Chemical Approaches to Quantum Science and Technology

The first quantum revolution already delivered such diverse benefits as lasers and magnetic resonance tomography, and allowed the development of semiconductor technologies. In recent years, the second quantum revolution has been gaining momentum. Here the focus is on developing a range of high-impact technologies that all benefit from quantum effects, such as superposition, coherence and entanglement. Such quantum technologies include quantum communication, quantum simulation, quantum computing and quantum sensing. Quantum communication employs specially prepared (entangled) photons to ensure that the channel is secure, before communication takes place. Quantum simulation and quantum computing promise exponentially faster computation speeds that will allow calculations that will never be tractable with current and future classical computers. Finally, quantum sensing uses sensors that detect electromagnetic fields or (biomedical) analytes with unprecedented precision. At the core of all quantum technologies are the quantum bits. Where classical bits can only assume values of “0” or “1”, quantum bits can be in superposition states of “0” and “1”. In colloquial terms, they can be “0” and “1” at the same time. Many platforms are currently being investigated at the University of Stuttgart and beyond for their potential in quantum technologies. These platforms range from photonics for quantum communication, to superconducting circuits for quantum computing, to colour centres in diamond for quantum sensing. Several PIs of the Faculty of Chemistry and Materials Science are active fellows of the Centre for Integrated Quantum Science and Technology IQST, which was founded over a decade ago by the Universities of Ulm and Stuttgart, in cooperation with the Max Planck Institute of Solid-State Research.

In fact, no platform has so far emerged that is generally applicable for all quantum technologies. Furthermore, in spite of great promise, and first commercialization attempts, no market breakthrough has been achieved. The reason for this lies in significant limitations of current quantum technological platforms, including scalability (many applications require millions of qubits), precise positioning of qubits, and tailoring of qubits to specific applications. These challenges may be overcome by using chemical quantum architectures.

In the Faculty of Chemistry and Materials Science we work on the synthesis, characterization and modelling of novel quantum materials. A special emphasis is given to the precise synthesis of molecular quantum bits of different structures such as organic radical species, transition metal complexes and open-shell main group compounds. These are characterized by advanced spectroscopic methods especially based on electron paramagnetic resonance (EPR). Furthermore, optical and electrical addressing of the qubits is investigated. This is supported by theoretical calculations enabling the rational design of novel quantum materials and gaining a deeper understanding of their properties.

Additionally, diamond based materials with colour centres are synthesized using chemical vapour deposition techniques. Namely, the nitrogen vacancy centre (NV centre) is a promising structure for quantum applications due to its stability and the possibility for quantum operations at room temperature. These materials are investigated in close collaboration with experimental and theoretical groups in physics.

We are working on the synthesis and production of highly defined diamond materials with colour centers and apply them for quantum sensing, e.g. in biological environments. Furthermore, we are synthesizing molecular quantum systems and work on their self-assembly in 2D. We also work on diamond-molecular hybrid systems to harness the beneficial properties of both classes of quantum materials.

Two- or one-dimensional confinement of electrons is realised in three dimensional crystal structures via anisotropic chemical bonding. Resulting phenomena are superconductivity, one dimensional metals or topologically non-trivial phases. Employing electrochemistry to change the crystal and electronic structure (“thermodynamic lever”), in combination with in-situ diffraction we try to reveal the interplay of structures and properties.

We work on the deposition of molecular quantum bits on surfaces and on the realization of plasmonic metasurface resonators to enhance magnetic fields on two dimensions. These resonators will be used to extend the investigation of molecular quantum bits on surface to Terahertz frequencies.

We investigate the electronic structure of potential molecular quantum bits by ab initio computations and model Hamiltonian simulations. We are interested in understanding spin-phonon and spin-spin interactions in order to understand dephasing mechanisms and enhance quantum bit lifetimes.