HIGH-SENSITIVITY JOSEPHSON LOGIC GATE USING LOW βC DEVICES

F. Chiarello, Maria Gabriella Castellano, Roberto Leoni +3 more

Computing tools, all based on classical logic at the moment, present intrinsic limitations that can be overcome by using quantum logic. In this direction, superconducting Josephson devices have been proved to be very suitable candidates for the realization of quantum computing tools. We present some basic elements of quantum computing, possible strategies for the implementation of quantum gates by using Josephson devices, and recent experimental results in this field.

P. D. Shaju, V. C. Kuriakose

John P. Hurrell, David C. Pridmore-Brown, Arnold H. Silver

Digital Josephson circuits that do not latch into the voltage state provide an opportunity for high-speed serial processing. These fast logic gates must ultimately generate and record small fast pulses generated by single fluxoid events. This is demonstrated in a concept for a high-speed analog-to-digital (A/D) converter. Low β-value unlatched SQUID's are used throughout for ultimate speed, sensitivity, and simplicity. The analog signal is quantized by a single-junction SQUID and converted into a pulse train resulting from fluxoid transitions. These are counted in a chain of bistable two-junction SQUID's which successively scale the pulse train by a factor 2. These SQUID's perform both logic and memory functions at the single fluxoid level. The bit count stored in the array is gated out each sampling interval to provide the digitized signal. The performance of this device has been simulated and criteria established for the unlatched SQUID design. These include dimensionality, impedance, damping, intra- and inter-SQUID delays and β factor. Large analog dynamic range is available with the high intrinsic linearity of the SQUID quantizer and a long chain of scalers.

Huang-Tian Chan

Yuriy Makhlin, Gerd Schön, Alexander Shnirman

Oleg V. Snigirev