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Opto-Electronics and Communications Conference (OECC)

Optical Components and System for Free-Space Quantum Key Distribution

Chun Ju Youn, Haesin Ko, Byung‐Seok Choi, Joong‐Seon Choe, Kap‐Joong Kim, Jong-Hoi Kim, Yongsoon Baek

Published Jul 1, 2018• 0 citations
Publisher

Abstract

A free-space quantum key distribution guarantees unconditional communication security with various applications between distant parties. In this paper, we show the integrated optical components and modules for the free-space quantum key distribution. Also, a free-space quantum key distribution system using newly developed and integrated optical components is demonstrated.

DOI
10.1109/oecc.2018.8730079

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•Apr 15, 2013•0 citations
A free-space quantum key distribution guarantees unconditional communication security with various applications between distant parties. In this paper, we show the integrated optical components and modules for the free-space quantum key distribution. Also, a free-space quantum key distribution system using newly developed and integrated optical components is demonstrated.
Free-space quantum key distribution opens up new possibilities for the development of quantum communication systems, facilitating the deployment of quantum networks in physically hard-to-reach areas and across wide landscapes without the use of optical fibers. This approach overcomes restrictions associated with cable laying and provides a more flexible infrastructure for quantum information transmission. Together with the use of continuous-variable protocols, it becomes possible to organize secure information transfer using optimal scalable communication systems despite deleterious environmental influences. This paper reviews key achievements and technical aspects of implementing continuous-variable quantum key distribution in atmospheric channels, considering the main atmospheric effects such as turbulence, scattering, and beam wandering. We present the current state of continuous-variable quantum key distribution systems in free space and their practical implementations, including successful experimental projects and prototypes. Prospects for further development, including integration with existing telecommunications networks and potential application areas, are discussed.
Nowadays, high security levels are required to transmit critical information for government, private and personal sectors. As a countermeasure, the Quantum Key Distribution systems are the best option in order to protect this information because it provides unconditional security. In addition, increasing the transmission distance is a highlight. Therefore, the Free-Space Optical Quantum Key Distribution systems (FSO-QKD) present an innovative way for sharing secure information between two parties located at ground stations, spacecraft or aircraft. However, these scenarios present several challenges regarding the hardware, protocols and techniques used that must be solved in order to enhance the performance parameters (security level, distance link, final secret key rate, among others) for any QKD system; although, in particular, a high transmission performance is required for both the classical and quantum channels. These issues impose the roadmap and trends in the research, academic and manufacturing sectors around the world.
The secure distribution of the secret random bit sequences known as 'key' material, is an essential precursor to their use for the encryption and decryption of confidential communications. Quantum cryptography is a new technique for secure key distribution with single-photon transmissions: Heisenberg's uncertainty principle ensures that an adversary can neither successfully tap the key transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed experimental quantum cryptography systems based on the transmission of non- orthogonal photon polarization states to generate shared key material over line-of-sight optical links. Key material is built up using the transmission of a single-photon per bit of an initial secret random sequence. A quantum-mechanically random subset of this sequence is identified, becoming the key material after a data reconciliation stage with the sender. We have developed and tested a free-space quantum key distribution (QKD) system over an outdoor optical path of approximately 1 km at Los Alamos National Laboratory under nighttime conditions. Results show that free-space QKD can provide secure real-time key distribution between parties who have a need to communicate secretly. Finally, we examine the feasibility of surface to satellite QKD.
An important issue in today’s information society is the security of data transmission against potential intruders, which always put at risk the confidentiality. Current methods to increase security require that the two parties wishing to transmit information, exchange or share one or more security keys. Once the key has been identified, the information can be transferred in a provable secure way using a one-time pad, i. e. the key length is as long as the plaintext. Therefore, the security of the information transmission is based exclusively on the security of the key exchange. Quantum cryptography, or more precisely quantum key distribution (QKD), guarantees absolutely secure key distribution based on the principles of quantum physics, according to which it is not possible to measure or reproduce a state (e.g. polarization or phase of a photon) without being detected. The key is generated out from the measurement of the information encoded into specific quantum states of a photon, named qubits. For example, a qubit can be created using properties such as the polarization or the phase of a photon. Achieved goals of this thesis are the development of a new class of high speed integrated photonic sources for applications in quantum key distribution systems, capable of producing unprecedented qubit rates (100 Mbps - 1 Gbps) and transmitting those over larger distances than those achieved so far (> 200 km). More specifically the work has been focused on developing faint pulse sources which can be used in very demanding environmental conditions, such as those in Space. For the development of these sources, apart from the optical design, essential is the opto-mechanical engineering as well as the integration with the electronics. One of the objectives was to achieve very high level of integration and power efficiency, e.g. volumes and power consumption between 10 and 100 times smaller than those typical of a laboratory experiment. Moreover, work in related parts of a whole QKD transmission system has been carried out. In particular, a new scheme for a compact, fast and simple random number generator has been demonstrated successfully achieving a random number generation rate of 1:1 Gbps. Also, during the course of this thesis, the development and engineering of a free-space QKD optical link has been initiated. This thesis makes use of novel ideas to alternatively demonstrate proof-of- concept experiments, which could then further develop into commercial products. To this end, close collaborations with world-wide leading companies in the field have been established. The Optoelectronics Group at ICFO has been involved in current European Space Agency (ESA) projects to develop a small footprint and low power consumption quantum transceiver and a high-flux entangled photon source.