Enhanced axion photon energy conversions for sensitive axion fields detection

TL;DR

The paper addresses the challenge of detecting dark matter axions with haloscope detectors by enabling in-situ, first-order axion-photon energy conversion through a transverse rf field that excites the cavity's magnetic resonant mode. The approach yields a linear scaling with the axion-photon coupling $g_{a\gamma\gamma}$ for the 1st-order EMR, offering a substantial sensitivity boost over conventional HTDs, which rely on second-order $g_{a\gamma\gamma}^2$ processes. The authors formalize the mechanism, derive the 1st- and 2nd-order energy transfer rates, and show that for realistic parameters the 1st-order signal can dominate by $4$–$7$ orders of magnitude, enabling detection in rf and microwave bands with current IQ-mixer and microwave single-photon technologies. They also analyze noise, integration time, and feasibility, arguing that the UHTD can reach axion parameter spaces previously inaccessible by HTDs and extend sensitivity to lighter axions at low temperatures.

Abstract

Haloscope is one of the typical installations to detect the electromagnetic responses (EMRs) of axion field in radio-frequency (rf) and microwave bands. Given the detectable signals of the usual Haloscope-type detectors (HTDs), biased only by high stationary magnetic fields, are just the second axion-photon energy converted effects and thus are very weak, here we propose a feasible approach to significantly improve their sensitivity by additionally applying a transverse rf- or microwave modulated magnetic field to excite the cavity's magnetic resonant mode for producing the first-order axion-photon energy converted signals. Accordingly, it can be argued that the achievable detection sensitivity of the upgrading HTD (i.e., UHTD) could be enhanced by almost 8 orders of magnitude, compared with that achieved by the existing HTDs without the transverse rf- or microwave modulated magnetic field driving. The feasibility of the proposed UHTD is also discussed.

Figures (4)

• Figure 1: Electromagnetic response detections of axions with a one-dimensional cavity biased by a high stationary magnetic field $\bar{B}$: (a) The generated EMR signal of the passing axion is coherently amplified ex-situ by applying an additional rf-field; and (b) the EMR signal of the axion is significantly enhanced in-situ, due to the interaction between the excited magnetic mode and the passing axion field.
• Figure 2: The influence of the axion mass $m_a$ and MMF amplitude $\tilde{B}$ on the ratio $\sigma_{rf}^{(1)}/\sigma_C^{(2)}$. Here, the other parameters are set as: $\bar{B}=8$ T, $g_{\gamma}=0.36$, $\rho_a=0.5\times10^{-24}$$\rm ~g/cm^3$, and $Q_l=10^4, C_l=1$, respectively.
• Figure 3: The achievable detection sensitivity for detecting the electromagnetic response signals of axions passing through the HTD (with $\bar{B}=8T$) and UTHD (with $\tilde{B}=1\mu$ T), by using a microwave single-photon detector with signal integration duration $\tau$. Here, the KSVZ- and DFSZ lines represent the limited sensitivities of axions in the KSVZ and DFSZ models, respectively.
• Figure 4: The detection sensitivity of the proposed UHTD. In this model, a rf-excited field has been applied additionally. Here, the other parameters are set as: $\bar{B}=8$ T, $Q_l=10^4$, and $C_l=1$, respectively.