In a research paper published in Physical Review Letters, scientists from Argonne National Laboratory and the University of Illinois Urbana-Champaign (UIUC) have demonstrated the first proof-of-concept hybrid circuit that couples propagating spin waves (magnons) in a magnetic thin film directly to a superconducting resonator on a single chip.
While superconducting circuits serve as standard microwave-processing components in quantum devices, they are susceptible to signal noise leaking backward through the circuit. Spin waves—magnetic excitations traveling through a material—naturally exhibit unidirectional (nonreciprocal) propagation under specific conditions. By fabricating a niobium nitride (NbN) superconducting coplanar waveguide resonator directly onto an epitaxial yttrium iron garnet (YIG) magnetic film, the team achieved strong coupling between microwave photons and propagating Damon-Eshbach and backward-volume spin wave modes.
| [ Hybrid Spin Wave / Superconducting Circuit Parameters ] | ||
|---|---|---|
| System Parameter | Material / Geometry Selection | Experimental Performance & Value |
| • Magnetic Layer | • Epitaxial Yttrium Iron Garnet (YIG, 100 nm) | • Ultralow-damping magnetic insulator film deposited via sputtering. |
| • Substrate Selection | • Rare-Earth-Free Y3Sc2Ga3O12 (YSGG) | • Eliminates low-temperature microwave absorption present in traditional GGG substrates. |
| • Circuit Layer | • Niobium Nitride (NbN) λ/4 & Meander Resonators | • Micrometer-scale widths match short spin-wave modes to millimeter microwave photons. |
| • Coupling Strength (g/2π) | • Up to 150 MHz (Damon-Eshbach mode) | • Achieves strong coupling regime with high cooperativity (C = 662). |
| • Signal Nonreciprocity | • 4 dB Isolation at degeneracy (10 dB antenna) | • Enables directional, one-way microwave signal flow on-chip. |
To overcome cryogenic signal absorption—a long-standing bottleneck when integrating YIG films with low-temperature superconducting electronics—the researchers replaced standard gadolinium gallium garnet (GGG) substrates with rare-earth-free YSGG substrates. The resulting hybrid architecture achieves a power isolation of 4 dB at the degenerate mode transmission peak, laying the foundation for compact, on-chip microwave isolators that protect fragile quantum circuits without external bulk magnets.
The device fabrication was executed at the Center for Nanoscale Materials at Argonne. This hybrid platform builds upon prior research into spin-wave magnonic systems and advances the development of integrated, directional quantum optical and microwave interconnects.
Review the technical pre-print manuscript on arXiv here and read institutional press details on the Argonne National Laboratory Portal here.
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