arXiv subjects

F. Jelezko

Publications and source records attributed to F. Jelezko.

At least 19 recordsLinked to original sources

arXiv2026

High yield creation of germanium vacancy centers in diamond by focused ion beam implantation and high temperature annealing

Negatively charged germanium vacancy centers (GeV) in diamond are a promising platform for quantum computing and quantum communication. However, these applications require the precise incorporation of GeV centers with good optical properties inside of nanophotonic structures. In this work, we demonstrate the highly efficient local creation of GeV centers in diamond via focused-ion-beam implantation, followed by high-temperature annealing. We report the successful creation of GeV centers over the depth range of 5.5 - 30 nm. Implantation at low fluence enables the creation of single GeV centers. The formation yield strongly depends on implantation energy and fluence, reaching up to 33% at energies of 35 and 70 keV. This method, therefore, enables the efficient creation of GeV centers within a small, well-defined local sample volume and offers a potential means of incorporating them into photonic structures.

quant-ph↗

arXiv2026

Phonon-assisted charge-cycling of nitrogen-vacancy centres in diamond

The nitrogen-vacancy (NV) centre in diamond is a leading platform for room-temperature quantum sensing. Improvements in sensitivity require precise control of the NV charge state. Transitions from the neutral NV$^0$ charge state to the negative NV$^-$ charge state can occur during excitation with photon energies below the ZPL transition of NV$^0$. These sub-resonant charge transitions limit modern initialisation protocols and have not been studied in full detail. In this paper we show that sub-resonant charge cycling arises from phonon-assisted anti-Stokes excitation. We further uncover the phonon states which contribute most strongly to the anti-Stokes transition via the development of novel quantitative models. The models indicate that low energy acoustic phonons strongly contribute to the transition close to the ZPL. At longer wavelengths a 43\,meV mode additionally impacts the charge cycling dynamics.

quant-ph↗

arXiv2021

Fabrication of $^{15}\textrm{NV}^{-}$ centers in diamond using a deterministic single ion implanter

Nitrogen Vacancy (NV) centers in diamond are a platform for several important quantum technologies, including sensing, communication and elementary quantum processors. In this letter we demonstrate the creation of NV centers by implantation using a deterministic single ion source. For this we sympathetically laser-cool single $^{15}\textrm{N}_2^+$ molecular ions in a Paul trap and extract them at an energy of 5.9\,keV. Subsequently the ions are focused with a lateral resolution of 121(35)\,nm and are implanted into a diamond substrate without any spatial filtering by apertures or masks. After high-temperature annealing, we detect the NV centers in a confocal microscope and determine a conversion efficiency of about 0.6\,$\%$. The $^{15}\textrm{NV}$ centers are characterized by optically detected magnetic resonance (ODMR) on the hyperfine transition and coherence time.

quant-ph↗

arXiv2020

Protecting quantum spin coherence of nanodiamonds in living cells

Due to its superior coherent and optical properties at room temperature, the nitrogen-vacancy (N-V ) center in diamond has become a promising quantum probe for nanoscale quantum sensing. However, the application of N-V containing nanodiamonds to quantum sensing suffers from their relatively poor spin coherence times. Here we demonstrate energy efficient protection of N-V spin coherence in nanodiamonds using concatenated continuous dynamical decoupling, which exhibits excellent performance with less stringent microwave power requirement. When applied to nanodiamonds in living cells we are able to extend the spin coherence time by an order of magnitude to the $T_1$-limit of up to $30μ$s. Further analysis demonstrates concomitant improvements of sensing performance which shows that our results provide an important step towards in vivo quantum sensing using N-V centers in nanodiamond.

quant-ph↗

arXiv2017

Narrowband quantum emitters over large spectral range with Fourier-limited linewidth in hexagonal boron nitride

Single defect centers in layered hexagonal boron nitride (hBN) are promising candidates as single photon sources for quantum optics and nanophotonics applications. However, until today spectral instability hinders many applications. Here, we perform resonant excitation measurements and observe Fourier-Transform limited (FL) linewidths down to $\approx 50$ MHz. We investigate optical properties of more than 600 quantum emitters (QE) in hBN. The QEs exhibit narrow zero-phonon lines (ZPL) distributed over a spectral range from 580 nm to 800 nm and with dipole-like emission with high polarization contrast. The emission frequencies can be divided into four main regions indicating distinct families or crystallographic structures of the QEs, in accord with ab-initio calculations. Finally, the emitters withstand transfer to a foreign photonic platform - namely a silver mirror, which makes them compatible with photonic devices such as optical resonators and paves the way to quantum photonics applications including quantum commmunications and quantum repeaters.

cond-mat.mes-hall↗

arXiv2017

Non-flipping 13C spins in NV diamond: Hyperfine and Spatial Characteristics by DFT Simulation of the C510[NV]H252 Cluster

Single NV centers in diamond coupled by hyperfine interaction to neighboring 13C nuclear spins are now widely used in the emerging quantum technologies as elements of quantum memory adjusted to NV center electron spin qubit. For nuclear spins with low flip-flop rate, single shot readout was demonstrated under ambient conditions. Here we report on the systematic search of such stable NV-13C systems using density functional theory (DFT) to simulate hyperfine and spatial characteristics of all possible NV-13C complexes in the H-terminated cluster C510 [NV]-H252 hosting the NV center. Along with the expected stable NV- axial 13C systems wherein the 13C nuclear spin is located on the NV axis, we found for the first time new families of positions for the 13C nuclear spin exhibiting negligible hyperfine-induced flipping rates due to near-symmetric local spin density distribution. Spatially, these positions are located in the diamond bilayer passing through the vacancy of the NV center and being perpendicular to the NV axis. Analysis of available publications showed that, apparently, some of the predicted non-axial near-stable systems NV-13C have already been observed experimentally. A special experiment done on one of these systems confirmed the prediction made

quant-ph↗

arXiv2017

A bright nanowire single photon source based on SiV centers in diamond

The practical implementation of many quantum technologies relies on the development of robust and bright single photon sources that operate at room temperature. The negatively charged silicon-vacancy (SiV-) color center in diamond is a possible candidate for such a single photon source. However, due to the high refraction index mismatch to air, color centers in diamond typically exhibit low photon out-coupling. An additional shortcoming is due to the random localization of native defects in the diamond sample. Here we demonstrate deterministic implantation of Si ions with high conversion efficiency to single SiV- centers, targeted to fabricated nanowires. The co-localization of single SiV- centers with the nanostructures yields a ten times higher light coupling efficiency than for single SiV- centers in bulk diamond. This enhanced photon out-coupling, together with the intrinsic scalability of the SiV- creation method, enables a new class of devices for integrated photonics and quantum science.

physics.app-ph↗

arXiv2017

Towards hyperpolarization of oil molecules via nitrogen-vacancy centers in diamond

Efficient polarization of organic molecules is of extraordinary relevance when performing nuclear magnetic resonance (NMR) and imaging. Commercially available routes to dynamical nuclear polarization (DNP) work at extremely low-temperatures, thus bringing the molecules out of their ambient thermal conditions and relying on the solidification of organic samples. In this work we investigate polarization transfer from optically-pumped nitrogen vacancy centers in diamond to external molecules at room temperature. This polarization transfer is described by both an extensive analytical analysis and numerical simulations based on spin bath bosonization and is supported by experimental data in excellent agreement. These results set the route to hyperpolarization of diffusive molecules in different scenarios and consequently, due to increased signal, to high-resolution NMR.

quant-ph↗

arXiv2017

Mapping the local spatial charge in defective diamond by means of NV sensors - A "self-diagnostic" concept

Electrically-active defects have a significant impact on the performance of electronic devices based on wide band-gap materials such as diamond. This issue is ubiquitous in diamond science and technology, since the presence of charge traps in the active regions of different classes of diamond-based devices (detectors, power diodes, transistors) can significantly affect their performances, due to the formation of space charge, memory effects and the degradation of the electronic response associated with radiation damage. Among the most common defects in diamond, the nitrogen-vacancy (NV) center possesses unique spin properties which enable high-sensitivity field sensing at the nanoscale. Here we demonstrate that NV ensembles can be successfully exploited to perform a direct local mapping of the internal electric field distribution of a graphite-diamond-graphite junction exhibiting electrical properties dominated by trap- and space-charge-related conduction mechanisms. By performing optically-detected magnetic resonance measurements, we performed both punctual readout and spatial mapping of the electric field in the active region at different bias voltages. In this novel "self-diagnostic" approach, defect complexes represent not only the source of detrimental space charge effects, but also a unique tool to directly investigate them, by providing experimental evidences on the conduction mechanisms that in previous studies could only be indirectly inferred on the basis of conventional electrical and optical characterization.

cond-mat.mtrl-sci↗

arXiv2017

Optical Cryocooling of Diamond

The cooling of solids by optical means only using anti-Stokes emission has a long history of research and achievements. Such cooling methods have many advantages ranging from no-moving parts or fluids through to operation in vacuum and may have applications to cryosurgery. However achieving large optical cryocooling powers has been difficult to achieve except in certain rare-earth crystals. Through study of the emission and absorption cross sections we find that diamond, containing either NV or SiV (Nitrogen or Silicon vacancy), defects shows potential for optical cryocooling and in particular, NV doping shows promise for optical refrigeration. We study the optical cooling of doped diamond microcrystals ranging 10-250 microns in diameter trapped either in vacuum or in water. For the vacuum case we find NV-doped microdiamond optical cooling below room temperature could exceed 10 Kelvin, for irradiation powers of P< 100 mW. We predict that such temperature changes should be easily observed via large alterations in the diffusion constant for optically cryocooled microdiamonds trapped in water in an optical tweezer or via spectroscopic signatures such as the ZPL width or Raman line.

quant-ph↗

arXiv2016

Fully robust qubit in atomic and molecular three-level systems

We present a new method of constructing a fully robust qubit in a three-level system. By the application of continuous driving fields, robustness to both external and controller noise is achieved. Specifically, magnetic noise and power fluctuations do not operate within the robust qubit subspace. Whereas all the continuous driving based constructions of such a fully robust qubit considered so far have required at least four levels, we show that in fact only three levels are necessary. This paves the way for simple constructions of a fully robust qubit in many atomic and solid state systems that are controlled by either microwave or optical fields. We focus on the NV-center in diamond and analyze the implementation of the scheme, by utilizing the electronic spin sub-levels of its ground state. In current state-of-the-art experimental setups the scheme leads to improvement of more than two orders of magnitude in coherence time, pushing it towards the lifetime limit. We show how the fully robust qubit can be used to implement quantum sensing, and in particular, the sensing of high frequency signals.

quant-ph↗

arXiv2016

Towards 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 $50\,$ $μ$s are demonstrated at depths of less than $5\,$nm in material with $1.1\,\%$ of $^{13}$C (depth estimated by spin relaxation (T$_1$) measurements). At the end, the limits of the helium irradiation technique at high ion fluences are also experimentally investigated.

cond-mat.mes-hall↗

arXiv2015

Optical hyperpolarization of 13C nuclear spins in nanodiamond ensembles

Here we propose and analyse in detail protocols that can achieve rapid hyperpolarization of 13C nuclear spins in randomly oriented ensembles of nanodiamonds at room temperature. Our protocols exploit a combination of optical polarization of electron spins in nitrogen-vacancy centers and the transfer of this polarization to 13C nuclei by means of microwave control to overcome the severe challenges that are posed by the random orientation of the nanodiamonds and their nitrogen-vacancy centers. Specifically, these random orientations result in exceedingly large energy variations of the electron spin levels that render the polarization and coherent control of the nitrogen-vacancy center electron spins as well as the control of their coherent interaction with the surrounding 13C nuclear spins highly inefficient. We address these challenges by a combination of an off-resonant microwave double resonance scheme in conjunction with a realization of the integrated solid effect which, together with adiabatic rotations of external magnetic fields or rotations of nanodiamonds, leads to a protocol that achieves high levels of hyperpolarization of the entire nuclear-spin bath in a randomly oriented ensemble of nanodiamonds even at room temperature. This hyperpolarization together with the long nuclear spin polarization lifetimes in nanodiamonds and the relatively high density of 13C nuclei has the potential to result in a major signal enhancement in 13C nuclear magnetic resonance imaging and suggests functionalized and hyperpolarized nanodiamonds as a unique probe for molecular imaging both in vitro and in vivo.

quant-ph↗

arXiv2015

Highly selective detection of individual nuclear spins using the rotary echo on an electron spin as a probe

We consider an electronic spin, such as a nitrogen-vacancy (NV) center in diamond, weakly coupled to a large number (bath) of nuclear spins, and subjected to the Rabi driving with a periodically alternating phase (multiple rotary echo). We show that by switching the driving phase synchronously with the precession of a given nuclear spin, the interaction to this spin is selectively enhanced, while the rest of the bath remains decoupled. The enhancement is of resonant character. The key feature of the suggested scheme is that the width of the resonance is adjustable, and can be greatly decreased by increasing the driving strength. Thus, the resonance can be significantly narrowed, by a factor of 10--100 in comparison with the existing detection methods. Significant improvement in selectivity is explained analytically and confirmed by direct numerical many-spin simulations. The method can be applied to a wide range of solid-state systems.

cond-mat.mes-hall↗

arXiv2015

Spectroscopy of Surface-Induced Noise Using Shallow Spins in Diamond

We report on the noise spectrum experienced by few nanometer deep nitrogen-vacancy centers in diamond as a function of depth, surface coating, magnetic field and temperature. Analysis reveals a double-Lorentzian noise spectra consistent with a surface electronic spin bath, with slower dynamics due to spin-spin interactions and faster dynamics related to phononic coupling. These results shed new light on the mechanisms responsible for surface noise affecting shallow spins at semiconductor interfaces, and suggests possible directions for further studies. We demonstrate dynamical decoupling from the surface noise, paving the way to applications ranging from nanoscale NMR to quantum networks.

quant-ph↗

arXiv2014

Isotopic identification of engineered nitrogen-vacancy spin qubits in ultrapure diamond

Nitrogen impurities help to stabilize the negatively-charged-state of NV$^-$ in diamond, whereas magnetic fluctuations from nitrogen spins lead to decoherence of NV$^-$ qubits. It is not known what donor concentration optimizes these conflicting requirements. Here we used 10-MeV $^{15}$N$^{3+}$ ion implantation to create NV$^-$ in ultrapure diamond. Optically detected magnetic resonance of single centers revealed a high creation yield of $40\pm3$% from $^{15}$N$^{3+}$ ions and an additional yield of $56\pm3$% from $^{14}$N impurities. High-temperature anneal was used to reduce residual defects, and charge stable NV$^-$, even in a dilute $^{14}$N impurity concentration of 0.06 ppb were created with long coherence times.

cond-mat.mes-hall↗

arXiv2014

Strong driving of a single spin using arbitrarily polarized fields

The strong driving regime occurs when a quantum two-level system is driven with an external field whose amplitude is greater or equal to the energy splitting between the system's states, and is typically identified with the breaking of the rotating wave approximation (RWA). We report an experimental study, in which the spin of a single nitrogen-vacancy (NV) center in diamond is strongly driven with microwave (MW) fields of arbitrary polarization. We measure the NV center spin dynamics beyond the RWA, and characterize the limitations of this technique for generating high-fidelity quantum gates. Using circularly polarized MW fields, the NV spin can be harmonically driven in its rotating frame regardless of the field amplitude, thus allowing rotations around arbitrary axes. Our approach can effectively remove the RWA limit in quantum-sensing schemes, and assist in increasing the number of operations in QIP protocols.

quant-ph↗

arXiv2013

Extending spin coherence times of diamond qubits by high temperature annealing

Spins of negatively charged nitrogen-vacancy (NV$^-$) defects in diamond are among the most promising candidates for solid-state qubits. The fabrication of quantum devices containing these spin-carrying defects requires position-controlled introduction of NV$^-$ defects having excellent properties such as spectral stability, long spin coherence time, and stable negative charge state. Nitrogen ion implantation and annealing enable the positioning of NV$^-$ spin qubits with high precision, but to date, the coherence times of qubits produced this way are short, presumably because of the presence of residual radiation damage. In the present work, we demonstrate that a high temperature annealing at 1000$^\circ$C allows 2 millisecond coherence times to be achieved at room temperature. These results were obtained for implantation-produced NV$^-$ defects in a high-purity, 99.99% $^{12}$C enriched single crystal chemical vapor deposited diamond. We discuss these remarkably long coherence times in the context of the thermal behavior of residual defect spins. [Published in Physical Review B {\bf{88}}, 075206 (2013)]

quant-ph↗