Nitrogen-vacancy Color Centers In Diamond Research Articles

Hot ion implantation to create dense NV center ensembles in diamond

Creating dense and shallow nitrogen-vacancy (NV) ensembles with good spin properties is a prerequisite for developing diamond-based quantum sensors exhibiting better performance. Ion implantation is a key enabling tool for precisely controlling spatial localization and density of NV color centers in diamond. However, it suffers from a low creation yield, while higher ion fluences significantly damage the crystal lattice. In this work, we realize N2+ ion implantation in the 30–40 keV range at high temperatures. At 800 °C, NV's ensemble photoluminescence emission is three to four times higher than room temperature implanted films, while narrow electron spin resonance linewidths of 1.5 MHz, comparable to well-established implantation techniques, are obtained. In addition, we found that ion fluences above 2 × 1014 ions/cm2 can be used without graphitization of the diamond film, in contrast to room temperature implantation. This study opens promising perspectives in optimizing diamond films with implanted NV ensembles that could be integrated into quantum sensing devices.

Magnetic-field-assisted optical fiber quantum temperature sensor with enhanced sensitivity.

In recent years, utilizing nitrogen-vacancy color centers in diamond for temperature sensing has drawn great attention. However, increasing the sensitivity has encountered challenges due to the intrinsic temperature-dependent energy level shift, i.e., temperature responsivity, being limited to -74 kHz/K. In this Letter, we take advantage of the magnetic field to regulate the energy level to enhance temperature sensitivity. The sensor is formed by adhering a micron-sized diamond on the end face of an optical fiber, and a small magnet is mounted at a certain distance with the diamond exploiting a cured polydimethylsiloxane block as the bridge. The temperature change leads to the variation of the distance between the diamond and the magnet, thus affecting the magnetic strength felt by the diamond. This finally contributes an additional temperature-induced energy level shift, giving rise to an enhanced sensitivity. Experimental results demonstrated the proposed scheme and achieved a 4.2-fold improvement in the temperature responsivity and a 2.1-fold enhancement in sensitivity. Moreover, the diamond and the fiber-optic integrated structure improve the portability of the sensor.

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

A Two-Frequency Resonator for Exciting Hyperfine Transitions in a Nitrogen-Vacancy Color Center in Diamond

A Two-Frequency Resonator for Exciting Hyperfine Transitions in a Nitrogen-Vacancy Color Center in Diamond

Diamond-optic enhanced photon collection efficiency for sensing with nitrogen-vacancy centers.

We present a design to increase the amount of collected fluorescence emitted by nitrogen-vacancy color centers in diamond used for quantum-sensing. An improvement was measured in collected fluorescence when comparing oppositely faced emitting surfaces by a factor of 3.8(1). This matches ray-tracing simulation results. This design therefore improves on the shot noise limited sensitivity in optical readout-based measurements of, for instance, magnetic and electric fields, pressure, temperature, and rotations.

High efficiency radio frequency antennas for amplifier free quantum sensing applications

Radio frequency (RF) signals are frequently used in emerging quantum applications due to their spin state manipulation capability. Efficient coupling of RF signals into a particular quantum system requires the utilization of carefully designed and fabricated antennas. Nitrogen vacancy (NV) defects in diamond are commonly utilized platforms in quantum sensing experiments with the optically detected magnetic resonance (ODMR) method, where an RF antenna is an essential element. We report on the design and fabrication of high efficiency coplanar RF antennas for quantum sensing applications. Single and double ring coplanar RF antennas were designed with −37 dB experimental return loss at 2.87 GHz, the zero-field splitting frequency of the negatively charged NV defect in diamond. The efficiency of both antennas was demonstrated in magnetic field sensing experiments with NV color centers in diamond. An RF amplifier was not needed, and the 0 dB output of a standard RF signal generator was adequate to run the ODMR experiments due to the high efficiency of the RF antennas.

Design of a High-Bandwidth Uniform Radiation Antenna for Wide-Field Imaging with Ensemble NV Color Centers in Diamond.

Radiation with high-efficiency, large-bandwidth, and uniform magnetic field radiation antennas in a large field of view are the key to achieving high-precision wide-field imaging. This paper presents a hollow Ω-type antenna design for diamond nitrogen-vacancy (NV) ensemble color center imaging. The uniformity of the antenna reaches 94% in a 4.4 × 4.4 mm2 area. Compared with a straight copper antenna, the radiation efficiency of the proposed antenna is 71.8% higher, and the bandwidth is improved by 11.82 times, demonstrating the effectiveness of the hollow Ω-type antenna.

Radio-frequency response of the optically detected level anticrossing signal in nitrogen-vacancy color centers in diamond in zero and weak magnetic fields

The response of the level anti-crossing signal to a quasi-resonant radio-frequency field, which appears in a zero magnetic field at NV color centers in diamond, is investigated. It is shown that the complex structure of this response can be explained by the Autler-Townes splitting. The possibility of controlling the parameters of the level anti-crossing signal is considered. It is shown that the slope of the central resonance recorded in this structure upon low-frequency modulation of the external magnetic field can be 2.3 times higher than the slope of the resonance recorded in the absence of an RF field. Conclusions are drawn about the nature of the level anti-crossing effect arising in zero field in NV color centers in diamond.

Proximal nitrogen reduces the fluorescence quantum yield of nitrogen-vacancy centres in diamond

The nitrogen-vacancy colour centre in diamond is emerging as one of the most important solid-state quantum systems. It has applications to fields including high-precision sensing, quantum computing, single photon communication, metrology, nanoscale magnetic imaging and biosensing. For all of these applications, a high quantum yield of emitted photons is desirable. However, diamond samples engineered to have high densities of nitrogen-vacancy centres show levels of brightness varying significantly within single batches, or even within the same sample. Here we show that nearby nitrogen impurities quench emission of nitrogen-vacancy centres via non-radiative transitions, resulting in a reduced fluorescence quantum yield. We monitored the emission properties of nitrogen-vacancy centre ensembles from synthetic diamond samples with different concentrations of nitrogen impurities. All samples were irradiated with high energy electrons to create high densities of nitrogen-vacancy centres relative to the concentration of nitrogen impurities. While at low nitrogen densities of 1.81 ppm we measured a lifetime of 13.9 ns, we observed a strong reduction in lifetime with increasing nitrogen density. We measure a lifetime as low as 4.4 ns at a nitrogen density of 380 ppm. The change in lifetime matches a reduction in relative fluorescence quantum yield from 77.4% to 32% with an increase in nitrogen density from 88 ppm to 380 ppm, respectively. These results will inform the conditions required to optimise the properties of diamond crystals devices based on the fluorescence of nitrogen-vacancy centres. Furthermore, this work provides insights into the origin of inhomogeneities observed in high-density nitrogen-vacancy ensembles within diamonds and nanodiamonds.

Observation of magnetic domain patterns with tilted uniaxial anisotropy using a single-spin magnetometer

Ferromagnets with uniaxial magnetocrystalline anisotropy have been a significant platform to explore applications in magnetic devices. Although it is commonly recognized that the magnetic anisotropy is crucial for the formation of noncollinear domain patterns, the effects of the anisotropy direction are usually neglected in recent studies. Here, we imaged stray fields generated by a polycrystalline MnNiGa sample with a nitrogen-vacancy color center in diamond and found that various stripe domains and magnetic bubbles exist in different regions. These domain patterns could be explained by the difference in anisotropy directions among crystallites via micromagnetic simulation. It can be inferred that the magnetic anisotropy direction plays a key role in energetically favorable domain structures based on our results. The magnetic anisotropy direction may be exploited as an ingredient to modulate domains and develop devices.

Narrow-linewidth diamond single-photon sources prepared via femtosecond laser

Nitrogen-vacancy (NV) color centers in diamonds with narrow optical linewidths are commonly used as solid-state single-photon sources that emit indistinguishable photons. However, NV color centers prepared using ion implantation typically have large optical linewidths of over 100 MHz. Herein, we used the femtosecond laser direct writing (FsLDW) technique to prepare single NV color centers in diamond with a narrow optical linewidth of 13.05 ± 0.2 MHz and a long decoherence time of 445 ± 27.6 μs. In addition, the density functional theory was adopted to establish calculation models and illustrate why single NV color centers prepared by FsLDW have narrower linewidths compared to those of the ion implantation method. Thus, this study provides an effective reference for the preparation of narrow-linewidth single-color centers in diamonds and other wide-gap crystals.

Ac Sensing Using Nitrogen-Vacancy Centers in a Diamond Anvil Cell up to 6 GPa

Nitrogen-vacancy color centers in diamond have attracted broad attention as quantum sensors for both static and dynamic magnetic, electrical, strain and thermal fields, and are particularly attractive for quantum sensing under pressure in diamond anvil cells. Optically-based nuclear magnetic resonance may be possible at pressures greater than a few GPa, and offers an attractive alternative to conventional Faraday-induction based detection. Here we present AC sensing results and demonstrate synchronized readout up to 6 GPa, but find that the sensitivity is reduced due to inhomogeneities of the microwave field and pressure within the sample space. These experiments enable the possibility for all-optical high resolution magnetic resonance of nanoliter sample volumes at high pressures.

Simultaneous high Q/V-ratio and optimized far-field emission pattern in diamond slot-bridge nanobeam cavity

We present a design for a slot-bridge nanobeam cavity that supports ultrahigh Q/V and optimized far-field emission pattern, and operates at the zero-phonon transition (637nm) of the nitrogen-vacancy color centers in diamond. The slot-bridge cavity is formed by introducing a diamond bridge at the center of the air region of a slotted cavity. As a result of the boundary condition on the parallel component of the electric field, the electric field in the bridge region is the same as that in the slot. This results in a further reduction of the mode volume. Optimized slot-bridge cavities with a calculated Q factor of 6×106 and mode volume of Veff=0.28(λ/n)3have been realized. In comparison to nanobeam cavities, the mode volume is reduced by a factor of 139. The far-field pattern of a slot-bridge cavity is optimized by using the band folding method and by adding small air-slot extensions to the two closest air-holes surrounding the cavity. A high Q of 9.8×105 and a small mode volume of Veff=0.011(λ/n)3 is realized for this design. Therefore, this type of cavities would allow for the realization of efficient single-photon sources. Our results are important for fundamental studies, like cavity quantum electrodynamics, as well as applications in quantum information processing based on diamond where high quality-factor and ultrasmall mode volume are required.

Exciton-polariton mediated interaction between two nitrogen-vacancy color centers in diamond using two-dimensional transition metal dichalcogenides

In this paper, starting from a quantum master equation, we discuss the interaction between two negatively charged Nitrogen-vacancy color centers in diamond via exciton-polaritons propagating in a two-dimensional transition metal dichalcogenide layer in close proximity to a diamond crystal. We focus on the optical 1.945 eV transition and model the Nitrogen-vacancy color centers as two-level (artificial) atoms. We find that the interaction parameters and the energy levels renormalization constants are extremely sensitive to the distance of the Nitrogen-vacancy centers to the transition metal dichalcogenide layer. Analytical expressions are obtained for the spectrum of the exciton-polaritons and for the damping constants entering the Lindblad equation. The conditions for occurrence of exciton mediated superradiance are discussed.

Exceptional Points from the Hamiltonian of a hybrid physical system: Squeezing and anti-Squeezing

We study the appearance of Exceptional Points in a hybrid system composed of a superconducting flux-qubit and an ensemble of nitrogen-vacancy colour centres in diamond. We discuss the possibility of controlling the generation of Exceptional Points, by the analysis of the model space parameters. One of the characteristic features of the presence of Exceptional Points, it is the departure from the exponential decay behaviour of the observables as a function of time. We study the time evolution of different initial states, in the presence of the hybrid system, by computing the reduced density matrix of each subsystem. We present the results we have obtained for the steady behaviour of different observables. We analyse the appearance of Squeezed Spin States and of anti-Squeezed Spin States.

A Diamond Temperature Sensor Based on the Energy Level Shift of Nitrogen-Vacancy Color Centers.

The nitrogen-vacancy (NV) color center in chemical vapor deposition (CVD) diamond has been widely investigated in quantum information and quantum biosensors due to its excellent photon emission stability and long spin coherence time. However, the temperature dependence of the energy level of NV color centers in diamond is different from other semiconductors with the same diamond cubic structure for the high Debye temperature and very small thermal expansion coefficient of diamond. In this work, a diamond sensor for temperature measurement with high precision was fabricated based on the investigation of the energy level shifts of NV centers by Raman and photoluminescence (PL) spectra. The results show that the intensity and linewidth of the zero-phonon line of NV centers highly depend on the environmental temperature, and the energy level shifts of NV centers in diamond follow the modified Varshni model very well, a model which is better than the traditional version. Accordingly, the NV color center shows the ability in temperature measurement with a high accuracy of up to 98%. The high dependence of NV centers on environmental temperature shows the possibility of temperature monitoring of NV center-based quantum sensors in biosystems.

Optical Magnetometry Based on Nanodiamonds with Nitrogen-Vacancy Color Centers.

Nitrogen-vacancy color centers in diamond are a very promising medium for many sensing applications such as magnetometry and thermometry. In this work, we study nanodiamonds deposited from a suspension onto glass substrates. Fluorescence and optically detected magnetic resonance spectra recorded with the dried-out nanodiamond ensembles are presented and a suitable scheme for tracking the magnetic-field value using a continuous poly-crystalline spectrum is introduced. Lastly, we demonstrate a remote-sensing capability of the high-numerical-aperture imaging fiber bundle with nanodiamonds deposited on its end facet.

Strong polarization of individual nuclear spins weakly coupled to nitrogen-vacancy color centers in diamond

We experimentally demonstrate high degree of polarization of 13C nuclear spins weakly interacting with nitrogen-vacancy (NV) centers in diamond. We combine coherent microwave excitation pulses with optical illumination to provide controlled relaxation and achieve a polarity-tunable, fast nuclear polarization of degree higher than 85% at room temperature for remote 13C nuclear spins exhibiting hyperfine interaction strength with NV centers of the order of 600 kHz. We show with the aid of numerical simulation that the anisotropic hyperfine tensor components naturally provide a route to control spin mixing parameter so that highly efficient nuclear polarization is enabled through careful tuning of nuclear quantization axis by external magnetic field. We further discuss spin dynamics and wide applicability of this method to various target 13C nuclear spins around the NV center electron spin. The proposed control method demonstrates an efficient and versatile route to realize, for example, high-fidelity spin register initialization and quantum metrology using nuclear spin resources in solids.

基于交叉克尔非线性和金刚石氮空穴色心-微环谐振腔的W态向GHZ态的转换

基于交叉克尔非线性和金刚石氮空穴色心-微环谐振腔的W态向GHZ态的转换

Wide-Field Planar Magnetic Imaging Using Spins in Diamond

The nitrogen-vacancy color centers in diamond can be used as an excellent magnetic sensor. In this work, we present a wide-field planar magnetic imaging technique based on nitrogen-vacancy color centers. Through optically detected magnetic resonance (ODMR) which is readout from a scientific CMOS camera to extract resonance frequency, we experimentally reconstruct the magnetic field distribution of permanent magnets and particles of magnetite (Fe3O4). Moreover, by using this method we imagined the magnetic field distribution of one integrated cell heater widely used in temperature control with magnetic field suppression. And the experiment shows that this technique can be applied in engineering. The imaging field of this technology can reach the sub-millimeter level and the spatial resolution can reach the optical diffraction limit. The presented wide-field NV imaging technique offers wide-field imaging, high spatial resolution, and high magnetic sensitivity.