James R. Rabeau

Room-temperature coherent coupling of single spins in diamond

Coherent coupling between single quantum objects is at the very heart of modern quantum physics. When the coupling is strong enough to prevail over decoherence, it can be used to engineer quantum entangled states. Entangled states have attracted widespread attention because of applications to quantum computing and long-distance quantum communication. For such applications, solid-state hosts are preferred for scalability reasons, and spins are the preferred quantum system in solids because they offer long coherence times. Here we show that a single pair of strongly coupled spins in diamond, associated with a nitrogen-vacancy defect and a nitrogen atom, respectively, can be optically initialized and read out at room temperature. To effect this strong coupling, close proximity of the two spins is required, but large distances from other spins are needed to avoid deleterious decoherence. These requirements were reconciled by implanting molecular nitrogen into high-purity diamond.

Observation and control of blinking nitrogen-vacancy centres in discrete nanodiamonds

Nitrogen-vacancy colour centres in diamond can undergo strong, spin-sensitive optical transitions under ambient conditions, which makes them attractive for applications in quantum optics, nanoscale magnetometry and biolabelling. Although nitrogen-vacancy centres have been observed in aggregated detonation nanodiamonds and milled nanodiamonds, they have not been observed in very small isolated nanodiamonds. Here, we report the first direct observation of nitrogen-vacancy centres in discrete 5-nm nanodiamonds at room temperature, including evidence for intermittency in the luminescence (blinking) from the nanodiamonds. We also show that it is possible to control this blinking by modifying the surface of the nanodiamonds.

Coherent population trapping of single spins in diamond under optical excitation

Coherent population trapping is demonstrated in single nitrogen-vacancy centers in diamond under optical excitation. For sufficient excitation power, the fluorescence intensity drops almost to the background level when the laser modulation frequency matches the 2.88 GHz splitting of the ground states. The results are well described theoretically by a four-level model, allowing the relative transition strengths to be determined for individual centers. The results show that all-optical control of single spins is possible in diamond.

Implantation of labelled single nitrogen vacancy centers in diamond using N15

Nitrogen-vacancy (NV−) color centers in diamond were created by implantation of 7 keV N15(I=1∕2) ions into type IIa diamond. Optically detected magnetic resonance was employed to measure the hyperfine coupling of single NV− centers. The hyperfine spectrum from NV−15 arising from implanted N15 can be distinguished from NV−14 centers created by native N14(I=1) sites. Analysis indicates 1 in 40 implanted N15 atoms give rise to an optically observable NV−15 center. This report ultimately demonstrates a mechanism by which the yield of NV− center formation by nitrogen implantation can be measured.

Single nitrogen vacancy centers in chemical vapor deposited diamond nanocrystals

Nanodiamond crystals containing single color centers have been grown by chemical vapor deposition (CVD). The fluorescence from individual crystallites was directly correlated with crystallite size using a combined atomic force and scanning confocal fluorescence microscope. Under the conditions employed, the optimal size for single optically active nitrogen-vacancy (NV) center incorporation was measured to be 60-70 nm. The findings highlight a strong dependence of NV incorporation on crystal size, particularly with crystals less than 50 nm in size.

Five-nanometer diamond with luminescent nitrogen-vacancy defect centers

A study was conducted to investigate the properties of weakly bound clusters of single-digit nanodiamonds (SND) using spectrally and temporally resolved luminescence detection, electron paramagnetic resonance (EPR) spectroscopy, and transmission electron microscopy (SEM). Nitrogen-vacancy (NV) centers were created in diamonds by high-energy proton irradiation followed by thermal annealing. Samples containing equal weights of 55-nm HTHP diamonds and SNDs were uniformly distributed on quartz substrates for luminescence measurements. It was observed that the SNDs exhibited significant luminescence in the red spectral region before irradiation. The emission was blue-shifted and the absence of the zero-phonon lines at 637 and 575 nm indicated that the luminescence did not originate from NV centers as compared with the NV spectrum.

Fabrication of single nickel-nitrogen defects in diamond by chemical vapor deposition

Fabrication of single nickel-nitrogen (NE8) defect centers in diamond by chemical vapor deposition is demonstrated. Under continuous-wave 745nm laser excitation single defects were induced to emit single photon pulses at 797nm with a linewidth of 1.5nm at room temperature. Photon antibunching of single centers was demonstrated using a Hanbury–Brown and Twiss interferometer. Confocal images revealed approximately 106 optically active sites∕cm2 in the synthesized films. The controlled fabrication of an NE8 based single photon source in synthetic diamond is important for fiber based quantum cryptography, and potentially linear optics quantum computing.

Characterization of three-dimensional microstructures in single-crystal diamond

We report on the Raman and photoluminescence characterization of three-dimensional microstructures fabricated in single crystal diamond with a Focused Ion Beam (FIB) assisted lift-off technique. The fabrication method is based on MeV ion implantation, followed by FIB micropatterning and selective chemical etching. In a previous publication we reported on the fabrication of a micro-bridge structure exhibiting waveguiding behavior [P. Olivero, S. Rubanov, P. Reichart, B. Gibson, S. Huntington, J. Rabeau, Andrew D. Greentree, J. Salzman, D. Moore, D. N. Jamieson, S. Prawer, Adv. Mater., 17 (20) (2005) 2427]. In the present work, Raman and photoluminescence spectroscopies are employed to characterize the structural quality of such microstructures, particularly as regards the removal of residual damage created during the machining process. Three-dimensional microstructures in high quality single crystal diamond have many applications, ranging from integrated quantum-optical devices to micro-electromechanical assemblies.

Prediction and Measurement of the Size-Dependent Stability of Fluorescence in Diamond over the Entire Nanoscale

Fluorescent defects in noncytotoxic diamond nanoparticles are candidates for qubits in quantum computing, optical labels in biomedical imaging, and sensors in magnetometry. For each application these defects need to be optically and thermodynamically stable and included in individual particles at suitable concentrations (singly or in large numbers). In this Letter, we combine simulations, theory, and experiment to provide the first comprehensive and generic prediction of the size, temperature, and nitrogen-concentration-dependent stability of optically active N-V defects in nanodiamonds.

CVD-diamond external cavity Raman laser at 573 nm

Recent progress in diamond growth via chemical vapor deposition (CVD) has enabled the manufacture of single crystal samples of sufficient size and quality for realizing Raman laser devices. Here we report an external cavity CVD-diamond Raman laser pumped by a Q-switched 532 nm laser. In the investigated configuration, the dominant output coupling was by reflection loss at the diamonds uncoated Brewster angle facets caused by the crystals inherent birefringence. Output pulses of wavelength 573 nm with a combined energy of 0.3 mJ were obtained with a slope efficiency of conversion of up to 22%.