Coherent Transport in Superconducting and Ferromagnetic Hybrid Systems

The potential application of topological superconductivity in quantum transport and quantum information has fueled an intense investigation of hybrid materials with emergent electronic properties, including magnet-superconductor heterostructures. Here, we report evidence of a topological nodal-point superconducting phase in a one-atom-thick in-plane ferromagnet in direct proximity to a conventional $s$ -wave superconductor. Low-temperature scanning tunneling spectroscopy data reveal the presence of a double-peak low-energy feature in the local density of states of the hybrid system, which is rationalized via model calculations to be an emergent topological nodal-point superconducting phase with tilted Weyl cones. Our results further establish the combination of in-plane ferromagnetism and conventional superconductivity as a route to design two-dimensional topological quantum phases.The potential application of topological superconductivity in quantum transport and quantum information has fueled an intense investigation of hybrid materials with emergent electronic properties, including magnet-superconductor heterostructures. Here, we report evidence of a topological nodal-point superconducting phase in a one-atom-thick in-plane ferromagnet in direct proximity to a conventional $s$-wave superconductor. Low-temperature scanning tunneling spectroscopy data reveal the presence of a double-peak low-energy feature in the local density of states of the hybrid system, which is rationalized via model calculations to be an emergent topological nodal-point superconducting phase with tilted Weyl cones. Our results further establish the combination of in-plane ferromagnetism and conventional superconductivity as a route to design two-dimensional topological quantum phases.

cond-mat.supr-conCross-listedarXiv:2601.03929Jan 8, 2026

Transport Studies of Superconductors for Quantum Applications

Kevin Michael Ryan

Jan 1, 20250 citations

Coupling of Two Superconductors through a Ferromagnet

J. Aarts, A. A. Golubov, V. A. Oboznov +3 more

Jan 1, 2001601 citations

Coherent coupling between ferromagnetic magnon and superconducting qubit

Yutaka Tabuchi, Seiichiro Ishino, Atsushi Noguchi +4 more

Rigidity of an ordered phase in condensed matter results in collective excitation modes spatially extending in macroscopic dimensions. Magnon is a quantum of an elementary excitation in the ordered spin system, such as ferromagnet. Being low dissipative, dynamics of magnons in ferromagnetic insulators has been extensively studied and widely applied for decades in the contexts of ferromagnetic resonance, and more recently of Bose-Einstein condensation as well as spintronics. Moreover, towards hybrid systems for quantum memories and transducers, coupling of magnons and microwave photons in a resonator have been investigated. However, quantum-state manipulation at the single-magnon level has remained elusive because of the lack of anharmonic element in the system. Here we demonstrate coherent coupling between a magnon excitation in a millimetre-sized ferromagnetic sphere and a superconducting qubit, where the interaction is mediated by the virtual photon excitation in a microwave cavity. We obtain the coupling strength far exceeding the damping rates, thus bringing the hybrid system into the strong coupling regime. Furthermore, we find a tunable magnon-qubit coupling scheme utilising a parametric drive with a microwave. Our approach provides a versatile tool for quantum control and measurement of the magnon excitations and thus opens a new discipline of quantum magnonics.Rigidity of an ordered phase in condensed matter results in collective excitation modes spatially extending in macroscopic dimensions. Magnon is a quantum of an elementary excitation in the ordered spin system, such as ferromagnet. Being low dissipative, dynamics of magnons in ferromagnetic insulators has been extensively studied and widely applied for decades in the contexts of ferromagnetic resonance, and more recently of Bose-Einstein condensation as well as spintronics. Moreover, towards hybrid systems for quantum memories and transducers, coupling of magnons and microwave photons in a resonator have been investigated. However, quantum-state manipulation at the single-magnon level has remained elusive because of the lack of anharmonic element in the system. Here we demonstrate coherent coupling between a magnon excitation in a millimetre-sized ferromagnetic sphere and a superconducting qubit, where the interaction is mediated by the virtual photon excitation in a microwave cavity. We obtain the coupling strength far exceeding the damping rates, thus bringing the hybrid system into the strong coupling regime. Furthermore, we find a tunable magnon-qubit coupling scheme utilising a parametric drive with a microwave. Our approach provides a versatile tool for quantum control and measurement of the magnon excitations and thus opens a new discipline of quantum magnonics.

arXiv:1410.3781Oct 14, 20145 citations

Competition of Quasiparticles and Magnetization Noise in Hybrid Ferromagnetic Transmon Qubits

Halima Giovanna Ahmad, Valentina Brosco, Alessandro Miano +14 more

The coexistence between ferromagnetic ordering and superconducting transport in tunnel ferromagnetic Josephson junctions (SFS JJs) accounts for a wide range of unconventional physical properties. The integration of both insulating ferromagnets or multi-layered insulator-ferromagnet barriers allows to combine ferromagnetic switching properties with peculiar low quasiparticle dissipation, which could enhance the capabilities of SFS JJs as active elements in quantum circuits. Here we show that split-transmon qubits based on tunnel ferromagnetic JJs realize an ideal playground to study noise fluctuations in ferromagnetic Josephson devices. By considering the transport properties of measured Al-based tunnel SFS JJs, we report on a theoretical study of the competition between intrinsic magnetization fluctuations in the barrier and quasiparticles dissipation, thus providing specific operation regimes to identify and disentangle the two noise sources, depending on the peculiar properties of the F layer and F/S interface.The coexistence between ferromagnetic ordering and superconducting transport in tunnel ferromagnetic Josephson junctions (SFS JJs) accounts for a wide range of unconventional physical properties. The integration of both insulating ferromagnets or multi-layered insulator-ferromagnet barriers allows to combine ferromagnetic switching properties with peculiar low quasiparticle dissipation, which could enhance the capabilities of SFS JJs as active elements in quantum circuits. Here we show that split-transmon qubits based on tunnel ferromagnetic JJs realize an ideal playground to study noise fluctuations in ferromagnetic Josephson devices. By considering the transport properties of measured Al-based tunnel SFS JJs, we report on a theoretical study of the competition between intrinsic magnetization fluctuations in the barrier and quasiparticles dissipation, thus providing specific operation regimes to identify and disentangle the two noise sources, depending on the peculiar properties of the F layer and F/S interface.

IEEE Transactions on Applied SuperconductivityFeb 8, 20238 citations

Coherent transport of single cooper pairs in Josephson arrays

A. A. Odintsov

ZhETF Pisma RedaktsiiuNov 1, 19940 citations

s

-wave superconductor. Low-temperature scanning tunneling spectroscopy data reveal the presence of a double-peak low-energy feature in the local density of states of the hybrid system, which is rationalized via model calculations to be an emergent topological nodal-point superconducting phase with tilted Weyl cones. Our results further establish the combination of in-plane ferromagnetism and conventional superconductivity as a route to design two-dimensional topological quantum phases.