Superconducting Technology Assessment - nitrd

Analog high temperature superconductor components operating at 55-80 K are already in use in commercial
CDMA networks. They offer greatly enhanced rejection of out-of-band signals and a much reduced system
(thermal) noise floor. Interference between users generally limits the capacity of any given base station and stringent
signal strength control measures are in place to reduce the tendency for one caller to drown out the others. Digital
signal processing, especially successive interference cancellation, has been implemented to filter out as much of
this interference as possible. However, the processing must be done in real-time. The maximum speed of a CMOS
digital filter of this type does not offer the increment over that of a CMOS digitizer with sufficient resolution to
capture the total signal needed to deliver as many resolved users as commercially desirable. Digital filters in the tens
of gigahertz such as are achievable in RSFQ logic should provide a solution. Indeed, there is an active program in
Sweden to demonstrate this early application of digital superconducting electronics and its significant potential
of return on investment. Since the wireless market has already accepted the use of cryo-cooled electronics in base
stations, the shift to low-temperature superconductor technology will be less of an issue. Small commercial
cryo-coolers are readily available at 4 K.
In the information assurance context, viruses, worms, and hacker break-ins have become all too common. Sensitive
information needs to be protected from “prying eyes.” At the same time, the information needs to be readily available
to authorized users, some local and some at remote locations. Like the wireless communications problem, CMOS
processing would be unacceptably slow, but a superconducting solution is possible. The potential market for
scanning firewalls is potentially very large: if available, these would be considered essential by any moderate to
large organization.
The low-power information server is a primary goal of the current Japanese digital superconductor effort. The
application core is a superconducting router, with additional superconducting logic to provide the necessary
intelligence. Such a server could support upwards of 100,000 transactions per second. The Japanese find the
low-power argument compelling; although the power argument is less compelling in the U.S., the information
server market is quite large and expanding. Again, there seems to be sufficient market for this to be a commercially
viable solution.
Spaceborne Applications
Near-Earth Surveillance and Communication
Near-earth applications come in at least three flavors:
■ Providing the military with interoperability, message prioritization, and routing
in otherwise optical high throughput communications networks among satellites.
■ On-orbit data reduction.
■ The ability to sense much weaker signals because of a reduction in thermal noise.
Unlike the commercial terrestrial communications and internet, there is no hardwired, high throughput backbone
to military communications. Nor is it feasible to consider laying long-lived cables among mobile nodes. What we
have is several disjointed systems of high altitude communications satellites. There are relatively advanced concept
studies looking into using optical communications among these satellites to form a multi-node network of high
capacity assets, the equivalent of the internet backbone. While an optical approach to the actual message traffic,
the task of reading the message header and rerouting the signal to the next node—especially when it is necessary to
resolve contention and implement message prioritization—is not currently within the optical domain’s abilities.
Moreover, the electronics domain is required to interconvert one satellite system’s message formats into another’s
in order to achieve interoperability and thereby to reduce the total system cost. The clock rates proposed for
superconducting digital systems match those of optical communications and make SCE an ideal candidate for
this application.
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