Andrej Denisenko

Coherent control of single spins in silicon carbide at room temperature

Spins in solids are cornerstone elements of quantum spintronics. Leading contenders such as defects in diamond or individual phosphorus dopants in silicon have shown spectacular progress, but either lack established nanotechnology or an efficient spin/photon interface. Silicon carbide (SiC) combines the strength of both systems: it has a large bandgap with deep defects and benefits from mature fabrication techniques. Here, we report the characterization of photoluminescence and optical spin polarization from single silicon vacancies in SiC, and demonstrate that single spins can be addressed at room temperature. We show coherent control of a single defect spin and find long spin coherence times under ambient conditions. Our study provides evidence that SiC is a promising system for atomic-scale spintronics and quantum technology.

Nanoengineered diamond waveguide as a robust bright platform for nanomagnetometry using shallow nitrogen vacancy centers.

Photonic structures in diamond are key to most of its application in quantum technology. Here, we demonstrate tapered nanowaveguides structured directly onto the diamond substrate hosting shallow-implanted nitrogen vacancy (NV) centers. By optimization based on simulations and precise experimental control of the geometry of these pillar-shaped nanowaveguides, we achieve a net photon flux up to ∼ 1.7 × 10(6) s(-1). This presents the brightest monolithic bulk diamond structure based on single NV centers so far. We observe no impact on excited state lifetime and electronic spin dephasing time (T2) due to the nanofabrication process. Possessing such high brightness with low background in addition to preserved spin quality, this geometry can improve the current nanomagnetometry sensitivity ∼ 5 times. In addition, it facilitates a wide range of diamond defects-based magnetometry applications. As a demonstration, we measure the temperature dependency of T1 relaxation time of a single shallow NV center electronic spin. We observe the two-phonon Raman process to be negligible in comparison to the dominant two-phonon Orbach process.

Enhancing the spin properties of shallow implanted nitrogen vacancy centers in diamond by epitaxial overgrowth

Scaling of diamond defect center based quantum registers relies on the ability to position nitrogen vacancy (NV) centers with high spatial resolution. Using ion implantation, shallow (<10 nm) NVs can be placed with accuracy below 20 nm, but generally show reduced spin properties compared to bulk NVs. We demonstrate the enhancement of spin properties for shallow implanted NVs using a diamond overgrowth technique. An increase of coherence times up to an order of magnitude (T2 = 250 μs) was achieved, ms decoherence times were realized using dynamical decoupling. This marks a further step towards achieving strong coupling among defects positioned with nm precision.

Nanoscale nuclear magnetic resonance with chemical resolution

NMR on diamonds gets down to chemistry Nuclear magnetic resonance (NMR) spectroscopy is immensely useful for chemical characterization, but it requires relatively large amounts of sample. Recent studies have leveraged nitrogen vacancy centers in diamond to detect NMR signals from samples of just a few cubic nanometers, but with low resolution. Aslam et al. optimized this technique to achieve a resolution of 1 part per million—sufficient to distinguish among alkyl, vinyl, and aryl protons in solution (see the Perspective by Bar-Gill and Retzker). They also demonstrated solid-state implementation and fluorine detection. Science, this issue p. 67; see also p. 38 Nuclear magnetic resonance spectra of miniscule samples via nitrogen vacancies in diamond resolve chemical functionality. Nuclear magnetic resonance (NMR) spectroscopy is a key analytical technique in chemistry, biology, and medicine. However, conventional NMR spectroscopy requires an at least nanoliter-sized sample volume to achieve sufficient signal. We combined the use of a quantum memory and high magnetic fields with a dedicated quantum sensor based on nitrogen vacancy centers in diamond to achieve chemical shift resolution in 1H and 19F NMR spectroscopy of 20-zeptoliter sample volumes. We demonstrate the application of NMR pulse sequences to achieve homonuclear decoupling and spin diffusion measurements. The best measured NMR linewidth of a liquid sample was ~1 part per million, mainly limited by molecular diffusion. To mitigate the influence of diffusion, we performed high-resolution solid-state NMR by applying homonuclear decoupling and achieved a 20-fold narrowing of the NMR linewidth.

Effect of low-damage inductively coupled plasma on shallow nitrogen-vacancy centers in diamond

Near-surface nitrogen-vacancy (NV) centers in diamond have been successfully employed as atomic-sized magnetic field sensors for external spins over the last years. A key challenge is still to develop a method to bring NV centers at nanometer proximity to the diamond surface while preserving their optical and spin properties. To that aim we present a method of controlled diamond etching with nanometric precision using an oxygen inductively coupled plasma process. Importantly, no traces of plasma-induced damages to the etched surface could be detected by X-ray photoelectron spectroscopy and confocal photoluminescence microscopy techniques. In addition, by profiling the depth of NV centers created by 5.0 keV of nitrogen implantation energy, no plasma-induced quenching in their fluorescence could be observed. Moreover, the developed etching process allowed even the channeling tail in their depth distribution to be resolved. Furthermore, treating a 12C isotopically purified diamond revealed a threefold increa...

Toward Optimized Surface δ-Profiles of Nitrogen-Vacancy Centers Activated by Helium Irradiation in Diamond

The negatively charged nitrogen-vacancy (NV) center in diamond has been shown recently as an excellent sensor for external spins. Nevertheless, their optimum engineering in the near-surface region still requires quantitative knowledge in regard to their activation by vacancy capture during thermal annealing. To this aim, we report on the depth profiles of near-surface helium-induced NV centers (and related helium defects) by step-etching with nanometer resolution. This provides insights into the efficiency of vacancy diffusion and recombination paths concurrent to the formation of NV centers. It was found that the range of efficient formation of NV centers is limited only to approximately 10 to 15 nm (radius) around the initial ion track of irradiating helium atoms. Using this information we demonstrate the fabrication of nanometric-thin (δ) profiles of NV centers for sensing external spins at the diamond surface based on a three-step approach, which comprises (i) nitrogen-doped epitaxial CVD diamond overgrowth, (ii) activation of NV centers by low-energy helium irradiation and thermal annealing, and (iii) controlled layer thinning by low-damage plasma etching. Spin coherence times (Hahn echo) ranging up to 50 μs are demonstrated at depths of less than 5 nm in material with 1.1% of (13)C (depth estimated by spin relaxation (T1) measurements). At the end, the limits of the helium irradiation technique at high ion fluences are also experimentally investigated.

Thin Circular Diamond Membrane with Embedded Nitrogen-Vacancy Centers for Hybrid Spin-Mechanical Quantum Systems

Hybrid quantum systems (HQSs) have attracted several research interests in the last years. In this Letter, we report on the design, fabrication, and characterization of a novel diamond architecture for HQSs that consists of a high quality thin circular diamond membrane with embedded near-surface nitrogen-vacancy centers (NVCs). To demonstrate this architecture, we employed the NVCs by means of their optical and spin interfaces as nanosensors of the motion of the membrane under static pressure and in-resonance vibration, as well as the residual stress of the membrane. Driving the membrane at its fundamental resonance mode, we observed coupling of this vibrational mode to the spin of the NVCs by Hahn echo signal. Our realization of this architecture will enable futuristic HQS-based applications in diamond piezometry and vibrometry, as well as spin-mechanical and mechanically mediated spin-spin coupling in quantum information science.

Tailoring spin defects in diamond by lattice charging

Atomic-size spin defects in solids are unique quantum systems. Most applications require nanometre positioning accuracy, which is typically achieved by low-energy ion implantation. A drawback of this technique is the significant residual lattice damage, which degrades the performance of spins in quantum applications. Here we show that the charge state of implantation-induced defects drastically influences the formation of lattice defects during thermal annealing. Charging of vacancies at, for example, nitrogen implantation sites suppresses the formation of vacancy complexes, resulting in tenfold-improved spin coherence times and twofold-improved formation yield of nitrogen-vacancy centres in diamond. This is achieved by confining implantation defects into the space-charge layer of free carriers generated by a boron-doped diamond structure. By combining these results with numerical calculations, we arrive at a quantitative understanding of the formation and dynamics of the implanted spin defects. These results could improve engineering of quantum devices using solid-state systems.

Protecting a Diamond Quantum Memory by Charge State Control

In recent years, solid-state spin systems have emerged as promising candidates for quantum information processing. Prominent examples are the nitrogen-vacancy (NV) center in diamond, phosphorus dopants in silicon (Si:P), rare-earth ions in solids, and VSi-centers in silicon-carbide. The Si:P system has demonstrated that its nuclear spins can yield exceedingly long spin coherence times by eliminating the electron spin of the dopant. For NV centers, however, a proper charge state for storage of nuclear spin qubit coherence has not been identified yet. Here, we identify and characterize the positively charged NV center as an electron-spin-less and optically inactive state by utilizing the nuclear spin qubit as a probe. We control the electronic charge and spin utilizing nanometer scale gate electrodes. We achieve a lengthening of the nuclear spin coherence times by a factor of 4. Surprisingly, the new charge state allows switching of the optical response of single nodes facilitating full individual addressability.

Efficient creation of dipolar coupled nitrogen-vacancy spin qubits in diamond

Coherently coupled pairs or multimers of nitrogen-vacancy defect electron spins in diamond have many promising applications especially in quantum information processing (QIP) but also in nanoscale sensing applications. Scalable registers of spin qubits are essential to the progress of QIP. Ion implantation is the only known technique able to produce defect pairs close enough to allow spin coupling via dipolar interaction. Although several competing methods have been proposed to increase the resulting resolution of ion implantation, the reliable creation of working registers is still to be demonstrated. The current limitation are residual radiation-induced defects, resulting in degraded qubit performance as trade-off for positioning accuracy. Here we present an optimized estimation of nanomask implantation parameters that are most likely to produce interacting qubits under standard conditions. We apply our findings to a well-established technique, namely masks written in electron-beam lithography, to create coupled defect pairs with a reasonable probability. Furthermore, we investigate the scaling behavior and necessary improvements to efficiently engineer interacting spin architectures.