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Quantum Interfaces and Processors in Semiconductors

Scalable qubit systems

Color centers in diamond and silicon carbide (SiC) are excellent quantum bits (qubits) due to their long coherence and short quantum gate times. In order to develop scalable quantum photonic systems, we develop material processing techniques for fabricating nanopillar arrays that host individual color centers. The nanopillars provide an efficient optical interface for manipulation and readout of the quantum emitter. We study silicon-vacancy (SiV) center in Stanford Diamond Collaboration with Chu, Shen and Melosh groups and silicon vacancy center in 4H-SiC in an international collaboration with Wrachtrup (Germany), Son (Sweden) and Ohshima (Japan) groups.

In the silicon carbide system, we study the silicon vacancy center as a spin-qubit operating at room temperature and use the nanopillar interface to optically read out its microwave driven spin-resonance (Figure 1a). In the diamond system, we perform complete coherent control of the optical transition of single SiV centers in nanopillars using picosecond pulses (Figure 1b-c). 

Emitter-Cavity systems

One of the important components for building a solid-state spin based quantum network interconnected with photons is an efficient spin-photon interface. A cavity-based spin-photon interface provides a solution for enhancing the coherent emission of photons into the zero-phonon line (ZPL), and can additionally act as an ultrafast single photon source, which finds applications in a broad range of quantum technologies. We investigate both monolithic and hybrid approaches to build such emitter-cavity systems.

In one monolithic approach, we demonstrate strong enhancement of spontaneous emission rate of a single silicon-vacancy center in diamond embedded within monolithic optical cavities (Fig 2a-b), reaching a regime where the excited state lifetime is dominated by the spontaneous emission into the cavity mode. In addition, direct growth of high quality diamond nanocrystals containing SiV and Cr-related color centers on SiC microdisk resonators provide a novel hybrid approach. In this system, we observed cavity enhanced emission signal at low temperatures, as shown in Fig. 2c.

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