Curator's Take
This research presents a fascinating pathway to create entanglement between two macroscopic magnetic systems, each containing over a quintillion spins - a scale that pushes quantum mechanics into truly macroscopic territory. The proposed scheme cleverly uses a superconducting qubit as an intermediary to entangle magnon modes in two separate yttrium-iron-garnet spheres through carefully orchestrated microwave driving, offering a practical route to test fundamental questions about quantum mechanics at unprecedented scales. What makes this particularly exciting is that the researchers demonstrate their approach is feasible with current experimental capabilities, potentially opening new avenues for studying how quantum effects manifest in large-scale systems and testing theories about quantum-to-classical transitions. Such macroscopic quantum entanglement could also have implications for developing quantum sensors and understanding decoherence mechanisms in real-world quantum devices.
— Mark Eatherly
Summary
The cavity-mediated coupling between magnons in an yttrium-iron-garnet (YIG) sphere and a superconducting qubit has recently been demonstrated as a new platform for preparing macroscopic quantum states. Here, based on this system, we propose to entangle two magnon modes in two YIG spheres by driving the qubit with a two-tone field and by appropriately choosing the frequencies and strengths of the two driving fields. We show that strong entanglement can be achieved with fully feasible parameters. We further provide a detection scheme for experimentally verifying the entanglement. Our results indicate that macroscopic entanglement between two magnon modes in two millimeter-sized YIG spheres, involving more than $10^{18}$ spins, can be realized using currently available parameters, which finds promising applications in fundamental studies, such as macroscopic quantum mechanics and the test of unconventional decoherence theories.