arXiv subjects

Jocelyn Achard

Publications and source records attributed to Jocelyn Achard.

18 recordsLinked to original sources

arXiv2026

Oxygen in diamond: thermal stability of ST1 spin centres and creation of oxygen-pair complexes

Little is known about oxygen-related defects in diamond. Recently, the promising room-temperature spin centre named ST1 was identified as an oxygen centre, but of still unknown atomic structure and thermal stability. In this work, we report on the optically active oxygen-related centres and the conditions for their formation, using ion implantation of oxygen in various conditions of depth and fluence. More specifically, we establish the temperature formation/stability range of the ST1 centre, which has a maximum at about 1100°C and is narrower than for NV centres. In these conditions, optically detected magnetic resonance (ODMR) on small ST1 ensembles was measured with a spin readout contrast of > 20% at 300K. In cathodoluminescence, the 535 nm ST1 peak is not observed. Besides, a broad peak centred at 460 nm is measured for implantation of O$_2$ molecular ions. For an annealing temperature of 1500°C, a different centre is formed (with ZPL at 584.5 nm) with an intensity increasing with a power law 1.5 < p < 1.9 dependence from the implantation fluence. This suggests that this centre contains two oxygen atoms. Besides, a new spectral feature associated to an intrinsic defect was also observed, with four prominent lines (especially at 594nm). Finally, the thermal formation and stability of oxygen centres in diamond presented here are important for the identification of the atomic structure of defects such as the ST1 and possible O$_2$V$_x$ complex by means of ab initio calculations. Indeed, the formation energies and charge states of defect centres are easier to compute than the full energy level scheme, which to date still remains unsuccessful regarding the ST1 centre.

cond-mat.mtrl-sci↗

arXiv2025

Enhanced magnetic field sensitivity of shallow NV$^-$ ensembles via high-temperature implantation

Dense and shallow ensembles of negatively charged nitrogen-vacancy centers (NV$^-$) with good optical and spin properties play a key role in the performance enhancement of diamond-based quantum sensors. Ion implantation enables precise control of NV$^-$ depth and density. However, at high ion fluence, this method is limited by low NV$^-$ creation yields and sample amorphization. Additionally, shallow NV$^-$ spin properties deteriorate due to surface proximity. In this paper, we study N$_2^+$ ion implantation at energies between 10 and 15 keV with fluences as high as 1e15 ions/cm2 at temperatures of 20, 400 and 800°C to investigate the influence of implantation temperature on lattice damage, NV$^-$ creation yield and NV$^-$ spin properties. Our results show that diamond maintains structural integrity at 800°C with fluences up to 1e15 ions/cm2 without amorphization. Furthermore, high-temperature implantation improves NV$^-$ creation yields up to five times without compromising T2$^*$, T2 and T1, making it a promising approach to enhance the magnetic field sensitivity of NV$^-$ ensembles.

quant-ph↗

arXiv2025

Interactions in Rare Earth Doped Nanoparticles: A Multi-Transition, Concentration, and Excitation Path Analysis

Understanding and modeling energy transfer mechanisms in rare-earth-doped nanomaterials is essential for advancing luminescent technologies used in bioimaging, optical thermometry, and solid-state lasers. In this work, we investigate the photoluminescence dynamics of Yb3+ and Er3+ ions in Y2O3 nanoparticles over a wide concentration range (0.5-17%), using both direct and upconversion excitation. Luminescence decays of green, red, and near-infrared transitions were measured and analyzed using a rate-equation model incorporating radiative and non-radiative processes, energy transfer mechanisms, and defect-related quenching. The model successfully reproduces experimental trends across most concentrations and excitation paths. This work provides a reliable and predictive framework for modeling energy transfer in rare-earth doped materials and offers valuable insights for optimizing photoluminescent properties in nanostructured systems.

cond-mat.mtrl-sci↗

arXiv2025

Nitrogen-Vacancy Centers in Epitaxial Laterally Overgrown Diamond: Towards Up-scaling of Color Center-based Quantum Technologies

Providing high-quality, single-crystal diamond (SCD) with a large area is desirable for up-scaling quantum technology applications that rely on color centers in diamond. Growth methods aiming to increase the area of SCD are an active research area. Native color centers offer a sensitive probe for local crystal quality in such novel materials e.g., via their reaction to stress. In this work, we investigate individual native nitrogen-vacancy (NV) centers in SCD layers manufactured via laterally overgrowing hole arrays in a heteroepitaxially grown large-scale substrate. Heteroepitaxy has become a common tool for growing large SCDs; however, achieving the high crystal quality needed for quantum applications remains a challenge. In the overgrown layer, we identify NV centers with spin-decoherence times in the order of hundreds of microseconds, comparable to high-purity homoepitaxial SCD. We quantify the effective crystal strain in different regions of the overgrown layer, indicating a low stress overall and a stress reduction in the diamond layer above the holes.

cond-mat.mtrl-sci↗

arXiv2023

Hot ion implantation to create dense NV centre 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 localisation and density of NV colour centres 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 to 40 keV range at high temperatures. At 800 C, NV 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 2E14 ions per 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.

physics.app-ph↗

arXiv2022

All-Optical Nuclear Quantum Sensing using Nitrogen-Vacancy Centers in Diamond

Solid state spins have demonstrated significant potential in quantum sensing with applications including fundamental science, medical diagnostics and navigation. The quantum sensing schemes showing best performance under ambient conditions all utilize microwave or radio-frequency driving, which poses a significant limitation for miniaturization, energy-efficiency and non-invasiveness of quantum sensors. We overcome this limitation by demonstrating a purely optical approach to coherent quantum sensing. Our scheme involves the $^{15}$N nuclear spin of the Nitrogen-Vacancy (NV) center in diamond as a sensing resource, and exploits NV spin dynamics in oblique magnetic fields near the NV's excited state level anti-crossing to optically pump the nuclear spin into a quantum superposition state. We demonstrate all-optical free-induction decay measurements - the key protocol for low-frequency quantum sensing - both on single spins and spin ensembles. Our results pave the way for highly compact quantum sensors to be employed for magnetometry or gyroscopy applications in challenging environments.

cond-mat.mes-hall↗

arXiv2022

Optical properties of SiV and GeV color centers in nanodiamonds under hydrostatic pressures up to 180 GPa

We investigate the optical properties of silicon-vacancy (SiV) and germanium-vacancy (GeV) color centers in nanodiamonds under hydrostatic pressure up to 180 GPa. The nanodiamonds were synthetized by Si or Ge-doped plasma assisted chemical vapor deposition and, for our experiment, pressurized in a diamond anvil cell. Under hydrostatic pressure we observe blue-shifts of the SiV and GeV zero-phonon lines by 17 THz (70 meV) and 78 THz (320 meV), respectively. These measured pressure induced shifts are in good agreement with ab initio calculations that take into account the lattice compression based on the equation of state of diamond and that are extended to the case of the tin-vacancy (SnV) center. This work provides guidance on the use of group-IV-vacancy centers as quantum sensors under extreme pressures that will exploit their specific optical and spin properties induced by their intrinsic inversion-symmetric structure.

quant-ph↗

arXiv2022

Microscopic-scale recording of brain neuronal electrical activity using a diamond quantum sensor

An important tool in the investigation of the early stages of neurodegenerative disease is the study of dissected living tissue from the brain of an animal model. Such investigations allow the physical structure of individual neurons and neural circuits to be probed alongside neuronal electrical activity, disruption of which can shed light on the mechanisms of emergence of disease. Existing techniques for recording activity rely on potentially damaging direct interaction with the sample, either mechanically as point electrical probes or via intense focused laser light combined with highly specific genetic modification and/or potentially toxic fluorescent dyes. In this work, we instead perform passive, microscopic-scale recording of electrical activity using a biocompatible quantum sensor based on colour centres in diamond. We record biomagnetic field induced by ionic currents in mouse corpus callosum axons without direct sample interaction, accurately recovering signals corresponding to action potential propagation while demonstrating in situ pharmacology during biomagnetic recording through tetrodotoxin inhibition of voltage gated sodium channels. Our results open a promising new avenue for the microscopic recording of neuronal signals, offering the prospect of high resolution imaging of electrical circuits in the living mammalian brain.

physics.bio-ph↗

arXiv2021

Laser stimulation of muscle activity with simultaneous detection using a diamond colour centre biosensor

The detection of physiological activity at the microscopic level is key for understanding the function of biosystems and relating this to physical structure. Current sensing methods often rely on invasive probes to stimulate and detect activity, bearing the risk of inducing damage in the target system. In recent years, a new type of biosensor based on color centers in diamond offers the possibility to passively, noninvasively sense and image living biological systems. Here, we use such a sensor for the \textit{in-vitro} recording of the local magnetic field generated by tightly focused, high intensity pulsed laser optogenetic neuromuscular stimulation of the extensor digitorum longus muscles. Recordings captured a compound action potential response and a slow signal component which we seek to explain using a detailed model of the biological system. We show that our sensor is capable of recording localized neuromuscular activity from the laser stimulation site without photovoltaic or fluorescence artifacts associated with alternative techniques. Our work represents an important step towards selective induction of localized neurobiological activity while performing passive sensing and imaging with diamond sensors, motivating further research into mapping of neural activity and intra-cellular processes.

physics.bio-ph↗

arXiv2021

Surface production of negative ions from pulse-biased nitrogen doped diamond within a low-pressure deuterium plasma

The production of negative ions is of significant interest for applications including mass spectrometry, materials surface processing, and neutral beam injection for magnetic confined fusion. Neutral beam injection sources maximise negative ion production through the use of surface production processes and low work function metals, which introduce complex engineering. Investigating materials and techniques to avoid the use of low work function metals is of interest to broaden the application of negative ion sources and simplify future devices. In this study, we use pulsed sample biasing to investigate the surface production of negative ions from nitrogen doped diamond. The use of a pulsed bias allows for the study of insulating samples in a preserved surface state at temperatures between 150$^{\circ}$C and 700$^{\circ}$C in a 2 Pa, 130 W, (n$_e$ $\sim$ $10^9$ cm$^{-3}$, T$_e$ $\sim$ 0.6 eV) inductively coupled deuterium plasma. The negative ion yield during the application of a pulsed negative bias is measured using a mass spectrometer and found to be approximately 20% higher for nitrogen doped diamond compared to non-doped diamond. It is also shown that the pulsed sample bias has a lower peak negative ion yield compared to a continuous sample bias, which suggests that the formation of an optimum ratio of defects on its surface can be favourable for negative ion production.

physics.plasm-ph↗

arXiv2020

Optimisation of a diamond nitrogen vacancy centre magnetometer for sensing of biological signals

Sensing of signals from biological processes, such as action potential propagation in nerves, are essential for clinical diagnosis and basic understanding of physiology. Sensing can be performed electrically by placing sensor probes near or inside a living specimen or dissected tissue using well established electrophysiology techniques. However, these electrical probe techniques have poor spatial resolution and cannot easily access tissue deep within a living subject, in particular within the brain. An alternative approach is to detect the magnetic field induced by the passage of the electrical signal, giving the equivalent readout without direct electrical contact. Such measurements are performed today using bulky and expensive superconducting sensors with poor spatial resolution. An alternative is to use nitrogen vacancy (NV) centres in diamond that promise biocompatibilty and high sensitivity without cryogenic cooling. In this work we present advances in biomagnetometry using NV centres, demonstrating magnetic field sensitivity of approximately 100 pT/$\sqrt{Hz}$ in the DC/low frequency range using a setup designed for biological measurements. Biocompatibility of the setup with a living sample (mouse brain slice) is studied and optimized, and we show work toward sensitivity improvements using a pulsed magnetometry scheme. In addition to the bulk magnetometry study, systematic artifacts in NV-ensemble widefield fluorescence imaging are investigated.

quant-ph↗

arXiv2020

Detection of biological signals from a live mammalian muscle using a diamond quantum sensor

The ability to perform noninvasive, non-contact measurements of electric signals produced by action potentials is essential in biomedicine. A key method to do this is to remotely sense signals by the magnetic field they induce. Existing methods for magnetic field sensing of mammalian tissue, used in techniques such as magnetoencephalography of the brain, require cryogenically cooled superconducting detectors. These have many disadvantages in terms of high cost, flexibility and limited portability as well as poor spatial and temporal resolution. In this work we demonstrate an alternative technique for detecting magnetic fields generated by the current from action potentials in living tissue using nitrogen vacancy centres in diamond. With 50pT/$\sqrt{Hz}$ sensitivity, we show the first measurements of sensing from mammalian tissue with a diamond sensor using mouse muscle optogenetically activated with blue light. We show these measurements can be performed in an ordinary, unshielded lab environment and that the signal can be easily recovered by digital signal processing techniques.

physics.bio-ph↗

arXiv2020

Enhancing surface production of negative ions using nitrogen doped diamond in a deuterium plasma

The production of negative ions is of significant interest for applications including mass spectrometry, particle acceleration, material surface processing, and neutral beam injection for magnetic confinement fusion. Methods to improve the efficiency of the surface production of negative ions, without the use of low work function metals, are of interest for mitigating the complex engineering challenges these materials introduce. In this study we investigate the production of negative ions by doping diamond with nitrogen. Negatively biased ($-20$ V or $-130$ V), nitrogen doped micro-crystalline diamond films are introduced to a low pressure deuterium plasma (helicon source operated in capacitive mode, 2 Pa, 26 W) and negative ion energy distribution functions (NIEDFs) are measured via mass spectrometry with respect to the surface temperature (30$^{\circ}$C to 750$^{\circ}$C) and dopant concentration. The results suggest that nitrogen doping has little influence on the yield when the sample is biased at $-130$ V, but when a relatively small bias voltage of $-20$ V is applied the yield is increased by a factor of 2 above that of un-doped diamond when its temperature reaches 550$^{\circ}$C. The doping of diamond with nitrogen is a new method for controlling the surface production of negative ions, which continues to be of significant interest for a wide variety of practical applications.

physics.plasm-ph↗

arXiv2019

R&D around a photoneutralizer-based NBI system (Siphore) in view of a DEMO Tokamak steady state fusion reactor

Since the signature of the ITER treaty in 2006, a new research programme targeting the emergence of a new generation of Neutral Beam (NB) system for the future fusion reactor (DEMO Tokamak) has been underway between several laboratories in Europe. The specifications required to operate a NB system on DEMO are very demanding: the system has to provide plasma heating, current drive and plasma control at a very high level of power (up to 150 MW) and energy (1 or 2 MeV), including high performances in term of wall-plug efficiency ($η$ > 60%), high availability and reliability. To this aim, a novel NB concept based on the photodetachment of the energetic negative ion beam is under study. The keystone of this new concept is the achievement of a photoneutralizer where a high power photon flux (~3 MW) generated within a Fabry Perot cavity will overlap, cross and partially photodetach the intense negative ion beam accelerated at high energy (1 or 2 MeV). The aspect ratio of the beam-line (source, accelerator, etc.) is specifically designed to maximize the overlap of the photon beam with the ion beam. It is shown that such a photoneutralized based NB system would have the capability to provide several tens of MW of D 0 per beam line with a wall-plug efficiency higher than 60%. A feasibility study of the concept has been launched between different laboratories to address the different physics aspects, i.e., negative ion source, plasma modelling, ion accelerator simulation, photoneutralization and high voltage holding under vacuum. The paper describes the present status of the project and the main achievements of the developments in laboratories.

physics.plasm-ph↗

arXiv2019

Alternative solutions to caesium in negative-ion sources: a study of negative-ion surface production on diamond in H 2 /D 2 plasmas

This paper deals with a study of H-/D-negative ion surface production on diamond in low pressure H2/D2 plasmas. A sample placed in the plasma is negatively biased with respect to plasma potential. Upon positive ion impacts on the sample, some negative ions are formed and detected according to their mass and energy by a mass spectrometer placed in front of the sample. The experimental methods developed to study negative ion surface production and obtain negative ion energy and angle distribution functions are first presented. Different diamond materials ranging from nanocrystalline to single crystal layers, either doped with boron or intrinsic, are then investigated and compared with graphite. The negative ion yields obtained are presented as a function of different experimental parameters such as the exposure time, the sample bias which determines the positive ion impact energy and the sample surface temperature. It is concluded from these experiments that the electronic properties of diamond materials, among them the negative electron affinity, seem to be favourable for negative-ion surface production. However, the negative ion yield decreases with the plasma induced defect density.

physics.plasm-ph↗

arXiv2019

Initialization and Readout of Nuclear Spins via negatively charged Silicon-Vacancy Center in Diamond

In this work, we demonstrate initialization and readout of nuclear spins via a negatively charged silicon-vacancy (SiV) electron spin qubit. Under Hartmann-Hahn conditions the electron spin polarization is coherently transferred to the nuclear spin. The readout of the nuclear polarization is observed via the fluorescence of the SiV. We also show that the coherence time of the nuclear spin (6 ms) is limited by the electron spin-lattice relaxation due to the hyperfine coupling to the electron spin. This work paves the way towards realization of building blocks of quantum hardware with an efficient spin-photon interface based on the SiV color center coupled to a long lasting nuclear memory.

quant-ph↗

arXiv2018

Microwave device characterisation using a widefield diamond microscope

Devices relying on microwave circuitry form a cornerstone of many classical and emerging quantum technologies. A capability to provide in-situ, noninvasive and direct imaging of the microwave fields above such devices would be a powerful tool for their function and failure analysis. In this work, we build on recent achievements in magnetometry using ensembles of nitrogen vacancy centres in diamond, to present a widefield microwave microscope with few-micron resolution over a millimeter-scale field of view, 130nT/sqrt-Hz microwave amplitude sensitivity, a dynamic range of 48 dB, and sub-ms temporal resolution. We use our microscope to image the microwave field a few microns above a range of microwave circuitry components, and to characterise a novel atom chip design. Our results open the way to high-throughput characterisation and debugging of complex, multi-component microwave devices, including real-time exploration of device operation.

quant-ph↗

arXiv2014

Photonic nano-structures on (111) oriented diamond

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 10${}^6$ 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.

cond-mat.mtrl-sci↗