Cryptography Reference
In-Depth Information
1 and 2 were in the singlet state, then she knows that photons 4 and 5 are also
in the singlet state. This effect can be seen as an application of entanglement
swapping [13]. A similar argument works for the other two possible photon
pairs on Alice's side. Thus, on these occasions, she effectively prepares for
Bob one of the three signal states from the one-way scheme of Figure 10.1(B).
The protocol then runs exactly as that of Figure 10.1(B). The security of the
scheme derives from the fact that only a triple of maximally entangled photon
pairs will produce the correlations that Alice and Bob measure. Therefore the
source can be controlled by the adversary without compromising security.
10.3 Noise-Immune Time-Bin-Coded
Schemes
10.3.1 Round-Trip Noise-Immune Time-Bin-Coded
QKD
Figure 10.4 contains a schematic and space-time diagram of round-trip
noise-immune time-bin-coded QKD (originally introduced as plug-and-play
quantum cryptography [4]). The protocol begins with Bob launching a strong
A)
Alice
Bob
D
AT
PM
PM
C
L
B)
Alice
Bob
D
t
B4
B3
A4
A3
A2
A1
B2
P2
B1
P1
L
z
Figure 10.4
Schematic (A) and space-time diagram (B) for round-trip noise-immune
time-bin-coded QKD. L is a source of laser pulses, C is a circulator, AT is an attenuator,
and PM is a phase modulator.
