Abstract
First experimental results from a room-temperature tabletop phase-sensitive axion haloscope experiment are presented. The technique exploits the axion-photon coupling between two photonic resonator oscillators excited in a single cavity, allowing low-mass axions to be upconverted to microwave frequencies, acting as a source of frequency modulation on the microwave carriers. This new pathway to axion detection has certain advantages over the traditional haloscope method, particularly in targeting axions below 1 μeV (240MHz) in energy. At the heart of the dual-mode oscillator, a tunable cylindrical microwave cavity supports a pair of orthogonally polarized modes (TM_{0,2,0} and TE_{0,1,1}), which, in general, enables simultaneous sensitivity to axions with masses corresponding to the sum and difference of the microwave frequencies. However, in the reported experiment, the configuration was such that the sum frequency sensitivity was suppressed, while the difference frequency sensitivity was enhanced. The results place axion exclusion limits between 7.44-19.38neV, excluding a minimal coupling strength above 5×10^{-7} 1/GeV, after a measurement period of two and a half hours. We show that a state-of-the-art frequency-stabilized cryogenic implementation of this technique, ambitious but realizable, may achieve the best limits in a vast range of axion space.
Highlights
First experimental results from a room-temperature tabletop phase-sensitive axion haloscope experiment are presented
The axion, a theorized Nambu-Goldstone boson emerging from the Peccei-Quinn (PQ) solution to the strong charge-parity (CP) problem in quantum chromodynamics (QCD) [2,3,4], is a popular candidate for cold dark matter, with a mass poorly constrained by theory; several orders of magnitude are available for exploration [5,6,7,8]
The majority of axion experiments that aim to detect the QCD axion are “haloscopes,” which are sensitive to power deposition from the conversion of galactic halo axions into photons through the inverse Primakoff effect, as predicted by the axion-augmented QCD Lagrangian [9,10,11,12]
Summary
Best tests of fundamental physics, including variations in fundamental constants and local position invariance [38,39,40], as well as tests of Lorentz invariance violation [41,42,43], with proven long-term performance of up to eight years [40], and if designed properly the sensitivity will be determined by the white frequency noise floor of the frequency stabilization system [41]. By searching for frequency deviations of the carrier frequencies of the oscillators, this experiment can be configured to cover a large portion of unexplored low-mass axion space, below the ADMX mass range, i.e., from dc to 240 MHz (< 1 μeV). This design enables a coherent phase or frequency modulation induced by the axion-photon interaction to be scanned. The results produced in this experiment place limits on axion-photon coupling in the MHz range by observing the absence of axion-induced frequency modulation in orthogonally oriented photonic modes oscillating within a small cylindrical copper cavity at room temperature. The axion-photon interaction Hamiltonian density is familiarly parameterized as IF
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