Cryptography Reference
In-Depth Information
detectors are inserted into this block, with fibers fed to the outside through a
hermetic seal. Microstrip RF connections lead from the side of the container to
the detectors. These two detectors are the two 1550.12 nm QKD cooled APDs,
i.e., one is D0 and the other is D1. Each detector has its own fiber lead through
which come the dim pulses for that detector. Each detector also has a set of
microstrip RF connectors by which the bias voltage can be applied and the
detector output led to electronics outside the chamber.
The block of copper rests between two five-stage Peltier coolers, also
known as thermoelectric coolers (TECs). We chose two coolers of this size to
ensure that we had an adequate margin for whatever range of temperatures
we wanted to explore; two or three stages would suffice for routine operation.
The chamber also contains a thermocouple to measure its current tempera-
ture. Electrical leads for the coolers and thermocouple pass through hermetic
feedthroughs to the outside equipment.
4.6 BBN QKD Protocols
Although a detailed discussion of BBN's QKD protocols is well beyond the
scope of this chapter, quantum cryptographic systems contain a surprising
amount of sophisticated software. It has been our observation that the optics
in quantum cryptography is perhaps the easiest part; the electronics are more
difficult. Moreover, for a real, functional system, the software is harder than
the electronics.
Figure 4.8 illustrates our software architecture in a high-level form. Here
we see that the QKD protocols have been integrated into a Unix operating
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Figure 4.8
The BBN QKD protocol suite in context.
