Description
Efficient microwave-to-optical transduction is a requirement for long-range networks between quantum devices such as sensors and many quantum computers. Achieving the optical nonlinearities required for transduction can be realised with a three-wave mixing process with near-resonant collective enhancement in a concentrated salt with narrow linewidths[1]. Stoichiometric erbium lithium fluoride ($\mathrm{ErLiF_4}$) has been identified as a promising candidate with optical resonances at telecom compatible frequencies with optical linewidths of up to $240~\text{MHz}$[2] and tunable magnon resonances in its antiferromagnetic phase that couple more strongly to microwave fields than spin transitions in dilute rare-earth crystals.
To effectively utilise these magnon resonances for transduction, their frequencies, mode profiles and microwave coupling strengths must be understood in order to engineer magnon modes for transduction. Efficient transduction requires good spatial overlap of the selected magnon mode with the micron-scale optical mode, which could be achieved with tailored microwave resonators. Existing models of magnons in rare-earth salts typically model the short-range exchange interaction and do not consider coupling to heterogeneous microwave resonator structures. In contrast, $\mathrm{ErLiF_4}$ is a dipolar magnet, with highly shape-dependent magnetic properties dictated by the long-range dipole interaction. The only existing model of magnons in $\mathrm{ErLiF_4}$ are for the homogeneous modes of ellipsoidal samples in homogeneous microwave resonators[3].
We present two complementary models developed to describe inhomogeneous magnons in arbitrarily shaped $\mathrm{ErLiF_4}$ crystals. The first is a many-body quantum Hamiltonian that predicts the low-order magnon spectrum, the effective magnetic moment and resonant susceptibility. The second is an effective-medium finite-element model which uses these predicted properties to calculate the microwave-magnon couplings. These models allow us to reproduce the results of microwave transmission measurements, predicting highly shape dependent low-order magnon modes in the $0-60~\text{GHz}$ range. We also present simulations of resonator-coupled systems and show how engineered resonator geometries impact transduction performance.
[1]Everts,J(https://doi.org/10.1103/PhysRevA.99.063830)
[2]Berrington,M(https://doi.org/10.1002/adom.202301167)
[3]Berrington,M(https://openresearch-repository.anu.edu.au/server/api/core/bitstreams/f89dc811-3226-4497-aa46-808d6eff2a50/content)
| I am the presenting author | Yes |
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