Towards a quantum interface between spin waves and paramagnetic spin baths

Abstract

Spin waves have risen as promising candidate information carriers for the next generation of information technologies. Recent experimental demonstrations of their detection using electron spins in diamond pave the way towards studying the back-action of a controllable paramagnetic spin bath on the spin waves. Here, we present a macroscopic quantum theory describing the interaction between spin waves and paramagnetic spins. As a case study, we consider an ensemble of nitrogen-vacancy spins in diamond in the vicinity of an yttriumiron-garnet thin film. We show how the back-action of the ensemble results in strong and tuneable modifications of the spin wave spectrum and propagation properties. These modifications include the full suppression of spin wave propagation and, in a different parameter regime, the enhancement of their propagation length by ∼50% for modes near resonance with the NV transition frequency. Furthermore, we show how the spin wave thermal fluctuations-even down to the quantum magnonic ground state-induce a measurable frequency shift of the paramagnetic spins in the bath. This shift results in a thermal dispersion force that can be measured optically and/or mechanically with a diamond mechanical resonator. In addition, we use our theory to compute the spin wave-mediated interaction between the spins in the bath. We show that all the above effects are measurable by state-of-the-art experiments. Our results provide the theoretical foundation for describing hybrid quantum systems of spin waves and spin baths and establish the potential of quantum spins as active control, sensing, and interfacing tools for spintronics.

Scanning Spin Probe Based on Magnonic Vortex Quantum Cavities

“…In addition to photons, the solid state offers a wide variety of bosonic excitations that can be emitted or absorbed such as, e.g., quantized spin waves or magnons. − In what follows, we will use g to denote both the spin–photon and spin–magnon coupling. Magnonic cavities could be used to perform spin qubit readout or to mediate spin–spin interactions, − offering the advantage of increasing the coupling by operating at reduced wavelengths (compared to electromagnetic resonators of the same frequency). This is possible since spin wave modulation is limited only by the lattice constant of the ferromagnet, allowing the downsizing to the nanometer range.…”

Fixing the rotating-wave approximation for strongly detuned quantum oscillators

“…This procedure becomes less precise when the system and drive frequencies are far detuned from one another, i.e., when the neglected terms are less rapid. Nevertheless, the RWA is a standard approach to find the response of driven systems [1,2], such as nanomechanical resonators [3][4][5], optical cavities [6][7][8][9][10][11][12], phononic and magnonic modes [13][14][15][16][17][18][19], and superconducting junctions [20][21][22]. Similarly, it is a common starting point for Floquet engineering and perturbative expansions of nonlinear driven systems [23][24][25][26][27].…”