Einstein–Podolsky–Rosen (EPR) steering is a type of directional quantum correlation that holds immense significance and broad applications in quantum information processing. While EPR steering has been achieved across various physical systems, research into its implementation in non-Hermitian systems remains in its early stages. In this study, we delve into the realm of non-Hermitian control of EPR steering by leveraging atomic coherence-controlled energy-level cascaded four-wave mixing (ELC-FWM) processes. We derive analytical expressions for the generation of EPR steering within such non-Hermitian nonlinear systems, demonstrating that exceptional points (EPs) and multimode EPR steering can be realized through introducing dressing-control fields. Furthermore, we illustrate that nonlinear coherent channels and the associated steerability distribution of the output modes can be tailored during the EPR steering generation process, which is directly linked to the eigenvalues of non-Hermitian processes. Additionally, we analyze the impact of loss effects on generated multimode EPR steering. Our findings suggest that non-Hermitian control offers a promising all-optical approach for constructing practical quantum networks.
Einstein–Podolsky–Rosen (EPR) steering is a type of directional quantum correlation that holds immense significance and broad applications in quantum information processing. While EPR steering has been achieved across various physical systems, research into its implementation in non-Hermitian systems remains in its early stages. In this study, we delve into the realm of non-Hermitian control of EPR steering by leveraging atomic coherence-controlled energy-level cascaded four-wave mixing (ELC-FWM) processes. We derive analytical expressions for the generation of EPR steering within such non-Hermitian nonlinear systems, demonstrating that exceptional points (EPs) and multimode EPR steering can be realized through introducing dressing-control fields. Furthermore, we illustrate that nonlinear coherent channels and the associated steerability distribution of the output modes can be tailored during the EPR steering generation process, which is directly linked to the eigenvalues of non-Hermitian processes. Additionally, we analyze the impact of loss effects on generated multimode EPR steering. Our findings suggest that non-Hermitian control offers a promising all-optical approach for constructing practical quantum networks.
Einstein-Podolsky-Rosen (EPR) steering, a distinct class of quantum correlation intermediate between entanglement and Bell nonlocality, exhibits unique asymmetry and directionality. EPR steering swapping, analogous to entanglement swapping, enables two initially independent particles to establish EPR steering correlations. Recent advances in all-optical entanglement and EPR steering swapping have overcome the limitation of mutual electro-optical conversions. However, for quantum information systems required in real-world applications, extending these capabilities to multimode regimes remains largely underexplored. Here, we propose an m -to- n multimode all-optical EPR steering swapping architecture based on energy-level-cascaded four-wave mixing processes. By harnessing fundamental light-atom interactions, we demonstrate scalable multimode EPR steering swapping and realize non-Hermitian control over dressing-induced coherent channels. Crucially, our multimode approach demonstrates distinctive, mode-dependent features of non-monotonicity and asymmetry, which are unattainable in conventional two-mode schemes. The flexible controllability afforded by such multimode quantum correlations also facilitates interfaces between non-Hermitian light-matter systems, paving the way for practical implementations of EPR steering and all-optical quantum networks.
Abstract Einstein–Podolsky–Rosen (EPR) steering for multipartite systems plays an important role in several quantum technologies and applications, e.g., quantum communication and quantum metrology. In this study, an energy‐level cascaded four‐wave mixing (EC‐FWM) process modulated by the dressing effect is proposed to generate three‐ and four‐mode EPR steering in the atomic medium of rubidium. The energy‐level simultaneously cascaded FWM and the energy‐level ordinally cascaded FWM are compared in three‐mode EPR steering, and monogamy relations for Gaussian steerability are also verified. Furthermore, multipartite EPR steerability is controlled by actively adjusting the dressing field. Different types of EPR steerability exhibit different modulation results when the dressing conditions of enhancement and suppression are satisfied. The proposed scheme exhibits advantages such as scalability, flexibility, and simplified experimental setup and can construct controllable large‐scale quantum networks.
Abstract Level-cascaded four-wave mixing systems with multimode quantum state squeezing are of great significance for non-Hermitian exceptional control. In this paper, based on non-Hermitian systems, we couple the energy level dressing to generate multimode quantum correlated beams. We have conducted an in-depth discussion on the quantum squeezing characteristics of the cascaded four-mode system. We use the gain squeezing matrix of the Hamiltonian matrix to introduce a pair of Einstein–Podolsky–Rosen (EPR) injections and two pairs of EPR injections at different positions in the cascaded four-mode system. We found several key phenomena: (1) In covariance squeezing, dual EPR injections not only disrupt the original squeezing strength but also produce varying numbers of Hamiltonians depending on injection location; (2) For intensity-difference squeezing, multiple coherent injections enhance squeezing coherence proportionally to injection count, while increased Hamiltonians strengthen intensity-difference correlations. Particularly noteworthy is the equivalence between single EPR injections and E 2 E 3 dual injections, as well as between position-B dual EPR injections and E 2 E 3 E 4 triple injections. The results establish that EPR injections exhibit superior intensity hierarchy compared to multiple coherent or Hamiltonian injections, with their configuration capable of actively modifying inter-mode hierarchical relationships.
Multipartite entanglement has emerged as a valuable quantum resource for constructing large-scale quantum networks. However, the presence of non-Hermitian features induced by natural microscopic quantum systems significantly modifies the overall response of nonlinear parametric processes, thereby enabling direct manipulation of multipartite entanglement properties. In this study, we demonstrate the generation of multimode entanglement through atomic four-wave mixing (FWM) and analyze the properties of exceptional points (EP) under dressing control in non-Hermitian systems. By leveraging dressing-controlled atomic nonlinearity, we achieve versatile EPs and higher-order EPs by carefully tuning the atomic multi-parameter in the cascading FWM system. Additionally, we investigate the entanglement properties of various permutations of the output signal modes using the positive partial transpose (PPT) criterion. Notably, under non-Hermitian control, the application of single-, double-, and N-dressing splits leads to coherent multichannel control and further extends the scale of quantum entanglement. The outcomes of our research offer a novel approach to actively control non-Hermitian quantum phenomena without relying on artificial photonic structures. Furthermore, this paves the way for the realization of complex quantum information tasks by exploiting the non-Hermitian characteristics of the light-matter interaction.
Collective multipartite Einstein-Podolsky-Rosen (EPR) steering is a type of quantum correlation shared among n parties, where the EPR paradox of one party can be realized only by performing local measurements on all the remaining $n\ensuremath{-}1$ parties. Here, we propose an efficient method to produce collective multipartite EPR steering via symmetrically and asymmetrically cascading parametric amplification processes, i.e., four-wave mixing (FWM) of rubidium atoms. The simplified collective-steering criterion is introduced using the Coffman-Kundu-Wootters monogamy relation. Moreover, by actively adjusting the parametric gains, the collective EPR steerability is optimized in our schemes. We find that the scale of collective steering can be extended by cascading more FWMs; in particular, introducing optical loss is useful for generating collective steering with more parties only in the asymmetry structure. Our results pave the way for the construction of quantum networks and provide a promising candidate for one-sided device-independent quantum cryptography among multiple users.
We explore the asymmetric Einstein-Podolsky-Rosen (EPR) steering of field modes via atomic coherent effects. A resonant four-level system in double-cascade configuration is under our consideration, where the atoms are excited by the applied fields from one cascade channel and two cavity modes are generated from the other cascade transition. The results show two cavity modes are suitable for achieving the steady-state one-way EPR steering. We analyze the physics in terms of the dressed-atom Bogoliubov-field-mode approach. It is found that one of two Bogoliubov modes is mediated by the resonant coupling of the dressed atoms and the other is decoupled from them. This leads to the so-called one-channel dissipation, by which the dressed atoms absorb the average excitations from one transformed mode and then two original modes are pulled into the asymmetric correlation. Remarkably, the present scheme is focused on the full-resonant interaction not only between the classical fields, the cavity modes and the bare atoms, but also between the Bogoliubov modes and dressed atoms, which will induce the one-way steering simply via adjusting the intensity of an external field. Furthermore, the EPR steering could occur between the field modes with the large frequency difference, such as optical and microwave fields, which is more useful for the practical quantum communication. Based on the one-channel dissipation, the obtainable one-way EPR steering is rather against the dynamic fluctuations and is regardless of the initial state.