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arXiv:2401.11684 · APL Quantum

Generating magnon Bell states via parity measurement

Jia‐shun Yan, Jun Jing

Published Apr 15, 2024• 3 citations
arXivHTMLPDF

Abstract

We propose a scheme to entangle two magnon modes based on parity measurements. In particular, we consider a system that two yttrium-iron-garnet spheres are coupled to a V-type superconducting qutrit through the indirect interactions mediated by cavity modes. An effective parity-measurement operator that can project the two macroscopic spin systems to the desired subspace emerges when the ancillary qutrit is projected onto the ground state. Consequently, conventional and multi-excitation magnon Bell states can be generated from any separable states with a nonvanishing population in the desired subspace. The target state can be distilled with a near-to-unit fidelity only by several rounds of measurements and can be stabilized in the presence of the measurement imperfection and environmental decoherence. In addition, a single-shot version of our scheme is obtained by shaping the detuning between magnon and qutrit in the time domain. Our scheme that does not rely on any nonlinear Hamiltonian brings insights into the entangled-state generation in massive ferrimagnetic materials via quantum measurements.

DOI
10.1063/5.0201228

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The generation of magnon entanglement and squeezing plays a crucial role in quantum information processing. In this study, we propose a scheme based on a chiral cavity-magnon system, which consists of a torus-shaped cavity and two yttrium iron garnet spheres. The magnon mode of each yttrium iron garnet sphere is selectively coupled to one of the two degenerate rotating microwave modes of the toroidal cavity. The system aims to achieve entangled and squeezed magnon states through the mediation of the cavity. We further show that bipartite entanglement can be achieved by tuning external driving parameters. Additionally, our scheme does not rely on the magnon Kerr nonlinearity, which is usually extremely weak in yttrium iron garnet spheres. This work provides insights and methods for the research of quantum states in cavity-magnon systems.
We present protocols to generate quantum entanglement on nonlocal magnons in hybrid systems composed of yttrium iron garnet (YIG) spheres, microwave cavities and a superconducting (SC) qubit. In the schemes, the YIGs are coupled to respective microwave cavities in resonant way, and the SC qubit is placed at the center of the cavities, which interacts with the cavities simultaneously. By exchanging the virtual photon, the cavities can indirectly interact in the far-detuning regime. Detailed protocols are presented to establish entanglement for two, three and arbitrary N magnons with reasonable fidelities.
Recent studies show that hybrid quantum systems based on magnonics provide a new and promising platform for generating macroscopic quantum states involving a large number of spins. Here, we show how to entangle two magnon modes in two massive yttrium-iron-garnet (YIG) spheres using cavity optomagnonics, where magnons couple to high-quality optical whispering gallery modes supported by the YIG sphere. The spheres can be as large as 1 mm in diameter and each sphere contains more than 1018{10}^{18}1018 spins. The proposal is based on the asymmetry of the Stokes and anti-Stokes sidebands generated by the magnon-induced Brillouin light scattering in cavity optomagnonics. This allows one to utilize the Stokes and anti-Stokes scattering process, respectively, for generating and verifying the entanglement. Our work indicates that cavity optomagnonics could be a promising system for preparing macroscopic quantum states.
Generation of entanglement between spatially separated macroscopic systems enables quantum networks and fundamental tests of quantum theory. Here, we propose a scheme to generate a long-range entangled state between two macroscopic spheres. The hybrid system under consideration consists of two massive ferromagnetic spheres and a superconducting transmon qubit, which are both coupled to a microwave cavity array. When the qubit or magnon frequency lies outside of the frequency band of the cavity array, the qubit or magnon mode can seed a tunable, localized cavity mode with an exponentially decaying envelope around its position. This effective cavity mediates the long-range qubit-magnon and magnon-magnon interactions in a coherent way, enabling the long-distance magnon-magnon entanglement via the superconducting qubit.
We study the hybrid system of a high-quality yttrium-iron-garnet (YIG) sphere magnetically coupled to a superconducting flux qubit via the magnetic fields created by two persistent-current quantum states. When the flux qubit is operated away from its sweet point, a coherent nonlinear two-magnon interaction can be predicted; that is, the qubit is excited by absorbing a pair of magnons. We show that the spontaneous emission of the qubit can be exploited to steer the magnon mode of the YIG sphere into a Schr\"odinger cat state with high fidelity. Our scheme has practical advantages in that it eliminates the need for precise control of the evolution time and the projective measurement, and is also insensitive to the qubit's pure dephasing.
We propose a scheme for preparing magnon squeezed states in a hybrid cavity-magnon-qubit system. The system consists of a microwave cavity that simultaneously couples to a magnon mode of a macroscopic yttrium-iron-garnet sphere via the magnetic-dipole interaction and to a transmon-type superconducting qubit via the electric-dipole interaction. By far detuning from the magnon-qubit system, the microwave cavity is adiabatically eliminated. The magnon mode and the qubit then get effectively coupled via the mediation of virtual photons of the microwave cavity. We show that by driving the qubit with two microwave fields and by appropriately choosing the drive frequencies and strengths, magnonic parametric amplification can be realized, which leads to magnon quadrature squeezing with the noise below vacuum fluctuation. We provide optimal conditions for achieving magnon squeezing, and moderate squeezing can be obtained using currently available parameters. The generated squeezed states are of a magnon mode involving more than 1018{10}^{18}1018 spins and thus macroscopic quantum states. This work may find promising applications in quantum information processing and high-precision measurements based on magnons and in the study of macroscopic quantum states.