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Résumé |
Magnets have recently been shown to naturally harbor quantum magnonic
superpositions and states, such as squeezed states, in equilibrium [1-3]. The
relatively mature field of quantum optics has realized and exploited such states
with photons, generated in nonequilibrium, for feats such as beyond quantum
ground state sensitivity of LIGO and quantum teleportation [4]. The equilibrium
nature of these phenomena with magnons presents fresh opportunities and
challenges for utilizing them in achieving feats beyond the reach of optical
platforms, while leveraging the established knowledge from quantum optics.
In this talk, we will introduce the concept of squeezed states in magnons and
photons thereby demonstrating a key similarity and difference between the two.
We will discuss how a simple examination of the Heisenberg uncertainty relation
for spins allows us to understand the quantum nature of magnons [1-3].
Finally, we will discuss one recent theoretical proposal on sensing the quantum
magnon superposition in the ground state of an anisotropic ferromagnet [5].
Here, we will discuss that an exchange coupling between a spin qubit and a
ferromagnet results in a “direct dispersive interaction” which causes the
frequency of the qubit to depend on the number of magnons in the ferromagnet.
Thus, a quantum superposition of magnon numbers causes the qubit frequency to
exhibit multiple values corresponding to superposition contributions.
Ultimately, this enables a quantum non-demolition (QND) measurement of the
magnon states via qubit excitation spectroscopy. If time permits, we will close
with an outlook on implementing such QND measurements in experiments.
[1] A. Kamra and W. Belzig, Physical Review Letters 116, 146601 (2016).
[2] A. Kamra et al. Applied Physics Letters 117, 090501 (2020).
[3] H. Y. Yuan et al. Physics Reports 965, 1 (2022).
[4] R. Schnabel, Physics Reports 684, 1 (2017).
[5] A. E. Römling et al. Phys. Rev. Lett. 131, 143602 (2023)
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