Seminar – Akashdeep Kamra

Akashdeep Kamra (Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau, Kaiserslautern, Germany), will give a seminar on April 07th 2025 at 11am, at the TRT Thales auditorium.

Title: Sensing and utilizing superpositions harbored by quantum magnonic states

Abstract:

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.

References :

• [1] Kamra and W. Belzig, Physical Review Letters 116, 146601 (2016).
• [2] Kamra et al. Applied Physics Letters 117, 090501 (2020).
• [3] Y. Yuan et al. Physics Reports 965, 1 (2022).
• [4] Schnabel, Physics Reports 684, 1 (2017).
• [5] E. Römling et al. Phys. Rev. Lett. 131, 143602 (2023)