The hybrid system between the transmon and the magnon plays an important role in quantum information science. Additionally, the cat states of the magnon are a valuable quantum resource and represent macroscopic quantum superpositions of large numbers of spins. In this paper, we propose an approach to generate magnonic Schr\"odinger cat states (SCSs) in a hybrid ferromagnet-superconductor system. Moreover, high-fidelity magnonic SCSs can be generated when the dissipation of the system is considered. The coherent amplitude and the fidelities of the cat states can be adjusted by controlling the parameters of the system.
The hybrid system between the transmon and the magnon plays an important role in quantum information science. Additionally, the cat states of the magnon are a valuable quantum resource and represent macroscopic quantum superpositions of large numbers of spins. In this paper, we propose an approach to generate magnonic Schr"odinger cat states (SCSs) in a hybrid ferromagnet-superconductor system. Moreover, high-fidelity magnonic SCSs can be generated when the dissipation of the system is considered. The coherent amplitude and the fidelities of the cat states can be adjusted by controlling the parameters of the system.
The direct coupling system between a magnon and a superconducting qubit exhibits a special advantage in the quantum information processing [Phys. Rev. Lett. 129, 037205 (2022) ]. In this paper, based on this direct coupling system, the magnonic squeezed Schr\"odinger cat states (MSSCSs) can be generated by the conditional displacement mechanism. Numerical simulation shows that our scheme is robust to the dissipation of the system. In particular, we find that the coherence amplitude of MSSCSs can be enhanced via a squeezed transformation. Our results have potential application in quantum information processing and quantum optics.
The magnon cat state represents a macroscopic quantum superposition of collective magnetic excitations of large number spins that not only provides fundamental tests of macroscopic quantum effects but also finds applications in quantum metrology and quantum computation. In particular, remote generation and manipulation of Schrödinger cat states are particularly interesting for the development of long-distance and large-scale quantum information processing. Here, we propose an approach to remotely prepare magnon even or odd cat states by performing local non-Gaussian operations on the optical mode that is entangled with the magnon mode through pulsed optomagnonic interaction. By evaluating key properties of the resulting cat states, we show that for experimentally feasible parameters, they are generated with both high fidelity and nonclassicality, as well as with a size large enough to be useful for quantum technologies. Furthermore, the effects of experimental imperfections such as the error of projective measurements and dark count when performing single-photon operations have been discussed, where the lifetime of the created magnon cat states is expected to be t∼1 μs.
We propose an efficient method for dissipative generation of magnonic cat states in a cavity-magnon-qubit hybrid system by exploiting a two-magnon driving and dissipation mechanism. When both the magnon and qubit are driven, a coherent nonlinear two-magnon interaction is induced, wherein the qubit and the magnon mode exchange energy through magnon pairs. The dissipation of the qubit is exploited to steer the magnon mode into a quantum superposition of distinct coherent states, where the magnon mode evolves into either an even or odd cat state, depending on the parity of the magnon initial state. For the case where the magnon initial state is a superposition state, e.g., of $|0\ensuremath{\rangle}$ and $|1\ensuremath{\rangle}$, the magnon mode can evolve into a weighted mixture of the even and odd cat states. We also find that magnon squeezed states may emerge during the short-time evolution, showcasing the capability of our mechanism in preparing diverse magnon nonclassical states. Magnonic cat and squeezed states are macroscopic quantum states and have applications in macroscopic quantum studies and quantum sensing, e.g., in the dark-matter search using ferromagnetic axion haloscopes.
Hybrid systems based on magnons in ferromagnetic materials, such as yttrium iron garnet, have achieved remarkable development in the last decade. These include the coupling of magnons to microwave and optical photons, superconducting qubits, phonons, spins, the center-of-mass motion of a ferromagnet, etc. Here, we review both the experimental and theoretical progress in this field, focusing on the generation of magnonic quantum states and their applications in a broad range of fields. Since the strong coupling is a prerequisite for achieving coherent quantum control of magnons and preparing magnonic quantum states, we start by introducing representative strong-coupling experiments in cavity magnonics, then review a series of protocols for creating various magnonic quantum states, such as Fock, cat, squeezed, and entangled states, and discuss their potential applications in macroscopic quantum studies, quantum information science, quantum sensing, magnonic quantum devices, dark matter detection, and so on. Finally, we summarize the review and give an outlook for the future study of quantum magnonics.
Abstract A scheme is proposed for effective and robust generation of magnon Schrödinger cat states in the hybrid optomagnonical system. The Schrödinger cat states can be generated from the vacuum states and the physical model is easy to be implemented. It is worth noting that the effective normalized coupling strength of the optomagnonical system is able to reach strong coupling regime, which leads to a fast evolution process. Thus, the high fidelity and fast preparation of Schrödinger cat states can be achieved. Besides, the numerical simulations show that the scheme is robust against the decay caused by environment and the additive white Gaussian noise (AWGN). It is the hope that the scheme may open a new path to the fast generation of Schrödinger cat states in the hybrid system.
Coherent coupling between a ferromagnetic magnon and a superconducting qubit demonstrates a special fascination in the quantum information field. Here, we construct a hybrid system to realize tunable strong coupling between a transmon and a magnon. In a hybrid system, the transmon couples to a cavity while the magnon couples to the other cavity. Meanwhile, the two cavities are coupled via a hopping interaction. In addition, we demonstrate some applications of this system to quantum information. Specifically, a high-fidelity iswap${}^{\ifmmode\dagger\else\textdagger\fi{}}$ gate and a maximally entangled state between the transmon and the magnon with this coupling system can be realized even if the dissipation is considered. Moreover, by employing more cavities and magnons, the W-type entangled state can be created with multiple transmons. This hybrid system provides an alternative platform for scalable quantum information processing.