High-speed measurement method of quantized energy levels in Josephson junctions using SFQ circuits

Abstract

A single flux quantum (SFQ) circuit has been designed to demonstrate an energy levels quantization in a Josephson Junction. The high-speed operation of SFQ circuits realizes applying a high-speed ramped bias current to a Josephson junction, which allows the noiseless experiment at higher temperature. A high-speed ramped bias current (d I/d t=2000 A/s) is applied to a Josephson junction using the proposed circuit. Although the energy levels quantization has not been observed yet, the obtained escape rate was high enough to observe the energy levels quantization. The proposed circuit indicates the effectiveness of SFQ circuits as experimental apparatuses.