Muhammad Kamran Kami

When combined with well-established theories of contemporary physics, quantum key distribution (QKD) has emerged as a safe method for secret key distribution that may be used to protect sensitive information. Numerous fascinating and creative ideas have been suggested for QKD since its inception in 1984 to enhance the security and efficiency of the system while also taking into consideration its applications and practical implementation. To achieve longer communication distances in QKD without compromising its security, schemes with high error rates for long-distance communication have been developed. One such scheme is the so-called KMB09 protocol, which was developed to make use of higher dimensional photon states, which are not possible with the standard BB84 scheme. However, because of the unique architecture of the KMB09 protocol, no practical implementation of the protocol has yet been disclosed to the public. Here we present a framework for the realistic construction of a QKD system that operates in two or more dimensions of photon states and executes the KMB09 protocol with a decoy-state scheme. We describe the design of a KMB09 protocol-based QKD system and its simulation for practical implementation, which is based on the encoding of secret bits in higher-order Gaussian beam spatial modes, as well as the modeling of the system. We use orbital angular momentum (OAM) degree of freedom which is the most dynamic and easy handle feature that researchers utilize for the implementation of robust and state-of-the-art HD-QKD systems. Laguerre Gaussian, a higher-order Gaussian beam having special features associated with the OAM. Photons carrying OAM in Laguerre Gaussians beams can create several mutually unbiased basis (MUBs), which are extensively employed for protocol implementation. We constructed three MUBs in four-dimensional Hilbert space, one is reserved for a standard basis and the remaining two behave as a measurement basis. Besides this, we also used intensity variation for the generations of the qubits to employ the decoy-state scheme (vacuum plus weak coherent pulses), which relieves us from Photon Number Splitting (PNS) attack and also helped in the safe transfer of secret keys. The suggested framework is assessed particularly in terms of efficiency or success rate while dealing with photon states in two and four dimensions. Here we initially plot the number of iterations data on fixed qubits length in comparison with the efficiency of the HD protocol (KMB09) observed during simulation per iteration. We also plot the percentage error of the simulated efficiency and the efficiency of the analytical model of the KMB09 based system. We discover that the simulation results using our proposed framework are consistent with the numerical and analytical findings obtained using the same QKD model that was previously published. We have so far reached our first milestone that is the development of the HD-QKD system based on the KMB09 protocol. Now we are focusing on the error rates developed in the system due to intrusion and also handle attacks like intercept-resend-attacks. We will also incorporate losses due to turbulence in the quantum channel of our free space HD QKD system in the future.