Experimental tests for the quantum behavior of a macroscopic degree of freedom: The phase difference across a Josephson junction
- 1 April 1987
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 35 (10), 4682-4698
- https://doi.org/10.1103/physrevb.35.4682
Abstract
Experiments are described that demonstrate the quantum behavior of a macroscopic degree of freedom, namely the phase difference δ across a current-biased Josephson tunnel junction. The behavior of δ was deduced from measurements of the escape rate Γ of the junction from its zero-voltage state. The relevant parameters of the junction, that is, its critical current and shunting admittance, were determined in situ in the thermal regime from the dependence of Γ on bias current and from resonant activation in the presence of microwaves. It was found that the shunting capacitance was dominated by the self-capacitance of the junction while the shunting conductance was dominated by the bias circuitry. For an underdamped junction in the quantum regime, Γ became independent of temperature at low temperatures with a value that, with no adjustable parameters, was in excellent agreement with predictions for macroscopic quantum tunneling at T=0. When the critical current was reduced with a magnetic field so that the junction remained in the thermal regime at low temperatures, Γ followed the predictions of the thermal model, thereby showing the influence of extraneous noise to be negligible. In a further series of experiments, the existence of quantized energy levels in the potential well of the junction was demonstrated spectroscopically. The positions of the energy levels agreed quantitatively with quantum-mechanical predictions involving junction parameters measured in the thermal regime. The relative heights and widths of the resonances are in reasonable agreement with the predictions of a simple model.Keywords
This publication has 31 references indexed in Scilit:
- Escape from a metastable stateJournal of Statistical Physics, 1986
- Effects of Dissipation and Temperature on Macroscopic Quantum TunnelingPhysical Review Letters, 1985
- Schrödinger's cat and her laboratory cousinsContemporary Physics, 1984
- Quantum tunnelling in a dissipative systemAnnals of Physics, 1983
- Decay of the Zero-Voltage State in Small-Area, High-Current-Density Josephson JunctionsPhysical Review Letters, 1981
- Macroscopic Quantum Tunneling in 1-μm Nb Josephson JunctionsPhysical Review Letters, 1981
- Macroscopic quantum electrodynamic effects in a superconducting ring containing a Josephson weak linkNature, 1981
- Macroscopic Quantum Systems and the Quantum Theory of MeasurementProgress of Theoretical Physics Supplement, 1980
- Supercurrents through barriersAdvances in Physics, 1965
- Possible new effects in superconductive tunnellingPhysics Letters, 1962