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The nanoscale localization of individual paramagnetic defects near an electrical circuit is an important step for realizing hybrid quantum devices with strong spin-microwave photon coupling. Here, we demonstrate the fabrication of an array of individual NV centers in diamond near a metallic nanowire deposited on top of the substrate. We determine the relative position of each NV center with $\sim$10\,nm accuracy, using it as a vector magnetometer to measure the field generated by passing a dc current through the wire., Comment: 6 pages, 5 figures

Controlled formation of porous silicon has been of primary importance for numerous landmark applications such as light emitting sources, sensors, actuators, drug delivery systems, and energy storage applications. Frequently explored methods to form the structures have long relied on selective etching of silicon, which still stands as the most controllable and reliable methods to highlight essence of the applications. Here, we demonstrate an unprecedented approach to form silicon framework, which is spontaneously formed with atomistic arrangement of silicon without gravimetric loss via single electrochemical (de)alloying with lithium. Carefully controlling bare crystallinity of Si and composite/electrode designs, we reveal that the key prerequisite to forming the structure lies in using unique dealloying dynamics of crystalline-amorphous phase transformations at room temperature. Using the feature, we clearly highlight that commercially available nano-structured silicon particles can abruptly yet uniformly transform into continuous sub-2 nm spherical silicon frameworks with size-tunable pores., Comment: Main body 24 pages (4 figures), Supplementary Information 14 pages (10 supplementary figures)

We developed a flare prediction model using machine learning, which is optimized to predict the maximum class of flares occurring in the following 24 h. Machine learning is used to devise algorithms that can learn from and make decisions on a huge amount of data. We used solar observation data during the period 2010-2015, such as vector magnetogram, ultraviolet (UV) emission, and soft X-ray emission taken by the Solar Dynamics Observatory and the Geostationary Operational Environmental Satellite. We detected active regions from the full-disk magnetogram, from which 60 features were extracted with their time differentials, including magnetic neutral lines, the current helicity, the UV brightening, and the flare history. After standardizing the feature database, we fully shuffled and randomly separated it into two for training and testing. To investigate which algorithm is best for flare prediction, we compared three machine learning algorithms: the support vector machine (SVM), k-nearest neighbors (k-NN), and extremely randomized trees (ERT). The prediction score, the true skill statistic (TSS), was higher than 0.9 with a fully shuffled dataset, which is higher than that for human forecasts. It was found that k-NN has the highest performance among the three algorithms. The ranking of the feature importance showed that the previous flare activity is most effective, followed by the length of magnetic neutral lines, the unsigned magnetic flux, the area of UV brightening, and the time differentials of features over 24 h, all of which are strongly correlated with the flux emergence dynamics in an active region., Comment: 27 pages, 3 figures

We propose a method for detecting the presence of a single spin in a crystal by coupling it to a high-quality factor superconducting planar resonator. By confining the microwave field in a constriction of nanometric dimensions, the coupling constant can be as high as $5-10$\,kHz. This coupling affects the amplitude of the field emitted by the resonator, and the integrated homodyne signal allows detection of a single spin with unit signal-to-noise ratio within few milliseconds. We further show that a stochastic master equation approach and a Bayesian analysis of the full time dependent homodyne signal improves this figure by $\sim 30\%$ for typical parameters., Comment: 11 pages, 7 figures

We analyze the impact of electric field and magnetic field fluctuations in the decoherence of the electronic spin associated with a single nitrogen-vacancy (NV) defect in diamond by engineering spin eigenstates protected either against magnetic noise or against electric noise. The competition between these noise sources is analyzed quantitatively by changing their relative strength through modifications of the environment. This study provides significant insights into the decoherence of the NV electronic spin, which is valuable for quantum metrology and sensing applications., Comment: 8 pages, 4 figures, including supplementary informations

This article reviews efforts to build a new type of quantum device, which combines an ensemble of electronic spins with long coherence times, and a small-scale superconducting quantum processor. The goal is to store over long times arbitrary qubit states in orthogonal collective modes of the spin-ensemble, and to retrieve them on-demand. We first present the protocol devised for such a multi-mode quantum memory. We then describe a series of experimental results using NV center spins in diamond, which demonstrate its main building blocks: the transfer of arbitrary quantum states from a qubit into the spin ensemble, and the multi-mode retrieval of classical microwave pulses down to the single-photon level with a Hahn-echo like sequence. A reset of the spin memory is implemented in-between two successive sequences using optical repumping of the spins., Comment: 27 pages, 7 figures

Spontaneous emission of radiation is one of the fundamental mechanisms by which an excited quantum system returns to equilibrium. For spins, however, spontaneous emission is generally negligible compared to other non-radiative relaxation processes because of the weak coupling between the magnetic dipole and the electromagnetic field. In 1946, Purcell realized that the spontaneous emission rate can be strongly enhanced by placing the quantum system in a resonant cavity -an effect which has since been used extensively to control the lifetime of atoms and semiconducting heterostructures coupled to microwave or optical cavities, underpinning single-photon sources. Here we report the first application of these ideas to spins in solids. By coupling donor spins in silicon to a superconducting microwave cavity of high quality factor and small mode volume, we reach for the first time the regime where spontaneous emission constitutes the dominant spin relaxation mechanism. The relaxation rate is increased by three orders of magnitude when the spins are tuned to the cavity resonance, showing that energy relaxation can be engineered and controlled on-demand. Our results provide a novel and general way to initialise spin systems into their ground state, with applications in magnetic resonance and quantum information processing. They also demonstrate that, contrary to popular belief, the coupling between the magnetic dipole of a spin and the electromagnetic field can be enhanced up to the point where quantum fluctuations have a dramatic effect on the spin dynamics; as such our work represents an important step towards the coherent magnetic coupling of individual spins to microwave photons., Comment: 8 pages, 6 figures, 1 table

We report pulsed electron-spin resonance (ESR) measurements on an ensemble of Bismuth donors in Silicon cooled at 10mK in a dilution refrigerator. Using a Josephson parametric microwave amplifier combined with high-quality factor superconducting micro-resonators cooled at millikelvin temperatures, we improve the state-of-the-art sensitivity of inductive ESR detection by nearly 4 orders of magnitude. We demonstrate the detection of 1700 bismuth donor spins in silicon within a single Hahn echo with unit signal-to-noise (SNR) ratio, reduced to just 150 spins by averaging a single Carr-Purcell-Meiboom-Gill sequence. This unprecedented sensitivity reaches the limit set by quantum fluctuations of the electromagnetic field instead of thermal or technical noise, which constitutes a novel regime for magnetic resonance., Comment: Main text : 10 pages, 4 figures. Supplementary text : 16 pages, 8 figures

We report the storage of microwave pulses at the single-photon level in a spin-ensemble memory consisting of $10^{10}$ NV centers in a diamond crystal coupled to a superconducting LC resonator. The energy of the signal, retrieved $100\, \mu \mathrm{s}$ later by spin-echo techniques, reaches $0.3\%$ of the energy absorbed by the spins, and this storage efficiency is quantitatively accounted for by simulations. This figure of merit is sufficient to envision first implementations of a quantum memory for superconducting qubits., Comment: 6 pages

An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing effort, devices for information processing, secure communication and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multi-tasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and the challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field.

A quantum memory at microwave frequencies, able to store the state of multiple superconducting qubits for long times, is a key element for quantum information processing. Electronic and nuclear spins are natural candidates for the storage medium as their coherence time can be well above one second. Benefiting from these long coherence times requires to apply the refocusing techniques used in magnetic resonance, a major challenge in the context of hybrid quantum circuits. Here we report the first implementation of such a scheme, using ensembles of nitrogen-vacancy (NV) centres in diamond coupled to a superconducting resonator, in a setup compatible with superconducting qubit technology. We implement the active reset of the NV spins into their ground state by optical pumping and their refocusing by Hahn echo sequences. This enables the storage of multiple microwave pulses at the picoWatt level and their retrieval after up to $35 \mu$s, a three orders of magnitude improvement compared to previous experiments., Comment: 8 pages, 5 figures + Supplementary information (text and 6 figures)

A new method for detecting the magnetic resonance of electronic spins at low temperature is demonstrated. It consists in measuring the signal emitted by the spins with a superconducting qubit that acts as a single-microwave-photon detector, resulting in an enhanced sensitivity. We implement this new type of electron-spin resonance spectroscopy using a hybrid quantum circuit in which a transmon qubit is coupled to a spin ensemble consisting of NV centers in diamond. With this setup we measure the NV center absorption spectrum at 30mK at an excitation level of \thicksim15\,\mu_{B} out of an ensemble of 10^{11} spins., Comment: 6 pages, 4 figures, submitted to PRX

We report the experimental realization of a hybrid quantum circuit combining a superconducting qubit and an ensemble of electronic spins. The qubit, of the transmon type, is coherently coupled to the spin ensemble consisting of nitrogen-vacancy (NV) centers in a diamond crystal via a frequency-tunable superconducting resonator acting as a quantum bus. Using this circuit, we prepare arbitrary superpositions of the qubit states that we store into collective excitations of the spin ensemble and retrieve back later on into the qubit. These results constitute a first proof of concept of spin-ensemble based quantum memory for superconducting qubits., Comment: 13 pages, 4 figures, plus supplementary information

We report the storage and retrieval of a small microwave field from a superconducting resonator into collective excitations of a spin ensemble. The spins are nitrogen-vacancy centers in a diamond crystal. The storage time of the order of 30 ns is limited by inhomogeneous broadening of the spin ensemble., Comment: 4 pages + supplementary material. Submitted to PRL

On 17 January 2010, STEREO-B observed in extreme ultraviolet (EUV) and white light a large-scale dome-shaped expanding coronal transient with perfectly connected off-limb and on-disk signatures. Veronig et al. (2010, ApJL 716, 57) concluded that the dome was formed by a weak shock wave. We have revealed two EUV components, one of which corresponded to this transient. All of its properties found from EUV, white light, and a metric type II burst match expectations for a freely expanding coronal shock wave including correspondence to the fast-mode speed distribution, while the transient sweeping over the solar surface had a speed typical of EUV waves. The shock wave was presumably excited by an abrupt filament eruption. Both a weak shock approximation and a power-law fit match kinematics of the transient near the Sun. Moreover, the power-law fit matches expansion of the CME leading edge up to 24 solar radii. The second, quasi-stationary EUV component near the dimming was presumably associated with a stretched CME structure; no indications of opening magnetic fields have been detected far from the eruption region., Comment: 18 pages, 10 figures. Solar Physics, published online. The final publication is available at http://www.springerlink.com

We show examples of excitation of coronal waves by flare-related abrupt eruptions of magnetic rope structures. The waves presumably rapidly steepened into shocks and freely propagated afterwards like decelerating blast waves that showed up as Moreton waves and EUV waves. We propose a simple quantitative description for such shock waves to reconcile their observed propagation with drift rates of metric type II bursts and kinematics of leading edges of coronal mass ejections (CMEs). Taking account of different plasma density falloffs for propagation of a wave up and along the solar surface, we demonstrate a close correspondence between drift rates of type II bursts and speeds of EUV waves, Moreton waves, and CMEs observed in a few known events., Comment: 30 pages, 15 figures. Solar Physics, published online. The final publication is available at http://www.springerlink.com

We report the realization of a quantum circuit in which an ensemble of electronic spins is coupled to a frequency tunable superconducting resonator. The spins are Nitrogen-Vacancy centers in a diamond crystal. The achievement of strong coupling is manifested by the appearance of a vacuum Rabi splitting in the transmission spectrum of the resonator when its frequency is tuned through the NV center electron spin resonance., Comment: 4 pages, 3 figures

We have investigated the intrinsic Josephson properties in slightly underdoped (Hg,Re)Ba2Ca2Cu3Oy [Hg(Re)1223] intrinsic Josephson junctions (IJJs) with a dimension of 1.0x1.5x0.11 um^3. The current-voltage characteristics of the IJJs exhibit clear multiple branches with subgap structures similar to those of other cuprate superconductors. The switching current distributions P(I) from the zero-voltage to the nonzero-voltage state in the current-biased IJJs agree well with the theoretical curves of the thermally assisted escape model at temperatures above ~5 K. The plasma frequency fp of the IJJs is estimated to be 1.3 THz from the fluctuation-free critical current density of 2.0x10^5 A/cm2, which is one of the highest among cuprate superconductors, reflecting the high Tc and a relatively low anisotropy of the Re doped Hg system. The P(I) gradually becomes independent of temperature below ~5 K, which suggests a crossover of the escape process from thermal activation to quantum tunneling at such a high temperature., Comment: 6 pages, 4 figures

We report the systematic investigations of the oscillation of the Josephson vortex (JV) flow resistance in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ micro-fabricated junctions with various geometries and superconducting anisotropy parameters. As the applied magnetic field parallel to the $ab$-plane is increased, oscillation with a period corresponding to a $\phi_0/2$ par atomic Josephson junction changes to oscillation with a doubled period. This crossover is scaled by both the junction length and the anisotropy parameter, indicating that the bulk inductive coupling that favors the triangular JV lattice is replaced with the surface deformation energy as the dominant interaction for a JV lattice. These results suggest that the in-phase square JV lattice is pronounced at a higher magnetic field in a smaller and more anisotropic sample., Comment: 4 pages, 3 figures

An electronic effect on a macroscopic domain structure is found in a strongly correlated half-doped manganite film Nd$_{0.5}$Sr$_{0.5}$MnO3 grown on a (011) surface of SrTiO3. The sample has a high-temperature (HT) phase free from distortion above 180K and two low-temperature (LT) phases with a large shear-mode strain and a concomitant twin structure. One LT phase has a large itinerancy (A-type), and the other has a small itinerancy (CE-type), while the lattice distortions they cause are almost equal. Our x ray diffraction measurement shows that the domain size of the LT phase made by the HT-CE transition is much smaller than that by the HT-A transition, indicating that the difference in domain size is caused by the electronic states of the LT phases., Comment: 9 pages, 4 figures

Single-crystalline (Lu, Ca)Ba2Cu3O7-d (Lu(Ca)123) whiskers have been successfully grown using the Te-doping method. X-ray diffraction patterns of Lu(Ca)123 whiskers showed sharp (0 0 l) peaks corresponding to REBa2Cu3O7-d phase (RE = rare earth elements). Transport measurements showed that the superconducting transition occurred at 83 K in the obtained whiskers., Comment: 3 pages, 3 figures, ISS2008

Structural study of orbital-ordered manganite thin films has been conducted using synchrotron radiation, and a ground state electronic phase diagram is made. The lattice parameters of four manganite thin films, Nd0.5Sr0.5MnO3 (NSMO) or Pr0.5Sr0.5MnO3 (PSMO) on (011) surfaces of SrTiO3 (STO) or [(LaAlO3){0.3}(SrAl0.5Ta0.5O3){0.7}] (LSAT), were measured as a function of temperature. The result shows, as expected based on previous knowledge of bulk materials, that the films' resistivity is closely related to their structures. Observed superlattice reflections indicate that NSMO thin films have an antiferro-orbital-ordered phase as their low-temperature phase while PSMO film on LSAT has a ferro-orbital-ordered phase, and that on STO has no orbital-ordered phase. A metallic ground state was observed only in films having a narrow region of A-site ion radius, while larger ions favor ferro-orbital-ordered structure and smaller ions stabilize antiferro-orbital-ordered structure. The key to the orbital-ordering transition in (011) film is found to be the in-plane displacement along [0-1 1] direction., Comment: 19pages, 11 figures

Photoinduced effects in a single crystal of bilayered manganites, La2-2xSr1+2xMn2O7 (x=0.38), were investigated in a wide range of temperatures by pump-probe measurement at a photon energy of 1.6eV. In a ferromagnetic metallic state, significant enhancement of positive rise in differential reflectivity with a slow relaxing time of hundred picoseconds was observed just below Tc=127K, indicating that the reflectivity change with the slow relaxation time constant is induced by laser heating. We have also observed an unconventional fast relaxing component that has a time constant of the order of ten picoseconds. This fast relaxing component, whose absolute value has an asymmetric peak at Tc, is presumably due to short-range correlation of Jahn-Teller distortion., Comment: 13 pages, 4 figures, accepted to Solid State Communications

A new method (NM) for filtering three-dimensional reconstructed densities is proposed. The algorithm is tested with simulated spectra and employed to study the electronic structure of the rare-earth compound LaB6. For this system, momentum densities are reconstructed from theoretical and experimental two-dimensional angular correlation of electron-positron annihilation radiation (2D ACAR) spectra. The experimental results are in good agreement with the band structure calculated with the full-potential linearized augmented-plane-wave (FLAPW) method within the local-density approximation (LDA), apart from the detection of small electron pockets in the 15th band. It is also shown that, unlike the electron-positron enhancement, the electron-electron correlations affect noticeably the momentum density.

Infrared magnetic circular dichloism (MCD), or equivalently magneto-optical Kerr effect, has been measured on the Tl2Mn2O7 pyrochlore, which is well known for exhibiting a large magnetoresistance around the Curie temperature T_C ~ 120 K. A circularly polarized, infrared synchrotron radiation is used as the light source. A pronounced MCD signal is observed exactly at the plasma edge of the reflectivity near and below T_c. However, contrary to the conventional behavior of MCD for ferromagnets, the observed MCD of Tl2Mn2O7 grows with the applied magnetic field, and not scaled with the internal magnetization. It is shown that these results can be basically understood in terms of a classical magnetoplasma resonance. The absence of a magnetization-scaled MCD indicates a weak spin-orbit coupling of the carriers in Tl2Mn2O7. We discuss the present results in terms of the microscopic electronic structures of Tl2Mn2O7., Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jpn

A TiS$_{2}$ crystal with a layered structure was found to have a large thermoelectric power factor.The in-plane power factor $S^{2}/ \rho$ at 300 K is 37.1~$\mu$W/K$^{2}$cm with resistivity ($\rho$) of 1.7 m$\Omega$cm and thermopower ($S$) of -251~$\mu$V/K, and this value is comparable to that of the best thermoelectric material, Bi$_{2}$Te$_{3}$ alloy. The electrical resistivity shows both metallic and highly anisotropic behaviors, suggesting that the electronic structure of this TiS$_{2}$ crystal has a quasi-two-dimensional nature. The large thermoelectric response can be ascribed to the large density of state just above the Fermi energy and inter-valley scattering. In spite of the large power factor, the figure of merit, $ZT$ of TiS$_{2}$ is 0.16 at 300 K, because of relatively large thermal conductivity, 68~mW/Kcm. However, most of this value comes from reducible lattice contribution. Thus, $ZT$ can be improved by reducing lattice thermal conductivity, e.g., by introducing a rattling unit into the inter-layer sites., Comment: 11 pages, 4 figures, to be published in Physical Review B

Optical conductivity data s(w) of the colossal magneto-resistance (CMR) pyrochlore Tl2Mn2O7 are presented as functions of temperature (T) and externalmagnetic field (B). Upon cooling and upon applying B near the Curietemperature, where the CMR manifests itself, s(w) shows a clear transition from an insulatorlike to a metallic electronic structure as evidenced by theemergence of a pronounced Drude-like component below 0.2 eV. Analyses on thes(w) spectra show that both T- and B-induced evolutions of the electronicstructure are very similar to each other, and that they are universally related to the development of macroscopic magnetization (M). In particular, the effective carrier density obtained from s(w) scales with M^2 over wide ranges of T and B. The contributions to the CMR from the carrier effective mass and scattering time are also evaluated from the data., Comment: 4 pages, 4 figures, submitted to Phys. Rev. B Rapid Commun

From measurements of the ^{63}Cu Knight shift (K) and the nuclear spin-lattice relaxation rate (1/T_{1}) under magnetic fields from zero up to 28 T in the slightly overdoped superconductor TlSr_{2}CaCu_{2}O_{6.8} (T_{c}=68 K), we find that the pseudogap behavior, {\em i.e.}, the reductions of 1/T_{1}T and K above T_{c} from the values expected from the normal state at high T, is strongly field dependent and follows a scaling relation. We show that this scaling is consistent with the effects of the Cooper pair density fluctuations. The present finding contrasts sharply with the pseudogap property reported previously in the underdoped regime where no field effect was seen up to 23.2 T. The implications are discussed., Comment: 10 pages, 4 GIF figures, to be published in Phys. Rev. Lett

Hall resistivity and magneto-thermopower have been measured for colossal magnetoresistive Tl2Mn2O7 over wide temperature and magnetic-field ranges. These measurements revealed that a small number of free electron-like carriers is responsible for the magneto-transport properties. In contrast to perovskite CMR materials, the anomalous Hall coefficient is negligible even in the ferromagnetic state due to negligibly small skew scattering. The characteristic feature in Tl2Mn2O7 is that the carrier density changes with temperature and the magnetic field. The carrier density increases around TC as the temperature is lowered or as the magnetic field is increased, which explains the CMR of this material. The conduction-band-edge shift, which is caused by the strong s-d interaction between localized Mn moments and s-like conduction electrons, is a possible mechanism for the carrier density change., Comment: 7 REVTeX pages, 5 eps figures, submitted to PRL

Presupernova evolution and explosive nucleosynthesis in massive stars for main-sequence masses from 13 $M_\odot$ to 70 $M_\odot$ are calculated. We examine the dependence of the supernova yields on the stellar mass, $^{12}C(\alpha, \gamma) ^{16}O}$ rate, and explosion energy. The supernova yields integrated over the initial mass function are compared with the solar abundances., Comment: 1 Page Latex source, 10 PostScript figures, to appear in Nuclear Physics A, Vol. A616 (1997)