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As a most important feature of non-Hermitian systems, exceptional points (EPs) lead to a variety of unconventional phenomena and applications. Here we discover that multitype entanglement dynamics can be induced by engineering different orders of EP. By studying a generic model composed of two coupled non-Hermitian qubits, we find that diverse entanglement dynamics on the two sides of the fourth-order EP (EP4) and second-order EP (EP2) can be observed simultaneously in the weak coupling regime. With the increase of the coupling strength, the EP4 is replaced by an additional EP2, leading to the disappearance of the entanglement dynamics transition induced by EP4 in the strong coupling regime. Considering the case of Ising type interaction, we also realize EP-induced entanglement dynamics transition without the driving field. Our study paves the way for the investigation of EP-induced quantum effects and applications of EP-related quantum technologies., Comment: 14 pages, 11 figures

The discovery of the non-Hermitian skin effect (NHSE) has revolutionized our understanding of wave propagation in non-Hermitian systems, highlighting unexpected localization effects beyond conventional theories. Here, we discover that NHSE, accompanied by multi-type spectral phases, can be induced by manipulating nonconservative couplings. By characterizing the spectrum through the windings of the energy bands, we demonstrate that band structures with identical, opposite, and even twisted windings can be achieved. These inequivalent types of spectra originate from the multi-channel interference resulting from the interplay between conservative and nonconservative couplings. Associated with the multi-type spectra, unipolar and bipolar NHSE with different eigenmode localizations can be observed. Additionally, our findings link the nonreciprocal transmission properties of the system to multiple spectral phases, indicating a connection with the skin modes. This work paves new pathways for investigating non-Hermitian topological effects and manipulating nonreciprocal energy flow., Comment: 6 pages, 4 figures

We study the mechanism for realizing non-Hermitian skin effect (NHSE) via dissipative couplings, in which the left-right couplings have equal strengths but the phases do not satisfy the complex conjugation. Previous realizations of NHSE typically require unequal left-right couplings or on-site gain and loss. In this work we find that when combined with the multichannel interference provided by a periodic dissipative-coherent coupling structure, the dissipative couplings can lead to unequal left-right couplings, inducing NHSE. Moreover, we show that the non-Hermiticity induced by dissipative couplings can be fully transformed into nonreciprocity-type non-Hermiticity without bringing extra gain-loss-type non-Hermiticity. Thus, this mechanism enables unidirectional energy transmission without introducing additional insertion loss. Our work opens a new avenue for the study of non-Hermitian topological effects and the design of directional optical networks.

Realization of nonreciprocal transmission with low insertion loss and high contrast simultaneously is in great demand for one-way optical communication and information processing. Here we propose a generic approach to achieving perfect nonreciprocity that allows lossless unidirectional transmission by engineering energy losses. The loss of the intermediate mode induces a phase lag impinging on the indirect channel for energy transmission, which does not depend on the energy transmission direction. When the direct transmission channel coexists with the indirect lossy transmission channel, the dual-channel interference can be tuned to be destructive simultaneously for backward transmission from the rightmost mode to the leftmost mode, and for forward transmission from the leftmost mode to the intermediate mode. The former interference outcome corresponds to 100% nonreciprocity contrast, and the latter guarantees zero insertion loss for forward transmission. Additionally, our scheme also allows a nonreciprocity response over a wide bandwidth by increasing the losses while keeping perfect nonreciprocity at resonance. The robustness against loss indicates that our scheme is advantageous in the implementation of nonreciprocal optical devices with high performance., Comment: 7 pages, 4 figures

Generation of quantum correlations between separate objects is of significance both in fundamental physics and in quantum networks. One important challenge is to create the directional "spooky action-at-a-distanc" effects that Schr\"{o}dinger called "steering" between two macroscopic and massive objects. Here, we analyze a generic scheme for generating steering correlations in cascaded hybrid systems in which two distant oscillators with effective masses of opposite signs are coupled to a unidirectional light field, a setup which is known to build up quantum correlations by means of quantum back-action evasion. The unidirectional coupling of the first to the second oscillator via the light field can be engineered to enhance steering in both directions and provides an active method for controlling the asymmetry of steering. We show that the resulting scheme can efficiently generate unconditional steady-state Einstein-Podolsky-Rosen steering between the two subsystems, even in the presence of thermal noise and optical losses. As a scenario of particular technological interest in quantum networks, we use our scheme to engineer enhanced steering from an untrusted node with limited tunability (in terms of interaction strength and type with the light field) to a trusted, highly tunable node, hence offering a path to implementing one-sided device-independent quantum tasks., Comment: 11 pages, 8 figures

The generation of entanglement between disparate physical objects is a key ingredient in the field of quantum technologies, since they can have different functionalities in a quantum network. Here we propose and analyze a generic approach to steady-state entanglement generation between two oscillators with different temperatures and decoherence properties coupled in cascade to a common unidirectional light field. The scheme is based on a combination of coherent noise cancellation and dynamical cooling techniques for two oscillators with effective masses of opposite signs, such as quasi-spin and motional degrees of freedom, respectively. The interference effect provided by the cascaded setup can be tuned to implement additional noise cancellation leading to improved entanglement even in the presence of a hot thermal environment. The unconditional entanglement generation is advantageous since it provides a ready-to-use quantum resource. Remarkably, by comparing to the conditional entanglement achievable in the dynamically stable regime, we find our unconditional scheme to deliver a virtually identical performance when operated optimally., Comment: Final version; 6 pages, 3 figures + Supplemental Material