The quantum space age has officially begun and many important milestones and achievements have recently been demonstrated, such as the exciting launch and results of the first quantum demonstration satellite, Micius. Previously with terrestrial applications, quantum key distribution was limited in distance to a few hundred kilometers through either free space or optical fiber. This had dampened progress towards a global quantum cryptographic network, but with the recent progress towards space implemented quantum systems, the door has been opened once again. \n \nIn this thesis, we begin by studying the effect of using an adaptive optics system to improve the efficiency of a free space link to a satellite for quantum key distribution. Adaptive optics has been used extensively in astronomy and has the potential to increase the average optical intensity received by the satellite. We study the effect of the atmosphere on the beam as it propagates from the ground station to the satellite. In the up-link configuration, the atmosphere is of special concern as it affects the beam at the beginning of the propagation, making the end effect worse. \n \nOne of the important components of a free space quantum key distribution satellite system is a fine pointing unit. We have, along with industry partners, designed and implemented such a unit for free space optical links. The device was designed to have little to no effect on the polarization of the photons used to transmit the key bits. The device was tested, both in the laboratory and outside and quantum key distribution was successfully performed while the fine pointing was active. \n \nThe main experiment of the thesis demonstrates quantum key distribution to a moving airplane from a ground station. The components of a quantum key distribution receiver prototype were tested locally around the University of Waterloo campus as well as some tests using private airplanes. The collaboration with the National Research Council of Canada really allowed the project to take flight by granting us access to a research aircraft to deploy our receiver prototype. This project spanned over three years and culminated in a two week flight campaign out of Ottawa and Smiths Falls Ontario. \n \nUsing only five flight hours we were able to successfully transmit finite size quantum secure keys from our optical ground station, located at Smiths Falls--Montague Airport to a Twin Otter Research Aircraft housing our quantum key distribution receiver prototype. Many of the components implemented in the receiver were designed and built with spaceflight in mind and have a clear path to flight for space application. \n \nFinally, we study the feasibility of implementing a quantum key distribution receiver onto a nano satellite. In partnership with the University of Toronto Institute for Aerospace Studies Space Flight Laboratory, we studied the various aspects such as optics, detection, cooling, power, mass, etc., to determine if it would be possible to perform quantum key distribution to a nano satellite. The main difference of this project from the previous Quantum Encryption and Science Satellite is the simpler pointing system, which doesn't utilize fine pointing. \n \nThrough various studies, experiments, and component design, we have shown the feasibility of implementing quantum key distribution to a moving aircraft in an up-link configuration. This work contributes to the long line of achievements leading towards satellite implementations of quantum key distribution for eventual global quantum cryptography.
The quantum space age has officially begun and many important milestones and achievements have recently been demonstrated, such as the exciting launch and results of the first quantum demonstration satellite, Micius. Previously with terrestrial applications, quantum key distribution was limited in distance to a few hundred kilometers through either free space or optical fiber. This had dampened progress towards a global quantum cryptographic network, but with the recent progress towards space implemented quantum systems, the door has been opened once again. \n \nIn this thesis, we begin by studying the effect of using an adaptive optics system to improve the efficiency of a free space link to a satellite for quantum key distribution. Adaptive optics has been used extensively in astronomy and has the potential to increase the average optical intensity received by the satellite. We study the effect of the atmosphere on the beam as it propagates from the ground station to the satellite. In the up-link configuration, the atmosphere is of special concern as it affects the beam at the beginning of the propagation, making the end effect worse. \n \nOne of the important components of a free space quantum key distribution satellite system is a fine pointing unit. We have, along with industry partners, designed and implemented such a unit for free space optical links. The device was designed to have little to no effect on the polarization of the photons used to transmit the key bits. The device was tested, both in the laboratory and outside and quantum key distribution was successfully performed while the fine pointing was active. \n \nThe main experiment of the thesis demonstrates quantum key distribution to a moving airplane from a ground station. The components of a quantum key distribution receiver prototype were tested locally around the University of Waterloo campus as well as some tests using private airplanes. The collaboration with the National Research Council of Canada really allowed the project to take flight by granting us access to a research aircraft to deploy our receiver prototype. This project spanned over three years and culminated in a two week flight campaign out of Ottawa and Smiths Falls Ontario. \n \nUsing only five flight hours we were able to successfully transmit finite size quantum secure keys from our optical ground station, located at Smiths Falls--Montague Airport to a Twin Otter Research Aircraft housing our quantum key distribution receiver prototype. Many of the components implemented in the receiver were designed and built with spaceflight in mind and have a clear path to flight for space application. \n \nFinally, we study the feasibility of implementing a quantum key distribution receiver onto a nano satellite. In partnership with the University of Toronto Institute for Aerospace Studies Space Flight Laboratory, we studied the various aspects such as optics, detection, cooling, power, mass, etc., to determine if it would be possible to perform quantum key distribution to a nano satellite. The main difference of this project from the previous Quantum Encryption and Science Satellite is the simpler pointing system, which doesn't utilize fine pointing. \n \nThrough various studies, experiments, and component design, we have shown the feasibility of implementing quantum key distribution to a moving aircraft in an up-link configuration. This work contributes to the long line of achievements leading towards satellite implementations of quantum key distribution for eventual global quantum cryptography.
Abstract Satellite-based quantum terminals are a feasible way to extend the reach of quantum communication protocols such as quantum key distribution (QKD) to the global scale. To that end, prior demonstrations have shown QKD transmissions from airborne platforms to receivers on ground, but none have shown QKD transmissions from ground to a moving aircraft, the latter scenario having simplicity and flexibility advantages for a hypothetical satellite. Here, we demonstrate QKD from a ground transmitter to a receiver prototype mounted on an airplane in flight. We have specifically designed our receiver prototype to consist of many components that are compatible with the environment and resource constraints of a satellite. Coupled with our relocatable ground station system, optical links with distances of 3–10 km were maintained and quantum signals transmitted while traversing angular rates similar to those observed of low-Earth-orbit satellites. For some passes of the aircraft over the ground station, links were established within 10 s of position data transmission, and with link times of a few minutes and received quantum bit error rates typically ≈3%–5% , we generated secure keys up to 868 kb in length. By successfully generating secure keys over several different pass configurations, we demonstrate the viability of technology that constitutes a quantum receiver satellite payload and provide a blueprint for future satellite missions to build upon.
As more aspects of modern society depend on digital communication, we increasingly rely on infrastructure that ensures the privacy and security of this communication. Classically, this has been provided by cryptographic protocols such as public-key encryption, in which secrets called keys are exchanged between different parties to enable secure communication. The rapid development of quantum algorithms which violate the assumptions of these protocols, however, poses a security challenge to modern cryptography. \n \nQuantum resources can also be used to strengthen cryptographic security, particularly the security of key exchange protocols. This approach, QKD, can be implemented by encoding in quantum systems such as single photons sent through free-space or a fiber. Fiber based QKD devices are already commercially available, but are fundamentally limited to distributing keys over a few hundred kilometers. To address this distance limitation, research QKD systems are being developed to exchange keys through free-space to satellites. This work considers practical challenges to building and testing both types of QKD devices. \n \nFirstly, we consider modeling and mission analysis for airborne demonstrations of QKD to stratospheric balloons and aircraft to simulate a satellite. Based on the mission parameters available for both platforms, we found aircraft platforms were more promising for testing prototype QKD satellite systems. We developed a mission planning tool to help design the flight geometries for testing the device. \n \nNext, we developed three new components for a QKD satellite prototype. The requirements for electro-optical devices in orbit are very different from lab environments, mandating new approaches to designing QKD devices. We developed a quad single photon detector package to meet the requirements for free-space links to low earth orbit. Moreover, we designed and built optical systems for analyzing the polarization of photons and an adaptive optics unit to increase the efficiency of collecting the encoded photons. All three devices were tested in conditions that simulated the time and loss of a satellite pass. \n \nFinally, we demonstrated a laser damage attack on a live commercial QKD system. Our attack injected additional optical power into the sender device to modify security-critical components. Specifically, our attack damaged the PIN diodes which monitor the encoded photon number, reducing their sensitivity or completely blinding them. Our damage could compromise the entire key, and was performed during system operation while raising no alarms. \n \nIn summary, this work shows the trade-offs of testing QKD payloads on different airborne platforms, develops components for a satellite QKD payload, and demonstrates a security vulnerability in a commercial QKD system that can fully compromise the key. These results help address practical challenges to building QKD devices, improving the security of modern cryptography.
Free-space quantum key distribution has recently achieved several milestones, such as \nthe launch and results of the first quantum satellite, Micius. The emergence of quantum satellites has certainly made progress towards the realization of a global quantum cryptographic network. In this thesis, two challenges in the development of an optical quantum ground station \nfor a free-space quantum satellite link are studied. The first is the development of a high brightness, fiber pigtailed waveguide that is to be used as a polarization entangled photon source. The high pair production rate is required in order to meet the requirements for a satellite up-link configuration. The portability, robustness and ease of alignment were motivations for choosing a fiber pigtailed source. Certain challenges that are fundamental to the source design were characterized and several solutions to these challenges were investigated. The other main investigation in this thesis, is the development of a passive polarization \ncompensation using polarization maintaining fibers. The birefringence in standard single mode optical fibers causes random polarization rotations to the light passing through the fiber. Polarization maintaining fibers, though very high in birefringence, are used with entangled photons and techniques from reference frame independent quantum key distribution protocols are shown to compensate for random polarization rotations while preserving the entanglement. In addition, the feasibility of the protocol using the polarization maintaining fibers is investigated. \nThrough various studies, experiments, and component design, the feasibility of a pigtailed waveguide entangled photon source has been shown to need further investigation, while the feasibility of implementing polarization maintaining fibers to the ground station has been shown to be effective. It is particularly effective as a passive polarization compensation system that uses entanglement, however a similar concept is effective for non-entangled single photons. This work contributes to a long line of achievements leading towards satellite implementations of quantum key distribution for an eventual global quantum cryptographic network.
Quantum key distribution (QKD), a novel cryptographic technique for secure distribution of secret keys between two parties, is the first successful quantum technology to emerge from quantum information science. The security of QKD is guaranteed by fundamental properties of quantum mechanical systems, unlike public-key cryptography whose security depends on difficult to solve mathematical problems such as factoring. Current terrestrial quantum links are limited to about 250 km. However, QKD could soon be deployed on a global scale over free-space links to an orbiting satellite used as a trusted node. \n \nEnvisioning a photonic uplink to a quantum receiver positioned on a low Earth orbit satellite, the Canadian Quantum Encryption and Science Satellite (QEYSSat) is a collaborative project involving Canadian universities, the Canadian Space Agency (CSA) and industry partners. This thesis presents some of the research conducted towards feasibility studies of the QEYSSat mission. \n \nOne of the main goals of this research is to develop technologies for data acquisition and processing required for a satellite-based QKD system. A working testbed system helps to establish firmly grounded estimates of the overall complexity, the computing resources necessary, and the bandwidth requirements of the classical communication channel. It can also serve as a good foundation for the design and development of a future payload computer onboard QEYSSat. \n \nThis thesis describes the design and implementation of a QKD post-processing system which aims to minimize the computing requirements at one side of the link, unlike most traditional implementations which assume symmetric computing resources at each end. The post-processing software features precise coincidence analysis, error correction based on low-density parity-check codes, privacy amplification employing Toeplitz hash functions, and a procedure for automated polarization alignment. \n \nThe system's hardware and software components integrate fully with a quantum optical apparatus used to demonstrate the feasibility of QKD with a satellite uplink. Detailed computing resource requirements and QKD results from the operation of the entire system at high-loss regimes are presented here.
Quantum key distribution is now a mature quantum communication protocol which allows the verifiably secure sharing of encryption keys between two communicating parties. It seeks to address potential vulnerabilities of data transmission and storage, offering a realistic possibility to share encryption keys which are robust to eavesdropping attacks and future-proof against hacking. Fibre-optic implementations of quantum key distribution currently have a limited practical transmission distance, of less than 400 km, making commercial applications limited. Quantum-specific amplifier/repeater technology is not yet mature enough to increase the transmission distance to achieve global capabilities. Optical fiber is also impractical and expensive for applications where a remote area or moving platform are involved. In recent years, long-distance free-space quantum communications using low-Earth orbit satellites has seen an increase in interest from the academic community as well as from industrial organisations and national research institutes. The source of this new interest was a series of proof-of-principle demonstrations of satellite-based quantum key distribution in 2017. The use of free-space channels implementing airborne or satellite platforms also opens a range of new applications for quantum communications, as they allow coverage of remote areas, moving platforms, and also avoid the requirement of spooling fibre through volatile regions. This presentation will give a general introduction to satellite-based quantum communications, an overview of the field, and discuss future endeavours. The talk will also include an overview of our research into novel photonic technology, such as the use of detector array technology, for the optical ground station receiver.
Technological realities limit terrestrial quantum key distribution (QKD) to single-link distances of a few hundred kilometers. One promising avenue for global-scale quantum communication networks is to use low-Earth-orbit satellites. Here we report the first demonstration of QKD from a stationary transmitter to a receiver platform traveling at an angular speed equivalent to a 600 km altitude satellite, located on a moving truck. We overcome the challenges of actively correcting beam pointing, photon polarization and time-of-flight. Our system generates an asymptotic secure key at 40 bits/s.