Events

IQC Special seminar - Sahel Ashhab, National Institute of Information and Communications, Japan

QNC building, 200 University Ave. Room 1201, Waterloo 

We use numerical optimal-control-theory methods to determine the minimum number of two-qubit CNOT gates needed to perform quantum state preparation and unitary operator synthesis for few-qubit systems. In the first set of calculations, we consider all possible gate configurations for a given number of qubits and a given number of CNOT gates, and we determine the maximum achievable fidelity for the specified parameters. This information allows us to identify the minimum number of gates needed to perform a specific target operation. It also allows us to enumerate the different gate configurations that can be used for a perfect implementation of the target operation. We find that there are a large number of configurations that all produce the desired result, even at the minimum number of gates. This last result motivates the second set of calculations, in which we consider only a small fraction of the super-exponentially large number of possible gate configurations for an increasing number of qubits. We find that the fraction of gate configurations that allow us to achieve the desired target operation increases rapidly as soon as the number of gates exceeds the theoretical lower bound for the required number of gates. As a result, a random search can be a highly efficient approach for quantum circuit synthesis. Our results demonstrate the important role that numerical optimal control theory can play in the development of quantum compilers.

QNC building, 200 University Ave. Room 0101, Waterloo 

This workshop focuses on encoding quantum information in more than two states.

The main theme is to go beyond binary encodings: from quBits to quDits, where D > 2.

Now is a very interesting time, as we see a lot of experimental progress and new possibilities in this area. This workshop brings together researchers  – both experimentalists and theorists – to explore quDit-based applications in all areas of quantum technology.

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.

Improving information transmission using correlated auxiliary noise

QNC building, 200 University Ave. Room 1201, Waterloo 

Communicating information is a fundamentally important task that is often limited by noise. The physical origin of noise in a quantum channel is an interaction between the transmitted system and its surrounding environment. This interaction leads to correlations between the system and its environment that contain information about the original state, but are inaccessible to the receiver. However, a receiver may be able to recover some of this lost information if they are given access to an additional auxiliary system that interacts with the environment. In this talk, I will formalize a particular type of receiver side information and characterize the resulting improvement in classical and quantum channel capacities for an augmented bit flip channel. I will then discuss information-theoretic bounds on imperfect one-time pad cryptography schemes and passive environment-assisted quantum channel capacities.

Quantum sensing of light with sub-wavelength resolution

Simulating the Anisotropic XY-model on a Trapped Ion Quantum Simulator

Location: QNC 1201

Efficient Circuit-Based Quantum State Tomography via Sparse Entry Optimization

Location: QNC 1201 and Online on Zoom

Efficient Circuit-Based Quantum State Tomography via Sparse Entry Optimization

Location: QNC 1201 and Online on Zoom

Quantum Polynomial Hierarchies

Location: QNC 1201