Correlations are central for our modern view on the foundations of quantum theory and applications like quantum information processing. So far, research concentrated on correlations between two or more particles. Indeed, for this situation it is well established that spatial quantum correlations are a useful resource for tasks like quantum cryptography and quantum metrology. There are, however, other types of correlations in quantum mechanics, which arise if a sequence of measurements on a single quantum system is made. These temporal quantum correlations have recently attracted attention, because they are central for the understanding of some differences between the quantum and the classical world. Moreover, due to experimental progress their observation has become feasible with trapped ions, polarized photons, or other quantum optical systems. This project aims at a full understanding and characterization of temporal quantum correlations. For that, we will derive criteria and measures for temporal quantum correlations and investigate their connection to information theory. Then, we will elucidate to which extent temporal correlations can be used to prove that a system is quantum and not classical. Finally, we consider implementations of temporal quantum correlations using continuous variable systems like nanomechanical oscillators and applications in quantum information processing.

Quantum computers hold the promise to efficiently solve certain computational problems that would be intractable using conventional computers. The latter are not able to efficiently incorporate quantum phenomena arising with superposition of states or entanglement. In order to realize a large-scale quantum computer, it is imperative to have superior control over the efficiency and reliability of already available quantum operations. Trapped ions, being a scalable quantum system, envisage the experimental realization of a large-scale universal quantum computer. The proposed project will demonstrate a novel route to implement a Quantum Fourier Transform (QFT), a crucial component of many quantum algorithms, in a small-scale quantum information processor based on a string of singly charged ytterbium ions confined in a linear Paul trap. In presence of a magnetic field gradient-induced coupling, simultaneous interaction between all pairs of qubits will be exploited for efficient execution of quantum algorithms. Thus, instead of decomposing a given quantum algorithm into its smallest possible elementary constituents (1- and 2-qubit gates), multi-qubit conditional quantum dynamics will be used to implement a QFT. Experiment and theory will collaborate at all stages to streamline the project. New collaborations will be established allowing to combine the tremendous knowledge and expertise already existing in the field. The breakthroughs envisioned in the project are, to explore and implement simultaneous couplings between N ≥ 4 qubits allowing for efficient execution of quantum algorithms, and to implement a Quantum Fourier Transform with N ≥ 4 qubits pointing into the future capability of realizing a large number factorization using a quantum factoring algorithm. In addition, career development plans are proposed to assist the fellow acquire new skills enabling a high level of professional maturity and independence to lead a successful career in academia.

The proposed project aims at the development of novel functional ligands whose association with ribonucleic acid (RNA) is reversibly activated by light. As several RNA forms are essential key elements in physiological processes, the control of their function or malfunction by the reversible binding of photoswitchable ligands possesses a great potential as a tool in anticancer, antiviral and antimicrobial therapy. Surprisingly, this innovative approach towards a controlled reversible generation of RNA binders was mainly neglected in this highly topical research field. Hence, in this project photochromic hemi-indigo and fulgide derivatives are chosen as a platform for the design of photo-responsive RNA ligands, because i) they exhibit general features of RNA binders; ii) their structure can be reversibly modified by light, iii) the core structures are readily synthesized, and iii) the substitution pattern can be easily varied to enable fine-tuning of binding selectivity based on structure-activity relationships. In addition, conjugates that comprise two photoactive RNA-binding units will be obtained and studied because such bifunctional binders are expected to have very high affinity and selectivity toward RNA. An extensive library of derivatives will be synthesized and tested for their photocontrollable association with RNA. As a special method, real-time NMR-spectroscopic studies with direct irradiation of the sample inside a specifically designed spectrometer will be used to assess in detail the dynamics in the course of the photoinduced ligand–RNA interactions. Overall, it is anticipated that this systematic approach will enable the identification and development of lead structures for controllable RNA-targeting drugs with a great pharmacological potential. Moreover, the high interdisciplinary, innovative character of this challenging project gives the researcher an excellent opportunity to achieve professional maturity and open up best career possibilities.

Lateral junctions between two-dimensional (2D) semiconductors are conceptually the smallest possible electronic devices. This project investigates the basic physics of these systems as the type of band alignment, the band bending and depletion region, which are decisive parameters for any application. Semiconductor junctions composed of 2D transition metal dichalcogenides (TMDs) will be prepared on hexagonal boron nitride (hBN) or graphene (Gr) on Ir(111). The use of the single-crystalline metal substrate allows the application of surface science methods for preparation and characterization, while the ultrathin buffer layer leaves the intrinsic properties of TMDs undisturbed. Intercalation of guest atoms between the buffer layer and Ir will be used as an elegant and non-invasive method for doping the TMDs. This will also tune intrinsic band bending at the 1D-interface of the TMD junctions, which is yet to be explored for various 2D systems. To separate the effect of inhomogeneous doping and inhomogeneous structure, two types of lateral TMD junctions will be prepared: Homojunctions will be achieved by doping only one part of the TMD island by extending it over the interface of intercalated patches in hBN. Heterojunctions will be composed of two different TMD materials grown on homogeneous vdW substrate, either fully intercalated or pristine. Samples will be prepared by combining two TMDs (ReS2 and WS2) and two dopants (n and p). Scanning tunneling spectroscopy (STS) and Kelvin probe force microscopy (KPFM) will be used for the characterization of the 1D-interfaces and the reconstruction of the band diagrams. Dielectric screening induced by the substrate will be analyzed by comparing values of the band gaps and shifts of critical energy points between different systems. This will deepen the understanding of the origin of band bending in 2D systems. Inelastic electron tunneling spectroscopy (IETS) will be used as a potentially new technique for detecting excitons.