Realizing a scalable quantum network is one of the grand challenges of quantum technology, with numerous potential applications in secure communication, quantum sensor networks, and distributed quantum computation. Single-photon sources and compatible quantum memories are key ingredients of quantum networks and the requirements on their performance are very stringent. In this project we will establish a scalable quantum networking platform that combines several high-performance elements: semiconductor quantum dot single-photon sources and compatible atomic vapor cell quantum memories implemented in scalable MEMS technology, operating with GHz bandwidth at convenient near-infrared wavelengths. Connectivity over long distance and to other platforms is enabled by efficient conversion of single photons to telecom wavelength using on-chip nonlinear optics. Combining these building blocks, we will demonstrate quantum networking tasks such as remote entanglement generation between quantum memories over a telecom fiber link. By demonstrating the basic functionality of a scalable quantum networking platform that operates at high efficiency and bandwidth, the project will lay the ground for the implementation of more advanced quantum networking protocols and scaling to multiple nodes.

Two-dimensional (2D) magnets have emerged as a new frontier in magnetism, both in terms of fundamental questions - including why such magnetism is stable at all - as well as from the device engineering point of view. In general, the stacking, twisting, and combining of van der Waals (vdW) materials with control down to individual atomic layers has started a revolution in heterostructure engineering. Layer-by-layer control offers a multitude of possible material combinations, without constraints imposed by lattice mismatch, along with the prospect of making compact devices, in which large electric fields can easily be applied. These new tools give researchers unprecedented control of interactions and band structure, as exemplified by the 2018 realization of superconducting twisted bilayer graphene. In the realm of magnetism, these methods can be used to tune the magnetic properties of a material or even to make materials, which are non-magnetic in the bulk, magnetic in 2D. Most importantly, both in view of understanding the physics of 2D magnetism and exploiting it for applications, vdW engineering may allow us to realize new and useful magnetic phases, which are only possible in 2D. In order to fully take advantage of these new developments, we must understand the role of anisotropy, disorder, inhomogeneity, and characteristic length-scales in 2D magnets and their heterostructures. Such investigations require sensitive local probes and techniques for measuring magnetism in small volumes. Our group, which has long worked at the forefront of sensitive magnetic imaging and torque magnetometry, is ideally positioned for such measurements. Here, we propose to apply our unique and highly sensitive tools to three types of measurements in 2D magnets: The characterization of static magnetism : determining the magnetic state and its dependence on the number of layers, anisotropy, as well as the presence of spatially modulated states, domains, defects, and inhomogeneities. The study of phase transitions and magnetic reversal : measuring the stability of magnetic phases, the nature of phase transitions, the process of magnetic reversal, and the role of domains and inhomogeneity therein. Understanding how to engineer 2D magnets : observing the effects of stacking, twisting, and applying electric fields to controllably induce phase transitions, magnetic reversal, magnetic texture, or new magnetic phases. The work of unravelling the mechanisms behind 2D magnetism is in its infancy. Given the inadequacy of conventional magnetic probes, we are convinced that our unique nanometer-scale magnetic field imaging and ultrasensitive torque magnetometry tools have much to contribute towards this effort. The results can be expected to have implications for 2D spintronic devices, 2D antiferromagnets, and the design of quantum materials via 2D vdW engineering in general.

Today, many technological devices exist which are built on the principles of quantum mechanics. These are mainly based on the concept of energy quantization and include the laser and the transistor. Currently there is an active quest in developing novel quantum technologies which harness the more elusive features of quantum theory such as coherent superposition and entanglement. While there are still numerous open questions concerning the nature of future quantum devices, they will rely on systems that are out of equilibrium and couple to their surrounding environment. Therefore, a thorough understanding of open quantum systems driven far from equilibrium is paramount for the development of devices based on quantum technology. The emerging field of quantum thermodynamics investigates concepts such as heat, work, and temperature in the quantum regime, with a focus on determining fundamental limitations on physically allowed processes. This theory therefore provides an ideal framework for addressing the capabilities of open quantum systems. While quantum theory follows a different set of rules than classical theories, it is often a non-trivial task to determine if a quantum device is able to outperform an analogous classical device, i.e., exhibits a quantum advantage . A promising route to determining such an advantage is provided by the investigation of fluctuations. Quantum fluctuations behave fundamentally different from their classical counterparts and are still far from being fully understood. Their implications are tightly connected to the measurement process, implying a close interrelation with the established fields of quantum sensing and information thermodynamics . This project constitutes a unifying investigation of fluctuations, sensing, and information; concepts which have so far mostly been studied independently. The long-term goals of this project are twofold: The first objective is to expand our understanding of the tasks that can be performed by out-of-equilibrium open quantum systems , including the potential provided by quantum features such as superposition and entanglement. The second objective is to develop novel technologies in the fields of quantum thermodynamics and quantum metrology . To this end, the project is focused on thermodynamic processes, such as the conversion of heat into electrical work and the estimation of low temperatures. The research will rely on well established methods, such as Markovian quantum master equations, methods which I (co-)developed, such as the Keldysh quasi- probability distribution, as well as methods that will be developed during the project. In addition to a unified understanding of the role of fluctuations, sensing, and information in quantum thermodynamics , a number of results going well beyond the state of the art are expected to emerge from the project. These include advances in understanding fundamental properties of quantum devices. For example I intend to clarify the role of the particle-wave duality in quantum thermal machines . Furthermore, a number of practical tools for both theorists and experimentalists will be developed including tests to certify non-classical behavior, as well as theories such as a novel input-output theory based on Keldysh path integrals . A particular focus of the project lies on bridging the gap between theory and experiment with examples being the certification of non-classical fluctuations, as well as the implementation of low-temperature thermometry schemes that are only limited by fundamental constraints. With these results, the project is expected to have a deep impact on topics ranging from the description of driven-dissipative systems to the state of the art in thermometry measurements.

The goal of the project is to explore potential commercial and industrial applications of electromagnetic field sensing with atomic vapour cells.

We will explore novel aspects of quantum synchronization in networks of self-sustained oscillators. This includes even-odd effects in the number of levels of the synchronization nodes and the dependence on network topology (number of neighbors and interaction range). Another interesting direction that we will study is frustration effects and possible links to frustrated quantum spin systems. Furthermore, we will investigate symmetry-breaking pattern formation in synchronization networks Using unsupervised machine-learning schemes, we will investigate phase diagrams of models that exhibit synchronization or other types of long-range order. We will also explore neural network architectures that involve physical insights and recent innovations in machine learning to compute steady states of driven dissipative quantum systems.

In this project we aim to combine the exceptional sensitivity of nanowire quantum dots as detectors of charge with scanning probe capabilities of customized cantilevers. The resulting scanning nanowire quantum dot will enable imaging of localized charges and electron densities with high sensitivity, high resolution, and under a large variety of environmental circumstances.

Ordinary matter comprises a limited set of elementary particles known as the first generation. Surprisingly, particle physics labs have identified two additional generations of elementary particles. These heavy and short-lived particles once thrived in the early universe's hot soup, only to decay to the first generation shortly after. This project aims to theoretically probe the origins of these three particle generations, leveraging cutting-edge experimental facilities like those at CERN. This multifaceted research project will follow three complementary research approaches. The first module is devoted to developing theoretical methods to analyze particle collisions and extracting information about their interactions that distinguish between different particle generations. The second module includes comparative studies of data sets at low and high energies. Finally, the third module will present new hypotheses about the origin of the three particle generations. This systematic approach will allow us to gain insight into the next unknown level of nature.

Das Departement für Physik der Philosophisch-Naturwissenschaftlichen Fakultät der Universität Basel und das Physikalische Institut der Fakultät für Mathematik und Physik der Albert Ludwigs-Universität Freiburg im Breisgau errichten partnerschaftlich ein neues Exzellenzzentrum mit den Forschungsschwerpunkten "Quantum Science and Quantum Computing" unter dem Dach von Eucor - The European Campus . Als tragende Säule dieses Exzellenzzentrums wird ein grenzüberschreitender Postdoc-Cluster zwischen den Universitäten Basel und Freiburg aufgebaut. Primäre Ziele des zukünftigen Postdoc-Clusters sind die hochwertige Ausbildung der Postdocs für den akademischen als auch wirtschaftlichen Arbeitsmarkt und die Positionierung als führende Forschungseinrichtung auf dem Gebiet "Quantum Science and Quantum Computing", im Speziellen durch die verstärkte grenzüberschreitende Zusammenarbeit im Dreiländereck Deutschland-Frankreich-Schweiz. Das Exzellenzzentrum "Quantum Science and Quantum Computing" wird von der Georg H. Endress Stiftung finanziell unterstützt.

SNI PhD School