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In the modular superconducting quantum processor architecture, high-fidelity, meter-scale microwave interconnect between processor modules is a key technology for extending system size beyond constraints imposed by device manufacturing equipment, yield, and signal delivery. While there have been many demonstrations of remote state transfer between modules, these relied on tomographic experiments for benchmarking, but this technique does not reliably separate State Preparation And Measurement (SPAM) error from error per state transfer. Recent developments based on randomized benchmarking provide a compatible theory for separating these two errors. In this work, we present a module-to-module interconnect based on Tunable-Coupling Qubits (TCQs) and benchmark, in a SPAM error tolerant manner, a remote state transfer fidelity of 0.988 across a 60cm long coplanar waveguide (CPW). The state transfer is implemented via superadiabatic transitionless driving method, which suppresses intermediate excitation in internal modes of CPW. We also introduce the frame tracking technique to correct unintended qubit phase rotations before and after the state transfers, which enables the SPAM-error-tolerant benchmarking of the state transfers. We further propose and construct a remote CNOT gate between modules, composed of local CZ gates in each module and remote state transfers, and report a high gate fidelity of 0.933 using randomized benchmarking method. The remote CNOT construction and benchmarking we present is a more complete metric that fully characterizes the module to module link operation going forward as it more closely represents interconnect operation in a circuit.

The research focuses on the explanation of a phenomenon observed in the spectra of electron nuclear resonance (ENDOR) pertaining to nitrogen atoms adjacent to the boron vacancy (VB) defect in hexagonal boron nitride (hBN). The phenomenon is manifested as a shift of the ENDOR spectrum lines with respect to the nitrogen Larmor frequency. It is hypothesized that these shifts are indicative of a substantial hyperfine interaction between the VB defect and the 14N nuclei in hBN. A calculation utilizing second-order perturbation theory was executed to determine the positions of the ENDOR spectrum lines, resulting in the formulation of correction equations. The values obtained from the perturbation theory corrections align well with the experimental results. The extent of nuclear state admixture into electron states was found to be around 0.04-0.07%.

High-spin defect centers in crystal matrices are used in quantum computing technologies, highly sensitive sensors, and single-photon sources. In this work, optically active nitrogen-vacancy color centers NV in a 28Si-enriched (nuclear spin I = 0) 6H-28SiC crystal have been studied using the photoinduced (980 nm) high-frequency (94 GHz, 3.4 T) pulsed electron paramagnetic resonance method at a temperature of 150 K. Three structurally nonequivalent types of NV- centers with axial symmetry have been identified and their spectroscopic parameters have been determined. Long spin-lattice, T1=1.3 ms, and spin-spin, T2=59 us, ensemble relaxation times of NV- centers with extremely narrow (450 kHz) absorption lines allow highly selective excitation of resonant transitions between sublevels caused by the weak hyperfine interaction (A = 1 MHz) with 14N (I = 1) nuclei for the quantum manipulation of the electron spin magnetization.

The nitrogen-vacancy (NV) centers (NCVSi) - in 4H silicon carbide (SiC) constitute an ensemble of spin S = 1 solid state qubits interacting with the surrounding 14N and 29Si nuclei. As quantum applications based on a polarization transfer from the electron spin to the nuclei require the knowledge of the electron-nuclear interaction parameters, we have used high-frequency (94 GHz) electron-nuclear double resonance spectroscopy combined with first-principles density functional theory to investigate the hyperfine and nuclear quadrupole interactions of the basal and axial NV centers. We observed that the four inequivalent NV configurations (hk, kh, hh, and kk) exhibit different electron-nuclear interaction parameters, suggesting that each NV center may act as a separate optically addressable qubit. Finally, we rationalized the observed differences in terms of distinctions in the local atomic structures of the NV configurations. Thus, our results provide the basic knowledge for an extension of quantum protocols involving the 14N nuclear spin., Comment: 9 pages, 7 figures

Optically active point defects in semiconductors have received great attention in the field of solid-state quantum technologies. Hexagonal boron nitride, with an ultra-wide band gap E_g = 6 eV, containing a negatively charged boron vacancy (V_B^-) with unique spin, optical, and coherent properties presents a new two-dimensional platform for the implementation of quantum technologies. This work establishes the value of V_B^ - spin polarization under optical pumping with {\lambda}ext = 532 nm laser using high-frequency ({\nu}mw = 94 GHz) electron paramagnetic resonance (EPR) spectroscopy. In optimal conditions polarization was found to be P = 38.4 %. Our study reveals that Rabi oscillations induced on polarized spin states persist for up to 30-40 microseconds, which is nearly two orders of magnitude longer than what was previously reported. Analysis of the coherent electron-nuclear interaction through the observed electron spin echo envelope modulation (ESEEM) made it possible to detect signals from remote nitrogen and boron nuclei, and to establish a corresponding quadrupole coupling constant Cq = 180 kHz related to nuclear quadrupole moment of 14N. These results have fundamental importance for understanding spin properties of boron vacancy.

The concept of optically addressable spin states of deep level defects in wide band gap materials is successfully applied for the development of quantum technologies. Recently discovered negatively charged boron vacancy defects (VB) in hexagonal boron nitride (hBN) potentially allow a transfer of this concept onto atomic thin layers due to the van der Waals nature of the defect host. Here, we experimentally explore all terms of the VB spin Hamiltonian reflecting interactions with the three nearest nitrogen atoms by means of conventional electron spin resonance and high frequency (94 GHz) electron-nuclear double resonance. We establish symmetry, anisotropy, and principal values of the corresponding hyperfine interaction (HFI) and nuclear quadrupole interaction (NQI). The HFI can be expressed in the axially symmetric form as Aperp = 45.5 MHz and Apar = 87 MHz, while the NQI is characterized by quadrupole coupling constant Cq = 1.96 MHz with slight rhombisity parameter n = (Pxx - Pyy)/Pzz = -0.070. Utilizing a conventional approach based on a linear combination of atomic orbitals and HFI values measured here, we reveal that almost all spin density (84 %) of the VB electron spin is localized on the three nearest nitrogen atoms. Our findings serve as valuable spectroscopic data and direct experimental demonstration of the VB spin localization in a single two dimensional BN layer.

By means of ab initio calculations within the density functional theory (DFT) electronic and magnetic properties of BaTiO3/LaMnO3 interface were investigated. An impact of ferroelectric overlayer thickness onto the interface properties was analysed through the spin-polarized density of states., Comment: arXiv admin note: substantial text overlap with arXiv:2201.09224

By means of ab initio calculations the possibilities of switchable spin-polarized two-dimensional electron gas (2DEG) at the interface of antiferromagnetic and ferroelectric perovskites, i.e., LaMnO3/BaTiO3 superlattice, were investigated. We demonstrate that at the heterostructure with TiO2/LaO interfacial layers the two-dimensional conducting state arises mainly localized within the interfacial MnO layer. The density of states at the Fermi-level can be tuned by ferroelectric polarization reversal. The conducting state coexists with magnetic one mainly arose from Mn atoms.

Coherent coupling of defect spins with surrounding nuclei along with the endowment to read out the latter, are basic requirements for an application in quantum technologies. We show that negatively charged boron vacancies (VB-) in electron-irradiated hexagonal boron nitride (hBN) meet these prerequisites. We demonstrate Hahn-echo coherence of the VB- electron spin with a characteristic decay time Tcoh = 15 us, close to the theoretically predicted limit of 18 us for spin defects in hBN. Modulation in the MHz range superimposed on the Hahn-echo decay curve are shown to be induced by coherent coupling of the VB- spin with the three nearest 14N nuclei through a nuclear quadrupole interaction of 2.11 MHz. Supporting DFT calculation confirm that the electron-nuclear coupling is confined to the defective layer. Our findings allow an in-depth understanding of the electron-nuclear interactions of the VB- defect in hBN and demonstrate its strong potential in quantum technologies.

We have demonstrated a novel type of superconducting transmon qubit in which a Josephson junction has been engineered to act as its own parallel shunt capacitor. This merged-element transmon (MET) potentially offers a smaller footprint and simpler fabrication than conventional transmons. Because it concentrates the electromagnetic energy inside the junction, it reduces relative electric field participation from other interfaces. By combining micrometer-scale Al/AlOx/Al junctions with long oxidations and novel processing, we have produced functional devices with $E_{J}$/$E_{C}$ in the low transmon regime ($E_{J}$/$E_{C}$ $\lesssim$30). Cryogenic I-V measurements show sharp dI/dV structure with low sub-gap conduction. Qubit spectroscopy of tunable versions show a small number of avoided level crossings, suggesting the presence of two-level systems (TLS). We have observed mean T1 times typically in the range of 10-90 microseconds, with some annealed devices exhibiting T1 > 100 microseconds over several hours. The results suggest that energy relaxation in conventional, small-junction transmons is not limited by junction loss., Comment: 7 pages, 4 figures Added references Performed minor editing for clarity Made minor formatting changes to figures

In this work we prove that for any dimension $d\geq 1$ and any $\gamma \in (0,1)$ super-Brownian motion corresponding to the log-Laplace equation \begin{equation*} \begin{split} \frac{\partial v(t,x)}{\partial t } & = \frac{1}{2}\bigtriangleup v(t,x) + v^\gamma (t,x) ,\: (t,x) \in \mathbb{R}_+\times \mathbb{R}^d,\\ v(0,x)&= f(x) \end{split} \end{equation*} is absolutely continuous with respect to the Lebesgue measure at any fixed time $t>0$. Our proof is based on properties of solutions of the \LL\ equation. We also prove that when initial datum $v(0,\cdot)$ is a finite, non-zero measure, then the \LL\ equation has a unique, continuous solution. Moreover this solution continuously depends on initial data.

The effect of green and ultraviolet laser light on Ba$_{0.8}$Sr$_{0.2}$TiO$_3$/LaMnO$_3$ heterostructure electrical resistance was studied. In 80-200 K range illumination induces transient resistance component at ~15% of the steady-state value, the time constant associated with the transient component is ~12 s. The negative photoresistance effect is found under green, infrared and ultraviolet illumination., Comment: 14 pages, 3 figures

We have studied transport and magnetotransport properties of the heterostructure consisting of the ferroelectric Ba$_{0.8}$Sr$_{0.2}$TiO$_3$ film deposited on the single crystalline manganite LaMnO$_3$. Two-dimensional electron gas arising at the interface transforms the interface region of the antiferromagnetic manganite to the ferromagnetic state with the reoriented magnetic moments. We obtained that the contribution of these ferromagnetic regions to the resistance of the heterostructure appears to be dependent on the external magnetic field applied perpendicularly to the interface (and parallel to {\it c}-axis of the ferromagnetic state of LaMnO$_3$). We believe that the decrease of the resistance of the studied heterostructure under the influence of the external magnetic field is caused by an appearance of the ferromagnetic order in the interface area. This leads to a relatively small resistance. In turn, the cycling of the applied magnetic field leads to the increase of the regions of the ferromagnetic order and, as a result, to decreasing scattering of the current carriers at the ferromagnetic disordering.

Porous silica materials offer wide range of possibilities for enhancement of the productivity of oil reservoirs. However the mechanism of adsorption of polar components of crude oil on silica surface is poorly understood that hinders technological improvement of supports and oil extraction. We have synthesized opal films with the silica microspheres size of about 360 nm, specific surface area of 5.2 m2/g and pore size of 230 nm. We have fractionated and characterized oil and oil asphaltenes from heavy (Ashalchinskoe) oil. By pulsed electron paramagnetic resonance (EPR) and double electron nuclear resonance (ENDOR) in the W band frequency range (microwave frequency of 94 GHz, magnetic field of 3.4 T) we have studied the adsorption of oil asphaltenes on the surface of opal samples using the intrinsic for asphaltenes paramagnetic vanadylporphyrins (VO) complexes. 1H ENDOR spectra are found to be different for initial and the adsorbed samples in their central parts (that is a sign of asphaltenes VO disaggregation) whereas no significant changes in the W band EPR spectra were detected. Contrasting to alumina support, no strong electron proton interaction with the protons on the surface of SiO2 (presumably, silanol groups) was found and infiltration of the oiled opal films with gasoline changes the central part of 1H ENDOR spectra. It shows that the proton containing groups on the surface of amorphous SiO2 sample can significantly change the asphaltene adsorption properties and ENDOR of the intrinsic for oil paramagnetic centers could be used for the characterization of surface state in porous media in situ or operando., Comment: 7 pages, 5 figures, 43 references

The studies of chemical processes in spatially confined conditions are of interest from the fundamental and industrial points of view. By means of the W band EPR and 1H Mims electron nuclear double resonance (ENDOR) we show that the radiation-induced paramagnetic centers (E') in the synthetic nanoporous silica opals could be used as sensitive probes to investigate the surface modification and, potentially, reactions of polymerization in the confined by opal pores., Comment: 6 pages

We have demonstrated electron-electron and electron-nuclear spin manipulations of Gd3+ ion in CaWO4 crystal. The results suggest that the studied system is perspective for multiqubit implementation in quantum computing., Comment: 2 Pages, 5 Figures

The conventional magnon Bose-Einstein condensation (BEC of magnons with k = 0) is a coherent state of excited magnons described by a common wave function. It was observed first in antiferromagnetic superfluid states of 3He. Here we report on the discovery of a very similar magnon BEC in ferrimagnetic film at room temperature. The experiments were performed in Yttrium Iron Garnet (YIG) films at a magnetic field oriented perpendicular to the film. The high-density quasiequilibrium state of excited magnon was formed by methods of pulse and/or Continuous Waves (CW) magnetic resonance. We have observed a Long Lived Induction Decay Signals (LLIDS), well known as a signature of spin superfluidity. We demonstrate that the BEC state may maintain permanently by continuous replenishment of magnons with a small radiofrequency (RF) field. Our finding opens the way for development of potential supermagnonic applications at an ambient conditions., Comment: 10 pages, 10 figures. arXiv admin note: text overlap with arXiv:1705.06594 by other authors

We report the first observation of superconductivity in heterostructure consisting of an insulating ferroelectric film (Ba$_{0.8}$Sr$_{0.2}$TiO$_3$) grown on an insulating parent compound of La$_2$CuO$_4$ with [001] orientation. The heterostructure was prepared by magnetron sputtering on a non-atomically-flat surface with inhomogeneities of the order of 1-2 nm. The measured superconducting transition temperature T$_c$ is about 30K. We have shown that superconductivity is confined near the interface region. Application of a weak magnetic field perpendicular to the interface leads to the appearance of the finite resistance. That confirms the quasi-two-dimensional nature of the superconductive state. The proposed concept promises ferroelectrically controlled interface superconductivity which offers the possibility of novel design of electronic devices., Comment: To be published in Phys. Rev. Lett

We have considered the model of the phase transition of the second order for the Coulomb frustrated 2D charged system. The coupling of the order parameter with the charge was considered as the local temperature. We have found that in such system, an appearance of the phase-separated state is possible. By numerical simulation, we have obtained different types ("stripes", "rings", "snakes") of phase-separated states and determined the parameter ranges for these states. Thus the system undergoes a series of phase transitions when the temperature decreases. First, the system moves from the homogeneous state with a zero order parameter to the phase-separated state with two phases in one of which the order parameter is zero and, in the other, it is nonzero ($\tau>0$). Then a first-order transition occurs to another phase-separated state, in which both phases have different and nonzero values of the order parameter (for $\tau<0$). And only a further decrease of temperature leads to a transition to a homogeneous ordered state., Comment: 7 pages, 7 figures, appears in Physical Review B

The demonstration of a quasi-two-dimensional electron gas (2DEG) and superconducting properties in LaAlO$_3$/SrTiO$_3$ heterostructures has stimulated intense research activity in recent ten years. The 2DEG has unique properties that are promising for applications in all-oxide electronic devices. The superconductivity in such heterostructures has been observed below 300 mK. For superconductivity applications it is desirable to have more wide temperature of the existence range and the ability to control superconductivity properties by external stimulus. Based on first-principles calculations and theoretical consideration we show that all-oxide heterostructures incorporating ferroelectric constituent, such as BaTiO$_3$/La$_2$CuO$_4$, allow creating 2DEG. We predict a possibility of a high temperature guasi-two-dimensional superconductivity state. This state could be switchable between superconducting and conducting states by ferroelectric polarization reversal. We also discuss that such structures must be more simple for preparation. The proposed concept of ferroelectrically controlled interface superconductivity offers the possibility to design novel electronic devices., Comment: 5 pages 3 figures. arXiv admin note: text overlap with arXiv:1710.03967

The first observation of the resolved Mims electron-nuclear double resonance (ENDOR) spectra from the nearby and remote nuclei of 19F and 7Li nuclei on impurity Ce3+ ions in LiYF4 crystal is reported. It shows that LiYF4:Ce3+ system can be exploited as a convenient matrix for performing spin manipulations and adjusting quantum computation protocols while ENDOR technique could be used for the investigation of electron-nuclear interaction with all the nuclei of the system and exploited for the electron-nuclear spin manipulations., Comment: 4 pages, 2 figures, 1 Table. Reported on Theor-2017 (Kazan, Russia) Conference

The temperature dependence of the electrical resistivity of the heterostructures consisting of single crystalline LaMnO$_3$ samples with different crystallographic orientations covered by the epitaxial ferroelectric Ba$_{0.8}$Sr$_{0.2}$TiO$_3$ film has been studied. Results obtained for the heterostructure have been compared with the electrical resistivity of the single crystalline LaMnO$_3$ without the film. It was found that for the samples with the films where the polarization axis is perpendicular to the crystal surface the electrical resistivity strongly decreases, and at the temperature below ~160 K undergoes the insulator-metal transition. Ab-initio calculations were also performed for the structural and electronic properties of the BaTiO$_3$/LaMnO$_3$ heterostructure. Transition to the 2D electron gas at the interface is shown., Comment: 5 pages, 4 fugures

Structural characterization of metalloporphyrins in complex systems such as native hydrocarbons is in the focus of scientific and industrial interests since many years. We describe electron-nuclear double resonance (ENDOR) of crude oil from the well without any additional sample treatment (i.e., in the native environment) in the magnetic field of about 3.4 T and temperature of 50 K by applying microwave pulses at 94 GHz (W-band) and radiofrequency pulses at near the proton Larmor frequencies of 144 MHz to probe the paramagnetic vanadyls. By means of density functional theory (DFT) calculations, ENDOR features are explained and ascribed to certain vanadyl porhyrin structural forms known to be present in crude oil., Comment: 20 pages including 4 Figures and Supporting Material with 1 Figure. Accepted for publication in ACS journal "Energy & Fuels"

We report the observation of pulsed electron-nuclear double resonance (ENDOR) spectrum caused by interactions of the nitrogen nuclei 14N with the unpaired electron of the paramagnetic vanadyl complexes VO2+ of vanadyl porphyrins in natural crude oil. We provide detailed experimental and theoretical characterization of the nitrogen hyperfine and quadrupole tensors., Comment: 6 pages, 2 Figures

Density functional theory based calculations within the framework of the plane-wave pseudopotential approach are carried out to define the phonon spectrum of hydroxyapatite Ca10(PO4)6(OH)2 (HAp). It allows to describe the temperature dependence of the electronic spin-lattice relaxation time T1e of the radiation-induced stable radical NO32- in HAp, which was measured in X-band (9 GHz, magnetic field strength of 0.34 T) in the temperature range T = (10-300) K. It is shown that the temperature behavior of T1e at T > 20 K can be fitted via two phonon Raman type processes with the Debye temperature of 280 K evaluated from the phonon spectrum., Comment: 6 pages, 3 Figures

Size-calibrated commercial nanodiamonds synthesized by high-pressure high-temperature (HPHT) technique were studied by high-frequency W and conventional X band electron paramagnetic resonance (EPR) spectroscopy. The numbers of spins in the studied samples were estimated. The core-shell model of the HPHT nanodiamonds was proposed to explain the observed dependence of the concentration of the N0 paramagnetic centers. Two other observed paramagnetic centers are attributed to the two types of structures in the nanodiamond shell., Comment: 8 pages

We show that electric field noise from surface charge fluctuations can be a significant source of spin decoherence for near-surface nitrogen-vacancy (NV) centers in diamond. This conclusion is based on the increase in spin coherence observed when the diamond surface is covered with high-dielectric-constant liquids, such as glycerol. Double resonance experiments show that improved coherence occurs even though the coupling to nearby electron spins is unchanged when the liquid is applied. Multipulse spin echo experiments reveal the effect of glycerol on the spectrum of NV frequency noise.

Multipulse sequences based on Carr-Purcell decoupling are frequently used for narrow-band signal detection in single spin magnetometry. We have analyzed the behavior of multipulse sensing sequences under real-world conditions, including finite pulse durations and the presence of detunings. We find that these non-idealities introduce harmonics to the filter function, allowing additional frequencies to pass the filter. In particular, we find that the XY family of sequences can generate signals at the 2fac, 4fac and 8fac harmonics and their odd subharmonics, where fac is the ac signal frequency. Consideration of the harmonic response is especially important for diamond-based nuclear spin sensing where the NMR frequency is used to identify the nuclear spin species, as it leads to ambiguities when several isotopes are present., Comment: 6 pages, 7 figures

Nuclear magnetic resonance (NMR) imaging with nanometer resolution requires new detection techniques with sensitivity well beyond the capability of conventional inductive detection. Here, we demonstrate two dimensional imaging of $^1$H NMR from an organic test sample using a single nitrogen-vacancy center in diamond as the sensor. The NV center detects the oscillating magnetic field from precessing protons in the sample as the sample is scanned past the NV center. A spatial resolution of 12 nm is shown, limited primarily by the scan accuracy. With further development, NV-detected magnetic resonance imaging could lead to a new tool for three-dimensional imaging of complex nanostructures, including biomolecules., Comment: Main text: 19 pages including 5 figures Supplementary Information: 9 pages including 3 figures

We discuss multipulse magnetometry that exploits all three magnetic sublevels of the S=1 nitrogen-vacancy center in diamond to achieve enhanced magnetic field sensitivity. Based on dual frequency microwave pulsing, the scheme works in arbitrary magnetic bias fields and is twice as sensitive to ac magnetic fields as conventional two-level magnetometry. We derive the spin evolution operator for dual frequency microwave excitation and show its effectiveness for double-quantum state swaps. Using multipulse sequences of up to 128 pulses under optimized conditions, we show enhancement of the SNR by up to a factor of 2 in detecting NMR statistical signals, with a 4 times enhancement theoretically possible., Comment: main text: 14 pages plus 4 pages figures (all in one pdf file); Supplementary material 13 pages, typos corrected in matrices on p. 6

Synthesized by the wet chemical precipitation technique hydroxyapatite powders (HAp) with the sizes of the crystallites of (20-50) nm and 1000 nm were analyzed by different analytical methods. By means of electron paramagnetic resonance (EPR) it is shown that during the synthesis process nitrate anions from the reagents (by-products) could incorporate into the HAp structure. The concentration of the stable NO32- radicals detected after X-ray irradiation of the product at room temperature does not decrease even after annealing up to 400 oC. The relaxation times and EPR parameters of the axially symmetric NO32- paramagnetic centers are measured with high accuracy. Increased sensitivity and resolution of high-frequency EPR (95 GHz) allows to reveal additional paramagnetic centre(s) which origin is discussed. Analyses of electron-nuclear double resonance (ENDOR) spectra from 1H and 31P nuclei and ab-initio density functional theory (DFT) calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO32- radicals preferably occupy PO43- site in the HAp structure., Comment: 10 pages, 5 figures

Near-surface nitrogen-vacancy (NV) centers have been created in diamond through low energy implantation of 15N to sense electron spins that are external to the diamond. By performing double resonance experiments, we have verified the presence of g=2 spins on a diamond crystal that was subjected to various surface treatments, including coating with a polymer film containing the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). Subsequent acid cleaning eliminated the spin signal without otherwise disrupting the NV center, providing strong evidence that the spins were at the surface. A clear correlation was observed between the size of the detected spin signal and the relaxation time T2 for the six NV centers studied. We have developed a model that takes into account the finite correlation time of the fluctuating magnetic fields generated by the external spins, and used it to infer the signal strength and correlation time of the magnetic fields from these spins. This model also highlights the sensitivity advantage of active manipulation of the longitudinal spin component via double resonance over passive detection schemes that measure the transverse component of spin., Comment: 18 pages + 7 figures

The effect of giant dielectric permittivity due to phase separation accompanied by charged inhomogeneities in low-doped manganites is discussed. The effect appears in the vicinity of the second-order magnetic phase transition and is caused by long-range Coulomb forces. The long-range Coulomb interaction is responsible for the formation of inhomogeneous charged states and determines their characteristic length scales. We derive the phase diagram of the inhomogeneous charged states in the framework of the phenomenological theory of phase transitions. The large value of the static dielectric function reduces the characteristic value of the Coulomb energy of the inhomogeneous state and makes the appearance of the magnetoelectric effect possible. We discuss the formation of a state with giant dielectric permittivity and magneto-capacitance effects in that case., Comment: 16 pages, 4 figures. arXiv admin note: text overlap with arXiv:0801.0854

We demonstrate nuclear double resonance for nanometer-scale volumes of spins where random fluctuations rather than Boltzmann polarization dominate. When the Hartmann-Hahn condition is met in a cross-polarization experiment, flip-flops occur between two species of spins and their fluctuations become coupled. We use magnetic resonance force microscopy to measure this effect between 1H and 13C spins in 13C-enriched stearic acid. The development of a cross-polarization technique for statistical ensembles adds an important tool for generating chemical contrast in nanometer-scale magnetic resonance., Comment: 14 pages, 4 figures

Recent advances in the fabrication of microelectromechanical systems (MEMS) and their evolution into nanoelectromechanical systems (NEMS) have allowed researchers to measure extremely small forces, masses, and displacements. In particular, researchers have developed position transducers with resolution approaching the uncertainty limit set by quantum mechanics. The achievement of such resolution has implications not only for the detection of quantum behavior in mechanical systems, but also for a variety of other precision experiments including the bounding of deviations from Newtonian gravity at short distances and the measurement of single spins. Here we demonstrate the use of a quantum point contact (QPC) as a sensitive displacement detector capable of sensing the low-temperature thermal motion of a nearby micromechanical cantilever. Advantages of this approach include versatility due to its off-board design, compatibility with nanoscale oscillators, and, with further development, the potential to achieve quantum limited displacement detection., Comment: 5 pages, 5 figures

Localized charged states and phase segregation are described in the framework of the phenomenological Ginzburg-Landau theory of phase transitions. The Coulomb interactions determines the charge distribution and the characteristic length of the phase separated states. The phase separation with charge segregation becomes possible because of the large dielectric constant and the small density of extra charge in the range of charge localization. The phase diagram is calculated and the energy gain of the phase separated state is estimated. The role of the Coulomb interaction is elucidated.

We report on measurements of the spin lifetime of nuclear spins strongly coupled to a micromechanical cantilever as used in magnetic resonance force microscopy. We find that the rotating-frame correlation time of the statistical nuclear polarization is set by the magneto-mechanical noise originating from the thermal motion of the cantilever. Evidence is based on the effect of three parameters: (1) the magnetic field gradient (the coupling strength), (2) the Rabi frequency of the spins (the transition energy), and (3) the temperature of the low-frequency mechanical modes. Experimental results are compared to relaxation rates calculated from the spectral density of the magneto-mechanical noise., Comment: 4 pages, 4 figures

When probing nuclear spins in materials on the nanometer scale, random fluctuations of the spin polarization will exceed the mean Boltzmann polarization for sample volumes below about (100nm)^3. In this work, we use magnetic resonance force microscopy to observe nuclear spin fluctuations in real time. We show how reproducible measurements of the polarization variance can be obtained by controlling the spin correlation time and rapidly sampling a large number of independent spin configurations. A protocol to periodically randomize the spin ensemble is demonstrated, allowing significant improvement in the signal-to-noise ratio for nanometer-scale magnetic resonance imaging., Comment: 5 pages, 4 figures

We report the direct evidence of the possibility of charge segregation in manganites. The high contrast of electric-field-induced local charged states is observed during more than 100 hours at room temperature. These induced states display a piezoelectric response and polar properties. This effect may be an example of a new kind of polar ordering in solid state., Comment: 13 pages, 4 figures

We use a 1.0-um-wide patterned Cu wire with an integrated nanomagnetic tip to measure the statistical nuclear polarization of 19F in CaF2 by magnetic resonance force microscopy (MRFM). With less than 350 uW of dissipated power, we achieve rf magnetic fields over 4 mT at 115 MHz for a sample positioned within 100 nm of the "microwire" rf source. A 200-nm diameter FeCo tip integrated onto the wire produces field gradients greater than 10^5 T/m at the same position. The large rf fields from the broadband microwire enable long rotating-frame spin lifetimes of up to 15 s at 4 K., Comment: 4 pages, 4 figures

Magnetic resonance imaging, based on the manipulation and detection of nuclear spins, is a powerful imaging technique that typically operates on the scale of millimeters to microns. Using magnetic resonance force microscopy, we have demonstrated that magnetic resonance imaging of nuclear spins can be extended to a spatial resolution better than 100 nm. The two-dimensional imaging of 19F nuclei was done on a patterned CaF2 test object, and was enabled by a detection sensitivity of roughly 1200 nuclear spins. To achieve this sensitivity, we developed high-moment magnetic tips that produced field gradients up to 1.4x10^6 T/m, and implemented a measurement protocol based on force-gradient detection of naturally occurring spin fluctuations. The resulting detection volume of less than 650 zl represents 60,000x smaller volume than previous NMR microscopy and demonstrates the feasibility of pushing magnetic resonance imaging into the nanoscale regime., Comment: 24 pages, 5 figures

We cool the fundamental mechanical mode of an ultrasoft silicon cantilever from a base temperature of 2.2 K to 2.9 +/- 0.3 mK using active optomechanical feedback. The lowest observed mode temperature is consistent with limits determined by the properties of the cantilever and by the measurement noise. For high feedback gain, the driven cantilever motion is found to suppress or "squash" the optical interferometer intensity noise below the shot noise level., Comment: 4 pages, 6 figures

Noise spectra of supersonic air jet