Switching current measurements of large area Josephson tunnel junctions

Abstract

We have developed a scheme for a high resolution measurement of the switching current distribution of a current biased Josephson tunnel junction using a timing technique. The measurement setup is implemented such that the digital control and read-out electronics are optically decoupled from the analog bias electronics attached to the sample. We have successfully used this technique to measure the thermal activation and the macroscopic quantum tunneling of the phase in a small Josephson tunnel junction with a high experimental resolution. This technique may be employed to characterize current-biased Josephson tunnel junctions for applications in quantum information processing.

Macroscopic Quantum Tunneling in ad-Wave High-TCBi2Sr2CaCu

“…We report below what is to our knowledge the first successful observation of the macroscopic quantum tunnelling (MQT) [2,3,4,5] of the phase variable of the superconducting order parameter through the potential barrier of an IJJ, opening up an entirely new direction for HTSC applications. While the corresponding phenomena had been observed at around 300 mK in conventional JJs [3,5,6], we have confirmed MQT behavior at approximately 1 K apparently reflecting the characteristically high plasma frequency of IJJs. Our results are highly nontrivial in that they also demonstrate the feasibility of MQT in spite of the presence of dissipative low energy quasiparticles [7,8,9,10], which is the other hallmark of HTSCs.…”

“…The physical nature of the escape process in JJs can be elucidated by analyzing the statistics of the stochastic switching [6,12,26] from a zero-voltage state to a finite voltage state. To this end measurement of I SW was repeated for 2000 times at each temperature with a current resolution ∆I of 20 nA, which we checked were sufficient to determine the switching current distribution P (I SW ).…”

A cryogen-free dilution refrigerator based Josephson qubit measurement system

“…[1][2][3][4] So far, most of these experiments are performed using dilution refrigerators that use liquid He 4 as cryogen for the first-stage cooling. However, for such traditional wet systems, there are several obvious disadvantages.…”

Experimental Observation of Fluxon Diffusion in Josephson Rings

“…Underdamped arrays display a richer variety of behavior but are more difficult to analyze, since the I-V curves are bistable. In many previous experiments on single junctions, switching current measurements have been utilized to study the dynamics of the Josephson phase when the I-V curves are bistable [14][15][16][17][18][19][20]. In these measurements, the value of the applied current at the point where the junction switches into the voltage state is recorded many times at each temperature.…”

“…In these measurements, the value of the applied current at the point where the junction switches into the voltage state is recorded many times at each temperature. Switching current measurements have been used to infer thermal activation [14,15], quantum tunneling [15,16], underdamped phase diffusion [17][18][19], and to infer the state of a quantum bit [20].…”