Quantum Information Technology Based on Diamond: A Step Towards Secure Information Transfer

The new field of quantum information technology uses qubits (quantum bits) instead of classical bits to carry out certain computation operations or for secure transfer of information (quantum cryptography). There are a number of physical systems that can act as qubits including a wide range of materials and technologies, e.g. ions in traps, local defect states in crystal lattices, superconducting junctions, etc. All these material systems offer different challenges and opportunities for the creation of qubit-based quantum devices. The search for defect states in solids with a capability to store and manipulate quantum information represents a exciting area of research. One of the most promising (and maybe the best studied) defects are the so-called nitrogen-vacancy (NV) centers in diamond, which are perspective candidates for a number of applications, including quantum computation and cryptography. A NV center represents a nitrogen atom in the diamond crystalline lattice adjacent to a vacancy, i.e. a site with a missing carbon atom. The attractiveness of this system stems from the long-lived quantum coherence, which can be initialized, acted upon, and measured using readily available techniques. A particularly exciting feature of these defects is the persistence of long coherence times even at room temperature. Single NV centers can be patterned on demand, and much like atomic defects surrounded by a stable environment (the crystalline lattice), they have highly reproducible properties. In order to exploit the outstanding properties of NV centers by increasing both the photon emission yield and the collection efficiency of the emitted photons, they should be embedded in an optical cavity, e.g. in all-diamond devices like nanopillars, photonic crystals, microrings, etc.