Josephson-qubit oscillations resonantly activated by axions.
Grimaudo R., Guarcello C., Filatrella G., Spagnolo B., Valenti D.
In the last years Josephson junctions (JJs) have been supposed to interact with axions, the hypothetical elementary particles candidate as a possible component of cold dark matter. Unexplained experimental effects on Josephson systems can be well justified on the basis of the axion-JJ theory. This hypothesis, thus, has paved the way for the possibility of thinking of JJs as possible axion detectors. Further, the interaction of axion-induced photons with Josephson qubit in a cavity has been recently proposed. In this contribution, an effective quantum description of the axion as a two-level dynamic system is proposed. The direct coupling (not mediated by photons in a cavity) with a Josephson qubit is studied through an effective spin-spin Hamiltonian model. When the axion and the Josephson frequencies match, the axion-Josephson qubit interaction can be responsible for a resonance effect. Thus, experimentally detectable oscillations induced in the Josephson qubit by the axion are clearly derived. This phenomenon, causing a periodic magnetization reversal in the junction, can be exploited for the axion detection in the quantum limit of low noise intensity.