A low-frequency superconductor oscillator with a 10^10-quality factor
  This letter describes a very simple electromechanical oscillator, consisting of a strong-pinning Nb-Ti superconductor loop subjected to static magnetic fields. A detailed calculation of the losses occurring during its low-frequency oscillations is carried out. The conclusion is that the quality factor for such oscillator might reach the 10^10-10^11 range, something comparable only to the best optical microcavities. Such device might permit the measurement of variations in static forces with the same precision a superconducting quantum interference device (SQUID) measures variations of magnetic field, providing a new tool for probing minute variations of the gravitational field. for instance. 
O.F.Schilling