The Fabrication And Property Characterization Of Superconducting Josephson Devices And Their Applications In Studying Stochastic Resonance

Josephson devices,based on Josephson tunnel Junctions, are of great prospect in various fields such as quantum computation, macroscopic quantum effect andnonlinear dynamics. In quanturn computation,superconducting quanturn bit(qubit)has become one of the most competitive candidates for its easy fabrication,macroscopic size and easy coupling with the outside world. Superconducting circuits such as radio frequency superconducting quanturn interference devices(RF SQUID),which can be easily tuned to any symmetric state and easily coupled to any manipulating signals, are widely used in studying nonlinear effect such as stochastic resonance. The thesis has sUidied the fbllowing aspects systematically: 1) the fabrication and property measurement of Jo%phson Uinnel junctions; 2) the design,fabrication and measurement of superconducting phase qubit; 3) the application of RF SQUID in studying stochastic resonance. The main researches are as followings.First,the research on the fabrication and property of superconducting Josephson tunnel junctions. "We studied the fabrication of superconducting Josephson tunnel junctions by DUV lithography and oblique e-beam evaporation and the parameters that affect the property of the junction. Josephson tunnel junctions with good quality are fabricated. The charackristic of the Josephson tunnel junction, and the interaction between the junction and microwave have been studied.Resonant peak and quantum jumps of the switching current are observed. Based on the experiment results,we proposed a new method to identify the energy gap of the tunnel junction by the resonant peak of the switchingcurrent.Second, the design, fabrication and property measurement of superconducting phase qubit. We have designed the size and structure of the superconducting phase qubit with the help of Fasthenry software and fabricated the sample by the method mentioned above. The qubit signal is observed in an Oxford Kelvinox MX400 dilution refrigerator. Meanwhile,based on a superconducting phase qubit of second order gradient meter, we have observed the quantum phcnomcnon such as resonant tunnelling, qubit spectrum, rabi oscillation, and decoherence et al. at an extremely low temperature of 20 mK.Third, the application of RF SQUID in stochastic resonance. Based on an RF SQUID,we proposed a method to identify the symmetry of a bi-stable system with the help of noise. The method is easily conducted and can be used to define the symmetry of any adjustable bi-stable system. Moreover,we studied a new way to characterize stochastic resonance by measuring the population distribution of the bi-stable system.Compared to the traditional method, this one avoids the fussy post-processing of data,is insensitive to the time span of the signal,and can identify the initial phase of the input signal.