Speaker
Dr
Maxim Goryachev
(University of Western Australia)
Description
We propose a new approach to axion detection based on precision frequency measurements as opposed to the traditional power detection approach. The approach utilises a high Quality Factor cavity supporting two mutually orthogonal modes. We demonstrate how axion modified Maxwell equations lead to either a beam splitter or parametric interaction terms in the axion up- or downconversion cases respectively. The term couples two modes of different frequencies with the axion frequency (mass) being either the difference (upconversion) or sum (downconversion) of the frequencies of the modes. The derivation introduces a unitless two-mode geometric coefficient characterising the coupling between two particular modes. The Hamiltonian term in the rotating wave approximation is propositional to axion complex amplitude and the axion-photon coupling constant.
The double mode cavity could be used for the traditional power detection when one or both modes are strongly pumped. Although such a method would be inefficient compared to the common DC magnet technique. On the other hand a possibility to employ a highly sensitive cross correlation technique may lead to comparable results.
Instead of measuring tiny amounts of power deposited in the cavity modes, we propose to measure frequency shifts associated with the axion coupling Hamiltonian terms. Based on the equation of motion of axion coupling modes, we calculate frequencies shifts of the modes that can be observed with one of a few frequency control techniques. We predict both real and imaginary parts of the resonance frequency to be sensitive to axions depending on the type of coupling. In our work, we consider a double oscillator approach.
We consider a simple cavity architecture based on a copper cylindrical cavity and TM020 and TE011 modes. The TM020 mode is at 9 GHz, and the TE011 mode is tunable in the 6-9 GHz range. Both modes have Quality factors on the order of 5,000-10,000. Mode overlap coefficients are on the order of unity. Building a loop oscillator based on this cavity would allow axion sensitivities approaching popular axion model bands.
The power of the new approach relies on the fact that unlike in the power detection method where the sensitivity is limited by the thermal (or quantum) noise in the readout, the frequency sensing is limited by resonator linewidths and their internal fluctuations. For modern cryogenic resonators, Quality factors exceed 109 giving fractional frequency stability better than 10-16 have been demonstrated. If implemented, such systems could exclude axion-photon couplings below the predicted DFSZ coupling.
Primary author
Dr
Maxim Goryachev
(University of Western Australia)
Co-authors
Mr
Ben McAllister
(University of Western Australia)
Prof.
Michael Tobar
(The University of Western Australia)
