Abstract: The present invention is directed, inter alia, to a switch comprising: (A) a superconducting material whose field cooled and zero field cooled ac permittivities differ from each other, and whose field cooled and zero field cooled ac susceptibilities differ from each other, in a range of temperature below the superconducting transition temperature of the material; (B) means for applying a static magnetic field to said material; (C) means for controllably applying to said material an oscillating magnetic field of a magnitude effective to convert said material from a state exhibiting filed cooled permittivity to a state exhibiting zero field cooled permittivity; and (D) means for applying to said material a heat pulse effective to convert said material from a state exhibiting zero field cooled permittivity to a state exhibiting field cooled permittivity, said switch operating between a superconducting zero field cooled state and a superconducting field cooled state.