Advances in Quantum Key Distribution: Protocols and Real-World Implementations for Secure Communications

• Alessandro Zavatta (Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), Italy)

Quantum Key Distribution (QKD) is a mature and reliable technology for establishing symmetric encryption keys between two distant parties with unconditional security. Several QKD protocols, such as BB84, form the foundation of this technology, ensuring secure communication through quantum principles. These protocols have been successfully implemented in real-world applications, including cross-border networks, underwater links, and Metropolitan Area Networks (MANs). We will explore the latest advancements in QKD technology and its protocols, highlighting recent real-world implementations that showcase its adaptability, robustness, and effectiveness in diverse environments.

Towards Quantum Networks

• Harald Weinfurter (Max Planck Institute for Quantum Optics, Germany)

While we are still at the beginning, recently a lot of progress with experiments on a variety of quantum systems made the grand goal of a quantum network a bit more realistic. At the end we will have a net connecting quantum computers thereby also providing secure communication in an efficient way over any distance.

Quantum optimal control for quantum technologies

• Tommaso Calarco (Universit`a di Bologna, Italy)

Quantum optimal control has emerged as a key tool in the advancement of quantum technologies, enabling the precise manipulation of quantum systems for a variety of applications, including quantum computation, sensing, and communication. In this talk, I will provide an overview of the fundamental principles of quantum optimal control and its role in enhancing the performance and robustness of quantum devices. By optimizing control pulses, we can mitigate the effects of noise, decoherence, and other operational imperfections, thus pushing the boundaries of what is achievable with current quantum systems. I will also discuss recent advancements in algorithmic methods for control optimization, as well as their implementation in current quantum platforms. The goal of this talk is to highlight the practical relevance of quantum optimal control in the ongoing development of scalable and reliable quantum technologies.

Quantum Metrology & Quantum Enhanced Measurements (with Photons)

• Ivo Pietro Degiovanni (Istituto Nazionale di Ricerca Metrologica, Italy)

The objective of the lesson is to cover different aspects of quantum metrology ranging from quantum enhanced measurements to metrology for quantum technology. Some specific examples in the field of quantum photonics will be discussed.

Optical quantum metrology, a story of modes

• Nicolas Treps (Laboratoire Kastler Brossel, France)

Quantum optical metrology aims at identifying the ultimate sensitivity bounds for the estimation of parameters encoded into an optical field, positioned at the intersection of quantum physics, signal processing, and electromagnetism. By leveraging the concepts of quantum and classical Fisher information, it is possible to both benchmark optical apparatus and propose strategies to optimize optical measurements. In this lecture, we will introduce the concepts of (Quantum) Fisher information and Cramér Rao bound, but also of practical estimators such as the method of moments. We will do so having in mind practical applications, such as imaging, and remote sensing, where the parameter of interest is encoded not only in the quantum state of the field but also in its spatio-temporal distribution, i.e., in its modal structure. We will illustrate this with the example of estimating the separation between two incoherent sources, and its extension to efficient multi-parameter estimation.

Quantum Sensing - Detecting Faint and Fleeting Signals using Quantum Systems

• Morgan Mitchell (ICFO - Institut de Ciències Fotòniques, Spain)

Our best sensors, used for fundamental physics, navigation, medical imaging, and many other applications, employ quantum systems such as atoms or photons, and use quantum interference to obtain signals that depend strongly on whatever physical variable we are trying to measure. Designing, building, and understanding such instruments is the topic of quantum sensing. Interference necessarily involves superposition states, and measuring superposition states necessarily leads to probabilistic outcomes. The statistics of quantum measurement is thus intrinsic to quantum sensing, and much effort has gone into designing strategies that minimize the resulting measurement uncertainty. Often these efforts involve entanglement, because entangled states allow for strong signals together with small uncertainties. Many important sensors moreover track the evolution of a quantum system such as a collection of atoms, as they coherently respond to a signal of interest over time. Because the act of observing necessarily disturbs a quantum system, there will be a trade-off between the precision of an observation now and the accuracy of an observation later. This "measurement back-action" (MBA) problem also involves quantum statistics, but now the statistics of monitored open quantum systems. This is a rather complex physics problem, and is far from fully solved. Nonetheless, it is known that some sensing strategies are fundamentally limited by MBA, while other strategies appear to evade MBA entirely. I will illustrate with recent experiments using squeezed and entangled states for sensing, and a high-performance magnetic sensor that avoids measurement back-action.

Near-Term Quantum Computers: Practical Applications and Overcoming Current Limitations

• Matteo Rossi (Algorithmiq Ltd, Finland)

In this lecture, we will explore the rapidly evolving landscape of near-term quantum computers, highlighting both the potential and the critical challenges that define the current state of quantum technology. The first part will provide a comprehensive introduction to near-term quantum devices, outlining their role in the broader quest for fault-tolerant quantum computation. We will discuss the significant progress made so far, focusing on the inherent limitations these systems face, such as noise and the high cost of accurate measurements. In the second part, the focus will shift to cutting-edge research aimed at overcoming these obstacles. We will delve into advanced techniques for error mitigation and informationally complete measurements, showcasing state-of-the-art methods and the latest breakthroughs from our research team. This session will provide a deep dive into the practical approaches that are paving the way for more reliable and scalable quantum computing in the near future.

Schemes for Quantum Imaging

• Ashley Lyons (University of Glasgow, United Kingdom)

In this lecture we will explore a number of different schemes common in the quantum imaging community. We will discuss whether each of these truly relies on quantum mechanics and which can effectively be replicated with classical optics. We will also look at some of the emerging, less common approaches to quantum imaging and how to perform the measurements in practice.

The Sagnac Effect for quantum sensing

• Maria Chiara Braidotti (University of Glasgow, United Kingdom)

In this lecture, we explore the Sagnac effect, a fundamental phenomenon in physics arising from rotational motion, and its implications for quantum sensing technologies. The Sagnac effect, observed when a beam of light is split and sent in opposite directions around a rotating loop, results in a measurable phase shift proportional to the angular velocity. This principle has been pivotal in the development of highly sensitive gyroscopes and navigation systems. We will delve into the theory of the Sagnac effect, review its classical applications, and transition to its utilization in quantum sensing. Emphasizing recent advancements, we will examine how the integration of quantum mechanics changes the precision and sensitivity of measurement devices, though enabling breakthroughs in the field of fundamental physics.

The device-independent scenario: quantum information processing based on Bell theorem

• Antonio Acín (ICFO - Institut de Ciencies Fotoniques, Spain)

Bell's theorem proves the existence of quantum correlations, often known as Bell nonlocal, that cannot be described by classical theories, in which measurement outcomes are predetermined. In recent years, Bell nonlocal correlations have also acquired the status of information resource, as they are crucial for the construction of quantum information protocols in the device-independent scenario, where no modeling of the devices is assumed in the implementation. Because of this absence of modeling, device-independent protocols offer the strongest form of security attainable in quantum theory. This lecture provides an introduction to all these concepts, going from quantum foundations to quantum information science and back. The main ideas and tools in the device-independent formalism are explained, together with an overview of the main results and remaining challenges.

Integrated photonics for quantum information processing

• Fabio Sciarrino (Sapienza Università di Roma, Italy)

Photonic quantum technologies represent a promising platform for several applications, ranging from long-distance communications to the simulation of complex phenomena. Indeed, the advantages offered by single photons do make them the candidate of choice for carrying quantum information in a broad variety of areas with a versatile approach. Furthermore, recent technological advances are now enabling the first concrete applications of photonic quantum information processing. The goal of this lecture t is to provide the audience with an overview of the state of the art in this active field, with a due balance between theoretical, experimental and technological results.

Quantum-enhanced diamond spin sensors

• Nicole Fabbri (stituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), Italy)

Spin qubits in the solid state may enable new capabilities in quantum sensing, thanks to the combination of sensitivity and spatial resolution. I will provide an introduction to sensing protocols exploiting quantum coherence and give an overview on frontier applications.

Introduction to Tensor Network Methods

• Simone Montangero (Università degli Studi di Padova, Italy)

We introduce tensor network methods, a powerful class of classical numerical algorithms to support future quantum simulations and computations, providing guidance, benchmarking and verification of the quantum computation and simulation results. Starting from the basics concepts and algorithms, we conclude the lesson with an overview of some of the latest developments: their application lattice gauge theories in regimes where Monte Carlo methods efficiency is hindered by the sign problem and to complex hard combinatorial problems. Finally, we review the application of tensor networks to perform machine learning tasks.