Quantum Magnonics

Spin waves or magnons — magnetization waves propagating in magnetic materials — are fascinating excitations with an unconventional combination of properties such as nonlinearity, tuneable frequencies and dispersion relations, and the ability to couple efficiently to multiple degrees of freedom, from superconducting and spin qubits to phonons, microwaves, or optical photons. Spin waves have been extensively studied in the classical domain due to their potential applications in classical information processing, but they are not fully understood in the quantum regime. Core questions such as how to generate quantum magnonic states in nanostructures or how to certify them remain unanswered.

Our team aims at developing a quantum theoretical description of magnons and to determine to which extent these excitations can be an asset in hybrid quantum platforms. We also aim at proposing experiments to generate and certify quantum magnonic states in nanostructures. This requires to develop models for magnon generation, decoherence, and detection by combining techniques from quantum optics and nanophotonics, open quantum systems, and classical magnonics. It also requires close collaboration with experimental colleagues.

[Translate to English:] schematische Darstellung eines auf Spin-Wellen basierenden Geräts. Durch einen Lichtstrahl werden Spin-Qubits angeregt.

Example of a future hybrid quantum magnonic device. An optical beam selectively activates the spin qubits. (Phys. Rev. B 105, 075410 (2022)).

Levitodynamics and high-Q Nanomechanics

Nanoparticles levitated in ultrahigh vacuum are a unique platform where both mechanical (center-of-mass motion, rotation) and internal degrees of freedom (phonons, magnons, etc) become extremely isolated from their environment. The precise control achieved over some of these degrees of freedom allows for the future exploration of many physical phenomena, from fundamental quantum science to unconventional regimes of condensed matter.

We are interested in developing a quantum theoretical description of this novel light-matter platform and of similar weakly clamped nanomechanical resonator systems. On the one hand, we develop models to describe the quantum dynamics of mechanical degrees of freedom of levitated nanoparticles in the presence of external systems such as optical cavities or other oscillators. The goal of this effort is to propose experiments able to generate and certify purely quantum motional states of levitated nanoparticles. On the other hand, we are interested in understanding and controlling what lies within these levitated objects, namely in their condensed-matter excitations such as phonons, magnons, etc. Describing these quantum excitations in such isolated systems requires to abandon various general assumptions undertaken in the theoretical description of bulk solids, potentially unveiling new regimes of condensed matter. We explore these systems using techniques from open quantum systems theory, quantum electrodynamics and quantum optomechanics.

[Translate to English:] Levitation auf Längenskalen von Metern (Magnetschwebebahn) bis Angstrom (Quantenmechanik))

By levitating or weakly clamping a small particle one may devise protocols to generate and detect quantum motional states of these macroscopic objects. (Science 374, abg3027 (2021))