Cryptography Reference
In-Depth Information
25 0
(a) 2 round trips
(b) 3 round trips
20 0
15 0
10 0
50
0
25 0
(c) 4 round trips
(d) 5 round trips
20 0
15 0
10 0
50
0
10
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30
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50
60
70
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20
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Relative Time (ns)
Figure 6.12
Experimental results from a prototype single-photon source. Figures (a)
through (d) show the relative probability of switching the photon out after one through
five round trips through the optical storage loop. (Reprinted with permission from
T.B. Pittman, B.C. Jacobs, and J.D. Franson, Phys. Rev. A, 66, 042303, 2002. Copyright
2002 by the American Physical Society.)
by using a polarizing Sagnac interferometer as the switching mechanism, as
illustrated in Figure 6.13. We have also performed a proof-of-principle exper-
iment [4] of this kind where, once again, there were significant losses due to
the optical switch.
6.5 Quantum Repeaters
In the ideal case, a quantum repeater should be able to correct for all forms of
errors that may occur in the transmission of a photon through an optical fiber,
including phase and bit-flip errors. But as a practical matter, the dominant
error source in fiber based QKD systems is simply the loss of photons due
to absorption or scattering. In the quantum key distribution systems that
we have implemented, all other sources of error are negligible; there is no
measurable decoherence of those photons that pass through the fiber, even
when the overall absorption rate is high.
