Color Centers In Diamond Research Articles

Robust diamond-embedded microwave antenna for optimizing quantum sensing using nitrogen-vacancy center ensembles

The nitrogen-vacancy (NV) color center in diamond has emerged as a promising candidate for quantum sensing. In this study, we propose a diamond-embedded metal antenna for magnetic detection utilizing NV center ensembles. Our approach involved employing nanofabrication and microwave plasma chemical vapor deposition techniques to fabricate the metal antenna and diamond epilayer. By directly embedding the antenna into the diamond, we effectively minimize external environmental interference, leading to improved device stability and reusability. Moreover, this integration enhances the device's compactness, making it highly suitable for on-chip quantum sensing applications. The innovative antenna design holds great potential for the development of future integrated quantum sensing devices based on NV centers in diamond.

On readout and initialisation fidelity by finite demolition single shot readout

Abstract Ideal projective quantum measurement makes the system state collapse in one of the observable operator eigenstates | ϕ α ⟩ , making it a powerful tool for preparing the system in the desired pure state. Nevertheless, experimental realisations of projective measurement are not ideal. During the measurement time needed to overcome the classical noise of the apparatus, the system state is often (slightly) perturbed, which compromises the fidelity of initialisation. In this paper, we propose an analytical model to analyse the initialisation fidelity of the system performed by the single-shot readout. We derive a method to optimise parameters for the three most used cases of photon counting based readouts for NV colour centre in diamond, charge state, nuclear spin and low temperature electron spin readout. Our work is of relevance for the accurate description of initialisation fidelity of the quantum bit when the single-shot readout is used for initialisation via post-selection or real-time control.

Reversible optical data storage below the diffraction limit.

Colour centres in wide-bandgap semiconductors feature metastable charge states that can be interconverted with the help of optical excitation at select wavelengths. The distinct fluorescence and spin properties in each of these states have been exploited to show storage of classical information in three dimensions, but the memory capacity of these platforms has been thus far limited by optical diffraction. Here we leverage local heterogeneity in the optical transitions of colour centres in diamond (nitrogen vacancies) to demonstrate selective charge state control of individual point defects sharing the same diffraction-limited volume. Further, we apply this approach to dense colour centre ensembles, and show rewritable, multiplexed data storage with an areal density of 21 Gb inch-2 at cryogenic temperatures. These results highlight the advantages for developing alternative optical storage device concepts that can lead to increased storage capacity and reduced energy consumption per operation.

SiV0 centres in diamond: effect of isotopic substitution in carbon and silicon.

The neutrally charged silicon-vacancy defect (SiV0) is a colour centre in diamond with spin S = 1, a zero-phonon line (ZPL) at 946 nm and long spin coherence, which makes it a promising candidate for quantum network applications. For the proper performance of such colour centres, all of them must have identical optical characteristics. However, in practice, there are factors that influence each individual centre. One of these factors is non-uniform isotope composition for both carbon atoms in diamond lattice and silicon atoms of dopant. In this work, we studied the isotopic shifts of SiV0 centres for CVD-grown epitaxial layers of isotopically enriched 12C and 13C diamonds, as well as for diamond with natural isotope composition but doped only with one isotope of Si (28Si, 29Si and 30Si). The detected shift was 1.60 meV for 12C/13C couple and 0.33 meV for 28Si/29Si and 29Si/30Si couples, which are close to the previously obtained values of the isotopic shift for the negatively charged silicon vacancy (SiV-), which indicates a similar model of interaction with the environment for these two charge states of the SiV colour centres. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.

Narrowband photoluminescence of Tin-Vacancy colour centres inSn-doped chemical vapour deposition diamond microcrystals.

Tin-Vacancy (Sn-V) colour centres in diamond have a spin coherence time in the millisecond range at temperatures of 2 K, so they are promising to be used in diamond-based quantum optical devices. However, the incorporation of large Sn atoms into a dense diamond lattice is a non-trivial problem. The objective of our work is to use microwave plasma-assisted chemical vapour deposition (CVD) to grow Sn-doped diamond with submicron SnO2 particles as a solid-state source of impurity. Well-faceted diamond microcrystals with sizes of afewmicrometres were formed on AlN substrates. The photoluminescence (PL) signal with zero-phonon line (ZPL) peak for Sn-V centre at ≈620 nm was measured at room temperature (RT) and at 7 K. The peak width (full width at half-maximum) was measured to be 1.1-1.7 nm at RT and ≈0.05 nm at 7 K. The observed variations of ZPL shape and position, in particular, narrowing of PL peak at RT and formation of single-line fine structure at low-T, are attributed to strain in the crystallites. The diamond doping with Sn via CVD process offers a new route to from Sn-V colour centre in the bulk of the diamond crystallites. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.

Absorption and birefringence study for reduced optical losses in diamond with high nitrogen-vacancy concentration.

The use of diamond colour centres such as the nitrogen-vacancy (NV) centre is increasingly enabling quantum sensing and computing applications. Novel concepts like cavity coupling and readout, laser-threshold magnetometry and multi-pass geometries allow significantly improved sensitivity and performance via increased signals and strong light fields. Enabling material properties for these techniques and their further improvements are low optical material losses via optical absorption of signal light and low birefringence. Here, we study systematically the behaviour of absorption around 700 nm and birefringence with increasing nitrogen- and NV-doping, as well as their behaviour during NV creation via diamond growth, electron beam irradiation and annealing treatments. Absorption correlates with increased nitrogen doping yet substitutional nitrogen does not seem to be the direct absorber. Birefringence reduces with increasing nitrogen doping. We identify multiple crystal defect concentrations via absorption spectroscopy and their changes during the material processing steps and thus identify potential causes of absorption and birefringence as well as strategies to fabricate chemical vapour deposition diamonds with high NV density yet low absorption and low birefringence. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.

Low-temperature characteristics of an AlN/Diamond surface acoustic wave resonator

Phonons confined in mechanical resonators can be coupled to a variety of quantum systems and are expected to be applied to hybrid quantum systems. Diamond surface acoustic wave (SAW) devices are capable of high efficiency in phonon interaction with color centers in diamond. The temperature dependence of the quality factor is crucial for inferring the governing mechanism of coupling efficiency between phonons and color centers in diamond. In this paper, we report on the temperature dependence of the quality factor of an AlN/diamond SAW device from room temperature to 5 K. The temperature dependence of the quality factor and resonant frequency suggests that the mechanism of SAW dissipation in the AlN/diamond SAW resonator at 5 GHz is the phonon–phonon scattering in the Akheiser regime and that further cooling can be expected to improve the quality factor. This result provides a crucial guideline for the future design of AlN/diamond SAW devices.

Shallow Silicon Vacancy Centers with Lifetime-Limited Optical Linewidths in Diamond Nanostructures.

The negatively charged silicon vacancy center (SiV-) in diamond is a promising, yet underexplored candidate for single-spin quantum sensing at sub-kelvin temperatures and tesla-range magnetic fields. A key ingredient for such applications is the ability to perform all-optical, coherent addressing of the electronic spin of near-surface SiV- centers. We present a robust and scalable approach for creating individual, ∼50 nm deep SiV- with lifetime-limited optical linewidths in diamond nanopillars through an easy-to-realize and persistent optical charge-stabilization scheme. The latter is based on single, prolonged 445 nm laser illumination that enables continuous photoluminescence excitation spectroscopy without the need for any further charge stabilization or repumping. Our results constitute a key step toward the use of near-surface, optically coherent SiV- for sensing under extreme conditions, and offer a powerful approach for stabilizing the charge-environment of diamond color centers for quantum technology applications.

Kelvin Probe Characterization of Nanocrystalline Diamond Films with SiV Centers as Function of Thickness

Optically active color centers in diamonds have been intensively studied due to their potential in photonics, energy harvesting, biosensing, and quantum computing. Silicon vacancy (SiV) center offers an advantage of suitable emission wavelength and narrow zero‐phonon line at room temperature. Measurement of surface potential and photovoltage can provide better understanding of the physics and control of SiV light emission, such as charge states and charging effects. Herein, optoelectronic properties of nanocrystalline diamond films with SiV centers at different layer thicknesses (10–200 nm, controlled by the growth time) under ambient conditions are studied. Time‐dependent measurements are performed in the light–dark–light cycle. Positive photovoltage arises on samples with SiV layer thicknesses below 55 nm on both H‐ and O‐terminated surfaces. Above 55 nm the photovoltage switches to negative. This layer thickness thus represents a halfway boundary between surface‐controllable and bulk SiV centers dominant contribution. A band diagram scheme explaining the photovoltage switching mechanism is provided.

Advances in Nitrogen-Vacancy color centers in diamond for magnetometry: Advantages and Challenges

Advances in Nitrogen-Vacancy color centers in diamond for magnetometry: Advantages and Challenges

Optical driving, spin initialization and readout of single SiV− centers in a Fabry-Perot resonator

Large-scale quantum communication networks require quantum repeaters due to the signal attenuation in optical fibers. Ideal quantum repeater nodes efficiently link a quantum memory with photons serving as flying qubits. Color centers in diamond, particularly the negatively charged silicon vacancy center, are promising candidates to establish such nodes. Inefficient connection between the color center’s spin to the optical fiber networks is a major obstacle, that could be resolved by utilizing optical resonators. Here, we couple individual silicon vacancy centers incorporated in a nanodiamond to a hemispherical, stable Fabry-Perot microcavity, achieving Purcell-factors larger than 1. We demonstrate coherent optical driving between ground and excited state with a Rabi-frequency of 330 MHz, all-optical initialization and readout of the electron spin in magnetic fields of up to 3.2 T. Spin initialization within 67 ns with a 80 % fidelity and a lifetime of 350 ns are reached. Our demonstration opens the way to realize quantum repeater applications.

Hyperfine Spectroscopy of Isotopically Engineered Group-IV Color Centers in Diamond

Hyperfine Spectroscopy of Isotopically Engineered Group-IV Color Centers in Diamond

Quantum Photonic Circuits Integrated with Color Centers in Designer Nanodiamonds.

Diamond has emerged as a leading host material for solid-state quantum emitters, quantum memories, and quantum sensors. However, the challenges in fabricating photonic devices in diamond have limited its potential for use in quantum technologies. While various hybrid integration approaches have been developed for coupling diamond color centers with photonic devices defined in a heterogeneous material, these methods suffer from either large insertion loss at the material interface or evanescent light-matter coupling. Here, we present a new technique that enables the deterministic assembly of diamond color centers in a silicon nitride photonic circuit. Using this technique, we observe Purcell enhancement of silicon vacancy centers coupled to a silicon nitride ring resonator. Our hybrid integration approach has the potential for achieving the maximum possible light-matter interaction strength while maintaining low insertion loss and paves the way toward scalable manufacturing of large-scale quantum photonic circuits integrated with high-quality quantum emitters and spins.

Spatial Microwave Field Frequency Measurement through Two‐Level Resonance of Nitrogen‐Vacancy Color Center in Diamond

This article presents a frequency measurement method for spatial microwave signals with solid‐state atom resonance, performing measurements based on the burnt hole in spectrum with two microwave fields acting on nitrogen vacancies (NVs) simultaneously. The population on |0⟩ of the NV color center in the ground state affected by the resonance of two microwave fields with similar frequencies responds excellently to external microwave frequencies, and a phenomenon named hole burning occurs. The full width at half maximum (FWHM) of the resonant peak at the hole is 18.9 kHz. When microwaves of different frequencies are applied, the resonant peak precisely follows the signal frequency in the experiment. Subsequently, the resonant peak is processed using the differential method to obtain a frequency measurement error on the order of 100 Hz. The spatial resolution of this method is within the millimeter scale. This study can provide technical support for applications in microwave frequency measurement and spatial mapping with quantum precision measurement.

Temperature/laser dependence of N3 optical centers in natural type Ia diamonds through photoluminescence spectroscopy

In this work, low-temperature photoluminescence spectroscopy was employed to investigate the N3 optical color center in natural type Ia diamond. The optical properties of the N3 center with regular changes in testing temperature and laser power were studied, and the energy level transition was also discussed. The results showed that the PL intensity of the N3 center enhanced sub-linearly with laser power increased, indicating that the electron transition of the N3 center was mainly radiative recombination with weak Auger recombination participation. In addition, the physical model was employed to analyze the change in the zero phonon line with the increase in the test temperature; it obtained thermal quenching activation energy (25.2 meV), bond softening, and strong interaction with acoustical phonons of the N3 center. The theoretical analysis of the broadening parameters revealed that the longitudinal optical phonon energy was 55.1 meV, and the electron–optic phonon coupling strength was 2.3 meV.

Millimeter‐Scale Temperature Self‐Calibrated Diamond‐Based Quantum Sensor for High‐Precision Current Sensing

AbstractThe negatively charged nitrogen vacancy (NV) color center in diamond is a type of point defect, which is extensively studied as a promising high‐sensitivity solid‐state magnetic field sensor. However, its transition from research to application is still limited due to the technical challenges of an integrated physical package. Here, an integrated diamond sensor is demonstrated with the essential component on the order of mm3, which is realized by a standard microfabrication process. A microfabrication‐compatible light guiding structure is constructed, providing photon detection efficiency of 66% and thus enabling a magnetic field detection sensitivity reaching 203 pT·Hz1/2. Incorporation of the sensor device with a magnetic yoke enables high‐precision wide‐range direct‐current sensing with current isolation. A current measuring range of 0–400 A with a minimum detection limit of 2 mA is achieved. By utilizing dual spin resonance modulation, the temperature drift is suppressed from 219 to 1.92 ppm∙°C−1. This configuration provides new possibilities as a robust and scalable platform for current quantum sensing technologies.

Integrating Fluorescent Nanodiamonds into Polymeric Microstructures Fabricated by Two-Photon Polymerization.

Nitrogen-vacancy (NV) and other color centers in diamond have attracted much attention as non-photobleaching quantum emitters and quantum sensors. Since microfabrication in bulk diamonds is technically difficult, embedding nanodiamonds with color centers into designed structures is a way to integrate these quantum emitters into photonic devices. In this study, we demonstrate a method to incorporate fluorescent nanodiamonds into engineered microstructures using two-photon polymerization (2PP). We studied the optimal concentration of nanodiamonds in the photoresist to achieve structures with at least one fluorescent NV center and good structural and optical quality. Fluorescence and Raman spectroscopy measurements were used to confirm the presence and location of the nanodiamonds, while absorbance measurements assessed scattering losses at higher concentrations. Our results show the feasibility of fabricating microstructures embedded within fluorescent nanodiamonds via 2PP for photonics and quantum technology applications.

Hybrid integration of ensemble nitrogen-vacancy centers in single-crystal diamond based on pick-flip-and-place transfer printing

Incorporating color centers in diamond with mature integrated photonics using hybrid integration techniques such as transfer printing provides a promising route toward scalable quantum applications. However, single-crystal diamond nanostructures fabricated using current etching technologies have triangular bottoms that are unsuitable for conventional pick-and-place integration. Herein, we present an alternative approach for deterministically integrating diamond nanostructures on chip. We demonstrate the hybrid integration of a diamond triangular nanobeam containing a nitrogen-vacancy ensemble on an SiO2 chip by picking it up using a weak adhesive film, flipping it, and transferring it to a stronger one. This “pick-flip-and-place” approach provides a flat diamond-chip interface, enabling the high-yield hybrid integration regardless of the shape of diamond nanostructures. Additionally, diamond nanofabrication is facilitated by transfer-printing hard masks for diamond etching. We also show that the integrated diamond nanobeam functions as a nanoscale quantum sensor. Our proposed approach paves the way toward scalable hybrid-diamond quantum photonics.

Graphene‐Enhanced Single Ion Detectors for Deterministic Near‐Surface Dopant Implantation in Diamond

AbstractDiamond color centers with applications to single photon sources, quantum computation, and magnetic field sensing down to the nanoscale have been investigated using ensembles of near‐surface implanted atoms. Deterministic ion implantation for ions stopping between 30 and 130 nm deep is demonstrated by configuring an electronic‐grade diamond substrate with a biased surface graphene electrode connected to charge sensitive electronics. The thin graphene electrode has a negligible surface dead layer, so implantation events are signaled from the drift of electron–hole pairs induced by the dissipation of ion kinetic energy in the substrate. Ion beam induced charge maps from a scanned 1 MeV He microbeam show the graphene electrode is highly effective with a charge collection efficiency up to 86% compared to an O‐terminated diamond surface of 30%. For lower energy ions, applicable to near surface implantation, single ion detection confidence is >99(1)% for 19.5 keV H and 85(2)% for 24 keV N ions to allow maps of device surface features by employing a focused ion beam microscope or an atomic force microscope cantilever incorporating a nanostencil beam collimator. In the near‐term, this system can be used to investigate the annealing dynamics for the conversion of single implanted ions into diamond color centers.

Heterogeneous Integration of Solid-State Quantum Systems with a Foundry Photonics Platform.

Diamond color centers are promising optically addressable solid-state spins that can be matter-qubits, mediate deterministic interaction between photons, and act as single photon emitters. Useful quantum computers will comprise millions of logical qubits. To become useful in constructing quantum computers, spin-photon interfaces must, therefore, become scalable and be compatible with mass-manufacturable photonics and electronics. Here, we demonstrate the heterogeneous integration of NV centers in nanodiamond with low-fluorescence silicon nitride photonics from a standard 180 nm CMOS foundry process. Nanodiamonds are positioned over predefined sites in a regular array on a waveguide in a single postprocessing step. Using an array of optical fibers, we excite NV centers selectively from an array of six integrated nanodiamond sites and collect the photoluminescence (PL) in each case into waveguide circuitry on-chip. We verify single photon emission by an on-chip Hanbury Brown and Twiss cross-correlation measurement, which is a key characterization experiment otherwise typically performed routinely with discrete optics. Our work opens up a simple and effective route to simultaneously address large arrays of individual optically active spins at scale, without requiring discrete bulk optical setups. This is enabled by the heterogeneous integration of NV center nanodiamonds with CMOS photonics.