37 Figure 3.3: Photon detection rate of the detector measuring the vertical SoP before and after compensation. 38 Figure 3.4: Photon detection rate of the detector measuring the horizontal SoP before and after compensation. 58 Figure 4.5: Testbed network layout for the QuantumCity project consists of a four-.
63 Figure 4.9: The installed equipment for the central hub (Pinetown Civic Centre) of the QuantumCity project consists of 3 sets of layer 1 QKD systems and layer 2 ciphers.
Introduction
Setting the Scene
The modular addition is performed for each character of the plaintext with a varied key value instead of a constant. So there is a uniform probability that the ciphertext is a permutation of bits that have the length of the plaintext.
Problem Statement
The trace of data flow ensures that the identity of the sender of a message is linked with the data. Fiber connections and are mainly used within a LAN and MAN, while the WAN and its access points will require free space technology.
Motivation and Scope
Contributions
Historically, QKD has been encoded via two methods: polarization encoding through a line-of-site free-space link [17] and phase encoding through a fiber channel [3]. This will allow for the exchange of quantum signals between free space and fiber channels without the need for a trusted node in the network. The development of the QKD devices and the key exchange process are of course fundamental to the realization of a quantum secure communication network.
While some units are available, there are many systems currently under active research, both in terms of protocol development and deployment, and as an engineering solution to improve system manufacturing. The development of quantum-activated random number generators (RNG) is essential for any QKD implementation, as well as various other gaming and security applications. Various randomization tests are performed to ensure sequence quality and a further development plan is proposed.
Free space mobile QKD units require an advanced tracking system to maintain a suitable uplink. An overview of the current state of the respective technology is presented, as well as a critical analysis for each technology. A detailed introduction to quantum cryptography is followed by the technical specifications of the primitives required for the construction of such a system.
Cryptography
A full analysis of the theoretical security of the KKD is beyond the scope of this thesis. This possibility of overlapping pure states is due to the quantum mechanical properties of the qubit and is significant in the security of QKD. The orientation of the polarizer is adjusted according to the selected condition as mentioned in Table 2.1.
An interferometric setup is used to realize encoding through the relative photon phase. QBERstray includes false detector counts due to stray light from the channel [ 39 ]. The network layers, illustrated in Figure 2.5, provide an understanding of the operational levels of quantum communication.
Each layer within the network provides functionality to the layer directly above it, regardless of implementation. Therefore, the optimal network configuration will have to be adapted to ensure network efficiency. Data flow noise and latency are affected by network speed.
System Development
Polarisation encoded QKD in Fibre
This is due to the inherent birefringence in optical fibers, which causes a shift in the state of polarization (SoP) of the incident photon. Given an arbitrary value of 𝜀, a photon can reach any polarization state within the Poincaré sphere, as shown in Figure 2.3 on page 18. The interaction between light traveling in these axes results in a change in the polarization state of the signal.
The birefringence causes a change in the SoP of the signal as it travels through the fiber. Bends in the fiber, pressure, heating and vibrations cause changes in the stress level of the fiber. A compensator applies an inverse transformation to the photon to realign the SoP before measuring the photons by detectors D0 and D1.
The external polarimeter measures the plane of polarization and communicates this to the controller drivers of the polarization cabinet. A stepwise search approach is used to incrementally rotate the plane of polarization equatorward of the Poincaré sphere to measure the desired linear modes. The QBER that would arise from the compensation technique described above would result from an inaccurate compensation of the plane of polarization to the equatorial plane.
Quantum Networks
This is achieved by using active switching mechanisms in the hardware layer of the network infrastructure [74]. Four nodes (GUD, ERD, SIE and BREIT) were in Vienna, while the last one was in St. QBB continuously generates keys and stacks them in the key management layer for use by nodes in the Quantum Access Network. The network managed to achieve high stability during the operation of the quantum network [103].
The network must operate at the physical and link layers of the network. The quantum systems used in the network setup were IDQ Cerberis systems. Since the network's point-to-point connections were concentrated in a central hub, this connection was assumed to be secure.
Visibility is measured to monitor the stability of the fiber due to environmental factors. Figure 4.9 shows an image of the installed units in the trusted node (Pinetown Civic Center). This was due to the active rollout of eThekweni fiber during this period.
Global Quantum Network Initiatives
Furthermore, the airports in each connected city have the appropriate supporting infrastructure to serve as the MAN's access point to the global network. The QKD process, implemented in the proposed plan, will take place while the aircraft is docked at the airport. By using a fiber optic channel, the solution avoids the additional synchronization techniques required when using a satellite network.
Information can be encrypted on-site and securely disseminated through conventional communication networks or the keys resold to the respective customers. QKD will be performed between the aircraft and the departing airport while docked at airport A. This initial key, kA generated between the aircraft and airport A, will then be stored in a secured memory in the QKD station of the aircraft.
After docking at the arriving airport, airport B, another key is generated between the aircraft and airport B, kB. The use of airports as an access point for quantum GAN is ideal for due to the facilities that offer ample redundancy, connectivity and storage for both MAN and GAN. Due to the fiber connections, the MAN gateway will be more reliable and robust, as such connections are not weather dependent.
Conclusion
Critical Assessment
The thesis focuses on the development of a physical random number generator based on the shock noise of a Zener diode. While the generator does not include quantum optics to produce quantum random number sequences, it promotes an inexpensive and easy-to-use product that has a quantum mechanical basis for the randomness process. Due to the electronic nature of the random number generator, electromagnetic shielding and robustness of the physical design still need to be developed and tested.
The polarization compensation technique presented in this work differs from previous works due to the analytical technique used to find the inverse rotational transform. The technique uses an active method of isolating the plane of polarization by stepwise search and not just points on the Poincaré sphere. This makes it possible to reduce the installation equipment and thus the cost of the unit.
While the initial calibration of the system takes longer than the previous efforts, the proposed system can in principle compensate for two arbitrary bases. The proposed tracking technique enables the QKD device to orient itself in line with the polarization axis of the transmitter. This needs to be investigated because of the possibility of various pollutants in the atmosphere and possible lines of sight that could cause phase retardation of light.
Future Work
QKD system development has focused on aspects including component prototyping, investigation of coding mechanisms, and system optimization techniques. The generator produces a good quality of random sequences as demonstrated through various tests. Along with the development of a system, this compensation technique will allow future investigations into free space fiber connected QKD connections.
The lack of birefringence in the atmosphere allows the current setup to provide adequate results for laboratory experiments. The optimal configuration of hybrid channels and devices must remain confined within the physical layer of the network. As the QuantumCity project focuses on customizing conventional network technology, further investigation into the routing of qubits within an optical network should be considered.
WDM must play an integral role in this deployment for combining quantum and bright signals on a single optical fiber. Such all-optical implementations parameterize the network for a natural progression toward quantum-enhanced network technology to generate improved quality of service from quantum communications.
Bibliography
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