This project is an investigation of a new approach to scalable quantum computing and communication. In this approach, small registers consisting of a few coupled quantum bits are coupled to each other by quantum optical communication channels that can be used to establish long-range entanglement and perform remote operations between distant quantum bits. In particular individual electron spins associated with a nitrogen-vacancy (NV) center in diamond coupled coherently to individual nearby carbon-13 nuclear spins in diamond lattice will be explored as qubits. The electron-nuclear spin system can be manipulated coherently and has exceptional coherence properties even at room temperature, indicating a potential for robust quantum memory. Specific goals of the proposed project include (i) detailed understanding of the coherence properties of electron and nuclear spin quantum bits in the solid-state and development of techniques for their accurate, coherent quantum state manipulation; (ii) robust quantum optical entanglement and quantum operations involving remote spin qubits, and (iii) development of robust architectures for quantum communication and quantum computation based on such systems. The ultimate goal of the project is to develop systems for efficient, scalable quantum information processing that can tolerate large imperfections. This work involves a team of researchers from the Harvard University and Texas A&M University. The research will contribute significantly to the knowledge base of Quantum Information Science (QIS). Beyond providing a new avenue toward quantum computation, the experimental approach is ideally suited for the realization of repeater nodes for long-distant quantum communication. The project provides exceptional opportunities for education and training in the new interdisciplinary area involving the interface of several fields of fundamental physics, material science, and device engineering. Innovative graduate and undergraduate courses in these areas will be developed and combined with outreach to local schools and public presentations. Finally, the concepts and techniques developed in this work will likely have a wide range of applications in diverse areas of science and technology.
The main outcome of this project is the development, realization and investigation of the unique new system for quantum information processing. This system involves the use of an atom-like defect in a diamond crystal, the so-called Nitrogen Vacancy (NV) center as an individual quantum bit. The NV center is a localized impurity in which a nitrogen atom is substituted for a carbon atom next to a missing carbon atom in the diamond lattice. This impurity behaves like an artificial atom and has non-zero electronic spin in its ground state, much like the hydrogen atom. By using optical techniques borrowed from Atomic, Molecular and Optical physics and single- molecule spectroscopy to isolate single NV centers within the diamond lattice we demonstrated the ability to manipulate individual electronic and even nuclear spins while maintaining excellent coherence even under ambient conditions at room temperature. (Usually at these temperatures, uncontrolled couplings to thermal excitations in the solid destroy all quantum behavior.) Our key results include the manipulation of small quantum processors composed from up to three electronic and nuclear spins, realization of repetitive, high fidelity readout of individual spins, and the demonstration of quantum memory with lifetime exceeding one second. In addition, we used coupling of individual spins to optical photons to produce spin-photon entangled states and demonstrated spin coupling to phonons in a mechanical resonator. This work laid ground for a realistic approach towards the realization of a solid-state quantum computer operating at room temperature. Finally, the first practical applications of these techniques in nanoscale sensing were explored. Specifically, we used spin qubits in diamond to demonstrate a nano-scale magnetic sensor that offers an unprecedented combination of sensitivity and spatial resolution. We are now exploiting this device for unique applications in biomedical and materials science, such as magnetic resonance imaging of single molecules. In addition, we also demonstrated that spin qubits can be used for local temperature sensing, and already showed that it can be used for monitoring and control of temperature inside living cells.
