D.N. Jamieson

A single-atom electron spin qubit in silicon

A single atom is the prototypical quantum system, and a natural candidate for a quantum bit, or qubit—the elementary unit of a quantum computer. Atoms have been successfully used to store and process quantum information in electromagnetic traps, as well as in diamond through the use of the nitrogen–vacancy-centre point defect. Solid-state electrical devices possess great potential to scale up such demonstrations from few-qubit control to larger-scale quantum processors. Coherent control of spin qubits has been achieved in lithographically defined double quantum dots in both GaAs (refs 3–5) and Si (ref. 6). However, it is a formidable challenge to combine the electrical measurement capabilities of engineered nanostructures with the benefits inherent in atomic spin qubits. Here we demonstrate the coherent manipulation of an individual electron spin qubit bound to a phosphorus donor atom in natural silicon, measured electrically via single-shot read-out. We use electron spin resonance to drive Rabi oscillations, and a Hahn echo pulse sequence reveals a spin coherence time exceeding 200 µs. This time should be even longer in isotopically enriched 28Si samples. Combined with a device architecture that is compatible with modern integrated circuit technology, the electron spin of a single phosphorus atom in silicon should be an excellent platform on which to build a scalable quantum computer.

The Raman spectrum of nanocrystalline diamond

Abstract Nanometre sized diamond powder has been purified by centrifugation to remove contamination from sp2 bonded carbon. The purified powder has been characterized using electron energy loss spectroscopy (EELS) and Raman spectroscopy. The EELS spectra confirmed the absence of sp2 bonded carbon and showed strong contributions from surface plasmons. Strong relatively sharp peaks are observed in the Raman spectra at 500, 1140, 1132 and 1630 cm −1 . By comparing the Raman spectra of the nanodiamond clusters with that of amorphized diamond and with calculations of the vibrational density of states we are able to suggest the origin of features in the vibrational spectrum from nanocrystalline diamond.

Dynamic analysis: on-line quantitative PIXE microanalysis and its use in overlap-resolved elemental mapping

Abstract General PIXE microanalysis benefits from the rapid extraction of quantitative results. The microanalysis of minerals demands continuous feedback on mineral composition in order to monitor changing zoning profiles, or else to detect the presence of inclusions or simply to confirm the identification of grains under analysis. Hence, we have developed a spectral decomposition transform that closely approximates the time-consuming nonlinear least-squares method. The transform can be performed in live time to obtain continuously updated quantitative PIXE analyses as the data accumulate. A spinoff from this dynamic analysis approach is the ability to accumulate on-line PIXE elemental maps that are inherently overlap-resolved and background-subtracted. This paper describes the dynamic analysis method, demonstrates its effectiveness and shows an application of the method in geology to project out true elemental maps of trace Au in a study of polished sections from the Emperor gold-telluride deposit in Fiji. The method produced Au maps that effectively rejected overlapping peaks from Zn and As present in inclusion phases and as minor elements in the pyrite, and hence revealed the real distribution of Au.

Storing quantum information for 30 seconds in a nanoelectronic device

The spin of an electron or a nucleus in a semiconductor naturally implements the unit of quantum information--the qubit. In addition, because semiconductors are currently used in the electronics industry, developing qubits in semiconductors would be a promising route to realize scalable quantum information devices. The solid-state environment, however, may provide deleterious interactions between the qubit and the nuclear spins of surrounding atoms, or charge and spin fluctuations arising from defects in oxides and interfaces. For materials such as silicon, enrichment of the spin-zero (28)Si isotope drastically reduces spin-bath decoherence. Experiments on bulk spin ensembles in (28)Si crystals have indeed demonstrated extraordinary coherence times. However, it remained unclear whether these would persist at the single-spin level, in gated nanostructures near amorphous interfaces. Here, we present the coherent operation of individual (31)P electron and nuclear spin qubits in a top-gated nanostructure, fabricated on an isotopically engineered (28)Si substrate. The (31)P nuclear spin sets the new benchmark coherence time (>30 s with Carr-Purcell-Meiboom-Gill (CPMG) sequence) of any single qubit in the solid state and reaches >99.99% control fidelity. The electron spin CPMG coherence time exceeds 0.5 s, and detailed noise spectroscopy indicates that--contrary to widespread belief--it is not limited by the proximity to an interface. Instead, decoherence is probably dominated by thermal and magnetic noise external to the device, and is thus amenable to further improvement.

High-fidelity readout and control of a nuclear spin qubit in silicon

Detection of nuclear spin precession is critical for a wide range of scientific techniques that have applications in diverse fields including analytical chemistry, materials science, medicine and biology. Fundamentally, it is possible because of the extreme isolation of nuclear spins from their environment. This isolation also makes single nuclear spins desirable for quantum-information processing, as shown by pioneering studies on nitrogen-vacancy centres in diamond. The nuclear spin of a 31P donor in silicon is very promising as a quantum bit: bulk measurements indicate that it has excellent coherence times and silicon is the dominant material in the microelectronics industry. Here we demonstrate electrical detection and coherent manipulation of a single 31P nuclear spin qubit with sufficiently high fidelities for fault-tolerant quantum computing. By integrating single-shot readout of the electron spin with on-chip electron spin resonance, we demonstrate quantum non-demolition and electrical single-shot readout of the nuclear spin with a readout fidelity higher than 99.8 per cent—the highest so far reported for any solid-state qubit. The single nuclear spin is then operated as a qubit by applying coherent radio-frequency pulses. For an ionized 31P donor, we find a nuclear spin coherence time of 60 milliseconds and a one-qubit gate control fidelity exceeding 98 per cent. These results demonstrate that the dominant technology of modern electronics can be adapted to host a complete electrical measurement and control platform for nuclear-spin-based quantum-information processing.

A new method for on-line true-elemental imaging using PIXE and the proton microprobe

A rapid matrix transform method called Dynamic Analysis (DA) has been developed for the production of true elemental images using PIXE and the Proton Microprobe that are free of image artefacts due to continuum background and overlap with X-ray lines and detector response features (e.g. tails and escape peaks) from other elements. The method has been installed at the CSIRO and the NAC for the on-line projection of true elemental images. These on-line images are also quantitative, and only require minor off-line correction (∼ 10% typically) to obtain accurate true elemental images at major and trace element levels. Correction issues discussed include the variation of PIXE yields with sample composition across a scan area, and dead-line corrections. The method is now in routine use and enables on-line quantitative true elemental imaging at the CSIRO and the NAC using a simple procedure involving the fitting of a preliminary scan spectrum to build the DA transform matrix; spectrum fitting and matrix construction are part of the GeoPIXE software package. The method has been extensively tested using samples which display complex multi-element overlaps, the DA method successfully projecting accurate images for elements obscured by the lines of interfering elements.

Implantation of labelled single nitrogen vacancy centers in diamond using N15

Nitrogen-vacancy (NV−) color centers in diamond were created by implantation of 7 keV N15(I=1∕2) ions into type IIa diamond. Optically detected magnetic resonance was employed to measure the hyperfine coupling of single NV− centers. The hyperfine spectrum from NV−15 arising from implanted N15 can be distinguished from NV−14 centers created by native N14(I=1) sites. Analysis indicates 1 in 40 implanted N15 atoms give rise to an optically observable NV−15 center. This report ultimately demonstrates a mechanism by which the yield of NV− center formation by nitrogen implantation can be measured.

Controlled shallow single-ion implantation in silicon using an active substrate for sub-20-keV ions

We demonstrate a method for the controlled implantation of single ions into a silicon substrate with energy of sub-20‐keV. The method is based on the collection of electron-hole pairs generated in the substrate by the impact of a single ion. We have used the method to implant single 14‐keV P31 ions through nanoscale masks into silicon as a route to the fabrication of devices based on single donors in silicon.

Measurement of (p, p) elastic cross sections for C, O and Si in the energy range 1.0–3.5 MeV

Abstract Cross sections for the elastic scattering of protons from thin natural C, O and Si targets have been measured for proton bombarding energies between 1.0 and 3.5 MeV at lab angles of 170°, 150° and 110°. The results have been presented graphically and have been fitted with Breit-Wigner functions. The parameters of the fits are provided. These parameters may be used to simulate spectra from backscattering spectrometry (BS) analysis of sample composition. Some examples are shown for the measurement of SiC and YBaCuO superconductor stoichiometry.

Fabrication of Ultrathin Single-Crystal Diamond Membranes†

A method for preparing ultrathin single-crystal diamond membranes suitable for post-processing and liftout, is reported. The proposed method used single-crystal diamond substrates and two-energy ion implant process for the fabrication of thin diamond membranes. Two ion-implant process was used in this method to prepare two different damage layers within diamond sample. This method can be used for preparing integrated quantum-photonic structure based on color center in diamond. This method can also be used for fabricating various structures including Bragg gratings and whispering gallery mode resonators. A significant application of the diamond nanostructures is to fabricate the micro- and nanoscale cantilevers. It was also observed that the fabricated single-crystal diamond are suitable for another FIB processing.