Nonlocal magnon entanglement generation in coupled hybrid cavity systems

Anomalous Long-Distance Coherence in Critically Driven Cavity Magnonics

Developing quantum networks necessitates coherently connecting distant systems via remote strong coupling. Here, we demonstrate long-distance coherence in cavity magnonics operating in the linear regime. By locally setting the cavity near critical coupling with traveling photons, nonlocal magnon-photon coherence is established via strong coupling over a 2-m distance. We observe two anomalies in this long-distance coherence: first, the coupling strength oscillates twice the period of conventional photon-mediated couplings; second, clear mode splitting is observed within the cavity linewidth. Both effects cannot be explained by conventional coupled-mode theory, which reveals the tip of an iceberg of photon-mediated coupling in systems under critical driving. Our Letter shows the potential of using critical phenomena for harnessing long-distance coherence in distributed systems.

Long-distance transmission of arbitrary quantum states between spatially separated microwave cavities

Long-distance transmission between spatially separated microwave cavities is a crucial area of quantum information science and technology. In this work, we present a method for achieving long-distance transmission of arbitrary quantum states between two microwave cavities, by using a hybrid system that comprises two microwave cavities, two nitrogen-vacancy center ensembles (NV ensembles), two optical cavities, and an optical fiber. Each NV ensemble serves as a quantum transducer, dispersively coupling with a microwave cavity and an optical cavity, which enables the conversion of quantum states between a microwave cavity and an optical cavity. The optical fiber acts as a connector between the two optical cavities. Numerical simulations demonstrate that our method allows for the transfer of an arbitrary photonic qubit state between two spatially separated microwave cavities with high fidelity. Furthermore, the method exhibits robustness against environmental decay, parameter fluctuations, and additive white Gaussian noise. Our approach offers a promising way for achieving long-distance transmission of quantum states between two spatially separated microwave cavities, which may have practical applications in networked large-scale quantum information processing and quantum communication.

Simultaneously enhanced magnomechanical cooling and entanglement assisted by an auxiliary microwave cavity

We propose a mechanism to simultaneously enhance quantum cooling and entanglement via coupling an auxiliary microwave cavity to a magnomechanical cavity. The auxiliary cavity acts as a dissipative cold reservoir that can efficiently cool multiple localized modes in the primary system via beam-splitter interactions, which enables us to obtain strong quantum cooling and entanglement. We analyze the stability of the system and determine the optimal parameter regime for cooling and entanglement under the auxiliary-microwave-cavity-assisted (AMCA) scheme. The maximum cooling enhancement rate of the magnon mode can reach 98.53%, which clearly reveals that the magnomechanical cooling is significantly improved in the presence of the AMCA. More importantly, the dual-mode entanglement of the system can also be significantly enhanced by AMCA in the full parameter region, where the initial magnon-phonon entanglement can be maximally enhanced by a factor of about 11. Another important result of the AMCA is that it also increases the robustness of the entanglement against temperature. Our approach provides a promising platform for the experimental realization of entanglement and quantum information processing based on cavity magnomechanics.

Parametrically amplified nonreciprocal magnon laser in a hybrid cavity optomagnonical system

We propose a scheme to achieve a tunable nonreciprocal magnon laser with parametric amplification in a hybrid cavity optomagnonical system, which consists a yttrium iron garnet (YIG) sphere and a spinning resonator. We demonstrate the control of magnon laser can be enhanced via parametric amplification, which make easier and more convenient to control the magnon laser. Moreover, we analyze and evaluate the effects of pump light input direction and amplification amplitude on the magnon gain and laser threshold power. The results indicate that we can obtian a higher magnon gain and a broader range of threshold power of the magnon laser. In our scheme both the nonreciprocity and magnon gain of the magnon laser can be increased significantly. Our proposal provides a way to obtain a novel nonreciprocal magnon laser and offers new possibilities for both nonreciprocal optics and spin-electronics applications.

Nonreciprocal sideband responses in a spinning microwave magnomechanical system

Nonreciprocal sideband responses in a spinning microwave magnomechanical system consists of a spinning resonator coupled with a yttrium iron garnet sphere are proposed. We show that the efficiency of sideband generation can be enhanced in one driving direction but restrained in the opposite. This nonreciprocity results from Sagnac effect induced by the spinning resonator, leading to asymmetric magnonic responses in two different driving directions. Beyond the conventional linearized description, the properties of nonreciprocal two-color second-order sideband are demonstrated. By adjusting Sagnac-Fizeau shift and the power of control field, the degree of asymmetric magnonic responses can be strengthened, therefore causing stronger nonreciprocity of sideband. Especially, for the case of strong Sagnac-Fizeau shift and the control field, high level of efficiency and isolation ratio of sideband are achieved simultaneously and the operational bandwidth of strong nonreciprocity can be expanded. Our proposal provides an effective avenue for the manipulation of the nonreciprocity of sideband and has potentially practical applications in on-chip microwave isolation devices and magnon-based precision measurement.