Optimized Photonic Band Gap Structures for High Frequency Axion Haloscopes

Optimized Photonic Band Gap Structures for High Frequency Axion Haloscopes



Aarav Sindhwad



Co-authors, UC Berkeley: Dillon Goulart, Nolan Kowitt, Pablo Castano Basurto, Andrei Dones, Heather Jackson, Alex Leder, Karl van Bibber





Extending microwave cavity searches for the QCD axion to higher masses poses numerous challenges for the resonator. Lattice-type and more recently, metamaterial-based resonators of suitably large volume show promise for attaining higher frequencies (>10 GHz) of the mode of interest, usually the TM₀₁₀. However, as the TM₀₁₀ is raised in frequency, the number of TE modes with which it will hybridize as it is tuned increases. Eventually the fraction of the frequency range which is rendered unusable due to mode-mixing becomes unacceptably large and ultimately there may be no identifiable TM₀₁₀-like mode at all. We have been investigating photonic band gap (PBG) structures as a potential solution to this problem. These can be designed to radiate away TE modes while trapping TM modes, which can then be tuned over the entire dynamic range of the resonator without mode crossings, except for the periodic TEM.¹ To date, resonators incorporating PBG structures have had an unfavorable effective volume, making them unattractive for practical haloscopes. Recently, we have developed PBG structures which are extremely thin and of flexible geometry, resulting in resonators of equivalent volume and quality factor to conventional microwave cavities. Such a resonator has been developed and will be deployed for the HAYSTAC Phase III run beginning in mid-2024.

1. Dillon Goulart et al., contribution to the April 2024 APS meeting (Sacramento, CA).

This work was performed under support of the National Science Foundation, Grant No. PHY-2209556.