Axion Haloscope Array With $\mathcal{PT}$ Symmetry

TL;DR

This paper proposes a generalized $ ext{PT}$-symmetric axion haloscope array that broadens response bandwidth and enhances scan rate and robustness, significantly improving axion detection capabilities over traditional single-mode methods.

Contribution

It introduces a larger array with $ ext{PT}$ symmetry, including a binary tree structure, to improve bandwidth, robustness, and scan rate in axion detection.

Findings

Enhanced scan rate due to broader response bandwidth.

Robustness maximized with binary tree $ ext{PT}$-symmetric structures.

Potential to probe most of the QCD axion parameter space above kHz.

Abstract

We generalize the recently proposed $\mathcal{P T}$-symmetric axion haloscope to a larger array with more $\mathcal{P T}$-symmetric structures. By broadening the response bandwidth of the signal without increasing the readout noise, the optimized scan rate of the axion haloscope is significantly enhanced, as well as is the signal power. Furthermore, we show that the robustness of the detector towards the variations of the array coupling is the strongest when a binary tree structure is introduced which contains a largely enhanced $\mathcal{P T}$ symmetry. The multiple allowed probing sensors can further increase the scan rate by a factor of the sensors' number due to the correlation of the signals. This type of array can strongly boost the search for an axion compared to single-mode resonant detection. The enhancement to the scan rate becomes the most manifest when applied to the proposed detection using a superconducting radio-frequency cavity with an ac magnetic field where most of the parameter space of the QCD axion above kHz can be probed.