Thursday, May 16, 2024 10:30 am - 11:30 am EDT (GMT -04:00)

Long-lived transmons with different electrode layouts

IQC Seminar - Universty of Maryland

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

 In the realm of quantum computing,non-equilibrium quasiparticle tunneling may be a significant loss mechanism in transmon qubits. Understanding the behavior of these quasiparticles across junctions may lead to improved qubit devices . One approach involves the fabrication of asymmetric transmons through gap-engineering techniques aimed at mitigating quasiparticle tunneling and subsequent loss. In our research, we have conducted repeated measurements of the relaxation time (T1) in Al/AlOx/Al transmons featuring electrodes with varying superconducting gap values. Specifically, one device utilized a first-layer electrode formed via thermal evaporation of nominally pure Al, while the counter-electrode incorporated oxygen-doped Al. This device exhibited notable fluctuations in T1, ranging from approximately 100 μs to slightly over 300 μs at 20 mK. Additionally, we explored different configurations of junction layouts in an effort to enhance device performance.

En francais

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.

Wednesday, July 10, 2024 11:45 am - 12:45 pm EDT (GMT -04:00)

Security implications of device imperfections in quantum key distribution

IQC Special Seminar, Jerome Wiesemann, Fraunhofer Heinrich Hertz Institute HHI

Quantum key distribution (QKD) is on the verge of becoming a robust security solution, backed by security proofs that closely model practical implementations.  As QKD matures, a crucial requirement for its widespread adoption is establishing standards for evaluating and certifying practical implementations, particularly against side-channel attacks resulting from device imperfections that can undermine security claims. Today, QKD is at a stage where the development of such standards is increasingly prioritized. This works aims to address some of the challenges associated with this task by focusing on the process of preparing an in-house QKD system for evaluation. We first present a consolidated and accessible baseline security proof for the one-decoy state BB84 protocol with finite-keys, expressed in a unified language. Building upon this security proof, we identify and tackle some of the most critical side-channel attacks by characterizing and implementing countermeasures both in the QKD system and within the security proof. In this process, we iteratively evaluate the risk of the individual attacks and re-assess the security of the system. Evaluating the security of QKD systems additionally involves performing attacks to potentially identify new loopholes. Thus, we also aim to perform the first real-time Trojan horse attack on a decoy state BB84 system, further highlighting the need for robust countermeasures. By providing a critical evaluation of our QKD system and incorporating robust countermeasures against side-channel attacks, our research contributes to advancing the practical implementation and evaluation of QKD as a trusted security solution.

Wednesday, May 8, 2024 - Friday, May 10, 2024 (all day)

IQC-PCQT Workshop

This workshop is centred around quantum computer science and brings together researchers in Canada and France, especially from IQC and the Paris Centre for Quantum Technologies. It aims to review the latest developments in the field while strengthening existing ties between the two communities and fostering new ones.

En francais

On April 18, Transformative Quantum Technologies (TQT) awarded six research teams and their design ideas for the Quantum for Environment (Q4Environment) Design Challenge, whose green-tech solutions address global environmental issues. Ideas included using quantum computing to improve medical devices, and sensors that can detect microplastics and toxic nanomaterials in our oceans. 

Friday, April 26, 2024

IQC Welcomes Dr. Bradley Hauer

En francais

Breakthroughs in understanding how gravity affects quantum mechanics could be on the horizon at the Institute for Quantum Computing (IQC) with the addition of Dr. Bradley Hauer as IQC's newest faculty member and Assistant Professor in the Department of Electrical and Computer Engineering. Hauer’s research focuses on studying cavity optomechanical systems and superconducting circuits and their applications in metrology, quantum information and non-classical state preparation.

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


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

Monday, May 27, 2024 2:30 pm - 3:30 pm EDT (GMT -04:00)

Semiconductor spin qubits for quantum networking

IQC Colloquium - Akira Oiwa, Osaka University

Quantum-Nano Centre, 200 University Ave West, Room QNC 1501 Waterloo, ON CA N2L 3G1

Semiconductor spin qubits are well recognized as a promising platform for scalable fault-tolerant quantum computers (FTQCs) because of relatively long spin coherence time in solid state devices and high-electrical tuneability of the quantum states [1]. In addition, semiconductors have a great potential for applications in quantum communications because of their abilities in optical devices. Therefore, especially in quantum repeater applications, the semiconductor spin qubits provide a route to efficiently connect qubit modules or quantum computers via optical fibers and construct global quantum networks, contributing to realize secure quantum communications and distributed quantum computing [2]. In this talk, we present the physical process enabling the quantum state conversion from single photon polarization states to single electron spin states in gate-defined quantum dots (QDs) and its experimental demonstration [3]. As recent significant achievements, we discuss that the enhancement of the conversion efficiency from a single photon to a single spin in a quantum dot using photonic nanostructures [4]. Finally, we present a perspective of high conversion efficiency quantum repeater operating directly at a telecom wavelength based on semiconductor spin qubits.

[1] G. Burkard et al., Rev. Mod. Phys. 95, 025003 (2023). [2] A. Oiwa et al., J. Phys. Soc. Jpn. 86, 011008 (2017); L. Gaudreau et al., Semicond. Sci. Technol. 32, 093001 (2017). [3] T. Fujita et al., Nature commun. 10, 2991 (2019); K. Kuroyama et al., Phys. Rev. B 10, 2991 (2019). [4] R. Fukai et al., Appl. Phys. Express 14, 125001 (2021); S. Ji et al., Jpn. J. Appl. Phys. 62, SC1018 (2023).