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978-3-8439-1974-6, Reihe Physik
The nitrogen vacancy center in internal and external fields
170 Seiten, Dissertation Universität Stuttgart (2014), Hardcover, A5
This dissertation investigates applications of the Nitrogen vacancy in diamond (NV). The NV is a unique quantum system allowing for optical polarization and read out of its electron spin even at ambient conditions. Its electron spin (S=1) has coherence times in the order of milliseconds and is therefore an ideal candidate to investigate the foundations of quantum mechanics as well as exploiting quantum effects in metrology and information processing applications.
To utilize the NV for quantum technologies, first the interaction of the NV with its surroundings has to be investigated. Here dynamical decoupling sequences (CPMG) were used to extend the NV coherence time to a few milliseconds by decoupling the NV from its surrounding spin bath. But the spin bath is not only a nuisance limiting NV coherence, but also a potential resource for quantum technologies. In order to harness the individual 13C nuclear spins, their interaction has to be investigated. To not be limited by the NV coherence times, a new spectroscopy method, only limited by the NV lifetime, was developed. This can in principle be extended by using a nuclear spin memory.
First advances in quantum technology were demonstrated in the field of metrology, where the Zeeman effect of the NV center allowed for precise nanoscale measurement of magnetic fields. This concept was extended to us the Stark effect to detect electric fields. A sensitivity of 142.6±3.6 V/(cmHz^1/2) was demonstrated, equivalent to the detection of a fundamental charge at a distance of 150 nm in one second. By using two NVs, the detection of nanoscale single fundamental charge was feasible.
Another keystone of quantum technology is the reliable on demand or heralded creation of entanglement. Here the successful entanglement of two electron spins in solid state at ambient conditions is demonstrated. In order to be able to harness weaker dipolar couplings, an entanglement protocol based on dynamical decoupling was developed. A fidelity of F=0.67±0.04 was demonstrated. By using the intrinsic nuclear spins of the nitrogen, it was possible to store the entangled state on the millisecond time scale. However, the theoretical limit for the fidelity given by the polarization and the coherence times is F=0.849. The discrepancy can be explained by pulse errors. These can be avoided by using optimal control yielding a fidelity of F=0.824±0.015. These experiments are first steps towards a room temperature quantum register.