Quantum key distribution(QKD) has emerged as a secure solution of secret key distribution utilizing the well established theories of modern physics. Since its introduction in 1984, many interesting and innovative ideas have been proposed for QKD in order to improve the security and efficiency of the scheme keeping in view of its applications and practicalimplementation. High error rate QKD scheme for long distance communication-theso-called KMB09 protocol is one such scheme which was designed to achieve longer communication distance in QKD, without compromising its security,by allowing the utilisation of higher dimensional photon states which is not possible with standard BB84 scheme. However the practical implementation of KMB09 protocol has not been presented yet because of its unique design. In this paper, we propose a framework for the practical implementation of QKD system that runs KMB09 protocol in two or more dimensions of photon states. We present the KMB09 based QKD system design and its simulation for practical implementation based on the encoding of secret bits in higher order Gaussian beam spatial modes. The proposed framework is specifically evaluated in terms of efficiency or success rate with two and four dimensions of photon states. We find that the simulation results of the proposed framework are inline with the numerical and analytical results of the same QKD model presented earlier.
Quantum key distribution(QKD) has emerged as a secure solution of secret key distribution utilizing the well established theories of modern physics. Since its introduction in 1984, many interesting and innovative ideas have been proposed for QKD in order to improve the security and efficiency of the scheme keeping in view of its applications and practicalimplementation. High error rate QKD scheme for long distance communication-theso-called KMB09 protocol is one such scheme which was designed to achieve longer communication distance in QKD, without compromising its security,by allowing the utilisation of higher dimensional photon states which is not possible with standard BB84 scheme. However the practical implementation of KMB09 protocol has not been presented yet because of its unique design. In this paper, we propose a framework for the practical implementation of QKD system that runs KMB09 protocol in two or more dimensions of photon states. We present the KMB09 based QKD system design and its simulation for practical implementation based on the encoding of secret bits in higher order Gaussian beam spatial modes. The proposed framework is specifically evaluated in terms of efficiency or success rate with two and four dimensions of photon states. We find that the simulation results of the proposed framework are inline with the numerical and analytical results of the same QKD model presented earlier.
Quantum key distribution (QKD) is an unconditionally secure way of sharing secret cryptographic keys on a public channel. Recently, high dimension QKD protocols have gained focus to achieve better security against various attack models. Here, we focus on the robustness of high dimensional QKD protocol against two realistic attack models, i.e. photon number splitting (PNS) attack and beam splitter (BS) attack. We present the high dimensional quantum key distribution system that incorporates a decoy-state scheme with complex structured light (OAM modes) using the KMB09 protocol. The complete QKD system design with experimental setup details and evaluation results are presented. The experimental results show that our proposed decoy-state scheme is robust against both PNS and BS attacks.
Secure exchange of cryptographic keys is extremely important for any communication system where security and privacy of data is desirable. Although classical cryptographic algorithms provide computationally secure methods for secret key exchange, quantum key distribution (QKD) provides an extraordinary means to this end by guaranteeing unconditional security. Any malicious interception of communication by a man-in-the-middle on a QKD link immediately alerts sender and receiver by introducing an unavoidable error-rate. Higher-dimensional QKD protocols such as KMB09 exhibit higher eavesdropping error-rates with improved intrusion detection but their practical implementation is still awaited. In this paper, we present the design and implementation of KMB09 protocol using Laguerre–Gaussian orbital angular momentum to demonstrate and highlight the advantages of using dynamic spatial modes in QKD system. A complete error-rate analysis of KMB09 protocol implementation is presented with two different types of eavesdropping error-rates. Furthermore, we also demonstrate the decoy state method to show the robustness of the protocol against photon-number-splitting attack.
Quantum communication over long distances is integral to information security and has been demonstrated in free space and fibre with two-dimensional polarisation states of light. Although increased bit rates can be achieved using high-dimensional encoding with spatial modes of light, the efficient detection of high-dimensional states remains a challenge to realise the full benefit of the increased state space. Here we exploit the entanglement between spatial modes and polarization to realise a four-dimensional quantum key distribution (QKD) protocol. We introduce a detection scheme which employs only static elements, allowing for the detection of all basis modes in a high-dimensional space deterministically. As a result we are able to realise the full potential of our high-dimensional state space, demonstrating efficient QKD at high secure key and sift rates, with the highest capacity-to-dimension reported to date. This work opens the possibility to increase the dimensionality of the state-space indefinitely while still maintaining deterministic detection and will be invaluable for long distance 'secure and fas' data transfer.
Abstract Quantum Key Distribution (QKD) enables the exchange of secret keys between two communicative parties. Compared to the simple two dimensional BB84 protocol , QKD protocols have progressively been developed to take advantage of higher dimension states. In this paper, we present performance analysis of a higher dimensional discrete value QKD protocols, the KXB10, over a free space optical channel with turbulence modeling. System performance results are presented in both the presence and absence of an eavesdropper. The performance is evaluated using the quantum bit error rate and index transmission error rate performance metrics. Results also show that an index transmission error rate value can be used to detect the presence of eavesdropper in the system. The results also show a significant improvement in system efficiency by using the higher dimensional KXB10.
While quantum key distribution (QKD) shows much potential as a solution to the looming threat that quantum computers place on today’s encryption protocols, efficient and robust systems that operate in free space are still limited. In this paper, we present a classical light analogy of QKD using spatial modes of light, which can provide a higher bit per photon rate than the more commonly used polarization state encoding.We start by demonstrating the BB84 protocol indoors, where we achieve a secure key rate of 1.55 bits per sifted photon. Then, using our outdoor environment, we propagate the signal outdoors over a distance of up to 90 m, modeling the real-world challenges of QKD in free-space applications and successfully demonstrating BB84 for dimensions 2 and 4.
It has been widely recognized that the underlying principles of quantum mechanics could be used to enable secure communications, without any additional conventional cryptographic systems, while utilizing the properties of the photons. Considerable research efforts have been invested to develop an efficient quantum key distribution (QKD) scheme over either free-space optical or fiber-optics channels. Most of these research efforts have been focused on a two-dimensional QKD, commonly realized by the use of the polarization state of photons. However, the data rates for the quantum key exchange in two-dimensional QKD are still low, while transmission distance is limited. On the other hand, it is well known that photons can carry both the spin angular momentum (SAM) and the orbital angular momentum (OAM), associated with the polarization and azimuthal phase of the complex electric field, respectively. Accordingly, we can define the combined-OAM-SAM state of a photon as |l, σ〉, where l and σ correspond to OAM and SAM indexes, respectively. Since the OAM eigenstates are orthogonal, an arbitrary number of bits per single photon can be transmitted, which could considerably increase the total secure bit rate. To improve secure data rates, we propose two types of protocols, namely, nonentangled-based (such as weak coherent state) and entanglement-assisted protocols, both employing the photon combined-OAM-SAM state, which can be used for secure key distribution over free-space optical and few-mode fiber channels. Two types of entanglement-assisted protocols are described, namely, two-basis and (D + 1)-basis protocols ( D is dimensionality of corresponding Hilbert space). We further describe how to implement the qudit gates required for implementation of these protocols. Finally, we discuss the security issues of the proposed protocols and determine both infinite and finite secret key fraction rates.