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Efficient detection of single optical centres in solids is essential for quantum information processing, sensing, and single-photon generation applications. In this work, we use radio-frequency (RF) reflectometry to electrically detect the photoionisation induced by a single Er3 + ion in Si. The high bandwidth and sensitivity of the RF reflectometry provide sub-100-ns time resolution for the photoionisation detection. With this technique, the optically excited state lifetime of a single Er3 + ion in a Si nano-transistor is measured for the first time to be 0.49 ± 0.04μs. Our results demonstrate an efficient approach for detecting a charge state change induced by Er excitation and relaxation. This approach could be used for fast readout of other single optical centres in solids and is attractive for large-scale integrated optical quantum systems thanks to the multi-channel RF reflectometry demonstrated with frequency multiplexing techniques.

Scanning tunneling luminescence microscopy (STLM) along with scanning tunneling spectroscopy (STS) is applied to a step-bunched, oxidized 4H-SiC surface prepared on the silicon face of a commercial, n-type SiC wafer using a silicon melt process. The step-bunched surface consists of atomically smooth terraces parallel to the [0001] crystal planes, and rougher risers consisting of nanoscale steps formed by the termination of these planes. The rather striking topography of this surface is well resolved with large tip biases of the order of -8 V and set currents of magnitude less than 1 nA. Hysteresis in the STS spectra is preferentially observed on the risers suggesting that they contain a higher density of surface charge traps than the terraces where hysteresis is more frequently absent. Similarly, at 50 K intense sub-gap light emission centered around 2.4 eV is observed mainly on the risers albeit only with larger tunneling currents of magnitude equal to or greater than 10 nA. These results demonstrate that STLM holds great promise for the observation of impurities and defects responsible for sub-gap light emission with spatial resolutions approaching the length scale of the defects themselves., Comment: 13 pages, 5 figures; work presented at the International Conference on the Physics of Semiconductors, Sydney, 2022

The use of superconducting microresonators together with quantum-limited Josephson parametric amplifiers has enhanced the sensitivity of pulsed electron spin resonance (ESR) measurements by more than four orders of magnitude. So far, the microwave resonators and amplifiers have been designed as separate components due to the incompatibility of Josephson junction–based devices with magnetic fields. This has produced complex spectrometers and raised technical barriers toward adoption of the technique. Here, we circumvent this issue by coupling an ensemble of spins directly to a weakly nonlinear and magnetic field–resilient superconducting microwave resonator. We perform pulsed ESR measurements with a 1-pL mode volume containing 6 × 10 7 spins and amplify the resulting signals within the device. When considering only those spins that contribute to the detected signals, we find a sensitivity of 2.8 × 1 0 3 spins / Hz for a Hahn echo sequence at a temperature of 400 mK. In situ amplification is demonstrated at fields up to 254 mT, highlighting the technique’s potential for application under conventional ESR operating conditions.

The surface of hydrogen-terminated diamond (H-terminated diamond) supports a p-type surface conductivity when interfaced with high electron-affinity surface acceptors through the surface transfer doping process. High electron-affinity transition metal oxides (TMOs), such as MoO3, have been regarded as superior candidates in surface transfer doping of diamond, holding great promise for enabling practical diamond electronic devices. In this work, a simple, solution-processed method is demonstrated to deposit a molybdenum trioxide (MoO3) layer on H-terminated diamond surface to achieve surface transfer doping of diamond. The surface of diamond following the deposition of solution-processed MoO3 (sp-MoO3) experienced significant reduction in sheet resistivity, corresponding to an increase in hole density, compared with the pristine air-doped diamond. This hole accumulation layer induced by sp-MoO3 is thermally stable up to 450 °C, and demonstrates metallic conductivity down to 250 mK with a strong spin-orbit interaction (SOI) in the induced two-dimensional (2D) surface conducting layer. Our study demonstrates that sp-MoO3 is comparable with thermally-evaporated MoO3 in doping performance but with great advantage as a simple, inexpensive and highly flexible fabrication method for developing diamond electronics.

Using sample-on-SSPD and photoluminescence excitation spectroscopy, we demonstrate Er sites in Si with inhomogeneous broadening below 100 MHz, a 350 kHz upper bound on the homogeneous linewidth, and electron T1 lower bound of 1 second.

Hydrogen-terminated diamond possesses an intriguing p-type surface conductivity which is induced via thermodynamically driven electron transfer from the diamond surface into surface acceptors such as atmospheric adsorbates, a process called surface transfer doping. High electron affinity transition metal oxides (TMOs) including MoO3 and V2O5 have been shown to be highly effective solid-state surface acceptors for diamond, giving rise to a sub-surface two-dimensional (2D) hole layer with metallic conduction. In this work, low temperature magnetotransport is used as a tool to show the presence of a Rashba-type spin-orbit interaction with a high spin-orbit coupling of 19.9 meV for MoO3 doping and 22.9 meV for V2O5 doping, respectively, through the observation of a transition in the phase-coherent backscattering transport from weak localization to weak antilocalization at low temperature. Surface transfer doping of diamond with TMOs provides a 2D hole system with spin-orbit coupling that is over two times larger than that reported for diamond surfaces with atmospheric acceptors, opening up possibilities to study and engineer spin transport in a carbon material system.

Electron-spin qubits have long coherence times suitable for quantum technologies. Spin–orbit coupling promises to greatly improve spin qubit scalability and functionality, allowing qubit coupling via photons, phonons or mutual capacitances, and enabling the realization of engineered hybrid and topological quantum systems. However, despite much recent interest, results to date have yielded short coherence times (from 0.1 to 1 μs). Here we demonstrate ultra-long coherence times of 10 ms for holes where spin–orbit coupling yields quantized total angular momentum. We focus on holes bound to boron acceptors in bulk silicon 28, whose wavefunction symmetry can be controlled through crystal strain, allowing direct control over the longitudinal electric dipole that causes decoherence. The results rival the best electron-spin qubits and are 104 to 105 longer than previous spin–orbit qubits. These results open a pathway to develop new artificial quantum systems and to improve the functionality and scalability of spin-based quantum technologies. Spin qubits in systems with strong spin–orbit coupling can be electrically controlled, but are usually affected by short coherence times. Here, coherence times up to 10 ms are obtained for strain-engineered hole states bound to boron acceptors in silicon 28.

We demonstrate locally the coherent formation of silicon carbide (SiC) on diamond, a rare example of heteroepitaxy with a lattice mismatch that exceeds 20%. High-resolution transmission electron mi...

The precise measurement of mechanical stress at the nanoscale is of fundamental and technological importance. In principle, all six independent variables of the stress tensor, which describe the direction and magnitude of compression/tension and shear stress in a solid, can be exploited to tune or enhance the properties of materials and devices. However, existing techniques to probe the local stress are generally incapable of measuring the entire stress tensor. Here, we make use of an ensemble of atomic-sized in situ strain sensors in diamond (nitrogen-vacancy defects) to achieve spatial mapping of the full stress tensor, with a submicrometer spatial resolution and a sensitivity of the order of 1 MPa (10 MPa) for the shear (axial) stress components. To illustrate the effectiveness and versatility of the technique, we apply it to a broad range of experimental situations, including mapping the stress induced by localized implantation damage, nanoindents, and scratches. In addition, we observe surprisingly large stress contributions from functional electronic devices fabricated on the diamond and also demonstrate sensitivity to deformations of materials in contact with the diamond. Our technique could enable in situ measurements of the mechanical response of diamond nanostructures under various stimuli, with potential applications in strain engineering for diamond-based quantum technologies and in nanomechanical sensing for on-chip mass spectroscopy.

The steady-state, space-charge-limited piezoresistance (PZR) of defect-engineered, silicon-on-insulator device layers containing silicon divacancy defects changes sign as a function of applied bias. Above a punch-through voltage ($V_t$) corresponding to the onset of a space-charge-limited hole current, the longitudinal $\langle 110 \rangle$ PZR $\pi$-coefficient is $\pi \approx 65 \times 10^{-11}$~Pa$^{-1}$, similar to the value obtained in charge-neutral, p-type silicon. Below $V_t$, the mechanical stress dependence of the Shockley-Read-Hall (SRH) recombination parameters, specifically the divacancy trap energy $E_T$ which is estimated to vary by $\approx 30$~$\mu$V/MPa, yields $\pi \approx -25 \times 10^{-11}$~Pa$^{-1}$. The combination of space-charge-limited transport and defect engineering which significantly reduces SRH recombination lifetimes makes this work directly relevant to discussions of giant or anomalous PZR at small strains in nano-silicon whose characteristic dimension is larger than a few nanometers. In this limit the reduced electrostatic dimensionality lowers $V_t$ and amplifies space-charge-limited currents and efficient SRH recombination occurs via surface defects. The results reinforce the growing evidence that in steady state, electro-mechanically active defects can result in anomalous, but not giant, PZR., Comment: 9 pages, 8 figures

Spins in the ``semiconductor vacuum'' of silicon-28 ($^{28}\mathrm{Si}$) are suitable qubit candidates due to their long coherence times. An isotopically purified substrate or epilayer of $^{28}\mathrm{Si}$ is required to limit the decoherence pathway caused by magnetic perturbations from surrounding $^{29}\mathrm{Si}$ nuclear spins ($I=1/2$), present in natural Si ($^{\text{nat}}\mathrm{Si}$) at an abundance of 4.67%. We isotopically enrich surface layers of $^{\text{nat}}\mathrm{Si}$ by sputtering using high fluence ${}^{28}{\text{Si}}^{\ensuremath{-}}$ implantation. Phosphorus (P) donors implanted into one such $^{28}\mathrm{Si}$ layer with $\ensuremath{\sim}3000$ ppm $^{29}\mathrm{Si}$, produced by implanting 30 keV ${}^{28}{\text{Si}}^{\ensuremath{-}}$ ions at a fluence of $4\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$, were measured with pulsed electron spin resonance, confirming successful donor activation upon annealing. The monoexponential decay of the Hahn echo signal indicates a depletion of $^{29}\mathrm{Si}$. A coherence time of ${T}_{2}=285\ifmmode\pm\else\textpm\fi{}14\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$ is extracted, which is longer than that obtained in ${}^{\text{nat}}\text{Si}$ for similar doping concentrations and can be increased by reducing the P concentration in the future. Guided by simulations, the isotopic enrichment was improved by employing one-for-one ion sputtering using 45 keV ${}^{28}{\text{Si}}^{\ensuremath{-}}$ implanted with a fluence of $2.63\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ into ${}^{\text{nat}}\text{Si}$. This resulted in an isotopically enriched surface layer $\ensuremath{\sim}100$ nm thick, suitable for providing a sufficient volume of $^{28}\mathrm{Si}$ for donor qubits implanted into the near-surface region. We observe a depletion of $^{29}\mathrm{Si}$ to 250 ppm as measured by secondary ion mass spectrometry. The impurity content and the crystallization kinetics via solid phase epitaxy are discussed. The $^{28}\mathrm{Si}$ layer is confirmed to be a single crystal using transmission electron microscopy. This method of Si isotopic enrichment shows promise for incorporation into the fabrication process flow of Si spin-qubit devices.

Individual optical emitters coupled via coherent interactions are attractive qubits for quantum communications applications. Here, we present the first study of single pairs of interacting rare earth ions and determine the interactions between ions in the pair with high resolution. We identify two examples of Er3+ pair sites in Er implanted Si and characterise the interactions using optical Zeeman spectroscopy. We identify one pair as two Er3+ ions in sites of at least C 2 symmetry coupled via a large, 200 GHz, Ising-like spin interaction in both optical ground and excited states. The high measurement resolution allows non-Ising contributions to the interaction of < 1 % to be observed, attributed to site distortion. By bringing two optical transitions into resonance with a magnetic field, we observe a 0.8 GHz optical interaction of unusual magnetic-dipole/electric-dipole character with strong polarization selection rules. We discuss the use of this type of strongly coupled, field-tunable rare earth pair system for quantum processing.

The quantum coherence and gate fidelity of electron spin qubits in semiconductors is often limited by noise arising from coupling to a bath of nuclear spins. Isotopic enrichment of spin-zero nuclei such as $^{28}$Si has led to spectacular improvements of the dephasing time $T_2^*$ which, surprisingly, can extend two orders of magnitude beyond theoretical expectations. Using a single-atom $^{31}$P qubit in enriched $^{28}$Si, we show that the abnormally long $T_2^*$ is due to the controllable freezing of the dynamics of the residual $^{29}$Si nuclei close to the donor. Our conclusions are supported by a nearly parameter-free modeling of the $^{29}$Si nuclear spin dynamics, which reveals the degree of back-action provided by the electron spin as it interacts with the nuclear bath. This study clarifies the limits of ergodic assumptions in analyzing many-body spin-problems under conditions of strong, frequent measurement, and provides novel strategies for maximizing coherence and gate fidelity of spin qubits in semiconductors., 11 pages, 5 figures

Electrodes in close proximity to an active area of a device are required for sufficient electrical control. The integration of such electrodes into optical devices can be challenging since low optical losses must be retained to realise high quality operation. Here, we demonstrate that it is possible to place a metallic shallow phosphorus doped layer in a silicon micro-ring cavity that can function at cryogenic temperatures. We verify that the shallow doping layer affects the local refractive index while inducing minimal losses with quality factors up to 10$^5$. This demonstration opens up a pathway to the integration of an electronic device, such as a single-electron transistor, into an optical circuit on the same material platform., Comment: 6 figures

Solid-state devices can be fabricated at the atomic scale, with applications ranging from classical logic to current standards and quantum technologies. While it is very desirable to probe these devices and the quantum states they host at the atomic scale, typical methods rely on long-ranged capacitive interactions, making this difficult. Here we probe a silicon electronic device at the atomic scale using a localized electronic quantum dot induced directly within the device at a desired location, using the biased tip of a low-temperature scanning tunneling microscope. We demonstrate control over short-ranged tunnel coupling interactions of the quantum dot with the device's source reservoir using sub-nm position control of the tip, and the quantum dot energy level using a voltage applied to the device's gate reservoir. Despite the $\sim 1$nm proximity of the quantum dot to the metallic tip, we find the gate provides sufficient capacitance to enable a high degree of electric control. Combined with atomic scale imaging, we use the quantum dot to probe applied electric fields and charge in individual defects in the device. This capability is expected to aid in the understanding of atomic-scale devices and the quantum states realized in them., Comment: 6 pages, 4 figures, 5 pages supplementary material

In this paper we use electrically detected optical excitation spectroscopy of individual erbium ions in silicon to determine their optical and paramagnetic properties simultaneously. We demonstrate that this high spectral resolution technique can be exploited to observe interactions typically unresolvable in silicon using conventional spectroscopy techniques due to inhomogeneous broadening. In particular, we resolve the Zeeman splitting of the 4I15/2 ground and 4I13/2 excited state separately and in strong magnetic fields we observe the anti-crossings between Zeeman components of different crystal field levels. We discuss the use of this electronic detection technique in identifying the symmetry and structure of erbium sites in silicon., 6 pages, 4 figures

The SiC/SiO2 interface is a central component of many SiC electronic devices. Defects intrinsic to this interface can have a profound effect on their operation and reliability. It is therefore crucial to both understand the nature of these defects and develop characterization methods to enable optimized SiC-based devices. Here we make use of confocal microscopy to address single SiC/SiO2-related defects and show the technique to be a noncontact, nondestructive, spatially resolved and rapid means of assessing thequality of the SiC/SiO2 interface. This is achieved by a systematic investigation of the defect density of the SiC/SiO2 interface by varying the parameters of a nitric oxide passivation anneal after oxidation. Standard capacitance-based characterization techniques are used to benchmark optical emission rates and densities of the optically active SiC/SiO2-related defects. Further insight into the nature of these defects is provided by low-temperature optical measurements on single defects.

Silicon chips containing arrays of single dopant atoms could be the material of choice for both classical and quantum devices that exploit single donor spins. For example, group-V-donors implanted in isotopically purified 28 Si crystals are attractive for large-scale quantum computers. Useful attributes include long nuclear and electron spin lifetimes of 31 P, hyperfine clock transitions in 209 Bi or electrically controllable 123 Sb nuclear spins. Promising architectures require the ability to fabricate arrays of individual near-surface dopant atoms with high yield. Here we employ an on-chip detector electrode system with 70 eV r.m.s. noise (∼ 20 electrons) to demonstrate near room temperature implantation of single 14 keV 31 P+ ions. The physics model for the ion-solid interaction shows an unprecedented upper-bound single ion detection confidence of 99.85±0.02% for near-surface implants. As a result, the practical controlled silicon doping yield is limited by materials engineering factors including surface gate oxides in which detected ions may stop. For a device with 6 nm gate oxide and 14 keV 31 P+ implants we demonstrate a yield limit of 98.1%. Thinner gate oxides allow this limit to converge to the upper-bound. Deterministic single ion implantation can therefore be a viable materials engineering strategy for scalable dopant architectures in silicon devices. This article is protected by copyright. All rights reserved.

Spin-qubits based on impurities such as phosphorus in silicon (Si) have attractive attributes for the development of quantum computing devices. Very long coherence times can be achieved for donor-based qubits in Si due to the availability of isotopically pure 28Si layers where the 29Si atoms, which otherwise lead to decoherence, are largely absent in the active region of the device. Well-behaved single donor qubits in Si can routinely be formed using ion implantation, and the key performance criteria needed to demonstrate the basis of a viable platform for quantum computing have been achieved. The crucial next stage of development is to demonstrate suitable pathways for scale-up that allow patterned arrays of donor qubits to be controllably coupled and that are robust against the inherent donor placement tolerances and material processing constraints that exist. Here, we review progress on the fabrication and measurement of donor-based qubits in silicon via the ion implantation pathway and discuss the key developmental milestones that have been achieved. We also provide an overview of the key scale-up strategies that are being actively pursued to take donor-based quantum computing in Si to the next stage.

The influence of surface topography on phase coherent transport in the two-dimensional (2D) hole band of surface transfer doped hydrogen-terminated (100) diamond is investigated. Low-temperature magneto-conductance measurements were carried out with an applied in-plane magnetic field to quantify the effect of electronic micro-roughness on spin dephasing in the 2D hole band for Hall bar devices with similar transport characteristics, but significantly different topographic roughness. The electronic micro-roughness of the 2D hole band, described by the parameter d2L, where d is the root-mean-square (rms) fluctuation in the width of the quantum well and L is the correlation length of the fluctuations, is found to increase for surfaces with increased roughness. Fluctuations in the well width likely arise from a locally varying hole carrier density, arising for example from a local variation in the concentration of ionic components in the surface water layer.

The bismuth (Bi) substitutional donor in silicon (Si) is an attractive qubit candidate for quantum computing proposals due to its large Hilbert space, clock transitions, and potential to couple to superconducting flux qubits. Single-qubit control, coupling, and readout by surface nanocircuitry requires a Bi depth of ∼20 nm in Si. This can be achieved using ion implantation of ∼25 keV Bi. This work explores the activation properties of Bi implanted at 26 keV with fluences of 1×1014 and 6×1012cm-2 into both crystalline and preamorphized Si. The Bi electrical activation yield was measured over a broad range of annealing conditions using resistivity and Hall effect measurements, enabling optimal annealing strategies to be proposed for the different implant parameters. For the high and low fluences, the maximum Bi activation yields achieved were 64% and 46%, respectively. Above a critical thermal budget, a substantial fraction of Bi forms electrically inactive complexes in the high fluence sample only. The substitutional fraction and diffusion of high fluence Bi was quantified, with diffusion coefficients D0=4.0±0.5 and 7.5±0.5cm2s-1 found for implantation into crystalline and preamorphized Si, respectively, using Rutherford backscattering spectrometry. To demonstrate the successful activation and quantum control of near-surface implanted Bi, the full hyperfine spectrum of these donors is obtained using continuous-wave electron spin resonance at 25 K, supporting the suitability for Bi donor qubits.

Nuclear spins are highly coherent quantum objects. In large ensembles, their control and detection via magnetic resonance is widely exploited, for example, in chemistry, medicine, materials science and mining. Nuclear spins also featured in early proposals for solid-state quantum computers

We analyze the electron spin relaxation rate $1/T_1$ of individual ion-implanted $^{31}$P donors, in a large set of metal-oxide-semiconductor (MOS) silicon nanoscale devices, with the aim of identifying spin relaxation mechanisms peculiar to the environment of the spins. The measurements are conducted at low temperatures ($T\approx 100$~mK), as a function of external magnetic field $B_0$ and donor electrochemical potential $��_{\rm D}$. We observe a magnetic field dependence of the form $1/T_1\propto B_0^5$ for $B_0\gtrsim 3\,$ T, corresponding to the phonon-induced relaxation typical of donors in the bulk. However, the relaxation rate varies by up to two orders of magnitude between different devices. We attribute these differences to variations in lattice strain at the location of the donor. For $B_0\lesssim 3\,$T, the relaxation rate changes to $1/T_1\propto B_0$ for two devices. This is consistent with relaxation induced by evanescent-wave Johnson noise created by the metal structures fabricated above the donors. At such low fields, where $T_1>1\,$s, we also observe and quantify the spurious increase of $1/T_1$ when the electrochemical potential of the spin excited state $|\uparrow\rangle$ comes in proximity to empty states in the charge reservoir, leading to spin-dependent tunneling that resets the spin to $|\downarrow\rangle$. These results give precious insights into the microscopic phenomena that affect spin relaxation in MOS nanoscale devices, and provide strategies for engineering spin qubits with improved spin lifetimes., 14 pages, 8 figures. Version 2 has extensive text revisions, typo corrections, and two extra authors

A giant, anomalous piezo-response of fully-depleted silicon-on-insulator (FD-SOI) devices under mechanical stress is demonstrated using impedance spectroscopy. This piezo-response strongly depends on the measurement frequency, $\omega$, and consists of both a piezoresistance (PZR) and piezocapacitance whose maximum values are $\pi_R = -1100 \times 10^{-11}$ Pa$^{-1}$ and $\pi_C = -900 \times 10^{-11}$ Pa$^{-1}$ respectively. These values should be compared with the usual bulk PZR in p-type silicon, $\pi_R= 70 \times 10^{-11}$ Pa$^{-1}$. The observations are well described using models of space charge limited electron and hole currents in the presence of fast electronic traps having stress-dependent capture ($\omega_c$) and emission rates. Under steady-state conditions (i.e. when $\omega \ll \omega_c$) where the impedance spectroscopy measurements yield results that are directly comparable with previously published reports of PZR in depleted, silicon nano-objects, the overall piezo-response is just the usual, bulk silicon PZR. Anomalous PZR is observed only under non-steady-state conditions when $\omega \approx \omega_c$, with a symmetry suggesting that the electro-mechanically active fast traps are native Pb$_0$ interface defects. The observations suggest new functionalities for FD-SOI, and shed light on the debate over the PZR of carrier depleted nano-silicon., Comment: 14 pages with 10 figures including appendices

The two-dimensional (2D) hole gas at the surface of transfer-doped diamond shows quantum-mechanical interference effects in magnetoresistance in the form of weak localization and weak antilocalization (WAL) at temperatures below about 5 K. Here we use the quenching of the WAL by an additional magnetic field applied parallel to the 2D plane to extract the magnitude of the in-plane $g$-factor of the holes and fluctuations in the well width as a function of carrier density. Carrier densities are varied between 1.71 and $4.35\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$ by gating a Hall bar device with an ionic liquid. Over this range, calculated values of $|g|$ vary between 1.6 and 2.3 and the extracted well-width variation drops from 3 to 1.3 nm rms over the phase coherence length of 33 nm for a fixed geometrical surface roughness of about 1 nm as measured by atomic force microscopy. Possible mechanisms for the extracted variations in the presence of the ionic liquid are discussed.

Nuclear spins are highly coherent quantum objects. In large ensembles, their control and detection via magnetic resonance is widely exploited, e.g. in chemistry, medicine, materials science and mining. Nuclear spins also featured in early ideas and demonstrations of quantum information processing. Scaling up these ideas requires controlling individual nuclei, which can be detected when coupled to an electron. However, the need to address the nuclei via oscillating magnetic fields complicates their integration in multi-spin nanoscale devices, because the field cannot be localized or screened. Control via electric fields would resolve this problem, but previous methods relied upon transducing electric signals into magnetic fields via the electron-nuclear hyperfine interaction, which severely affects the nuclear coherence. Here we demonstrate the coherent quantum control of a single antimony (spin-7/2) nucleus, using localized electric fields produced within a silicon nanoelectronic device. The method exploits an idea first proposed in 1961 but never realized experimentally with a single nucleus. Our results are quantitatively supported by a microscopic theoretical model that reveals how the purely electrical modulation of the nuclear electric quadrupole interaction, in the presence of lattice strain, results in coherent nuclear spin transitions. The spin dephasing time, 0.1 seconds, surpasses by orders of magnitude those obtained via methods that require a coupled electron spin for electrical drive. These results show that high-spin quadrupolar nuclei could be deployed as chaotic models, strain sensors and hybrid spin-mechanical quantum systems using all-electrical controls. Integrating electrically controllable nuclei with quantum dots could pave the way to scalable nuclear- and electron-spin-based quantum computers in silicon that operate without the need for oscillating magnetic fields., Comment: Main text and figures followed by methods, extended data, and supplementary information

We present a scalable strategy to manufacture quantum computer devices, by encoding quantum information in the combined electron-nuclear spin state of individual ion-implanted phosphorus dopant atoms in silicon. Our strategy allows a typical pitch between quantum bits of order 200 nm, and retains compatibility with the standard fabrication processes adopted in classical CMOS nanoelectronic devices. We theoretically predict fast and high-fidelity quantum logic operations, and present preliminary experimental progress towards the realization of a “flip-flop” qubit system.

The rhombohedral phase of Si (r8-Si), a promising semiconducting material, is formed by indentation together with the body-centered cubic phase (bc8-Si). Using a novel sample preparation method, x-ray diffraction is used to determine the relative volume of these phases in indented Si and allow observation of a distorted unit cell along the direction of indentation loading. Theoretical calculations together with these observations suggest the indent contains an intrinsic compression of ∼4 GPa that stabilizes the r8 phase.

Diamond, a wide band-gap semiconductor, can be engineered to exhibit superconductivity when doped heavily with boron. The phenomena has been demonstrated in samples grown by chemical vapor deposition where the boron concentration exceeds the critical concentration for the metal-to-insulator transition of nMIT4×1020/cm3. While the threshold carrier concentration for superconductivity is generally well established in the literature, it is unclear how well correlated higher critical temperatures are with increased boron concentration. Previous studies have generally compared several samples grown under different plasma conditions, or on substrates having different crystallographic orientations, in order to vary the incorporation of boron into the lattice. Here, we present a study of a single sample with unchanging boron concentration, and instead modify the charge-carrier concentration by introducing compensating defects via high-energy ion irradiation. Superconductivity is completely suppressed when the number of defects is sufficient to compensate the hole concentration to below threshold. Furthermore, we show it is possible to recover the superconductivity by annealing the sample in vacuum to remove the compensating defects.

The understanding of weak measurements and interaction-free measurements has greatly expanded the conceptual and experimental toolbox to explore the quantum world. Here we demonstrate single-shot variable-strength weak measurements of the electron and nuclear spin states of a P31 single-atom donor in silicon. We first show how the partial collapse of the nuclear spin due to measurement can be used to coherently rotate the spin to a desired pure state. We explicitly demonstrate that phase coherence is preserved with high fidelity throughout multiple sequential single-shot weak measurements and that the partial state collapse can be reversed. Second, we use the relation between measurement strength and perturbation of the nuclear state as a physical meter to extract the tunnel rates between the P31 donor and a nearby electron reservoir from data conditioned on observing no tunneling events. Our experiments open avenues to measurement-based state preparation, steering and feedback protocols for spin systems in the solid state, and highlight the fundamental connection between information gain and state modification in quantum mechanics.

Surfaces and interfaces can dominate charge carrier transport dynamics in electronic devices, impeding realization of a material's full potential. Here, we investigate transport in a two-terminal diamond device comprising a conductive channel defined by a hydrogen-terminated diamond surface, bridging two TiC contacts. The surface charge distribution was imaged by monitoring the photoluminescence of nitrogen vacancy centers incorporated below the active device layer. A strong charge accumulation near the TiC contact/H-terminated channel interface is observed and is discussed in terms of deviation from Ohmic behavior evident in the DC electrical measurements. Small voltage steps applied to the device result in current transients due to carrier trapping at the contact/diamond interface. This gives rise to dynamic negative capacitance at low AC frequencies and is discussed in detail.

Diamond exhibits many desirable properties that could benefit the development of future carbon-based electronic devices. Its hydrogen-terminated surface, in conjunction with a suitable surface acceptor, develops a two-dimensional (2D) p-type surface conductivity through the surface transfer doping mechanism which can then be harvested for constructing functional devices. In this study, we have revisited the surface transfer doping of diamond by a high electron affinity (EA) transition metal oxide, V2O5. Through a combination of in-situ electrical measurements, Hall effect measurements and first-principles density functional theory (DFT) calculations, we explicitly show the intrinsic surface transfer doping behavior of V2O5, with doping performance superior to other competing TMOs such as MoO3. The metallic surface conduction of diamond induced by V2O5 is persistent down to 250 mK; this when coupled with the high hole density exceeding 7 × 1013 cm−2 offers a promising platform for the development of advanced diamond surface electronics exploiting many interesting quantum transport properties of the 2D hole layer of diamond.

Hydrogen-terminated diamond possesses due to transfer doping a quasi-two-dimensional (2D) hole accumulation layer at the surface with a strong, Rashba-type spin-orbit coupling that arises from the highly asymmetric confinement potential. By modulating the hole concentration and thus the potential using an electrostatic gate with an ionic-liquid dielectric architecture the spin-orbit splitting can be tuned from 4.6-24.5 meV with a concurrent spin relaxation length of 33-16 nm and hole sheet densities of up to 7.23 × 10(13) cm(-2). This demonstrates a spin-orbit interaction of unprecedented strength and tunability for a 2D hole system at the surface of a wide band gap semiconductor. With a spin relaxation length that is experimentally accessible using existing nanofabrication techniques, this result suggests that hydrogen-terminated diamond has great potential for the study and application of spin transport phenomena.

We will review recent demonstrations of single photon emission in different silicon carbide (SiC) polytypes, in both bulk and nano-structured form. Due to well established doping, and micro- and nanofabrication procedures deep defects photoluminescence (PL) can be electrically excited and incorporated in SiC nanomaterials. Finally we will report on preliminary results to incorporate near infrared defects in SiC nanoparticles.

Hydrogen-terminated (H-terminated) diamond, when surface transfer doped, can support a sub-surface two-dimensional (2D) hole band that possesses a strong Rashba-type spin–orbit interaction. By incorporating a V2O5/Al2O3 bilayer gate dielectric in a diamond-based metal–oxide–semiconductor architecture, metallic surface conductivity can be maintained at low temperature, avoiding the carrier freeze out exhibited by devices with an Al2O3 gate dielectric alone. Hole densities of up to 2.5 × 1013 cm−2 are achieved by the electrostatic gating of the device, and the spin–orbit interaction strength can be tuned from 3.5 ± 0.5 meV to 8.4 ± 0.5 meV, with a concurrent reduction in the spin coherence length from 40 ± 1 nm to 27 ± 1 nm. The demonstration of a gated device architecture on the H-terminated that avoids the need to cycle the temperature, as is required for ionic liquid gating protocols, opens a pathway to engineering practical devices for the study and application of spin transport in diamond.

Surface transfer doping of diamond using high electron affinity transition metal oxides (TMOs), such as MoO3, has emerged as a key enabling technology for the development of diamond-based surface two-dimensional (2D) electronics. However, the omission of a critical pre-annealing step in the device fabrication process to remove atmospheric adsorbates prior to TMO deposition, as seen in numerous studies, makes the role of TMOs ambiguous in light of air-induced surface conductivity, preventing a full understanding of the intrinsic surface transfer doping behavior of TMO-based surface acceptors. Here, using in-situ four-probe electrical measurements we explicitly show the insulating-to-conducting transition in diamond surface driven by MoO3 induced surface transfer doping. Variable-temperature Hall-effect measurements reveal weak temperature-dependence down to 250 mK, evidencing the 2D Fermi liquid nature of the resulting surface conducting channel on diamond. Using first-principles calculations, we confirm the interfacial charge exchange upon MoO3 adsorption leading to a degenerate hole conducting layer on diamond. This work provides significant insights into understanding the surface transfer doping of diamond induced by TMOs, and paves the way for the investigations of many interesting quantum transport properties in the resulting 2D hole conducting layer, such as phase-coherent magnetotransport, on diamond surface.

A hydrogen-terminated diamond (H-terminated diamond) surface supports a two-dimensional (2D) p-type surface conductivity when exposed to the atmosphere, as a result of the surface transfer doping process. The formation of reliable Ohmic contacts that persist to cryogenic temperature is essential for the exploration of quantum transport in the diamond 2D conducting channel. Herein, the contact properties of Pd on H-terminated diamond have been fully investigated down to 4 K using transmission line method measurements. Pd is shown to form an Ohmic contact on H-terminated diamond with linear I-V characteristics and low specific contact resistance in the range of (8.4 ± 1) ×10-4 ω·cm2 to (1.3 ± 0.2) ×10-3 ω·cm2 for the temperature range of 300 K-4 K. This is in stark contrast to reference devices with Au/Pt/Ti contacts, which exhibit a significant temperature dependence and non-Ohmic behavior at low temperature. Using 2D thermionic emission theory, a negative Schottky barrier height (SBH), - 23 ± 1 meV, between Pd and H-terminated diamond has been determined, in comparison to a positive SBH of 42 ± 1 meV for the Au/Pt/Ti/H-terminated diamond interface. These results show that Pd serves as an excellent candidate for forming reliable Ohmic contacts on H-terminated diamond for enabling precise electrical transport measurements at cryogenic temperature.