Quantum Magnetism

The Quantum Magnetism group focuses on exploring the quantum states, e.g. spins, in artificially built atomic and molecular structures on surfaces and on designing their quantum functionalities in pursuit of quantum information science, quantum sensing, and quantum simulations at the atomic scale. As electronic devices are scaled down to the point where quantum size effects become prominent, individual quantized states of charge, spin or light play central roles in determining the electronic, magnetic and optical properties of the system. It is thus critical to resolve and control these individual quantum states, which requires highly advanced techniques. In our research, the enabling technique is scanning tunneling microscopy (STM) integrated with electron spin resonance (ESR), which combines single spin sensitivity with atomic resolution.

Quantum coherent manipulation of atomic and molecular spin structures
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The last few decades have witnessed remarkable revolutions in the field of quantum information science, driven by the desire to utilize quantum states for transmitting and processing information. While various material platforms have been extensively studied to find optimal systems with robust coherence properties, the realization of reliable quantum devices strongly depends on precise lab fabrication procedures. To tackle this challenge, we achieve atomic precision in building quantum architectures through a bottom-up approach, and control their spin states in a coherent manner using the ESR-STM technique as both a manipulation and a read-out tool. With this capability in our experiments, our special focus lies on material systems such as unpaired electrons in carbon-based nanomaterials and atomic spin centers in molecular frameworks.

Atomic scale quantum sensing
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Quantum sensing harnesses the innate sensitivity of quantum systems to external perturbations, enabling precise measurements of physical quantities. The most prevalent platforms like color centers in insulators and superconducting circuits excel in detecting magnetic or electric fields, but ultimate spatial resolution remains elusive. In contrast, conventional scanning probe techniques, such as STM, achieve atomic-scale resolution routinely. By functionalizing the STM probe tip with ESR-active spin centers, we aim at realizing a mobile quantum sensor whose spin state can be read out electrically and provides highest sensitivity to electric and magnetic fields. We anticipate that such mobile single atom / molecule sensing and read-out unit can further facilitate the characterization of spin ordering in newly emerging materials, thereby advancing the application of quantum sensing technologies to the realm of atomic scale quantum materials.

Atomic scale quantum simulation
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Strongly interacting (quasi)particles are the main source of many interesting physical phenomena such as superconductivity, magnetism, topological and other exotic behaviors of matter. The construction and characterization of atomically precise structures to simulate this kind of interacting fermionic systems have been an ambition in pursuit of analogue quantum simulation. Based on an on-surface synthesis approach, we aim at building up interesting quantum spin systems with atomic precision and at characterizing the resulting collective spin states, which gives atomic scale access to the underlying quantum many-body states.