ON THE TRANSFER-FUNCTION OF A WEAK-LINK ULTRA-LOW CAPACITY RF-SQUID

In the investigation of the transfer function (field sensitivity) of a weak link ultra-low capacity RF-SQUID, there is a problem which conce rns the response of the quantum nonlinear oscillator formed by the geo metrical inductance of the superconducting ring, the Josephson inducta nce and the weak link capacity, to the external magnetic flux. In orde r to account for the influence of the small quantum charge fluctuation on the Josephson potential, a phenomenological approach is-proposed, which leads to a phase shift consisting of two additives. The first ad ditive is a constant depending on the weak link parameters, and the se cond is linear in the external magnetic flux. The influence of the qua ntum fluctuation is effectively reduced to increasing the period of th e current-phase relation for the RF-SQUID in the external magnetic flu x, which leads to a reduction of the response of such a quantum SQUID in comparison with the usual RF SQUID.