Research ArticleQUANTUM MAGNETISM

Resolving quanta of collective spin excitations in a millimeter-sized ferromagnet

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Science Advances  05 Jul 2017:
Vol. 3, no. 7, e1603150
DOI: 10.1126/sciadv.1603150

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Abstract

Combining different physical systems in hybrid quantum circuits opens up novel possibilities for quantum technologies. In quantum magnonics, quanta of collective excitation modes in a ferromagnet, called magnons, interact coherently with qubits to access quantum phenomena of magnonics. We use this architecture to probe the quanta of collective spin excitations in a millimeter-sized ferromagnetic crystal. More specifically, we resolve magnon number states through spectroscopic measurements of a superconducting qubit with the hybrid system in the strong dispersive regime. This enables us to detect a change in the magnetic moment of the ferromagnet equivalent to a single spin flipped among more than 1019 spins. Our demonstration highlights the strength of hybrid quantum systems to provide powerful tools for quantum sensing and quantum information processing.

Keywords
  • Hybrid Quantum Systems
  • quantum magnonics
  • superconducting qubits
  • ferromagnetic insulators
  • magnons

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