Search

With a highly coherent, optically addressable electron spin, the nitrogen-vacancy (NV) center in diamond is a promising candidate for a node in a quantum network. A resonant microcavity can boost the flux of coherent photons emerging from single NV centers. Here, we present an open Fabry–Pérot microcavity geometry containing a single-crystal diamond membrane, which operates in a regime where the vacuum electric field is strongly confined to the diamond membrane. There is a field anti-node at the diamond–air interface. Despite the presence of surface losses, a finesse of F = 11 500 was observed. The quality (Q) factor for the lowest mode number is 120 000 ; the mode volume V is estimated to be 3.9 λ 0 3 , where λ 0 is the free-space wavelength. We investigate the interplay between different loss mechanisms and the impact these loss channels have on the performance of the cavity. This analysis suggests that the surface waviness (roughness with a spatial frequency comparable to that of the microcavity mode) is the mechanism preventing the Q / V ratio from reaching even higher values. Finally, we apply the extracted cavity parameters to the NV center and calculate a predicted Purcell factor exceeding 150. [ABSTRACT FROM AUTHOR]

The article discusses the development of sensing techniques for magnetism have led to a series of revolutions, from the first compass to the MRI scanner. It mentions that their ability to detect weak signals down to the molecular level unlocks new perspectives, for example to characterize magnetic nanostructures as used in magnetic random access memory (MRAM) technologies.

Magnons can transfer information in metals and insulators without Joule heating, and therefore are promising for low-power computation. The on-chip magnonics however suffers from high losses due to limited magnon decay length. In metallic thin films, it is typically on the tens of micrometre length scale. Here, we demonstrate an ultra-long magnon decay length of up to one millimetre in multiferroic/ferromagnetic BiFeO3(BFO)/La0.67Sr0.33MnO3(LSMO) heterostructures at room temperature. This decay length is attributed to a magnon-phonon hybridization and is more than two orders of magnitude longer than that of bare metallic LSMO. The long-distance modes have high group velocities of 2.5 km s−1 as detected by time-resolved Brillouin light scattering. Numerical simulations suggest that magnetoelastic coupling via the BFO/LSMO interface hybridizes phonons in BFO with magnons in LSMO to form magnon-polarons. Our results provide a solution to the long-standing issue on magnon decay lengths in metallic magnets and advance the bourgeoning field of hybrid magnonics. Long-distance magnon transport is highly desired for magnonics. Here, the authors demonstrate a millimetre-long magnon decay length in multiferroic heterostructures, which is attributed to magnon-polarons induced by the magnetoelastic coupling. [ABSTRACT FROM AUTHOR]

The electronic spin of the nitrogen vacancy (NV) center in diamond forms an atomically sized, highly sensitive sensor for magnetic fields. To harness the full potential of individual NV centers for sensing with high sensitivity and nanoscale spatial resolution, NV centers have to be incorporated into scanning probe structures enabling controlled scanning in close proximity to the sample surface. Here, we present an optimized procedure to fabricate single-crystal, all-diamond scanning probes starting from commercially available diamond and show a highly efficient and robust approach for integrating these devices in a generic atomic force microscope. Our scanning probes consisting of a scanning nanopillar (200 nm diameter, 1–2 μm length) on a thin (<1 μm) cantilever structure enable efficient light extraction from diamond in combination with a high magnetic field sensitivity (ηAC ≈ 50 ± 20 nT/ √ Hz). As a first application of our scanning probes, we image the magnetic stray field of a single Ni nanorod. We show that this stray field can be approximated by a single dipole and estimate the NV-to-sample distance to a few tens of nanometer, which sets the achievable resolution of our scanning probes. [ABSTRACT FROM AUTHOR]

We demonstrate the controlled preparation of heteroepitaxial diamond nano- and microstructures on silicon wafer based iridium films as hosts for single color centers. Our approach uses electron beam lithography followed by reactive ion etching to pattern the carbon layer formed by bias enhanced nucleation on the iridium surface. In the subsequent chemical vapor deposition process, the patterned areas evolve into regular arrays of (001) oriented diamond nano-islands with diameters of <500 nm and a height of ≈60 nm. In the islands, we identify single SiV color centers with narrow zero phonon lines down to 1 nm at room temperature. [ABSTRACT FROM AUTHOR]

The Stokes and the anti-Stokes Raman spectra from the high energy carbon-carbon stretching modes in graphene and diamond are studied, with a focus on their intensity dependence on the excitation laser power. For diamond, the experiment was performed on a 50 μm slice of chemical vapour deposition grown single crystal using a 785 nm laser, in both the continuous wave (CW) and pulsed mode-locked (ML-130 fs pulses) excitation regimes. For graphene, the experiments were performed on suspended samples, including single layer, bilayer with AB-staking, twisted bi-layer and a sample with 4-6 layers, using λ = 532 and 633 nm CW lasers. The Stokes and anti-Stokes intensities vary largely from sample to sample, and the anti-Stokes/Stokes intensity ratio shows different excitation laser power behaviours. These differences can be explained on the basis of laser heating or correlated Stokes-anti-Stokes scattering phenomena. [ABSTRACT FROM AUTHOR]

Magnetic resonance techniques not only provide powerful imaging tools that have revolutionized medicine, but they have a wide spectrum of applications in other fields of science such as biology, chemistry, neuroscience and physics. However, current state-of-the-art magnetometers are unable to detect a single nuclear spin unless the tip-to-sample separation is made sufficiently small. Here, we demonstrate theoretically that by placing a ferromagnetic particle between a nitrogen-vacancy magnetometer and a target spin, the magnetometer sensitivity is improved dramatically. Using materials and techniques that are already experimentally available, our proposed set-up is sensitive enough to detect a single nuclear spin within ten milliseconds of data acquisition at room temperature. The sensitivity is practically unchanged when the ferromagnet surface to the target spin separation is smaller than the ferromagnet lateral dimensions; typically about a tenth of a micrometre. This scheme further benefits when used for nitrogen-vacancy ensemble measurements, enhancing sensitivity by an additional three orders of magnitude. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of single-crystalline diamond nanopillars on a (111)-oriented chemical vapor deposited diamond substrate. This crystal orientation offers optimal coupling of nitrogen-vacancy (NV) center emission to the nanopillar mode and is thus advantageous over previous approaches. We characterize single native NV centers in these nanopillars and find one of the highest reported saturated fluorescence count rates in single crystalline diamond in excess of 106 counts per second. We show that our nano-fabrication procedure conserves the preferential alignment as well as the spin coherence of the NVs in our structures. Our results will enable a new generation of highly sensitive probes for NV magnetometry and pave the way toward photonic crystals with optimal orientation of the NV center's emission dipole. [ABSTRACT FROM AUTHOR]

Solid-state quantum emitters, such as the nitrogen-vacancy centre in diamond, are robust systems for practical realizations of various quantum information processing protocols and nanoscale magnetometry schemes at room temperature. Such applications benefit from the high emission efficiency and flux of single photons, which can be achieved by engineering the electromagnetic environment of the emitter. One attractive approach is based on plasmonic resonators, in which sub-wavelength confinement of optical fields can strongly modify the spontaneous emission of a suitably embedded dipole despite having only modest quality factors. Meanwhile, the scalability of solid-state quantum systems critically depends on the ability to control such emitter-cavity interaction in a number of devices arranged in parallel. Here, we demonstrate a method to enhance the radiative emission rate of single nitrogen-vacancy centres in ordered arrays of plasmonic apertures that promises greater scalability over the previously demonstrated bottom-up approaches for the realization of on-chip quantum networks. [ABSTRACT FROM AUTHOR]

The nitrogen-vacancy (NV) defect center in diamond has demonstrated great capability for nanoscale magnetic sensing and imaging for both static and periodically modulated target fields. However, it remains a challenge to detect and image randomly fluctuating magnetic fields. Recent theoretical and numerical works have outlined detection schemes that exploit changes in decoherence of the detector spin as a sensitive measure for fluctuating fields. Here we experimentally monitor the decoherence of a scanning NV center in order to image the fluctuating magnetic fields from paramagnetic impurities on an underlying diamond surface. We detect a signal corresponding to roughly 800 μB in 2 s of integration time, without any control on the target spins, and obtain magnetic-field spectral information using dynamical decoupling techniques. The extracted spatial and temporal properties of the surface paramagnetic impurities provide insight to prolonging the coherence of near-surface qubits for quantum information and metrology applications.

The detection of ensembles of spins under ambient conditions has revolutionized the biological, chemical and physical sciences through magnetic resonance imaging1 and nuclear magnetic resonance2, 3. Pushing sensing capabilities to the individual-spin level would enable unprecedented applications such as single-molecule structural imaging; however, the weak magnetic fields from single spins are undetectable by conventional far-field resonance techniques4. In recent years, there has been a considerable effort to develop nanoscale scanning magnetometers5, 6, 7, 8, which are able to measure fewer spins by bringing the sensor in close proximity to its target. The most sensitive of these magnetometers generally require low temperatures for operation, but the ability to measure under ambient conditions (standard temperature and pressure) is critical for many imaging applications, particularly in biological systems. Here we demonstrate detection and nanoscale imaging of the magnetic field from an initialized single electron spin under ambient conditions using a scanning nitrogen-vacancy magnetometer. Real-space, quantitative magnetic-field images are obtained by deterministically scanning our nitrogen-vacancy magnetometer 50 nm above a target electron spin, while measuring the local magnetic field using dynamically decoupled magnetometry protocols. We discuss how this single-spin detection enables the study of a variety of room-temperature phenomena in condensed-matter physics with an unprecedented combination of spatial resolution and spin sensitivity., Engineering and Applied Sciences, Physics

We demonstrate an integrated nanophotonic network in diamond, consisting of a ring resonator coupled to an optical waveguide with grating in- and outcouplers. Using a nitrogen-vacancy color center embedded inside the ring resonator as a source of photons, single photon generation and routing at room temperature is observed. Furthermore, we observe a large overall photon extraction efficiency (10%) and high quality factors of ring resonators (3200 for waveguide-coupled system and 12 600 for a bare ring)., Engineering and Applied Sciences, Physics

We demonstrate coherent quantum control of a single spin driven by the motion of a mechanical resonator. The motion of a mechanical resonator is magnetically coupled to the electronic spin of a single nitrogen-vacancy center in diamond. Synchronization of spin-addressing protocols to the motion of the driven oscillator is used to fully exploit the coherence of this hybrid mechanical-spin system. We demonstrate applications of this coherent mechanical spin-control technique to nanoscale scanning magnetometry., Physics

The nitrogen-vacancy defect centre in diamond has potential applications in nanoscale electric and magnetic-field sensing, single-photon microscopy, quantum information processing and bioimaging. These applications rely on the ability to position a single nitrogen-vacancy centre within a few nanometres of a sample, and then scan it across the sample surface, while preserving the centre’s spin coherence and readout fidelity. However, existing scanning techniques, which use a single diamond nanocrystal grafted onto the tip of a scanning probe microscope, suffer from short spin coherence times due to poor crystal quality, and from inefficient far-field collection of the fluorescence from the nitrogen-vacancy centre. Here, we demonstrate a robust method for scanning a single nitrogen-vacancy centre within tens of nanometres from a sample surface that addresses both of these concerns. This is achieved by positioning a single nitrogen-vacancy centre at the end of a high-purity diamond nanopillar, which we use as the tip of an atomic force microscope. Our approach ensures long nitrogen-vacancy spin coherence times \(\textrm{(∼75 }\mu \textrm{s)}\), enhanced nitrogen-vacancy collection efficiencies due to waveguiding, and mechanical robustness of the device (several weeks of scanning time). We are able to image magnetic domains with widths of 25 nm, and demonstrate a magnetic field sensitivity of \(56\textrm{ nT Hz}^{–1/2}\) at a frequency of 33 kHz, which is unprecedented for scanning nitrogen-vacancy centres., Engineering and Applied Sciences, Physics, Other Research Unit

Solid-state quantum emitters, such as the nitrogen-vacancy centre in diamond, are robust systems for practical realizations of various quantum information processing protocols and nanoscale magnetometry schemes at room temperature. Such applications benefit from the high emission efficiency and flux of single photons, which can be achieved by engineering the electromagnetic environment of the emitter. One attractive approach is based on plasmonic resonators, in which sub-wavelength confinement of optical fields can strongly modify the spontaneous emission of a suitably embedded dipole despite having only modest quality factors. Meanwhile, the scalability of solid-state quantum systems critically depends on the ability to control such emitter–cavity interaction in a number of devices arranged in parallel. Here, we demonstrate a method to enhance the radiative emission rate of single nitrogen-vacancy centres in ordered arrays of plasmonic apertures that promises greater scalability over the previously demonstrated bottom-up approaches for the realization of on-chip quantum networks., Engineering and Applied Sciences, Physics

We report on direct, real-space imaging of the stray magnetic field above a micro-scale disc of a thin film of the high-temperature superconductor YBa2Cu3O7−δ (YBCO) using scanning single spin magnetometry. Our experiments yield a direct measurement of the sample's London penetration depth and allow for a quantitative reconstruction of the supercurrents flowing in the sample as a result of Meissner screening. These results show the potential of scanning single spin magnetometry for studies of the nanoscale magnetic properties of thin-film superconductors, which could be readily extended to elevated temperatures or magnetic fields. [ABSTRACT FROM AUTHOR]

Many promising applications of single crystal diamond and its color centers as sensor platform and in photonics require free-standing membranes with a thickness ranging from several micrometers to the few 100 nm range. In this work, we present an approach to conveniently fabricate such thin membranes with up to about one millimeter in size. We use commercially available diamond plates (thickness 50 μ m) in an inductively coupled reactive ion etching process which is based on argon, oxygen and SF 6 . We thus avoid using toxic, corrosive feed gases and add an alternative to previously presented recipes involving chlorine-based etching steps. Our membranes are smooth (RMS roughness <1 nm) and show moderate thickness variation (central part: <1 μ m over ≈200 × 200 μ m 2 ). Due to an improved etch mask geometry, our membranes stay reliably attached to the diamond plate in our chlorine-based as well as SF 6 -based processes. Our results thus open the route towards higher reliability in diamond device fabrication and up-scaling. [ABSTRACT FROM AUTHOR]

Magnetism of oxide antiferromagnets (AFMs) has been studied in single crystals and extended thin films. The properties of AFM nanostructures still remain underexplored. Here, we report on the fabrication and magnetic imaging of granular 100 nm-thick magnetoelectric Cr 2 O 3 films patterned in circular bits with diameters ranging from 500 down to 100 nm. With the change of the lateral size, the domain structure evolves from a multidomain state for larger bits to a single domain state for the smallest bits. Based on spin-lattice simulations, we show that the physics of the domain pattern formation in granular AFM bits is primarily determined by the energy dissipation upon cooling, which results in motion and expelling of AFM domain walls of the bit. Our results provide a way toward the fabrication of single domain AFM-bit-patterned memory devices and the exploration of the interplay between AFM nanostructures and their geometric shape.

The exchange bias phenomenon, inherent in exchange-coupled ferromagnetic and antiferromagnetic systems, has intrigued researchers for decades. Van der Waals materials, with their layered structures, offer an ideal platform for exploring exchange bias. However, effectively manipulating exchange bias in van der Waals heterostructures remains challenging. This study investigates the origin of exchange bias in MnPS 3 /Fe 3 GeTe 2 van der Waals heterostructures, demonstrating a method to modulate nearly 1000% variation in magnitude through simple thermal cycling. Despite the compensated interfacial spin configuration of MnPS 3 , a substantial 170 mT exchange bias is observed at 5 K, one of the largest observed in van der Waals heterostructures. This significant exchange bias is linked to anomalous weak ferromagnetic ordering in MnPS 3 below 40 K. The tunability of exchange bias during thermal cycling is attributed to the amorphization and changes in the van der Waals gap during field cooling. The findings highlight a robust and adjustable exchange bias in van der Waals heterostructures, presenting a straightforward method to enhance other interface-related spintronic phenomena for practical applications. Detailed interface analysis reveals atom migration between layers, forming amorphous regions on either side of the van der Waals gap, emphasizing the importance of precise interface characterization in these heterostructures., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

We present a comprehensive study of the temperature- and magnetic-field-dependent photoluminescence (PL) of individual NV centers in diamond, spanning the temperature-range from cryogenic to ambient conditions. We directly observe the emergence of the NV's room-temperature effective excited-state structure and provide a clear explanation for a previously poorly understood broad quenching of NV PL at intermediate temperatures around 50 K, as well as the subsequent revival of NV PL. We develop a model based on two-phonon orbital averaging that quantitatively explains all of our findings, including the strong impact that strain has on the temperature dependence of the NV's PL. These results complete our understanding of orbital averaging in the NV excited state and have significant implications for the fundamental understanding of the NV center and its applications in quantum sensing.

Neutral silicon vacancy centers (SiV^{0}) in diamond are promising candidates for quantum applications; however, stabilizing SiV^{0} requires high-purity, boron-doped diamond, which is not a readily available material. Here, we demonstrate an alternative approach via chemical control of the diamond surface. We use low-damage chemical processing and annealing in a hydrogen environment to realize reversible and highly stable charge state tuning in undoped diamond. The resulting SiV^{0} centers display optically detected magnetic resonance and bulklike optical properties. Controlling the charge state tuning via surface termination offers a route for scalable technologies based on SiV^{0} centers, as well as charge state engineering of other defects.

We investigate the magnetic field dependent photophysics of individual nitrogen-vacancy (NV) color centers in diamond under cryogenic conditions. At distinct magnetic fields, we observe significant reductions in the NV photoluminescence rate, which indicate a marked decrease in the optical readout efficiency of the NV's ground state spin. We assign these dips to excited state level anticrossings, which occur at magnetic fields that strongly depend on the effective, local strain environment of the NV center. Our results offer new insights into the structure of the NVs' excited states and a new tool for their effective characterization. Using this tool, we observe strong indications for strain-dependent variations of the NV's orbital g factor, obtain new insights into NV charge state dynamics, and draw important conclusions regarding the applicability of NV centers for low-temperature quantum sensing.

Thin films of the magnetoelectric insulator α-Cr 2 O 3 are technologically relevant for energy-efficient magnetic memory devices controlled by electric fields. In contrast to single crystals, the quality of thin Cr 2 O 3 films is usually compromised by the presence of point defects and their agglomerations at grain boundaries, putting into question their application potential. Here, the impact of the defect nanostructure, including sparse small-volume defects and their complexes is studied on the magnetic properties of Cr 2 O 3 thin films. By tuning the deposition temperature, the type, size, and relative concentration of defects is tailored, which is analyzed using the positron annihilation spectroscopy complemented with electron microscopy studies. The structural characterization is correlated with magnetotransport measurements and nitrogen-vacancy microscopy of antiferromagnetic domain patterns. Defects pin antiferromagnetic domain walls and stabilize complex multidomain states with a domain size in the sub-micrometer range. Despite their influence on the domain configuration, neither small open-volume defects nor grain boundaries in Cr 2 O 3 thin films affect the Néel temperature in a broad range of deposition parameters. The results pave the way toward the realization of spin-orbitronic devices where magnetic domain patterns can be tailored based on defect nanostructures without affecting their operation temperature., (© 2022 The Authors. Small published by Wiley-VCH GmbH.)

Twisted-bilayer graphene (tBLG) exhibits van Hove singularities in the density of states that can be tuned by changing the twisting angle θ. A θ-defined tBLG has been produced and characterized with optical reflectivity and resonance Raman scattering. The θ-engineered optical response is shown to be consistent with persistent saddle-point excitons. Separate resonances with Stokes and anti-Stokes Raman scattering components can be achieved due to the sharpness of the two-dimensional saddle-point excitons, similar to what has been previously observed for one-dimensional carbon nanotubes. The excitation power dependence for the Stokes and anti-Stokes emissions indicate that the two processes are correlated and that they share the same phonon.