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Congratulations to Dr. Rajibul Islam, a faculty member at the Institute for Quantum Computing (IQC) and a professor in the Department of Physics and Astronomy, who has been awarded the 2024 Excellence in Science Teaching Award.

This annual award, selected by the University of Waterloo’s Faculty of Science, recognizes instructors who have demonstrated sustained, high-quality teaching in their undergraduate or graduate courses.

Events

Tuesday, May 21, 2024 3:00 pm - 4:00 pm EDT (GMT -04:00)

Synthesis and Arithmetic of Single Qutrit Circuits

IQC CS/Math Seminar - Amolak Ratan Kalra, University of Waterloo

Quantum-Nano Centre, 200 University Ave West, Room QNC 1201 Waterloo, ON CA N2L 3G1

In this talk I will discuss qutrit circuit synthesis over various families of universal gate sets. I will describe a method which relates the question of exact synthesis for both single qubits and single qutrits to the problem of solving a system of polynomial equations mod p.
 

Wednesday, May 22, 2024 8:30 am - 9:30 am EDT (GMT -04:00)

Paul Oh PhD Thesis Defense

Entangled photon source for a long-distance quantum key distribution

Remote

Satellite-based Quantum Key Distribution (QKD) leverages quantum principles to offer unparalleled security and scalability for global quantum networks, making it a promising solution for next-generation secure communication systems. However, many technical challenges need to be overcome. This thesis focuses on theoretical modeling and experimental validation for long-distance QKD, as well as the development and testing of the quantum source necessary for its implementation, to take strides towards realization. While various approaches exist for demonstrating long-distance QKD, here we focus on discussing the approach of sending entangled photon pairs from an optical quantum ground station (OQGS), one through free-space on one end (uplink), and the other one through ground on the other end. This is also because our research team at the Quantum Photonics Laboratory (QPL), collaborating with the Canadian Space Agency (CSA), is planning to demonstrate Canada's first ground-to-space QKD in the near future. The mission is called Quantum Encryption and Science Satellite (QEYSSat) mission, which is planned to deploy a Low-Earth Orbit (LEO) satellite for the purpose for demonstrating QKD.

In the thesis, we first discuss the considerations relevant to establishing a long-distance quantum link. Since a substantial amount of research has already been conducted on optical fiber communication through ground-based methods, our focus is specifically directed towards ground-to-space (i.e., free space) quantum links. One of the most concerning aspects in free- space quantum communication is signal attenuation caused by environmental factors. We particularly examine pointing errors that arise from satellite tracking systems. To investigate this further, we designed a tracking system employing a specific tracking algorithm and conducted tracking tests to validate its accuracy, using the International Space Station (ISS) as a test subject. Our findings illustrate the potentially significant impact of inaccurate ground station-to- satellite alignment on link attenuation, according to our theoretical model. Given that photons serve as the signals for the QKD, we also investigate the background light noise resulting from light pollution, which is another concerning aspect, as it could worsen the link attenuation. Conducting light pollution measurements around our Optical Quantum Ground Station (OQGS), we estimate the minimum photon pair rate required for successful QKD, taking into account both the obtained values from these measurements and the expected level of link loss.

Having determined the minimum photon pair rate and other requirements for the long-distance QKD, we proceed to fully elaborate on the development process of the Entangled Photon Source (EPS), which is one of the crucial devices for demonstrating entanglement-based QKD. We use a nonlinear crystal for generating photon pairs, and experimentally obtain the photon pair rate produced from it. Here, the thesis also includes a detailed explanation of the customization process for the crystal oven. Next, we implement a beam displacer scheme along with the Sagnac loop scheme to create a robust interferometer, responsible for creating quantum entanglement. In addition, we demonstrate a novel approach to effectively compensate for the major weaknesses of the interferometer, namely spatial and temporal walk-offs. Finally, we conduct the entanglement test and demonstrate its suitability for long-distance QKD. As a side project, we

investigate the performance degradation of nonlinear crystals in response to proton radiation, exploring the potential of deploying the EPS in space for downlink QKD in the future. This thesis provides a comprehensive analysis and testing of elements required for long-distance QKD, contributing to the advancement of future global quantum networks.

Supervisor: Thomas Jennewein

Wednesday, May 22, 2024 12:00 pm - 1:00 pm EDT (GMT -04:00)

IQC Student Seminar Featuring Nachiket Sherlekar

Stable and Localized Emission from Ambipolar Dopant-Free Lateral p-n Junctions

Quantum-Nano Centre, 200 University Ave West, Room QNC 1201 Waterloo, ON CA N2L 3G1

Combining the architectures of a dopant-free lateral p-n junction and a single-electron pump in a GaAs/AlGaAs heterostructure material system could yield high-rate, electrically-driven quantum emitters with performances surpassing the competition in quantum sensing, communication and cryptography. Observed drawbacks of the dopant-free p-n junctions are a rapid decay in electroluminescence during operation, as well as delocalized emission that lowers the measured quantum efficiency. This talk details novel measurement protocols and gate architectures implemented by us to overcome these challenges.