Verification of long range quantum phase coherence in superconducting tin utilizing electromagnetically stabilized Josephson junctions

• Main Author: Vant-Hull, Lorin Lee
• Format: Others
• Published: 1967
• Online Access: https://thesis.library.caltech.edu/3705/1/Vant-Hull_ll_1967.pdf; Vant-Hull, Lorin Lee (1967) Verification of long range quantum phase coherence in superconducting tin utilizing electromagnetically stabilized Josephson junctions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/PHBD-K565. https://resolver.caltech.edu/CaltechETD:etd-09232002-105509 <https://resolver.caltech.edu/CaltechETD:etd-09232002-105509>

<p>de Broglie wave interferometers have been constructed, successfully utilizing extended superconducting links of tin to couple coherently the quantum phases of two Josephson junctions. The current transmitted by these devices was periodic in the enclosed flux (periodicity (.9 &#177; .3) h/2e) demonstrating unambiguously coherence of the superconducting order parameter over 1.33 meters.</p> <p>We may define a "normal" Josephson junction as one for which the quantum mechanical coupling energy is insufficient to overcome the disruptive effects of noise. Consequently, the relative phase of the coupled superconductors is not stabilized and the "zero voltage" Josephson current fluctuates, (bandwidth ~ 2eV_noise/h) averaging to zero. Two such "normal" junctions have been coupled to an electromagnetic cavity formed by the superconducting arms of a quantum interferometer (junction separation 1. 33 meters). With an applied steady voltage such that the Josephson current excites a normal mode of the cavity, a coherent radiation field is built up. This coherent radiation feeds back to the junctions forcing time coherence on the phase precession, resulting in a dynamic stabilization of the junctions.</p> <p>Under these conditions a series of "constant voltage steps" has been observed in the I-V characteristic of one interferometer. The Josephson frequency associated with these steps is shown to be characteristic of the electromagnetic resonant modes of the cavity. Frequency modulation analysis, combined with a detailed analysis of the cavity-junction combination, predicts such maxima in the tunneling of pairs when a "selection rule", (m + n) even, is obeyed. Here m/2 is the number of flux quanta (h/2e) linking the interferometer and n is the order of the cavity resonance excited. Experimental confirmation of the detailed predictions of the analysis is presented.</p>