Magnon cat states in a cavity-magnon-qubit system via two-magnon driving and dissipation (2501.08675v1)

Abstract: 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 $|0\rangle$ and $|1\rangle$, 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 non-classical states. Magnonic cat and squeezed states are macroscopic quantum states and find applications in macroscopic quantum studies and quantum sensing, e.g., in the dark matter search using ferromagnetic axion haloscopes.

• The paper demonstrates the generation of robust magnonic cat states via two-magnon driving and dissipation.
• It employs a hybrid setup combining a microwave cavity, superconducting qubit, and YIG sphere to enable nonlinear magnon interactions.
• Numerical simulations confirm high-fidelity cat state formation that is resilient to qubit dephasing under low magnon dissipation.

Magnon Cat States in a Cavity-Magnon-Qubit System via Two-Magnon Driving and Dissipation

The presented paper explores the generation of magnonic cat states in a hybrid system comprised of a cavity, magnons, and a qubit. The methodology involves employing a two-magnon driving and dissipation mechanism to effectively steer the magnon mode into a superposition state, known as a cat state. This work advances the field of quantum state engineering, particularly within systems that bridge the gap between quantum information science and classical optics.

System and Methodology

The system under discussion integrates components that include a microwave cavity, a superconducting qubit, and a magnon mode derived from a yttrium iron garnet (YIG) sphere. The YIG sphere, when subjected to a uniform magnetic field, hosts magnons which are essentially quantized spin waves. These magnons exhibit potential for strong coupling with a microwave photon cavity and superconducting qubits, facilitated by their high spin density and low dissipation rate.

The paper details a novel approach that utilizes two-magnon driving, involving multiple drives applied to both the qubit and the magnon mode. When these components are detuned appropriately, it results in a nonlinear two-magnon process where energy is exchanged via magnon pairs. This process is essential for producing states like the macroscopic quantum superpositions or "cat states".

Key Parameters and Setup:

• Magnon Mode: Frequency of approximately 8.17 GHz with a low dissipation rate.
• Superconducting Qubit: Coupling achieved through virtual photons in the microwave cavity.
• Cavity Mode: Detuned to prevent energy loss during magnon-qubit interactions.

Results

The researchers outline the successful generation of magnonic cat states, which are superpositions of distinct coherent magnon states. These cat states take the form of even and odd states determined by the initial parity of the magnon state in the system.

• The effective two-magnon interaction, quantified by a coupling strength $g_\text{eff}$, allows for transitions that drive the system into a steady-state magnon cat state. The paper ensures that such states are robust against qubit dephasing, though they are sensitive to magnon dissipation.
• Numerical simulations confirm that the proposed system dynamics lead to high-fidelity cat states under low magnon dissipation conditions, highlighting the robustness of the methodology provided the system can be maintained at low loss levels.

Theoretical and Practical Implications

The theoretical implications of this research are substantial, showing that hybrid systems could transition more naturally between quantum and classical realms, enhancing their applicability in quantum technology and information processing. Practically, the realization of magnonic cat states on a macroscopic scale could facilitate more robust quantum sensing technologies, with potential applications in areas like dark matter searches through axion haloscopes.

Future Directions:

• Investigation of quantum state transfer and entanglement protocols that leverage the macroscopic scale and coherent nature of magnonic states.
• Application in improving precision measurements via quantum sensing utilizing magnon cat states.

The paper sets a precedent in the efficient generation of macroscopic quantum states in solid-state systems, showcasing a promising path for future explorations bridging quantum mechanics and nanotechnology.