5. Answer the following questions.
What laws of physics is quantum cryptography based on?
Why can't you measure every aspect of a particle at the same time?
How do polarization filters work?
How can the laws of quantum mechanics be used in cryptography? Base on the diagram below.
6. Mark the following statements true or false. Correct the false statements.
The communication channel can be protected from the eavesdropper by the laws of physics.
No eavesdropper can intercept the transmission protected by quantum cryptography.
All characteristics of particles as studied by quantum mechanics can be easily measured.
Polarization filters let polarized photons pass through the communication channel in any direction.
If we turn the vertically polarized filter 90 degrees the horizontally polarized photons won’t get through.
You can learn the polarization only if you measure it in the basis it is polarized.
If we turn the horizontally polarized filter 30 degrees the vertically polarized photons will get through.
In quantum mechanics particles can change the polarization to get through the filter.
Quantum cryptography is still theoretical.
According to quantum mechanics particles can adapt to the polarization of the filter.
Vocabulary tasks
7. Give English equivalents of the following Russian words and words combinations.
Неопределенность, передача (информации), возможность, под углом, в определенном направлении, избежать, проходить сквозь что-либо.
8. Give Russian equivalents of the following English words and words combinations.
Expand, disturb the transmission, over an insecure channel, discrepancy, the parity of subsets, discard, recover the bits.
Make the word combinations.
1. polarization
a) channel
2. rectilinear
b) of subsets
3. the parity
c) bit commitment
4. communication
d) on the idea
5. quantum
e) channel
6. random
f) polarization
7. expand
g) code
8. insecure
h) filter
9. pre-arranged
i) polarization
10. diagonal
j) result
Complete the text using the terms and word combinations given below.
An eavesdropper, guarantees, without disturbing, vulnerable, access
It is impossible to obtain information about physical system … it in a random, uncontrollable way. This fundamental quantum-mechanical law … the security of Quantum Key Exchange (QKE) protocols. QKE protocols such as BB84 have been proved to be secure under the assumption that the known laws of physics hold. Given this assumption, QKE is unconditionally secure, i.e. secure even in the presence of … with unlimited computational power.
QKE requires that the parties have … to an authentic channel. Any QKE protocol that does not fulfill this requirement is … to a man-in-the middle attack.
Render the following passage in Russian.
Quantum Channels.
The single-photon source and the detectors must be connected by a “quantum channel”. Such a channel is not especially quantum, except that it is intended to carry information encoded in individual quantum systems. The idea is that the information is coded in a physical system only once, in contrast to classical communication, in which many photons carry the same information. Note, that the present-day limit for fiber-based classical optical communication is already down to a few tens of photons, although in practice one usually uses many more.
Individual quantum systems are usually two-level systems, called qubits. During their propagation they must be protected from environmental noise. Here “environment” refers to everything outside the degree of freedom used for the encoding, which is not necessarily outside the physical system. If, for example, the information is encoded in the polarization state, then the optical frequencies of the photon are part of the environment. Hence coupling between the polarization and the optical frequency has to be mastered. Moreover, the sender of the qubits should avoid any correlation between the polarization and the spectrum of the photons.