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Lasersystem für die Detektion einzelner Farbzentren in Festkörpern

Subject Area Condensed Matter Physics
Term Funded in 2013
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 240249468
 
Final Report Year 2017

Final Report Abstract

Laser system for selective excitation of single colour centers was installed at Ulm University. Using new lasers we have been able to show that new color centers associated with silicon and germanium possess unique photophysical properties making them promising as elements of quantum light matter interface. 1. Multiple intrinsically identical single-photon emitters in the solid state. Emitters of indistinguishable single photons are crucial for the growing field of quantum technologies. To realize scalability and increase the complexity of quantum optics technologies, multiple independent yet identical single-photon emitters are required. However, typical solid-state single-photon sources are inherently dissimilar, necessitating the use of electrical feedback or optical cavities to improve spectral overlap between distinct emitters. We have been able to demonstrate bright silicon vacancy (SiV-) centres in low-strain bulk diamond, which show spectral overlap of up to 91% and nearly transform-limited excitation linewidths in bulk diamond and nanodiamonds. This is the first time that distinct single-photon emitters in the solid state have shown intrinsically identical spectral properties. We also have been able to demonstrate that silicon-vacancy (SiV) centers in diamond can be used to efficiently generate coherent optical photons with excellent spectral properties. We show that these features are due to the inversion symmetry associated with SiV centers. The generation of indistinguishable single photons from separated emitters at 5 K is demonstrated in a Hong-Ou- Mandel interference experiment. 2. Spectroscopy of SiV and GeV centers in diamond and unraveling of their energy level structure. The negatively charged silicon-vacancy (SiV-) center in diamond is a promising single-photon source for quantum communications and information processing. However, the center's implementation in such quantum technologies is hindered by contention surrounding its fundamental properties. Wer were able to realise optical polarization measurements of single centers in bulk diamond that resolve this state of contention and establish that the center has a split-vacancy structure. Optical transition line widths, transition wavelength and excited state lifetimes are measured for the temperature range 4 K-350 K. The ground state orbital relaxation rates were measured using time-resolved fluorescence techniques. A microscopic model of the thermal broadening in the excited and ground states of the SiV-centre was developed. A vibronic process involving single-phonon transitions was found to determine orbital relaxation rates for both the ground and the excited states at cryogenic temperatures. In addition to optical spectroscopy of electronic state we were able to demonstrate optical access to spin states. We were able to show optical initialization and readout of electronic spin in a single SiV- center with a spin relaxation time of 2.4 ms. Coherent population trapping (CPT) was used to demonstrate coherent preparation of dark superposition states with a spin coherence time of 35 ns. Hyperfine structure was observed in CPT measurements with the Si29 isotope which allows access to nuclear spin. We reported a novel color center in diamond, composed of a germanium (Ge) and a vacancy (V) and named the GeV center, which has a sharp and strong photoluminescence band with a zerophonon line at 602 nm at room temperature (and higher quantum yield compared to SiV defect). We demonstrated that this new color center works as an efficient single photon source. Both ion implantation and chemical vapor deposition techniques enabled fabrication of GeV centers in diamond. A first-principles calculation revealed the atomic crystal structure and energy levels of the GeV center. We were able to demonstrate an efficient spin polarization using optical pumping and optically detected magnetic resonance (ODMR). 3. An integrated diamond nanophotonics platform for quantum-optical networks. Quantum light–matter interfaces operating at optical wavelengths are key to emerging applications in quantum information processing such as distributed quantum computing and secure quantum communication. In the past decade, such interfaces have been successfully implemented across platforms ranging from trapped atoms and ions to quantum dots to defect centers in diamond. Spectroscopy of new colour centers based on Si and Ge dopants allowed us to demonstrate key elements of quantum networks. By placing SiV centers inside diamond photonic crystal cavities, we realized a quantum-optical switch controlled by a single color center. We were able to control the switch using SiV metastable states and observe optical switching at the single photon level. Raman transitions were used to realize a single-photon source with a tunable frequency and bandwidth in a diamond waveguide. By measuring intensity correlations of indistinguishable Raman photons emitted into a single waveguide, we have been able to observe a quantum interference effect resulting from the superradiant emission of two entangled SiV centers.

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