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arXiv:2401.02251 · Advanced Quantum Technologies

Nonreciprocal Unconventional Photon Blockade with Kerr Magnons

Xiao‐Hong Fan, Yi‐Ning Zhang, Junpo Yu, Mingyue Liu, Wen‐Di He, Hai‐Chao Li, Wei Xiong

Published May 8, 2024• 34 citations

Abstract

Abstract Nonreciprocal devices, allowing to manipulate one‐way signals, are crucial to quantum information processing and quantum networks. Here a nonlinear cavity‐magnon system is proposed, consisting of a microwave cavity coupled to one or two yttrium–iron–garnet (YIG) spheres supporting magnons with Kerr nonlinearity, to investigate nonreciprocal unconventional photon blockade. The nonreciprocity originates from the direction‐dependent Kerr effect, distinctly different from previous proposals with spinning cavities and dissipative couplings. For a single sphere case, nonreciprocal unconventional photon blockade can be realized by manipulating the nonreciprocal destructive interference between two active paths, via varying the Kerr coefficient from positive to negative, or vice versa. By optimizing the system parameters, the perfect and well‐tuned nonreciprocal unconventional photon blockade can be predicted. For the case of two spheres with opposite Kerr effects, only reciprocal unconventional photon blockade can be observed when two cavity‐magnon coupling strengths Kerr strengths are symmetric. However, when coupling strengths or Kerr strengths become asymmetric, nonreciprocal unconventional photon blockade appears. This implies that two‐sphere nonlinear cavity‐magnon systems can be used to switch the transition between reciprocal and nonreciprocal unconventional photon blockades. This study offers a potential platform for investigating the nonreciprocal photon blockade effect in nonlinear cavity magnonics.

DOI: 10.1002/qute.202400043

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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 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.

We propose a scheme to achieve nonreciprocal unconventional magnon blockade (NUMB) based on the Barnett and Sagnac effects in a hybrid nonlinear system, in which a microwave cavity with two modes and a yttrium iron garnet (YIG) sphere are included. Two cavity modes with the fundamental and the second-harmonic frequencies are coupled by virtue of the χ (2) nonlinear materials, and meanwhile, the fundamental mode interacts with the magnon mode via the magnetic dipole interaction. Under weak driving and coupling conditions, the magnon blockade is obtained, where the second-order correlation function has been used to analyze the magnon antibunching based on the numerical simulations and analytical calculations. The underlying mechanism is that quantum destructive interference occurs between different transition paths. In addition, the combination of the Barnett and Sagnac effects, which leads to the simultaneous frequency shifts of the magnon and two microwave modes, could induce the nonreciprocity of magnon antibunching due to the positive and negative detunings via changing the direction of the external fields. The scheme we present is based on the weak near-resonant coupling between quantum modes and the weak driving of magnon and photon modes, which may demonstrate the potential for achieving the single-magnon resource in a hybrid cavity magnonic system and provide valuable guidance for the design of nonreciprocal magnon devices.

We demonstrate nonreciprocal macroscopic entanglement between magnon modes in two yttrium-iron-garnet (YIG) spheres induced by the Kerr effect stemming from magnetocrystalline anisotropy. The two YIG spheres with different sizes are placed in a microwave cavity, and the magnon modes couple to the microwave cavity photons by the magnetic dipole interaction. The microwave cavity can be adiabatically eliminated by far detuning from the magnon modes, and thus mediates the indirect interaction between two magnon modes. The magnon Kerr nonlinearity of the small YIG sphere is enhanced by the appropriate drive. Meanwhile, the sign of the Kerr coefficient can be manipulated by changing the direction of the bias magnetic field, in turn causing the nonreciprocity of magnon-magnon entanglement. We numerically analyze the optimal parameter regions for generating the entanglement. The properties of the nonreciprocal entanglement are explored by analyzing the defined bidirectional contrast ratio, which reveals the different strategies for controlling the nonreciprocity of the entanglement. The presented scheme provides an alternative method for the nonreciprocal macroscopic entanglement and may have potential applications in nonreciprocal quantum devices and macroscopic quantum effects.

Abstract We propose to utilize magnon Kerr nonlinearity to generate and control microwave–microwave Einstein–Podolsky–Rosen (EPR) steering in a cavity magnonic system consisting of two microwave cavities and an yttrium iron garnet (YIG) sphere, where the magnon mode in the YIG sphere is driven by an electromagnetic field. The results show that Kerr nonlinearity of the magnon could not only sensibly induce enhanced entanglement of two microwave fields but also produce asymmetric EPR steering with different ratios of two damping rates and coupling constants. Moreover, it is found that the nonreciprocity of the steady-state EPR steering is obtainable by controlling the sign of the magnon Kerr parameter, which could be tuned from positive to negative by changing the direction of the static magnetic field. The demonstrated nonreciprocal EPR steering is of fundamental interest for the manipulation of quantum states, and may provide potential applications in quantum information tasks.

We propose a hybrid cavity-magnon system scheme that integrates a yttrium iron garnet sphere with a microwave cavity filled with Kerr medium, aiming to achieve both conventional and unconventional photon blockade simultaneously. Our research demonstrates that by tuning the strength of the Kerr nonlinearity and adjusting the two-photon driving intensity, we can realize quantum effects associated with both types of photon blockade. Furthermore, through careful selection of system parameters, we have obtained optimal results for photon blockade under ideal conditions. This scheme fully exploits the advantages offered by both conventional and unconventional photon blockade mechanisms, effectively reducing the equal-time second-order photon correlation function while also achieving a higher mean photon number. It provides an alternative and experimentally feasible platform for preparing single-photon sources characterized by enhanced purity and brightness.

We propose a scheme to achieve nonreciprocal magnon blockade via the Barnett effect in a magnon-based hybrid system. Due to the rotating yttrium iron garnet (YIG) sphere, the Barnett shift induced by the Barnett effect can be tuned from positive to negative via controlling magnetic field direction, leading to nonreciprocity. We show that a nonreciprocal unconventional magnon blockade (UMB) can emerge only from one magnetic field direction but not from the other side. Particularly, by further tuning system parameters, we simultaneously observe a nonreciprocal conventional magnon blockade (CMB) and a nonreciprocal UMB. This result achieves a switch between efficiency (UMB) and purity (CMB) of a single-magnon blockade. Interestingly, stronger UMB can be reached under stronger qubit-magnon coupling, even the strong coupling regime. Moreover, the nonreciprocity of the magnon blockade is sensitive to temperature. This work opens up a way for achieving quantum nonreciprocal magnetic devices and chiral magnon communications.