Color center qubits are encoded in electron orbital and spin eigenstates associated with single- or few- atomic impurities in solid-state host crystals, most commonly diamond. The nitrogen-vacancy (NV) center in diamond is the most widely studied system in the field of coherent optically active quantum defects owing to its long coherence time even at room temperature and the possibility of optical measurement of spin states through spin-dependent fluorescence.
While there are ongoing numerous efforts to realize a position-controlled, dense array of NV centers toward integrated quantum chips in diamond, deterministically positioning NV centers with atomic resolution is challenging. Another possibility is to use naturally given, coherent resources around an NV center, the 13C nuclear spins having spin-1/2. In this case NV center can be a sensitive probe of surrounding 13C nuclear spins, and through hyperfine interaction, quantum operation on the 13C nuclear spins can be also performed. In DKim lab at SNU, we are actively studying advanced quantum and classical control schemes toward realization of coherently controllable electron-nuclear spin registers in diamond.
Measurement and control of e-n spin register
Project description: NV center + surrounding nuclear spin system offers a unique platform to study coherent quantum dynamics using the NV center as a sensitive probe and nuclear spins as coherent resources. Through dynamical decoupling and single-shot measurement at cryogenic temperatures, we are developing methods to efficiently control the electron-nuclear spin register in the diamond. The project includes building a cryogenic quantum measurement set-up with single-shot capability, fabrication of diamond nanostructures, and material process development for generating stable quantum defects in diamond.
Machine learning approach for nuclear spectroscopy
Project description: Localizing individual nuclear spins is the essential step to build coherently controllable spin resisters, which provides us with a robust base for the quantum networks, quantum simulation platforms, or quantum memory. Based on artificial neural networks, we develop novel ways to automatically characterize atomic resolution NMR spectrum and extract hyperfine interaction parameters from experimental data. The long term goal of this project is to build a unified machine learning model capable of detecting > 50 nuclear spins around an NV center and at the same time characterize nuclear-nuclear interactions that can lead to 3D localization of nuclear spins.
Quantum sensing applications of NV centers
Project description: Among many possible applications using NV centers, we focus on using NV centers for highly sensitive quantum metrology, especially detecting small nuclear magnetic fields and temperature. The project includes the development of novel pulse sequences for ac and dc measurement using spin-echo and dynamic decoupling sequences and compact integrated quantum sensors for practical applications.