Study of Macroscopic Coherence and Decoherence in the SQUID by Adiabatic Inversion.pdfVIP

April 2000 Preprint MPI-Pth/2000-15 Study of Macroscopic Coherence and Decoherence in the SQUID by Adiabatic Inversion P. Silvestrini Instituto di Cibernetica del CNR, via Toiano 6, I- 80072, Arco Felice, Italy and MQC group, INFN/Napoli, Italy L. Stodolsky 0 Max-Planck-Institut f¨ur Physik (Werner-Heisenberg-Institut), F¨ohringer Ring 6, 80805 M¨unchen, Germany 0 (April 2000) 0 2 We suggest a procedure for demonstrating quantum coherence and measuring decoherence times r between different fluxoid states of a SQUID by using “adiabatic inversion”, where one macroscopic p fluxoid state is smoothly transferred into the other, like a spin reversing direction by following A a slowly moving magnetic field. This is accomplished by sweeping an external applied flux, and depends on a well-defined quantum phase between the two macroscopic states. Varying the speed of 7 the sweep relative to the decoherence time permits one to move from the quantum regime, where such 2 a well-defined phase exists, to the classical regime where it is lost and the inversion is inhibited. Thus observing whether inversion has taken place or not as a function of sweep speed offers the possibility 1 v of measuring the decoherence time. The main requirement for the feasibility of the scheme appears 2 to be that the low temperature relaxation