Topics in the physics of underdamped Josephson systems

 
 
 
 

Topics in the physics of underdamped Josephson systems

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Title: Topics in the physics of underdamped Josephson systems
Author: Tornes, Ivan Edward
Description: We describe a variety of numerical models to characterize the behavior of several types of underdamped Josephson systems. We first discuss a stack of small junctions in a single mode resonant cavity. Our results show self-induced-resonant-steps in the current voltage (IV) curve. These steps represent a coherent phase locking between the junctions in the stack and the resonant cavity. Next we generalize these results to treat a single long junction coupled to a single mode resonant cavity. Our numerical results show that if the electromagnetic fields of the cavity mode are spatially periodic, we again see steps in the IV curve and furthermore, for sufficiently large coupling, the cavity frequency is shifted by coupling to the long junction. We then turn to some properties of single junctions in the quantum regime where the phase/number non-commutation is important. This quantum regime is crucial to all proposals to use such junctions as solid state quantum bits (qubits). We show that such qubits, when subjected to external a.c. perturbations, exhibit not only the expected Rabi oscillations but also multiphoton transitions between the quasi-bound states of the junction. We also consider the behavior of Josephson junction ladders in an external magnetic field. For magnetic fields equal to 1/n flux quanta per plaquette, we observe a periodic vortex lattice; here n is an integer evenly divisible into the total number of plaquettes, N, in the ladder. When a single fluxon is added to such a ladder, we show that it does not enter that ladder as a single unit of flux. Instead, it produces n fractional vortices. Our final chapter is motivated by some dramatic recent experiments on Josephson junctions formed between high temperature cuprate superconductors and low temperature s-wave superconductors. These experiments are intended to test phase sensitivity, i.e., the dependence of the measured critical current on an external magnetic field. We consider a ladder array of alternating 0 and π junctions with open boundary conditions in the presence of an external magnetic field to model this zigzag junction. Our calculations show many of the salient features seen in the experiments.
Permanent Link: http://rave.ohiolink.edu/etdc/view?acc_num=osu1141585985
http://hdl.handle.net/2374.OX/6238
Date: 2006

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