Magnetic materials and devices play a tremendous role in information technology to meet current societal challenges. Antiferromagnet (AFM) spintronics is considered as a disruptive approach, enabling scalable and efficient spintronic devices. Ultimate stability and speed, combined with recent observations, e.g. the enhancement of the spin current transport when a thin AFM layer is sandwiched between Yttrium Iron Garnet and Pt, and along with theoretical predictions of superfluid spin transport, indicate significant untapped potential of this class of materials. I tackle the key open questions on spin transport in AFMs: (i) To develop and employ an all-electrical read-out of the Néel vector. The Néel vector can be set, by studying AFMs across the spin-flop field, and then compared with the resulting magnetotransport signal. In collinear antiferromagnetic conductors, the anisotropic magnetoresistance/planar Hall effect will be used, while in these and others collinear AFMs, a read-out by the Spin-Hall Magneto-resistance (SMR) at the interface between the AFM and a heavy metal will be employed, e.g. in NiO/Pt and MnN/Pt. The SMR will be additionally correlated with direct imaging of the AFM domain structure, performed in synchrotrons. (ii) To explore a new writing method, based on the voltage control of magnetic properties, via the migration of oxygen ions, as demonstrated in ferromagnets, where the anisotropies can be tailored. (iii) To transport spin in antiferromagnets. By thermally generating spin currents via the spin Seebeck effect, I will study the transport in AFM metals and insulators. Temperature-dependent measurements allow us to ascertain the role of the different spin current magnon modes. Finally, the spin injection in NiO and the exciting predicted spin superfluidity in AFMs will be probed. This work is expected to be important, not only to understand the rich physics of spin transport in AFMs, but also toward using AFMs for novel spintronic devices.

Three decades ago, it was proposed that quantum computers (i.e. quantum systems where information can be encoded, processed and read out) could outperform classical devices for information processing. For instance, they may allow the factoring of integer numbers in a time which scales polynomially with the size of the input, while known classical algorithms require an exponential time. However, in practice, it has not yet been possible to build a quantum computer large enough to beat classical machines. This has raised the question as to whether this difficulty is only technical, and will be overcome one day, or due to fundamental reasons. In trying to answer this question, physicists and computer scientists have developed "sub-universal" quantum computing models, which aim at solving very specific problems, simpler than factoring, but still displaying a quantum advantage. Among those is the so-called boson sampling protocol, which enables to compute the permanent of a unitary matrix. In other words, scientists now seek for the observation of a minimal supremacy of quantum computers over classical ones. Inspired by recent experimental achievements (Paris, Japan, Virginia), in this project I will study at the theoretical level new models of sub-universal quantum computers, based on original photonic architectures. Indeed, these models have been only poorly studied, so far, in the promising context of the "Continuous Variable" (CV) encoding, which has recently allowed to reach the record-size for quantum computing resource states. This project articulates through two main objectives: 1) The design of new sub-universal quantum circuits in CV, providing proof of their classical computational hardness 2) The study of viable experimental quantum optics platforms where these protocols may be efficiently implemented. Among those, I will design the first experimentally accessible protocol for CV boson sampling.

The project aims at developing a full coherent control of cold, trapped ions excited to Rydberg states. The experiment will be implemented using laser-cooled atomic ions at microkelvin temperatures in a microfabricated radiofrequency ion trap. The superb control over internal and external degrees of freedom in cold ions will be combined with the high flexibility offered by the Rydberg interaction that enables accurately tuning the strength as well as the angular dependence of the interaction. Building on this control, the researcher will investigate fundamental physics in long-range interactions between such highly controllable quantum systems. New techniques will be developed to generate quantum states that are independent from the trapping field using specific dressed states in a microwave field as well as a fast switching electric field. This will enable the excitation to high-laying Rydberg states, and thus the observation of new quantum effects, i.e., the Rydberg blockade effect in cold ions. Furthermore, coherent excitation of these quantum systems will be achieved based on a two-photon excitation scheme, while the focus will be on experiment with multi ions in linear as well as two-dimensional arrays. The project will establish a novel approach for understanding the physics of strongly correlated many-body systems. Therefore, the proposed research will pave the way for the implementation of quantum simulators based on fast switchable Rydberg ions as well as for the exploration of the underlying mechanism of symmetry-breaking defect formations. This quantum technology has the potential application for simulating the transport of vibrational excitations along protein chains.

Axions and other very light axion-like particles (ALPs) appear in many extensions of the Standard Model and are well motivated theoretically: ALPs can solve the well-known strong CP problem, act as a dark matter candidate and could also explain the famous muon (g-2) discrepancy. The experimental effort to search for ALPs as dark matter candidates is ongoing and has been considerably intensified in recent years, leading to the proposal and construction of a wide range of dedicated experiments. However, none of these dedicated experiments is sensitive to those ALPs that can explain low-energy anomalies such as (g-2). I propose therefore to pioneer an alternative search strategy for axion-like particles via their decay into two photons, using data collected at the Large Hadron Collider. This approach requires fundamental innovations on the photon identification capabilities of the current detectors as well as radically new analysis strategies. Within the LightAtLHC project, I will study proton-proton and lead-lead collisions, collected during LHC Run-3, and search for Higgs Boson decays in two ALPs as well as the direct production of ALPs via photon fusion and their subsequent decay into two low-energy photons. To achieve the required sensitivity, I will develop highly specialized photon reconstruction algorithms for the ATLAS detector. These efforts will largely cover the relevant parameter space, leaving out only a small region. To also close this gap, I will extend the upcoming FASER experiment at the LHC by an innovative presampler detector, which allows for an unambiguous ALPs detection. By the end of the LightAtLHC project, I can either rule out the most promising ALP models in a mass range from 10 MeV to 1 TeV, or discover a new elementary particle.