Coherence properties of a single dipole emitter in diamond

On-demand, high repetition rate sources of indistinguishable, polarised single photons are the key component for future photonic quantum technologies. Colour centres in diamond offer a promising solution, and the narrow line-width of the recently identified nickel-based NE8 centre makes it particularly appealing for realising the transform-limited sources necessary for quantum interference. Here we report the characterisation of dipole orientation and coherence properties of a single NE8 colour centre in a diamond nanocrystal at room-temperature. We observe a single photon coherence time of 0.21 ps and an emission lifetime of 1.5 ns. Combined with an emission wavelength that is ideally suited for applications in existing quantum optical systems, these results show that the NE8 is a far more promising source than the more commonly studied nitrogen-vacancy centre and point the way to the realisation of a practical diamond colour centre-based single photon source.Comment: 10 pages, 4 colour figure

Nanodiamond-enhanced MRI via in situ hyperpolarization

Nanodiamonds are of interest as nontoxic substrates for targeted drug delivery and as highly biostable fluorescent markers for cellular tracking. Beyond optical techniques, however, options for noninvasive imaging of nanodiamonds in vivo are severely limited. Here, we demonstrate that the Overhauser effect, a proton–electron polarization transfer technique, can enable high-contrast magnetic resonance imaging (MRI) of nanodiamonds in water at room temperature and ultra-low magnetic field. The technique transfers spin polarization from paramagnetic impurities at nanodiamond surfaces to 1H spins in the surrounding water solution, creating MRI contrast on-demand. We examine the conditions required for maximum enhancement as well as the ultimate sensitivity of the technique. The ability to perform continuous in situ hyperpolarization via the Overhauser mechanism, in combination with the excellent in vivo stability of nanodiamond, raises the possibility of performing noninvasive in vivo tracking of nanodiamond over indefinitely long periods of time

Room temperature coherent control of coupled single spins in solid

Coherent coupling between single quantum objects is at the heart of modern quantum physics. When coupling is strong enough to prevail over decoherence, it can be used for the engineering of correlated quantum states. Especially for solid-state systems, control of quantum correlations has attracted widespread attention because of applications in quantum computing. Such coherent coupling has been demonstrated in a variety of systems at low temperature1, 2. Of all quantum systems, spins are potentially the most important, because they offer very long phase memories, sometimes even at room temperature. Although precise control of spins is well established in conventional magnetic resonance3, 4, existing techniques usually do not allow the readout of single spins because of limited sensitivity. In this paper, we explore dipolar magnetic coupling between two single defects in diamond (nitrogen-vacancy and nitrogen) using optical readout of the single nitrogen-vacancy spin states. Long phase memory combined with a defect separation of a few lattice spacings allow us to explore the strong magnetic coupling regime. As the two-defect system was well-isolated from other defects, the long phase memory times of the single spins was not diminished, despite the fact that dipolar interactions are usually seen as undesirable sources of decoherence. A coherent superposition of spin pair quantum states was achieved. The dipolar coupling was used to transfer spin polarisation from a nitrogen-vacancy centre spin to a nitrogen spin, with optical pumping of a nitrogen-vacancy centre leading to efficient initialisation. At the level anticrossing efficient nuclear spin polarisation was achieved. Our results demonstrate an important step towards controlled spin coupling and multi-particle entanglement in the solid state

Production of multiple diamond-based single-photon sources

Fluorescent emitters in diamond are considered to be a valuable resource for fields such as quantum communication, quantum photonics, and biological imaging. In this paper, we report a wide range of narrow bandwidth ( ~ 1.5 nm) spectral emission lines arising from different color centers at room temperature. The defects were created by chemical vapor deposition of thin diamond films grown on silica substrates seeded with nanoparticles of diamond and nickel. These fluorescent lines also possess single or few centers photon statistics. We correlate the zero-phonon lines, observed using confocal microscopy, with previously identified nickel-related centers which have been observed in high-pressure high-temperature diamond, with a Si/Ni complex and silicon vacancy defects. We compare our findings with recent results demonstrating single-photon emission in diamond associated with nickel-related centers to clarify and summarize previous studies concerning this specific dopant. The great variety of emission lines observed in the synthesized material, mainly associated with nickel-related centers, could be an important resource for applications relying on the presence of several emitters of single photons in the same sample. Moreover, the possibility of mass production of these centers in nanodiamonds in colloidal suspension may provide an important resource for biomarking and microscopy.7 page(s

Spin polarization in single spin experiments on defects in diamond

Generation of pure spin states is an important step towards coherent control of single spin systems. Especially for nitrogen-vacancy defects in diamond, where readout of single spins using optical detection is available, fast initialization of spin is significant in the context of quantum computing applications. In this system the spin polarization is caused by an intersystem crossing process via the metastable singlet state 1A. The slowest relaxation rate is the intersystem to the triplet ground-state 3A on a timescale of 400 ns. The intersystem crossing process mainly populates the ms = 0 spin sublevels of the paramagnetic ground state. Although no direct nuclear spin polarization is seen for low magnetic fields, frequency selective microwave pulses can be used to transfer electron spin polarization to ¹³C nuclear spin states.6 page(s

Processing 15-nm nanodiamonds containing nitrogen-vacancy centres for single-molecule FRET

Colour centres in nanodiamonds have many properties such as chemical and physical stability, biocompatibility, straightforward surface functionalisation as well as bright and stable photoluminescence, which make them attractive for biological applications. Here we examine the use of fluorescent nanodiamonds containing a single nitrogen-vacancy (NV) centre, as an alternative nano-label over conventional fluorophores. We describe a series of chemical treatments and air oxidation to reliably produce small (∼15nm) oxidised nanodiamonds suitable for applications in bioscience. We use Frster resonance energy transfer to measure the coupling efficiency from a single NV centre in a selected nanodiamond to an IRDye 800CW dye molecule absorbed onto the surface. Our single-molecule Frster resonance energy transfer analysis, based on fluorescence lifetime measurements, locates the position of the photostable NV centre deep within the core of the nanodiamond.8 page(s