Ensemble Of Nitrogen-vacancy Centers Research Articles

Highly nitrogen-vacancy doped diamond nanostructures fabricated by ion implantation and optimum annealing

Nitrogen-vacancy (NV) centers in diamond photonic nanostructures have attracted much attention as efficient single photon emitters and quantum bits. These quantum optical devices mostly require single or low-density NV centers doped in thin diamond membranes. In contrast, this study focuses on diamond photonic nanostructures with a high concentration of NV centers to achieve a diamond color center laser with a sufficient gain available as a visible light source and a sensitive magnetic-field sensor. We employ high-dose helium ion implantation to type-Ib diamond substrates and thermal annealing, which enables us to obtain uniform thin diamond membranes containing a dense ensemble of NV centers. Luminescence spectroscopy reveals the kinetics of NV centers at high temperature from which we find an optimum annealing temperature maximizing the NV center emission while suppressing the transformation from NV to H3 centers. Furthermore, fine photonic nanowires are also successfully fabricated in the air-suspended diamond membrane, and they exhibit intense photoluminescence from the NV centers with a concentration as high as 7 × 1016 cm−3 (0.4 ppm). These results suggest a route to the fabrication of diamond photonic nanostructures containing a dense ensemble of NV centers, which can be a key material for developing diamond-based light emitting and magnetic-field sensing devices.

Enhanced Widefield Quantum Sensing with Nitrogen-Vacancy Ensembles Using Diamond Nanopillar Arrays.

Surface micro- and nano-patterning techniques are often employed to enhance the optical interface to single photoluminescent emitters in diamond, but the utility of such surface structuring in applications requiring ensembles of emitters is still open to investigation. Here, we demonstrate scalable and fault-tolerant fabrication of closely packed arrays of fluorescent diamond nanopillars, each hosting its own dense, uniformly bright ensemble of near-surface nitrogen-vacancy centers. We explore the optimal sizes for these structures and realize enhanced spin and photoluminescence properties resulting in a 4.5 times increase in optically detected magnetic resonance sensitivity when compared to unpatterned surfaces. Utilizing the increased measurement sensitivity, we image the mechanical stress tensor in each diamond pillar across the arrays and show that the fabrication process has a negligible impact on in-built stress compared to the unpatterned surface. Our results represent a valuable pathway toward future multimodal and vector-resolved imaging studies, for instance in biological contexts.

A hand-held magnetometer based on an ensemble of nitrogen-vacancy centers in diamond

The development of practical applications of the magnetometer based on ensemble of nitrogen-vacancy centers has been impeded by the large size of the system. In this paper, we present an integrated and miniaturized magnetic field sensor with a volume of approximately 10 cm3. Compared to the previous design, with the fluorescence waveguide excitation and collection structure, both the optical excitation system and collection system are integrated into a compact device by combining the optical fiber, so that it can be a handheld sensing head. We demonstrated experimentally that this sensor head enables the optically detected magnetic resonance measurements with or without the external magnetic field. Subsequently, we verified that the magnetic-field sensitivity is approximately 67 , and projected the photon shot noise limited sensitivity to be 2.04 . This novel system has considerable performance regarding previous designs while greatly reducing dimensions.

Spatiotemporal Mapping of a Photocurrent Vortex in Monolayer MoS2 Using Diamond Quantum Sensors

The detection of photocurrents is central to understanding and harnessing the interaction of light with matter. Although widely used, transport-based detection averages over spatial distributions and can suffer from low photocarrier collection efficiency. Here, we introduce a contact-free method to spatially resolve local photocurrent densities using a proximal quantum magnetometer. We interface monolayer MoS2 with a near-surface ensemble of nitrogen-vacancy centers in diamond and map the generated photothermal current distribution through its magnetic field profile. By synchronizing the photoexcitation with dynamical decoupling of the sensor spin, we extend the sensor's quantum coherence and achieve sensitivities to alternating current densities as small as 20 nA per micron. Our spatiotemporal measurements reveal that the photocurrent circulates as vortices, manifesting the Nernst effect, and rises with a timescale indicative of the system's thermal properties. Our method establishes an unprecedented probe for optoelectronic phenomena, ideally suited to the emerging class of two-dimensional materials, and stimulates applications towards large-area photodetectors and stick-on sources of magnetic fields for quantum control.

Dynamic Quantum Sensing of Paramagnetic Species Using Nitrogen-Vacancy Centers in Diamond.

Naturally occurring paramagnetic species (PS), such as free radicals and paramagnetic metalloproteins, play an essential role in a multitude of critical physiological processes including metabolism, cell signaling, and immune response. These highly dynamic species can also act as intrinsic biomarkers for a variety of disease states, while synthetic paramagnetic probes targeted to specific sites on biomolecules enable the study of functional information such as tissue oxygenation and redox status in living systems. The work presented herein describes a new sensing method that exploits the spin-dependent emission of photoluminescence (PL) from an ensemble of nitrogen-vacancy centers in diamond for rapid, nondestructive detection of PS in living systems. Uniquely this approach involves simple measurement protocols that assess PL contrast with and without the application of microwaves. The method is demonstrated to detect concentrations of paramagnetic salts in solution and the widely used magnetic resonance imaging contrast agent gadobutrol with a limit of detection of less than 10 attomol over a 100 μm × 100 μm field of view. Real-time monitoring of changes in the concentration of paramagnetic salts is demonstrated with image exposure times of 20 ms. Further, dynamic tracking of chemical reactions is demonstrated via the conversion of low-spin cyanide-coordinated Fe3+ to hexaaqua Fe3+ under acidic conditions. Finally, the capability to map paramagnetic species in model cells with subcellular resolution is demonstrated using lipid membranes containing gadolinium-labeled phospholipids under ambient conditions in the order of minutes. Overall, this work introduces a new sensing approach for the realization of fast, sensitive imaging of PS in a widefield format that is readily deployable in biomedical settings. Ultimately, this new approach to nitrogen vacancy-based quantum sensing paves the way toward minimally invasive real-time mapping and observation of free radicals in in vitro cellular environments.

Quantum Bath Control with Nuclear Spin State Selectivity via Pulse-Adjusted Dynamical Decoupling.

Dynamical decoupling (DD) is a powerful method for controlling arbitrary open quantum systems. In quantum spin control, DD generally involves a sequence of timed spin flips (π rotations) arranged to either average out or selectively enhance coupling to the environment. Experimentally, errors in the spin flips are inevitably introduced, motivating efforts to optimize error-robust DD. Here we invert this paradigm: by introducing particular control "errors" in standard DD, namely, a small constant deviation from perfect π rotations (pulse adjustments), we show we obtain protocols that retain the advantages of DD while introducing the capabilities of quantum state readout and polarization transfer. We exploit this nuclear quantum state selectivity on an ensemble of nitrogen-vacancy centers in diamond to efficiently polarize the ^{13}C quantum bath. The underlying physical mechanism is generic and paves the way to systematic engineering of pulse-adjusted protocols with nuclear state selectivity for quantum control applications.

Noncovalent force spectroscopy using wide-field optical and diamond-based magnetic imaging

A realization of the force-induced remnant magnetization spectroscopy technique of specific biomolecular binding is presented, where detection is accomplished with wide-field optical and diamond-based magnetometry using an ensemble of nitrogen-vacancy color centers. This diamond-based technique that has both optical and magnetic detection modalities may be adapted for massively parallel screening of arrays of nanoscale samples.

Thermal-demagnetization-enhanced hybrid fiber-based thermometer coupled with nitrogen-vacancy centers

Nitrogen-vacancy centers in diamond are attractive as quantum sensors owing to their remarkable optical and spin properties under ambient conditions. Here we experimentally demonstrated a hybrid fiber-based thermometer coupled with nitrogen-vacancy center ensemble and a permanent magnet, where the temperature sensitivity was improved by converting the temperature variation to the magnetic field change based on the thermal-demagnetization of the permanent magnet. We have achieved both large temperature working range (room temperature to 373 K) and millikelvin sensitivity (1.6 mK/sqrt(Hz)), nearly 6-fold improvement compared with conventional technique. This stable and compact hybrid thermometer will enable a wide range of applications for large-area detection and imaging with high temperature sensitivity.

Imaging crystal stress in diamond using ensembles of nitrogen-vacancy centers

We present a micrometer-resolution millimeter-field-of-view stress imaging method for diamonds containing a thin surface layer of nitrogen vacancy (NV) centers. In this method, we reconstruct stress tensor elements over a two-dimensional field of view from NV optically-detected magnetic resonance (ODMR) spectra. We use this technique to study how stress inhomogeneity affects NV magnetometry performance, and show how NV stress imaging is a useful and direct way to assess these effects. This new tool for mapping stress in diamond will aid optimization of NV-diamond sensing, with wide-ranging applications in the physical and life sciences.

A Modified Spin Pulsed Readout Method for NV Center Ensembles Reducing Optical Noise

The optical-noise-limited spin readout sensitivity determines the precision of quantum measurement based on nitrogen-vacancy (NV) center. This article investigates the fluorescence dynamics of NV centers by solving the optical rate equations and obtains complete theoretical formulas for the existing optical spin readout method. A transfer coefficient of optical noise to signal noise in the existing differential methods at different frequencies is introduced so as to analyze the optical noise suppression ability and the signal-to-noise ratio (SNR) results under the influence of photon shot noise and optical noise. To further reduce the influence of optical noise on the signal, we propose a modified method to minimize the transfer coefficient by adding a first-order compensation term. Compared with conventional methods, our modified method showed a twofold optical noise suppression ability improvement in the measurement frequency bandwidth. The experiment proves that the final SNR is increased by 43.4% for a long-term measurement. This modified method should lead to immediate improvements in pulsed spin readout of NV center ensembles without extra instrumentation for applications in magnetic field, electric field, and temperature measurements.

Optimizing the formation of depth-confined nitrogen vacancy center spin ensembles in diamond for quantum sensing

Spin ensembles of nitrogen vacancy (NV) centers in diamond are emerging as powerful spin-based sensors for magnetic, electric and thermal field imaging with high spatial and temporal resolution. Here we characterize the formation of depth-confined NV center ensembles, activated by electron irradiation in diamond layers grown by plasma enhanced chemical vapor deposition with nitrogen co-doping. To do so, we exploit the high magnetic sensitivity of ensembles of NV centers to probe their spin environment as a function of growth and irradiation parameters. We engineer an NV ensemble whose magnetic sensitivity is within a factor of two of the static NV-NV dipolar interaction limit, thus demonstrating a powerful platform for quantum sensing.

Hybrid spin-superconducting quantum circuit mediated by deterministically prepared entangled photonic states

In hybrid quantum systems, a controllable coupling can be obtained by mediating the interactions with dynamically introduced photons. We propose a hybrid quantum architecture consisting of two nitrogen vacancy center ensembles coupled to a tunable flux qubit, which is contained on the transmission line of a multimode nonlinear superconducting coplanar waveguide resonator with an appended Josephson mixing device. We discuss the use of entangled propagating microwaves photons, which through our nonlinear wave-mixing procedure are made into macroscopically distinct quantum states. We use these states to steer the system and show that, with further amplification, we can create a similar photonic state, which has a more distinct reduction of its uncertainty. Furthermore, we show that all of this leads to a lengthened coherence time, a reasonable fidelity that decays to 0.94 and then later increases upward to stabilize at 0.6, as well as a strengthened entanglement.

Magnetometry by cross-relaxation-resonance detection in ensembles of nitrogen-vacancy centers

We study cross-relaxation-based magnetometry in ensembles of nitrogen-vacancy (NV) centers using the protocol suggested by Akhmedzhanov et al. [R. Akhmedzhanov, L. Gushchin, N. Nizov, V. Nizov, D. Sobgayda, I. Zelensky, and P. Hemmer, Microwave-free magnetometry based on cross-relaxation resonances in diamond nitrogen-vacancy centers, Phys. Rev. A 96, 013806 (2017)]. We suggest a processing scheme that allows us to perform measurements without precise sample orientation. It is shown theoretically and experimentally that using an additional magnetic field can significantly simplify vector magnetic-field measurements.

Publisher’s Note: “Microstrip-line resonator with broadband, circularly polarized, uniform microwave field for nitrogen vacancy center ensembles in diamond” [AIP Advances 9, 075213 (2019)

Publisher’s Note: “Microstrip-line resonator with broadband, circularly polarized, uniform microwave field for nitrogen vacancy center ensembles in diamond” [AIP Advances 9, 075213 (2019)

Experimental and Theoretical Analysis of Noise Strength and Environmental Correlation Time for Ensembles of Nitrogen-Vacancy Centers in Diamond

We experimentally and theoretically investigate the Hahn echo decay curve for nitrogen vacancy centers in diamond with different spin concentrations. The Hahn echo results show a non-exponential decay for low spin concentrations, while an exponential decay is dominant for high spin concentrations. By fitting the decay curve with a theoretical model, we show that both the amplitude and correlation time of the environmental noise have a clear dependence on the spin concentration. These results are essential for optimizing the NV center concentration in high-performance quantum devices, particularly quantum sensors.

Creation of superposition of arbitrary states encoded in two high-Q cavities.

The principle of superposition is a key ingredient for quantum mechanics. A recent work [Phys. Rev. Lett.116, 110403 (2016)10.1103/PhysRevLett.116.110403] has shown that a quantum adder that deterministically generates a superposition of two unknown states is forbidden. Here we consider the implementation of the probabilistic quantum adder in the 3D cavity-transmon system. Our implementation is based on a three-level superconducting transmon qubit dispersively coupled to two cavities. Numerical simulations show that high-fidelity generation of the superposition of two coherent states is feasible with current circuit QED technology. Our method also works for other physical systems such as two optical cavities coupled to a three-level atom or two nitrogen-vacancy center ensembles interacted with one three-level superconducting flux qubit.

Preservation of quantum correlation between nitrogen-vacancy-center ensembles by squeezed-reservoir engineering

We propose a theoretical scheme to investigate the dynamics of quantum correlation between two nitrogen-vacancy-center ensembles (NVEs) coupled to a common superconducting coplanar waveguide resonator, driven by a broadband microwave squeezed field working as a squeezed-vacuum reservoir. Based on the reduced master equation for NVEs by the adiabatical elimination method in the bad-resonator limit, our results reveal quantum correlation preservation due to the interplay between the nonclassical feature of the squeezing reservoirs and the original dissipation mechanisms. The required operations are very close to the capabilities of current superconducting circuit-QED techniques. Our work may open interesting perspectives for devising active decoherence-immune quantum information devices.

Telecom photon interface of solid-state quantum nodes

Solid-state spins such as nitrogen-vacancy (NV) center are promising platforms for large-scale quantum networks. Despite the optical interface of NV center system, however, the significant attenuation of its zero-phonon-line photon in optical fiber prevents the network extended to long distances. Therefore a telecom-wavelength photon interface would be essential to reduce the photon loss in transporting quantum information. Here we propose an efficient scheme for coupling telecom photon to NV center ensembles mediated by rare-earth doped crystal. Specifically, we proposed protocols for high fidelity quantum state transfer and entanglement generation with parameters within reach of current technologies. Such an interface would bring new insights into future implementations of long-range quantum network with NV centers in diamond acting as quantum nodes.

Dc Magnetometry with Engineered Nitrogen-Vacancy Spin Ensembles in Diamond.

The exquisite optical and spin properties of nitrogen-vacancy (NV) centers in diamond have made them a promising platform for quantum sensing. The prospect of NV-based sensors relies on the controlled production of these atomic-scale defects. Here we report on the fabrication of a preferentially oriented, shallow ensemble of NV centers and their applicability for sensing dc magnetic fields. For the present sample, the residual paramagnetic impurities are the dominant source of environmental noise, limiting the dephasing time (T2*) of the NVs. By controlling the P1 spin-bath, we achieve a 4-fold improvement in the T2* of the NV ensemble. Further, we show that combining spin-bath control and homonuclear decoupling sequence cancels NV-NV interactions and partially protects the sensors from a broader spin environment, thus extending the ensemble T2* up to 10 μs. With this decoupling protocol, we measure an improved dc magnetic field sensitivity of 1.2 nT μm3/2 Hz-1/2. Using engineered NVs and decoupling protocols, we demonstrate the prospects of harnessing the full potential of NV-based ensemble magnetometry.

Quantum state transfer between nitrogen vacancy center ensembles in hybrid quantum system

We propose a system for quantum state transfer (QST) between two nitrogen-vacancy center ensembles (NVEs) coupled to two transmission line resonators (TLRs) via flux qubits (FQs). We study the transfer of an arbitrary quantum state by various system's controlling parameters i.e., the coupling between nitrogen vacancy ensembles g, the coupling strength between resonators λ for both the resonant and non-resonant interactions in the presence of decoherence. Furthermore, we investigate the dynamics of QST for three different cases, i.e., , and in detail. It is found that the quantum state can be efficiently transferred between NVEs for suitable values of controlling parameters. We observe that the fidelity of quantum state transfer is about in all cases for short operational time while in the presence of decoherence fidelity is above . This reveals that decoherence has no prominent effect on quantum state transfer.