We propose a method to achieve a coherent switch of optomagnonic entanglement in a cavity optomagnonic system with non-Hermitian coupling. The strength of photon-photon and photon-magnon entanglement can be controlled by tuning the relative phase angle of two nanoparticles and optimizing the detuning of two optical modes. We show that the bipartite entanglement is significantly enhanced by selecting a suitable optomagnonics coupling strength in the presence of the exceptional points (EPs). The relative phase not only enhances the entanglement strength but also increases the entanglement domain over a wide range of detuning compared to the Hermitian system. By manipulating the system toward or away from EPs, versatile tunability of the tripartite entanglement, mean photon, and magnon numbers can be achieved. Additionally, the direction of asymmetric transmission can also be well tuned in a highly asymmetric way via non-Hermitian coupling. The study of controlled entanglement may provide the theoretical basis and reference for the research and development of new tunable quantum devices.
We propose a method to achieve a coherent switch of optomagnonic entanglement in a cavity optomagnonic system with non-Hermitian coupling. The strength of photon-photon and photon-magnon entanglement can be controlled by tuning the relative phase angle of two nanoparticles and optimizing the detuning of two optical modes. We show that the bipartite entanglement is significantly enhanced by selecting a suitable optomagnonics coupling strength in the presence of the exceptional points (EPs). The relative phase not only enhances the entanglement strength but also increases the entanglement domain over a wide range of detuning compared to the Hermitian system. By manipulating the system toward or away from EPs, versatile tunability of the tripartite entanglement, mean photon, and magnon numbers can be achieved. Additionally, the direction of asymmetric transmission can also be well tuned in a highly asymmetric way via non-Hermitian coupling. The study of controlled entanglement may provide the theoretical basis and reference for the research and development of new tunable quantum devices.
We study the periodic entanglement and asymmetric steering at exceptional points for a non-Hermitian cavity magnetomechanics system in which exceptional points (EPs) emerge periodically by controlling the relative phase angle of the nanoparticles. First, we analyze this hybrid system and identify parametric regimes where different types of entanglement and steering are enhanced. Entanglement and steering can be significantly enhanced due to the external control method and are thus more robust to thermal noises. This provides an active method to manipulate the asymmetry of steering instead of adding asymmetric losses or noises to subsystems at the cost of reducing steering ability. Moreover, the relative phase angle (RPA) not only enhances the strength of entanglement but also increases the domain of entanglement over a wider space of detunings compared to a system in which no RPA is present. Another important consequence of the RPA is that it controls the directivity of quantum steering. Specifically, steering reaches a maximal value at EPs as well, and we can get rich properties of Einstein-Podolsky-Rosen steering; e.g., the asymmetry of the overall state is stepwise, including one-way quantum steering, no-way quantum steering, and two-way quantum steering. We believe that the presented scheme is a step forward in realizing robust quantum entanglement using current technology. Our results indicate that cavity magnetomechanics systems could provide a promising platform for the study of macroscopic quantum phenomena.
We theoretically propose a scheme to generate and control continuous variable bipartite entanglement and Gaussian quantum steering in an optical whispering gallery mode (WGM)-based cavity optomagnonical system that consists of two macroscopic YIG resonator. Owing to the well-known Faraday effect, both the magnon modes are coupled to single-mode optical WGM through nonlinear interaction. We investigate in detail the impact of several physical parameters such as effective cavity detuning, input laser power, environment temperature, optomagnonical coupling strengths and magnon decay rate on different bipartite entanglement. We also found a suitable parameter regime to obtain maximum cavity-magnon and magnon-magnon bipartite entanglement in our proposed system. It is interesting to note that the numerical simulation result shows that magnon-magnon entanglement persists up to 60K. With a proper choice of optomagnonical coupling strengths and normalized effective cavity detuning, we can effectively control the nature and strength of Gaussian quantum steering. In the WGM-based cavity optomagnonical system, our current work will offer a new way of greatly controlling a variety of nonclassical quantum correlations of macroscopic objects, which may find use in a number of contemporary quantum technology fields.
The ability to harness the ubiquitous dissipation in realistic quantum systems holds great promise for developing advanced quantum technologies. In particular, the presence of dissipation violates the fundamental premise of Hermiticity and results in the non-Hermitian singularities associated with coalesced eigenstates in parameter space known as exceptional points (EPs), providing a new strategy to manipulate quantum states in both dynamical evolution and stationary limit. In this work, we show that for a microcavity supporting chiral EPs, light-matter interaction between the cavity photons and a quantum emitter can be flexibly switched from coherent to fully dissipative by tuning the phase factor of a complex coupling rate, an additional degree of freedom offered by the chiral EPs of a microcavity. The tunable coherent and dissipative light-matter interactions are evidenced by the distinguishing quantum dynamics and optical spectra, where the dispersion of a coupled quantum system changes from level repulsion to level attraction. While dissipation is generally considered fatal for quantum effects and should be suppressed, here we find that the EP-enabled dissipative light-matter interaction shows a unique advantage in achieving high-efficiency single-photon emission in a weak-coupling regime through the non-Hermitian photon blockade, which originates from the anharmonicity in the losses instead of in the eigenenergy levels for the conventional photon blockade (CPB). A giant enhancement of more than 5 orders of magnitude is found for both photon correlations and intensity compared to that of CPB in coherent light-matter interaction. We expect our work to enrich the understanding of light-matter interaction in open photonic resonators and provide insight into the manipulation of quantum states and quantum correlations in a wide variety of quantum systems by utilizing the non-Hermicity of electromagnetic environments.
We propose an enhanced entanglement generation scheme in the non-Hermitian system by introducing an ancillary qubit with adjustable driven field to control the target entanglement, making this model more suitable for the switch operation at the quantum interface. Moreover, through adiabatic elimination, the mode of the qubit has been eliminated, and direct coupling between the cavities has been realized. The effective coupling strength between two non-Hermitian microwave cavities can be adjusted as an optimal value to satisfy a specific phase condition that realizes the maximally entangled state on a timescale. To prove the ability of our scheme to improve the performances of entanglement generation in the non-Hermitian system, the numerical simulations are performed based on a model where two microwave cavities are indirectly coupled through a superconducting qubit. It is evident that non-Hermitian cavities can be entangled significantly faster than Hermitian cavities, with the relative speedup increasing significantly as the perturbation is decreased, and the fourth-order exceptional points at J=0 are approached. Last but not least, our scheme has good robustness against parameter errors, crosstalk, and Gaussian white noise and is a feasible scheme for enhanced entanglement generation via approaching to higher-order exceptional points in a non-Hermitian network system.
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.
Abstract We propose to generate and control stationary one-way steering with strong entanglement between photon and magnon modes by the cooperative effect of coherent coupling and dissipative coupling. Due to the combination of two couplings, the system becomes a parity-time-like symmetric non-Hermitian system, and two exceptional points (EPs)-like appear in the real and imaginary parts of the eigenvalues. We demonstrate that the especially obvious quantum entanglement and perfect one-way steering can be obtained around two EPs-like. The continuous variable entanglement and steering produced by this cooperative effect show stronger robustness to environment temperature and system dissipation than that induced by nonlinearity. The one-way steering directivity can be controlled by the relative phase of cooperative dissipation and the frequency detuning of the magnon mode. Our work shows the controllability advantage of the open cavity magnonic system and may open up a platform for the generation of stationary one-way steering.