Session V3: Controlling Quantum Interactions of Single Spins and Photons in Diamond

Spin quantum measurements on diamond defects

Diamond defects allow for precise measurement of single electron and nuclear spin quantum states. The excellent controllability of these spins as well as efficient decoupling from environment make them an ideal playground for engineering complex quantum states and development of elaborate control schemes. The talk will describe how nuclear spin states can be efficiently read-out and used as Qbits in spin clusters. Routs towards the controlled engineering of extended spin arrays as well as coupling to control structures will be discussed.   

Observation of spin-light coherence for single spin measurement and control in diamond

The long spin coherence and optical addressability of nitrogen-vacancy (NV) centers in diamond makes them excellent candidates for studies of quantum information science with potential technological applications. We demonstrate the coherent coupling of light to the electronic spin of a single NV center for both non-destructive, single-spin readout via the Faraday effect and unitary, single-spin control via the optical Stark effect\footnote{B. B. Buckley, G. D. Fuchs, L. C. Bassett, D. D. Awschalom, {\em Science Express} (DOI: 10.1126/science.1196436)}. By monitoring the Faraday effect of laser light focused on a single NV center and detuned from optical resonances, we are able to read out an NV center's spin state without destroying it, in contrast to traditional spin readout techniques which polarize the spin during measurement. In a complimentary way, the spin coherently rotates in response to the light through the optical Stark effect, which we demonstrate as a method of all-optical spin control. These measurements have important consequences for future single-spin quantum non-demolition measurements and spin-photon entanglement schemes in diamond that may be exploited for the development of quantum repeater technologies and photonic coupling of spins over large distances.   

Quantum entanglement between an optical photon and a solid-state spin qubit

Quantum entanglement is among the most fascinating aspects of quantum theory. In this work quantum entanglement between the polarization of a single optical photon and a solid-state spin qubit is realized. The experimental entanglement verification demonstrates that a high degree of control over interactions between a solid-state qubit associated with the single electronic spin of a nitrogen vacancy centre in diamond and the quantum light field can be achieved. The reported entanglement source can be used in studies of fundamental quantum phenomena and provides a key building block for the solid-state realization of quantum optical networks.\footnote{Quantum entanglement between an optical photon and a solid-state spin qubit, Nature 466, 730-734, (2010)}   

Coupling single electron spins in diamond to integrated optical structures

Diamond is an attractive material for some electronic and photonic applications because of its excellent chemical stability and high thermal conductivity and carrier mobility. Diamond appears to be an excellent material for quantum information processing and magnetic sensing applications as well, with many optically active paramagnetic centers. Of these, the most carefully studied to date has been the nitrogen-vacancy (NV) color center, since it is optically addressable and can exhibit electron spin coherence lifetimes exceeding 1 ms at room temperature. This long-lived coherence is usually attributed to the nuclear spin-zero environment of the diamond lattice, which can be further improved with isotopic purification. These capabilities have recently allowed for some remarkable demonstrations in this system such as controlled coupling between single electronic and nuclear spins. For quantum information technologies, NV centers that are mutually optically coupled could enable long-distance quantum communication through repeaters. However, given the low branching ratio of natural emission from NV centers in bulk diamond into the zero phonon line, coupling these centers to cavities with at least moderately large Purcell factors is a critically important step. In this talk I will describe our recent progress in realizing microcavities with low loss and small mode volume in two hybrid systems: silica microdisks coupled to diamond nanoparticles, and gallium phosphide microdisks coupled to single-crystal diamond. In both cases, we have demonstrated coupling between NV centers and whispering-gallery-type cavity modes. Finally, I will present our most recent progress toward fabricating waveguides and microcavities directly in diamond.   

Quantum control and decoherence of a single spin in diamond

Nitrogen-vacancy (NV) impurity centers in diamond have recently emerged as a unique platform for investigating quantum dynamics and quantum control of single spins in solid-state environments. NV centers demonstrate an unusual combination of spin-dependent optical properties, individual addressability, and long spin coherence times. The NV spin state can be manipulated both optically and magnetically, and very fast quantum control operations can be performed with high fidelity [1,2]. Due to these uniquely favorable properties, quantum dynamics of a single NV spin can be investigated in great detail. I will present the results of our work on decoherence of NV spins by spin baths of atomic nitrogen impurities (P1 centers) and the spins of $^{13}$C nuclei, and discuss different regimes of the decoherence dynamics. We will consider modern dynamical decoupling techniques which aim at preserving coherence of quantum spins, and the experimental implementation of the decoupling protocols, as well as more advanced quantum control of NV spins. Using a variety of analytical and numerical tools, we can characterize and optimize the factors which limit our control over these quantum spin systems [2]. We will also examine how the quantum control approaches can be used to elucidate the quantum dynamics of NV centers and the properties of the spin bath [3]. \\[4pt] [1] G. D. Fuchs, V. V. Dobrovitski, D. M. Toyli, F. J. Heremans, and D. D. Awschalom, Science 326, 1520 (2009).\\[0pt] [2] V. V. Dobrovitski, G. de Lange, D. Riste, and R. Hanson, Phys. Rev. Lett. 105, 077601 (2010).\\[0pt] [3] G. de Lange, Z. H. Wang, D. Riste, V. V. Dobrovitski, and R. Hanson, Science 330, 60 (2010).