Welcome to the Institute for Quantum Computing

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).

CS/Math Seminar - Amir Arqand, IQC 

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

The entropy accumulation theorem, and its subsequent generalized version, is a powerful tool in the security analysis of many device-dependent and device-independent cryptography protocols. However, it has the drawback that the finite-size bounds it yields are not necessarily optimal, and furthermore, it relies on the construction of an affine min-tradeoff function, which can often be challenging to construct optimally in practice. In this talk, we address both of these challenges simultaneously by deriving a new entropy accumulation bound. Our bound yields significantly better finite-size performance, and can be computed as an intuitively interpretable convex optimization, without any specification of affine min-tradeoff functions. Furthermore, it can be applied directly at the level of R´enyi entropies if desired, yielding fully-R´enyi security proofs. Our proof techniques are based on elaborating on a connection between entropy accumulation and the frameworks of quantum probability estimation or f-weighted R´enyi entropies, and in the process we obtain some new results with respect to those frameworks as well.

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.