Centers In Nanodiamonds Research Articles

Optical localization of a nitrogen-vacancy center in three-dimensional space via probe absorption

We demonstrate the three-dimensional localization of a single nitrogen-vacancy (NV) center in nanodiamond by the use of position-dependent standing-wave laser fields in an external magnetic field. We show that various localization phenomena including cask-like, disc-like, cylinder-like, and sphere-like patterns can be achieved by monitoring the probe absorption spectrum in two different coupling formalisms. By selecting an appropriate combination of system parameters, we can localize an individual NV center within a subspace at a deterministic position, which is a consequence of quantum interference. Furthermore, this deterministic positional control of coherent NV centers may have potential applications in NV-based nanostructures, such as sensing and quantum information-processing devices.

Spectrally selective modification in the emission lifetimes of nitrogen-vacancy centers in nanodiamonds

The nitrogen-vacancy (NV) center is one of the most prominent candidates for quantum technologies, and its efficient utilization requires control over its spontaneous emission rate. Here, we report the wavelength-selective enhancement and suppression of NV center emission lifetime at room temperature by modifying the local density of optical states (LDOS) around them. The results are explained using the Barnett–Loudon sum rule and also supported by the LDOS calculations. Two complementary measurement geometries are employed to study the direction-dependent emission behavior from the nanodiamonds decorated on the top of photonic crystals. The lifetime distributions are compared with a proper reference sample using the Kolmogorov–Smirnov test to verify the distinct nature of lifetime distributions. The wavelength-selective enhancement or suppression of emission rates would be useful for NV center-based high-resolution imaging and effective readout of its charge states.

Nanoscale Dynamic Readout of a Chemical Redox Process Using Radicals Coupled with Nitrogen-Vacancy Centers in Nanodiamonds.

Biocompatible nanoscale probes for sensitive detection of paramagnetic species and molecules associated with their (bio)chemical transformations would provide a desirable tool for a better understanding of cellular redox processes. Here, we describe an analytical tool based on quantum sensing techniques. We magnetically coupled negatively charged nitrogen-vacancy (NV) centers in nanodiamonds (NDs) with nitroxide radicals present in a bioinert polymer coating of the NDs. We demonstrated that the T1 spin relaxation time of the NV centers is very sensitive to the number of nitroxide radicals, with a resolution down to ∼10 spins per ND (detection of approximately 10-23 mol in a localized volume). The detection is based on T1 shortening upon the radical attachment, and we propose a theoretical model describing this phenomenon. We further show that this colloidally stable, water-soluble system can be used dynamically for spatiotemporal readout of a redox chemical process (oxidation of ascorbic acid) occurring near the ND surface in an aqueous environment under ambient conditions.

Reduction of surface spin-induced electron spin relaxations in nanodiamonds

Nanodiamonds (NDs) hosting nitrogen-vacancy (NV) centers are promising for applications of quantum sensing. Long spin relaxation times (T1 and T2) are critical for high sensitivity in quantum applications. It has been shown that fluctuations of magnetic fields due to surface spins strongly influence T1 and T2 in NDs. However, their relaxation mechanisms have yet to be fully understood. In this paper, we investigate the relation between surface spins and T1 and T2 of single-substitutional nitrogen impurity (P1) centers in NDs. The P1 centers located typically in the vicinity of NV centers are a great model system to study the spin relaxation processes of the NV centers. By employing high-frequency electron paramagnetic resonance spectroscopy, we verify that air annealing removes surface spins efficiently and significantly reduces their contribution to T1.

Chip‐Compatible Quantum Plasmonic Launcher

AbstractIntegrated on‐demand single‐photon sources are critical for the implementation of photonic quantum information processing systems. To enable practical quantum photonic devices, the emission rates of solid‐state quantum emitters need to be substantially enhanced and the emitted signal must be directly coupled to an on‐chip circuitry. The photon emission rate speed‐up is best achieved via coupling to plasmonic antennas, while on‐chip integration can be realized by directly coupling emitters to photonic waveguides. The realization of practical devices requires that both the emission speed‐up and efficient out‐coupling are achieved in a single architecture. Here, a novel architecture is proposed that combines chip compatibility with high radiative emission rates—a quantum plasmonic launcher. The proposed launchers contain single nitrogen‐vacancy (NV) centers in nanodiamonds as quantum emitters that offer record‐high average fluorescence lifetime shortening factors of about 7000 times. Nanodiamonds with single NVs are sandwiched between two silver films that couple more than half of the emission into in‐plane propagating surface plasmon polaritons. This simple, compact, and scalable architecture represents a crucial step toward the practical realization of high‐speed on‐chip quantum networks.

Purcell-enhanced emission from individual SiV− center in nanodiamonds coupled to a Si3N4-based, photonic crystal cavity

Abstract Hybrid quantum photonics combines classical photonics with quantum emitters in a postprocessing step. It facilitates to link ideal quantum light sources to optimized photonic platforms. Optical cavities enable to harness the Purcell-effect boosting the device efficiency. Here, we postprocess a free-standing, crossed-waveguide photonic crystal cavity based on Si3N4 with SiV− center in nanodiamonds. We develop a routine that optimizes the overlap with the cavity electric field utilizing atomic force microscope (AFM) nanomanipulation to attain control of spatial and dipole alignment. Temperature tuning further gives access to the spectral emitter-cavity overlap. After a few optimization cycles, we resolve the fine-structure of individual SiV− centers and achieve a Purcell enhancement of more than 4 on individual optical transitions, meaning that four out of five spontaneously emitted photons are channeled into the photonic device. Our work opens up new avenues to construct efficient quantum photonic devices.

Laser-Synthesis of NV-Centers-Enriched Nanodiamonds: Effect of Different Nitrogen Sources.

Due to the large number of possible applications in quantum technology fields—especially regarding quantum sensing—of nitrogen-vacancy (NV) centers in nanodiamonds (NDs), research on a cheap, scalable and effective NDs synthesis technique has acquired an increasing interest. Standard production methods, such as detonation and grinding, require multistep post-synthesis processes and do not allow precise control in the size and fluorescence intensity of NDs. For this reason, a different approach consisting of pulsed laser ablation of carbon precursors has recently been proposed. In this work, we demonstrate the synthesis of NV-fluorescent NDs through pulsed laser ablation of an N-doped graphite target. The obtained NDs are fully characterized in the morphological and optical properties, in particular with optically detected magnetic resonance spectroscopy to unequivocally prove the NV origin of the NDs photoluminescence. Moreover, to compare the different fluorescent NDs laser-ablation-based synthesis techniques recently developed, we report an analysis of the effect of the medium in which laser ablation of graphite is performed. Along with it, thermodynamic aspects of the physical processes occurring during laser irradiation are analyzed. Finally, we show that the use of properly N-doped graphite as a target for laser ablation can lead to precise control in the number of NV centers in the produced NDs.

Molecular-Scale Nanodiamond with High-Density Color Centers Fabricated from Graphite by Laser Shocking

Nanodiamonds (NDs) with nitrogen vacancy (NV) color centers have the potential for quantum information science and bioimaging due to their stable and non-classical photon emission at room temperature. Large-scale fabrication of molecular-size nanodiamonds with sufficient color centers may economically promote their application in versatile multidisciplinary fields. Here, the manufacture of molecular-size NV center-enriched nanodiamonds from graphite powder is reported. We use an ultrafast laser shocking technique to generate intense plasma, which transforms graphite to nanodiamonds under the confinement layer. Molecular dynamics simulations suggest that the high pressure of 35 GPa and the high temperature of 3,000K result in the metaphase transition of graphite to nanodiamonds within 100 ps. A high concentration of NV centers is observed at the optimal laser energy of 3.82 GW/cm 2 , at which point molecular-size (∼5 nm) nanodiamonds can individually host as many as 100 NV centers. Consecutive melamine annealing following ultrafast laser shocking enriches the number of NV centers >10-fold and enhances the spontaneous decay rate of the NV center by up to 5 times. Our work may enhance the feasibility of nanodiamonds for applications, including quantum information, electromagnetic sensing, bioimaging, and drug delivery. Ultrafast laser shock is used to transform graphite to nanodiamonds at ambient conditions The nanodiamonds can individually host ∼100 NV centers Annealing greatly enriches number of NV centers and enhances spontaneous decay rate Motlag et al. describe an ultrafast laser shocking technique to obtain ultrahigh concentrations of color centers in nanodiamonds (∼5 nm) under ambient conditions. Each nanodiamond can individually host ∼100 NV centers, which is orders of magnitude higher than the state of the art.

Charge-state conversion in nitrogen-vacancy centers mediated by an engineered photonic environment

The nitrogen-vacancy (NV) center in nanodiamonds has emerged as an excellent platform in quantum technologies due to its applications in spin manipulation and nanoscale sensing. However, their use is limited by the unavoidable charge-state conversion under optical pumping. In this study, we investigate the control of charge-state conversion in NV centers using an engineered photonic environment and thus change the available local density of optical states (LDOS). The spectral- and pump-dependent decay rate measurements are performed to study the redistribution of emission rates due to the change in LDOS and their effect on charge-state conversion. We have achieved an 8% enhancement of emission rate at the zero phonon line which is accompanied with a 10% suppression in the phonon sideband emission rate in the low-pump-power regime. In the high-pump-power regime, the charge-state conversion becomes inevitable and leads to the deterioration of LDOS-induced modification in the NV center emission lifetimes. The results are useful for efficient NV center spin readout and charge-state depletion microscopy utilizing reversible charge-state conversion.

Ultrabright single-photon emission from germanium-vacancy zero-phonon lines: deterministic emitter-waveguide interfacing at plasmonic hot spots

Abstract Striving for nanometer-sized solid-state single-photon sources, we investigate atom-like quantum emitters based on single germanium-vacancy (GeV) centers isolated in crystalline nanodiamonds (NDs). Cryogenic characterization indicated symmetry-protected and bright (>106 counts/s with off-resonance excitation) zero-phonon optical transitions with up to 6-fold enhancement in energy splitting of their ground states as compared to that found for GeV centers in bulk diamonds (i.e. up to 870 GHz in highly strained NDs vs. 150 GHz in bulk). Utilizing lithographic alignment techniques, we demonstrate an integrated nanophotonic platform for deterministic interfacing plasmonic waveguides with isolated GeV centers in NDs, which enables 10-fold enhancement of single-photon decay rates along with the emission direction control by judiciously designing and positioning a Bragg reflector. This approach allows one to realize the unidirectional emission from single-photon dipolar sources, thereby opening new perspectives for the realization of quantum optical integrated circuits.

Identification of novel split-vacancy transition metal color centers in nanodiamond via time-dependent density functional theory

With a growing interest in optically active sites in diamond and related materials, the need exists to identify novel defects that operate at desired wavelengths. In this study, we employ time-dependent density functional theory to search a large compositional space for novel color centers in diamond. Results are benchmarked against bulk computational approaches as well as experimental literature, and correspondence is observed between molecular and bulk values. Novel defects with potential for infrared emission are identified.

Fast Relaxation on Qutrit Transitions of Nitrogen-Vacancy Centers in Nanodiamonds

Thanks to their versatility, nitrogen-vacancy (NV) centers in nanodiamonds have been widely adopted as nanoscale sensors. However, their sensitivities are limited by their short coherence times relative to NVs in bulk diamond. A more complete understanding of the origins of decoherence in nanodiamonds is critical to improving their performance. Here we present measurements of fast spin relaxation on qutrit transitions between the energy eigenstates composed of the $m_s = \pm1$ states of the NV$^-$ electronic ground state in $\sim40$-nm nanodiamonds under ambient conditions. For frequency splittings between these states of $\sim20~$MHz or less the maximum theoretically achievable coherence time of the NV spin is $\sim2~$orders of magnitude shorter than would be expected if the NV spin is treated as a qubit. We attribute this fast relaxation to electric field noise. We observe a strong falloff of the qutrit relaxation rate with the splitting between the states, suggesting that, whenever possible, measurements with NVs in nanodiamonds should be performed at moderate axial magnetic fields ($>60$ G). We also observe that the qutrit relaxation rate changes with time. These findings indicate that surface electric field noise is a major source of decoherence for NVs in nanodiamonds.

Formation of interstitial silicon defects in Si- and Si,P-doped nanodiamonds and thermal susceptibilities of SiV− photoluminescence band

We have produced two types of synthetic nanodiamonds Si- and Si,P-doped and have characterized the thermal susceptibilities of the spectral band of silicon-vacancy (SiV−) centers at approximately 740 nm in each case. The covered temperature range from 295 to 350 K is of interest for thermometry in biological systems. Comparison of the relative brightness of the Si- and Si,P-doped crystals shows that phosphorous significantly increases average concentration and homogeneity of distribution of SiV− centers in nanodiamonds. Moreover, linear dependence on temperature of the zero-phonon line width in Si-doped crystals is 0.061(2) nm K−1 but is 0.047(3) nm K−1, about 35% smaller in Si,P-doped nanodiamonds. This proves control of SiV− properties with additional chemical doping and close proximity of Si and P atoms.

Coupling of SiV-containing nanodiamonds to a Fabry-Perot microcavity

The possibility of increasing the spontaneous emission rate for silicon-vacancy (SiV) centers in nanodiamonds placed in a Fabry-Perot microcavity was studied. For this purpose, a plano-concave open access microcavity was designed. The cavity was tested using diamond nanocrystallites, placed on a flat mirror. Nanodiamonds were synthesized from adamantane and Si-containing adamantane derivative by high pressure, high temperature (HPHT) technique. The controlled room temperature cavity coupling gives rise to a resonant Purcell enhancement of the SiV zero-phonon line by a factor 1.4.

Protecting Quantum Spin Coherence of Nanodiamonds in Living Cells

Due to its superior coherent and optical properties at room temperature, the nitrogen-vacancy (N-V ) center in diamond has become a promising quantum probe for nanoscale quantum sensing. However, the application of N-V containing nanodiamonds to quantum sensing suffers from their relatively poor spin coherence times. Here we demonstrate energy efficient protection of N-V spin coherence in nanodiamonds using concatenated continuous dynamical decoupling, which exhibits excellent performance with less stringent microwave power requirement. When applied to nanodiamonds in living cells we are able to extend the spin coherence time by an order of magnitude to the $T_1$-limit of up to $30\mu$s. Further analysis demonstrates concomitant improvements of sensing performance which shows that our results provide an important step towards in vivo quantum sensing using N-V centers in nanodiamond.

Optimal architecture for diamond-based wide-field thermal imaging

Nitrogen-vacancy centers in diamonds possess an electronic spin resonance that strongly depends on temperature, which makes them efficient temperature sensors with sensitivity down to a few mK/Hz. However, the high thermal conductivity of the host diamond may strongly damp any temperature variations, leading to invasive measurements when probing local temperature distributions. In the view of determining possible and optimal configurations for diamond-based wide-field thermal imaging, here, we investigate both experimentally and numerically the effect of the presence of diamonds on microscale temperature distributions. Three geometrical configurations are studied: a bulk diamond substrate, a thin diamond layer bonded on quartz, and diamond nanoparticles dispersed on quartz. We show that the use of bulk diamond substrates for thermal imaging is highly invasive in the sense that it prevents any substantial temperature increase. Conversely, thin diamond layers partly solve this issue and could provide a possible alternative for microscale thermal imaging. Dispersions of diamond nanoparticles throughout the sample appear as the most relevant approach as they do not affect the temperature distribution, although NV centers in nanodiamonds yield lower temperature sensitivities than bulk diamonds.

Purcell enhancement of light emission in nanodiamond using a trenched nanobeam cavity

In this article, we propose a trenched nanobeam cavity as an efficient on-chip optical system that can be used to enhance light emission from color centers in nanodiamonds. The trench is created at the center of nanobeam cavity, and it is filled with a nanodiamond. The trench—nanodiamond system significantly perturbs the electric field profile of the original cavity mode. The antinodes of the electric fields relocate to the nano-sized air gap regions between the trench and the nanodiamonds, which lead to a large shrinking in the mode volume. By tuning the trench depth, a right balance is achieved between the deterioration of the quality factor and the reduction in the mode volume. At this depth, the ratio of quality factor to mode volume is maximized. Using silicon nitride nanobeam cavities of moderate experimental quality factors (∼1500), we are able to demonstrate a significant enhancement of the light emission compared to the conventional evanescent coupling approach.

Stable ensemble brightness from nitrogen vacancy centers in nanodiamonds through optimized surface composition

Stable ensemble emission from nitrogen vacancy (NV) centers in nanodiamonds (NDs) is highly desirable for diverse areas ranging from bio-imaging to quantum optics. The uniqueness of NV centers lies in their opto-spin properties like energy level structure, emission range (620-850 nm) and optical spin polarization. The host matrix (NDs), however, put some limitation on the photo-physical properties of these color centers. One of the major issues is surface proximity (where high concentration of defects are present) of NV centers. The NV centers being highly sensitive to the neighboring environment are unstable in such circumstances. The surface of NDs mainly exhibit non-diamond carbon which is well-known quencher of emission due to NV centers. The surface composition for desirable photo-physical properties of NV centers is still unknown. Here, we have systemically studied the effect of oxidation time at low oxidation temperature (450 oC) on the selective removal of sp2 carbon, aqueous dispersion of NDs and emission collection due to NV centers at ensemble level. Among different air oxidations, heat treatment at 450 oC at residual time of 8 hours has been found to be suitable air oxidation conditions for the enhancement of brightness and ensemble photo-stability of NV centers.

Coherent remote control of quantum emitters embedded in polymer waveguides

We report on the coherent internal-state control of single-crystalline nanodiamonds, containing on average 1200 nitrogen-vacancy (NV) centers, embedded in three-dimensional direct-laser-written waveguides. We excite the NV centers by light propagating through the waveguide, and we show that emitted fluorescence can be efficiently coupled to the waveguide modes. We find an average coupling efficiency of 21.6% into all guided modes. Moreover, we investigate optically detected magnetic-resonance spectra as well as Rabi oscillations recorded through the waveguide-coupled signal. Our work shows that the system is well suited for magnetometry and remote readout of spin coherence in a freely configurable waveguide network, overcoming the need for direct optical access of NV centers in nanodiamonds. These waveguide-integrated sensors might open up new applications, such as determining magnetic field distributions inside opaque or scattering media, or photosensitive samples, such as biological tissue.

Photodynamics and quantum efficiency of germanium vacancy color centers in diamond

Color centers in diamond—especially group IV defects—have been advanced as a viable solid-state platform for quantum photonics and information technologies. We investigate the photodynamics and characteristics of germanium-vacancy (GeV) centers hosted in high-pressure high-temperature diamond nanocrystals. Through back-focal plane imaging, we analyze the far-field radiation pattern of the investigated emitters and derive a crossed-dipole emission, which is strongly aligned along one axis. We use this information in combination with lifetime measurements to extract the decay rate statistics of the GeV emitters and determine their quantum efficiency, which we estimated to be ∼ ( 22 ± 2 ) % . Our results offer further insight into the photodynamic properties of the GeV center in nanodiamonds and confirm its suitability as a desirable system for quantum technologies.