Switching Probability and Performance in Single-Chip SQUIDs

Fujimaki, Tamura, Imamura +1 more

Toshiyuki Miyazaki, Shinichi Yorozu, Masaaki Maezawa +2 more

Norio Fujimaki, K. Gotoh, T. Imamura +1 more

The single-chip superconducting quantum interference device (SQUID) we made using niobium Josephson junctions integrates a two-junction SQUID and a superconducting feedback circuit. The switching probability, its derivative to input flux, and the flux spectral density measured by varying the sinusoidal bias frequency and amplitude agree well with thermal noise theory. The best sensitivity and cutoff frequency were 6.2×10−6 Φ0■√Hz and 1.1 kHz for a bias frequency at 10 MHz. The dynamic range was 2.5×105. These data show the SQUID to be suited to practical biomagnetic application.

Xinyu Wu, Jianshe Liu, Wei Chen

Feedback circuits, which act as functional units in superconducting quantum interference device (SQUID) readout circuits, such as positive feedback circuits for suppressing the preamplifier noise contribution or negative feedback circuits for increasing the linear flux range of SQUID, enable SQUIDs to achieve high performance in practical applications. Integrating feedback circuits with different functions into a single SQUID chip contributes to the construction of highly compact SQUID electronics. Here, we propose a SQUID readout circuit with tunable feedback polarity (TFP). The switching of the feedback polarity is easily realized by applying a control current to the superconducting switches integrated into the SQUID chip. The enhancement of the flux-to-voltage transfer coefficient or the linear flux range depends on the choice of feedback polarity. In addition, we introduce a two-stage scheme to address the degraded noise performance induced by negative feedback. This work attempts to develop a compact and versatile architecture of SQUID readout by using a set of compatible superconducting technologies.

Alex I. Braginski, K. Barthel, Boris Chesca +5 more

J. Pleikies, Horst Rogalla, Jakob Flokstra