Atsushi Asano

Measurement using a current-axis-independent Josephson sampler

We have improved measurement of the current‐axis‐independent Josephson sampler. We use a new chopping detection circuit in the feedback system for sampling point control. Two channels of the sampling head are utilized to cancel drift in the time base. Drift is about 3 ps. We have measured the output of a short pulse generating circuit and obtained a transition duration of 15 ps.

Abstract: A new single level masking approach to the fabrication of a magnetic bubble memory chip

We have developed a new method for the fabrication of the magnetic bubble memory chip which enables the realization of a memory chip with two separate levels of fine overlay patterns (Permalloy propagation and Al‐Cu conductor patterns) by employing a single level masking process. To fabricate a memory chip, four levels of thin films (SiO2, Al‐Cu, SiO2 and Permalloy) were coated on the bubble material first; then the photoresist patterns were delineated on top of these films. (AIP)

Switching dynamics of ac superconducting quantum interference devices and determination of rest currents

Switching dynamics have been considered for a simple closed loop composed of a Josephson junction and inductors (an ac superconducting quantum interference device). The rest current which remains in the junction after self‐resetting was calculated by either (1) assuming that the junction closes instantaneously after its current is reduced to below Imin, or (2) by means of simulation for t→∞. It is shown from a free energy viewpoint that the introduction of flux quanta is favorable. However, the final state is not the absolute minimum energy, but a metastable state.