Toward coherent quantum control of propagating spin waves

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Carlos Gonzalez-Ballestrero

Spin waves, or magnons, are major candidate information carriers in next-generation classical information processing, as evidenced by the development of numerous nanoscale magnonic devices [1]. Bringing these devices to the quantum regime is a challenge but also an opportunity: on the one hand, their advanced development level could open a shortcut to efficient quantum information processing. On the other hand, due to the exotic properties of magnons (e.g. tunable frequencies, high nonlinearity, micron-sized wavelengths at microwave frequencies), absent or difficult to achieve with photons, quantum magnonic nanodevices could be the ideal complement to existing platforms, especially quantum devices based on microwave photons and superconducting qubits. Despite the high stakes, and despite encouraging quantum magnonics experiments in single-mode macroscopic resonators [2], no experiment has yet shown quantum behavior of magnons propagating in nanostructures.
Reaching such quantum regime requires unlocking several intermediate milestones, such as quantum-limited detection, efficient coupling to other quantum systems, or protection from decoherence. In my talk, I will present our team’s research toward one of these milestones, namely coherent control of magnon propagation. First, I will show our proposal to externally and dynamically tune the propagation of magnons via their controlled interaction with an ensemble of solid state spins such as NV centres [3]. Among other effects, the propagation length and velocity of spin waves in the classical regime can be fully suppressed or enhanced, in analogy with the slow and fast light phenomena in optics. In the second part of my talk, I will discuss how self-compressing spin wave pulses can be generated in magnonic nanowaveguides [4] and used to locally address single qubits within an ensemble with sub-wavelength resolution [5]. Our work shows that magnons can be coherently controlled in the classical domain. Furthermore, our theoretical description is fully quantum, thus providing the tools to explore quantum control of propagating magnonic states.

[1] AV Chumak et al, IEEE Trans Mag 58, 1 (2022)
[2] Lachance-Quirion et al, Science 367, 425 (2020)
[3] C Gonzalez-Ballestero, T van der Sar, O Romero-Isart, Phys Rev B 105, 075410 (2022)
[4] S Casulleras, S Knauer, Q Wang, O Romero-Isart, A V Chumak, C Gonzalez-Ballestero, arXiv:2209.06608 (2022)
[5] S Casulleras et al, Phys Rev Lett 126, 103602 (2021)