Nb-based RSFQ cells operate at helium temperatures of about 4.2 K,
processing picosecond SFQ pulses, and the problem of input-output
interfacing with room-temperature electronics might seem intimidating
at first. It was, however, fully solved (see [17]) for
output frequencies of up to 
. For output frequencies in
the range of 
and below, standard SFQ-to-DC converters
[1] can be used. For broadband ( 
)
signals, the output voltage of an SFQ-to-DC converter (typically, of the
order of 
) is clearly unacceptable (rms voltage of
the thermal noise in a 
load at room temperature is 
for 
signals). SQUID amplifiers
[18], HUFFLEs [17], SFQ-to-latch
converters [19] or voltage multipliers [20]
can be used to achieve a high-voltage ( 
a few mV), high-speed
( a few GHz) output of RSFQ circuits. Other I/O problems, such
as cross-talk and thermal load from the leads (which could be less
than 
per channel) are not as important at the current level of
RSFQ circuit complexity but will grow with the number of I/O pins.
Optical interfaces between superconductor chips and room-temperature
devices are also possible and the first successful experiments have been
reported by several groups [21, 22, 23].
All the experiments described in this thesis were performed using existing room-temperature electronics (see [17, 24]) and library layouts of DC-to-SFQ and SFQ-to-DC converters, very similar to the ones described in [1].