scenarios. The optimal filtering operation is determined by the maximization of assemblage fidelity. Analytical and numerical results indicate the advantage of the proposed filtering operation when N is finite and the steerability of initial assemblages is weak. Experimentally, a proof-of-principle demonstration of two-copy distillation is realized with the optical system. The advantage of the optimal local filtering operation is confirmed by the distilled assemblage in terms of higher assemblage fidelity with perfectly genuine tripartite steerable assemblages, as well as the greater violation of the inequality to witness genuine tripartite steerable assemblages. Our results benefit the distillation of multipartite EPR steering in practice, where the number of copies of initial assemblages is generally finite.

Graph states of atomic ensembles engineered by photon-mediated entanglement

Graph states are a broad family of entangled quantum states, each defined by a graph composed of edges representing the correlations between subsystems. Such states constitute versatile resources for quantum computation and quantum-enhanced measurement. Their generation and engineering require a high level of control over entanglement. Here we report on the generation of continuous-variable graph states of atomic spin ensembles, which form the nodes of the graph. We program the entanglement structure encoded in the graph edges by combining global photon-mediated interactions in an optical cavity with local spin rotations. By tuning the entanglement between two subsystems, we either localize correlations within each subsystem or enable Einstein–Podolsky–Rosen steering—a strong form of entanglement that enables the extraction of precise information from one subsystem through measurements on the other. We further engineer a four-mode square graph state, highlighting the flexibility of our approach. Our method is scalable to larger and more complex graphs, laying groundwork for measurement-based quantum computation and advanced protocols in quantum metrology.

Enhancing quantum features and teleportation fidelity of two-mode non-Gaussian states using conditional measurements

The family of two-mode non-Gaussian entangled states, including the pair coherent states (PCSs) and their genealogies, has been extensively investigated regarding their quantum properties and their practical applications in quantum information. Specifically, certain states, such as the multiphoton catalytic pair coherent states (MCPCSs), have been newly introduced under specific experimental conditions. For a more feasible approach, in this paper, we introduce novel nonclassical states obtained by subtracting photons through conditional measurements using beam splitters applied to the two modes of the PCSs. These states are called pair coherent states with conditional measurements (PCSCMs). Our purpose is to demonstrate that the quantum features, such as entanglement, Einstein–Podolsky–Rosen (EPR) correlation, EPR steering, and the average fidelity in teleportation can be enhanced in comparison with both the original PCSs and the MCPCSs. In specific cases, several characteristics are observed in PCSCMs but not inspected in both PCSs and MCPCSs. In our findings, we prove that the quantum characteristics within the PCSCMs are influenced not just by the number of detected photons, denoted by variables k and l, but also by the discrepancy in photon numbers, especially by the difference of k − l.

Controlling Remote Entanglement and One‐Way Steering Via a Squeezed Vacuum Field and an Optical Parametric Amplifier

AbstractA scheme is proposed for generating remote entanglement and one‐way Einstein‐Podolsky‐Rosen (EPR) steering between two mechanical resonators in a cavity optomechanical system. Both mechanical resonators are coupled to a common cavity, which contains an optical parametric amplifier (OPA) and is driven by a squeezed vacuum field. The entanglement and EPR steering can be generated by the squeezed vacuum field and significantly enhanced by the gain of OPA. By manipulating the ratio of two effective optomechanical coupling strengths, the asymmetric EPR steering with excellent controllability on the direction, even the one‐way EPR steering can be achieved. Moreover, both the squeezed vacuum field and the OPA can effectively enhance the robustness of EPR steering against the environment temperature, and the temperature‐dependent one‐way EPR steering is explored. This work paves the way toward generating macroscopic mechanical entanglement and EPR steering with potential applications in quantum information processing.

Ascertaining the influences of auxiliary qubits on the Einstein–Podolsky–Rosen steering and its directions

Einstein–Podolsky–Rosen (EPR) steering is an example of nontrivial quantum nonlocality and characteristic in the non-classical world. The directivity (or asymmetry) is a fascinating trait of EPR steering, and it is different from other quantum nonlocalities. Here, we consider the strategy in which two atoms compose a two-qubit X state, and the two atoms are owned by Alice and Bob, respectively. The atom of Alice suffers from a reservoir, and the atom of Bob couples with a bit flip channel. The influences of auxiliary qubits on EPR steering and its directions are revealed by means of the entropy uncertainty relation. The results indicate that EPR steering declines with growing time t when adding fewer auxiliary qubits. The EPR steering behaves as damped oscillation when introducing more auxiliary qubits in the strong coupling regime. In the weak coupling regime, the EPR steering monotonously decreases as t increases when coupling auxiliary qubits. The increases in auxiliary qubits are responsible for the fact that the steerability from Alice to Bob (or from Bob to Alice) can be more effectively revealed. Notably, the introductions of more auxiliary qubits can change the situation that steerability from Alice to Bob is certain to a situation in which steerability from Bob to Alice is certain.

Certification of non-Gaussian Einstein–Podolsky–Rosen steering

Non-Gaussian quantum states are a known necessary resource for reaching a quantum advantage and for violating Bell inequalities in continuous variable systems. As one kind of manifestation of quantum correlations, Einstein–Podolsky–Rosen steering enables verification of shared entanglement even when one of the subsystems is not characterized. However, how to detect and classify such an effect for non-Gaussian states is far from being well understood. Here, we present an efficient non-Gaussian steering criterion based on the high-order observables and conduct a systematic investigation into the hierarchy of non-Gaussian steering criteria. Moreover, we apply our criterion to three experimentally-relevant non-Gaussian states under realistic conditions and, in particular, propose a feasible scheme to create multi-component cat states with tunable size by performing a suitable high-order quadrature measurement on the steering party. Our work reveals the fundamental characteristics of non-Gaussianity and quantum correlations, and offers new insights to explore their applications in quantum information processing.

The generation of genuine quadripartite Einstein–Podolsky–Rosen steering in an optical superlattice

Einstein–Podolsky–Rosen (EPR) steering is a quantum effect based on quantum entanglement and it is the key resource for building quantum networks because of its useful properties. Based on the criterion for genuine multipartite EPR steering, the genuine quadripartite EPR steering is confirmed and it can be generated by a spontaneous parametric down-conversion cascaded process with two sum-frequency generations in an optical superlattice. This occurs either below the oscillation threshold and without oscillation threshold. The influence of the parameters of cascaded nonlinear process on the quadripartite EPR steering among signal, idler, and two sum-frequency beams are also discussed. Choosing appropriate nonlinear parameters can achieve good quadripartite quantum steering. This scheme of the generation of genuine quadripartite EPR steering has potential applications in quantum communication and computing.

Dephasing-assisted preparation of asymmetric steering in coupled quantum wells.

It is shown that the dephasing rates are usually harmful for quantum correlations in various systems. Nevertheless, we explore that the dephasing rates in the coupled quantum wells (QWs), as a major contribution of the decay processes, can assist to generate one-way Einstein-Podolsky-Rosen (EPR) steering. By applying two strong fields to drive two dipole-allowed transitions while the other transitions are coupled with two quantized modes, the asymmetric EPR steering is possible to obtain at steady state through a single-pathway dissipation in the three-well system. According to dressed-state and Bogoliubov mode transformation, we find that the dephasing rates play a role in modifying the dressed-state populations and the dissipation rate through multiple quantum interference mechanisms. The positive effect of the dephasing rates from a nanostructure on quantum correlation is expected to find potential applications in quantum information processing.

Einstein–Podolsky–Rosen steering and coherence in structured environments

We examine the quantum steering and coherence for two qubits that are immersed in an isotropic (I) and anisotropic (A) photonic band-gab (PBG) crystal. We show how the steerability and coherence of the qubits’ state depends on the essential parameters of the model and initial state setting of the qubits. We find that the prevention of the amount of quantum steering and coherence can be achieved in the presence of PBG materials by a considerable choice of the system parameters. Furthermore, we show that the quantum steering and coherence can resist the degradation during the dynamics in IPBG more than in APBG according to the same physical conditions. Finally, we illustrate the relationship between the quantum steering and coherence with respect to the system parameters under the decoherence effect. These obtained results reveal that quantum systems in PBG materials are very useful to implement diverse applications of quantum technology with optimal performance.

Observation of Non-Markovian Evolution of Einstein-Podolsky-Rosen Steering.

Einstein-Podolsky-Rosen (EPR) steering is a type of characteristic nonlocal correlation and provides an important resource in quantum information tasks, especially in view of its asymmetric property. Although plenty of works on EPR steering have been reported, the study of non-Markovian evolution of EPR steering, in which the interactions between the quantum system and surrounding environment are taken into consideration, still lacks intuitive experimental evidence. Here, we experimentally observe the non-Markovian evolution of EPR steering including its sudden death and revival processes, during which the degree of memory effect plays a key role in the recovery of steering. Additionally, a strict unsteerable feature is sufficiently verified during the non-Markovian evolution within multisetting measurements. This Letter, revealing the whole evolution of EPR steering under the non-Markovian process, provides incisive insight into the applications of EPR steering in quantum open systems.

Relating EPR steering with the fidelity of quantum teleportation for two- and three-qubit states

Einstein–Podolsky–Rosen (EPR) steering is an important quantum resource in quantum information and computation. The relationships between EPR steering and the fidelity of quantum teleportation for two- and three-qubit states are investigated in this paper. For two-qubit states, the upper bound of the average teleportation fidelity based on the EPR steering is derived. When the receiver can only perform the identity or the Pauli rotation operations, the two-qubit X-type states which violate the three-setting measurements steering inequality could be used for teleportation. In the end, the steering observables and the average teleportation fidelities of two-qubit reduced states for three-qubit pure states maintain the same ordering. The complementary relations between the steering observables and the average teleportation fidelities for three-qubit pure states are also established.

Steerability criteria based on Heisenberg–Weyl observables

Einstein–Podolsky–Rosen (EPR) steering is an intermediate form of nonlocality which interpolates between entanglement and Bell nonlocality. It has been shown that EPR steerable states are fundamental resources for one-sided device-independent quantum information tasks. Nevertheless, distinguishing quantum steerable states from the unsteerable ones in general cases remains a big challenge under active studies. The generalized Bloch representation of density matrices in terms of the Heisenberg observables is a useful tool for analyzing characteristics of quantum systems and plays an important role in quantum information. In this work, the role of this representation in detection of EPR steering is studied. More specifically, based on the correlation matrices of the Heisenberg–Weyl observables, a family of steerability criteria for arbitrary dimensional bipartite systems are proposed. A large class of Hermitian operators, which can conveniently witness steering in some scenarios, are further provided. Finally, these criteria are illustrated through several examples, are compared with some existing ones, and their power and advantages are exhibited in certain cases.

Deterministic manipulation of steering between distant quantum network nodes.

Multipartite Einstein-Podolsky-Rosen (EPR) steering is a key resource in a quantum network. Although EPR steering between spatially separated regions of ultracold atomic systems has been observed, deterministic manipulation of steering between distant quantum network nodes is required for a secure quantum communication network. Here, we propose a feasible scheme to deterministically generate, store, and manipulate one-way EPR steering between distant atomic cells by a cavity-enhanced quantum memory approach. While optical cavities effectively suppress the unavoidable noises in electromagnetically induced transparency, three atomic cells are in a strong Greenberger-Horne-Zeilinger state by faithfully storing three spatially separated entangled optical modes. In this way, the strong quantum correlation of atomic cells guarantees one-to-two node EPR steering is achieved, and can perserve the stored EPR steering in these quantum nodes. Furthermore, the steerability can be actively manipulated by the temperature of the atomic cell. This scheme provides the direct reference for experimental implementation for one-way multipartite steerable states, which enables an asymmetric quantum network protocol.

Three-color and tripartite steering generated by intracavity cascaded processes

Einstein–Podolsky–Rosen (EPR) steering has important practical applications in secure quantum communication because of its unique characters. Multicolor and multipartite EPR steering is an important resource for connecting different physical systems in the quantum networks with several nodes. We investigate three-color and tripartite steering properties based on the intracavity cascaded nonlinear processes of down conversion and sum frequency. Based on the criteria proposed by Kogias [Phys. Rev. Lett. 114, 060403 (2015)], the steering parameters among down-conversion fields and sum-frequency field versus the normalized frequency and the pump parameter are studied. Our research shows that the direction of steering and steerability can be manipulated flexibly. We also show that quantum secret sharing can be realized in our scheme. And the results of asymmetric quantum steering and joint quantum steering among different modes provide a technical reference for the construction of secure quantum information network.

Manipulation and enhancement of Einstein-Podolsky-Rosen steering between two mechanical modes generated by two Bogoliubov dissipation pathways

We consider a three-mode optomechanical system in which two mechanical oscillators are independently coupled to a cavity mode driven by two controllable lasers. By controlling the two-tone driving, one can prepare the entanglement and Einstein-Podolsky-Rosen (EPR) steering of two mechanical modes, in which the cavity mode acts as a single reservoir to cool two Bogoliubov modes. We find that the direction of EPR steering can be manipulated effectively by adjusting the damping rates and the thermal noises of two mechanical modes. In addition, we show that the entanglement and EPR steering between two mechanical modes can be enhanced by adding a parametric amplifier (PA) into the cavity. The effects of the strength and phase of the PA on the mechanical entanglement and EPR steering are analyzed and discussed in detail. Meanwhile, the additional PA can also expand the region of the one-way steering and strengthen the robustness of the entanglement and EPR steering against the thermal noise. The present scheme may provide effective resources for quantum information processing.