Quantum mechanics

Quantum computer

Coherence (philosophical gambling strategy)

Ferromagnetism

Degenerate energy levels

Magnon

Dissipation

Physics

Charge qubit

Superconductivity

Condensed matter physics

Phase qubit

Quantum

Dephasing

Qubit

Quantum fluctuation

Physical Review Letters

Hybrid quantum devices expand the tools and techniques available for quantum sensing in various fields. Here, we experimentally demonstrate quantum sensing of a steady-state magnon population in a magnetostatic mode of a ferrimagnetic crystal. Dispersively coupling the magnetostatic mode to a superconducting qubit allows for the detection of magnons using Ramsey interferometry with a sensitivity on the order of 10−3 magnons/Hz. The protocol is based on dissipation as dephasing via fluctuations in the magnetostatic mode reduces the qubit coherence proportionally to the number of magnons.Received 19 May 2020Revised 22 July 2020Accepted 29 July 2020DOI:https://doi.org/10.1103/PhysRevLett.125.117701Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCavity quantum electrodynamicsHybrid quantum systemsMagnonsQuantum sensingQuantum InformationAtomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics

Dissipation-Based Quantum Sensing of Magnons with a Superconducting Qubit