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Nanoscale spin interactions and dynamics on superconducting surfaces (NanoSpin)
Start date: May 1, 2014, End date: Apr 30, 2019 PROJECT  FINISHED 

The latest concepts for quantum computing and data storage envision the use of single spins, which can be addressed and manipulated reliably. One of the main limitations towards this challenging goal is the ultra-short lifetime of excited spin states due to the interaction with the contacting leads. Another limitation is that coherence between individual spins is quickly lost. Already the measurement process for resolving coherent electron-spin interactions at the single atom level is highly challenging and has not been achieved so far.Within our proposal, we will construct a low-temperature scanning tunneling microscope with a radio-frequency current detection system and a microwave source close to the tip. With this unique machine, we will be able to carry out state-of-the-art STM experiments combined with atomic-scale precision of measuring electron-spin resonance signals. With the approach of measuring in the frequency domain, we increase our energy resolution beyond the thermal energy level broadening into the µeV range and can thus investigate magnetic coupling, hyperfine interactions and spin coherence properties, which are not accessible in conventional STM experiments. We will also be able to probe the timescales of spin-lattice and spin-spin relaxations by pump-probe excitation schemes.We will use this machine for resolving magnetic properties of single atoms and atomic-size nanostructures on superconducting substrates. These substrates exhibit two peculiarities, which are of crucial importance for quantum information processing. The spin lifetimes are orders of magnitudes larger than on normal metal surfaces. Furthermore, the long coherence length of Cooper pairs mediates coherent coupling of the spin states of paramagnetic atoms. We will manipulate the spin states by the intrinsic Josephson current as well as with external microwave radiation. Our model systems on superconductors will provide crucial steps towards quantum spin processing.
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