Nonreciprocal magnon blockade via the Barnett effect

Nonreciprocal bipartite and tripartite entanglement in cavity-magnon optomechanics via the Barnett effect

We theoretically propose a scheme for generating nonreciprocal macroscopic bipartite and tripartite entanglement using the Barnett effect in cavity-magnon optomechanics. The system consists of an optomechanical cavity and a rotatable yttrium iron garnet (YIG) sphere. Our results indicate that under appropriate parameter conditions, both bipartite entanglement and genuine tripartite entanglement can be generated between the cavity mode, mechanical mode, and magnon mode. Moreover, when the YIG sphere rotates, adjusting the magnetic field direction can induce a positive or negative Barnett shift, which leads to the nonreciprocity of entanglement, where entanglement exists in one chosen magnetic field direction and disappears in the other. Meanwhile, the macroscopic tripartite entanglement in the system is robust against thermal noise. Our work provides a possible avenue for quantum information processing, quantum chiral device integration, and multi-node quantum networks construction.

Nonreciprocal unconventional magnon blockade induced by Barnett effect and parametric amplification

We propose a scheme to achieve nonreciprocal unconventional magnon blockade (UMB) via the Barnett effect in a spinning ferrimagnetic yttrium-iron-garnet sphere coupled to a microwave cavity that interacts with a parametric amplifier. We show that, with a strong cavity-magnon coupling regime, giant nonreciprocal UMB can emerge by appropriately choosing two sets of parameters in this system, i.e., strong magnon antibunching occurs only from one direction of the magnetic field but not from the other side. This nonreciprocity originates from the fact that the Barnett shift induced by the Barnett effect can be adjusted from positive to negative values by changing the magnetic field direction, resulting in different frequencies of the magnon mode. Moreover, we demonstrate that parametric amplification is an indispensable factor for constructing the pathways of quantum destructive interference to achieve strong UMB. Furthermore, we give analytical parameter conditions to realize strong UMB, which is proven to be in great agreement with numerical results. Interestingly, the nonreciprocity against magnon thermal occupation is remarkably enhanced by increasing the amplitude of the driving field. Notably, the critical temperature for observing nonreciprocal UMB is as high as 133 mK, and the sphere needs to spin at MHz values to achieve the UMB effect. Our work provides an avenue to realize nonreciprocal single-magnon devices and has potential applications in quantum information processing and quantum communication.

Controllable antibunching of two-magnon bundle in a hybrid ferromagnet-superconductor system

We propose an alternative scheme for implementing the antibunching effects of two-magnon bundle in a hybrid ferromagnet-superconductor system, where a magnon mode from the yttrium iron garnet (YIG) sphere interacts with a three-level superconducting qubit via photon virtual excitation in the microwave cavity. With the help of the qubit driving from the ground state to the excited state, the cascaded emission of magnon occurs and then the two-magnon bundle is formed. By analyzing the ordinary and generalized second-order correlation functions, it is found that the antibunched two-magnon bundle could be achieved via properly choosing the system parameters, which is originated from the anharmonicity of dressed energy levels induced by magnon-qubit couplings. The distinct feature is that high-proportion n-magnon emission could be obtained via relaxing the restriction on the strong qubit driving and magnon-qubit coupling, which may provide a feasible method to realize the high-quality multimagnon source for quantum metrology and quantum information processing.

Nonreciprocal magnon laser in a spinning cavity optomagnonic system

We introduce a novel, to the best of our knowledge, method to achieve a highly efficient nonreciprocal magnon laser within a spinning cavity optomagnonic system, which integrates a magnon mode and two optical modes. The rotation of the YIG sphere triggers the Barnett effect in the magnon mode and the Sagnac effect in the optical modes. The directional input of a pump light leads to opposite Sagnac-Fizeau frequency shifts in these modes. By adjusting the angular velocity, we can simultaneously control both the Barnett and Sagnac effects. Significantly, increasing the spin angular velocity enhances the system's nonreciprocity and magnon gain, yielding an isolation rate of 38.7 dB and a low-threshold magnon laser. This method presents a promising avenue for developing a nonreciprocal magnon laser, with implications for spintronics and the advancement of nonreciprocal optical devices.

Magnetic-field-direction-controlled slow light and second-order sidebands in a cavity-magnon optomechanical system

We theoretically study how the magnetic field direction controls both the transmission rate and the group delay of the signal, as well as the second-order sideband process in a hybrid cavity-magnon optomechanical system. By tuning the direction of the bias magnetic field, either a positive or negative magnon Kerr coefficient can be achieved, leading to a corresponding shift in the magnon frequency. As a result, the transmission rate can be significantly modified, resulting in a Fano-like transparency spectrum governed by the magnetic field direction, along with a slow-to-fast light switch also influenced by that direction. Moreover, we study the impact of magnetic field direction on the second-order sidebands, revealing that the enhancement of the second-order sideband effect is dependent on this direction. These findings pave the way to engineering magnon Kerr nonlinearity-assisted optomechanical devices for applications in signal propagation and storage.

Nonreciprocal magnon blockade based on nonlinear effects

We present an alternative scheme to achieve nonreciprocal unconventional magnon blockade (NUMB) in a hybrid system formed by two microwave cavities and one yttrium iron garnet (YIG) sphere, where the pump and signal cavities interact nonlinearly with each other and the signal cavity is coupled to the YIG sphere. It is found that the nonlinear coupling occurs between the pump cavity and magnon modes due to the dispersive interactions among three bosonic modes. Meanwhile, the Kerr nonlinearity is present in the pump cavity. Based on these nonlinear effects, a nonreciprocal magnon blockade could be achieved with the help of the weak parametric driving of the pump cavity. The present work provides an alternative method to prepare single magnon resource, which may be helpful for quantum information processing.