OBSERVATION OF FINAL-STATE EFFECTS ON MACROSCOPIC QUANTUM TRANSITIONS

We have observed macroscopic quantum transitions in a symmetric double well potential (a SQUID with Φ0/2 of external flux). The transition rate Γ α exp[-BΔU/ħω0] has been measured vs. ΔU, the barrier height, for fixed temperature. This is achieved by modulating the barrier height in situ with the use of a tunable rf SQUID whose parameters have been accurately determined. The tunneling exponent obtained from these measurements, B = 10.3 ± 0.6, is in good agreement with the theoretical prediction. Γ has also been measured as a function of temperature (well below the crossover temperature to thermal activation) for fixed ΔU. A power law (T1.8) dependence has been observed as predicted for incoherent relaxation in contrast to the exponential rate en ancement observed in previous tunneling measurements. © 1990, Elsevier Science Publishers B.V. (North-Holland). All rights reserved.