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The main idea in the original Grover search (Phys. Rev. Lett. 79, 325 (1997)) is to single out a target state containing the solution to a search problem by amplifying the amplitude of the state, following the Oracle's job, i.e., a black box giving us information about the target state. We design quantum circuits to accomplish a complete Grover search involving both the Oracle's job and the amplification of the target state, which are employed to solve Satisfiability (SAT) problems. We explore how to carry out the quantum circuits by currently available ion-trap quantum computing technology., Comment: 14 pages, 6 figures

We have investigated the dispersion renormalization $Z_{disp}$ in La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) over the wide doping range of $x=0.03-0.30$, for binding energies extending to several hundred meV's. Strong correlation effects conspire in such a way that the system exhibits an LDA-like dispersion which essentially `undresses' ($Z_{disp}\to 1$) as the Mott insulator is approached. Our finding that the Mott insulator contains `nascent' or `preformed' metallic states with a vanishing spectral weight offers a challenge to existing theoretical scenarios for cuprates., Comment: 7 pages, 4 figures. PRB 2008 in press

Here we report pressure effect on superconducting transition temperature (Tc) of ReFeAsO0.85 (Re= Sm and Nd) system without fluorine doping. In-situ measurements under high pressure showed that Tc of the two compounds decrease monotonously over the pressure range investigated. The pressure coefficients dTc/dP in SmFeAsO0.85 and Nd FeAsO0.85 were different, revealing the important influence of the deformation in layers on Tc. Theoretical calculations suggested that the electron density of states decrease with increasing pressure, following the same trend of experimental data., Comment: 13 pages and 4 figures

To date, angle-resolved photoemission spectroscopy has been successful in identifying energy scales of the many-body interactions in correlated materials, focused on binding energies of up to a few hundred meV below the Fermi energy. Here, at higher energy scale, we present improved experimental data from four families of high-Tc superconductors over a wide doping range that reveal a hierarchy of many-body interaction scales focused on: the low energy anomaly ("kink") of 0.03-0.09eV, a high energy anomaly of 0.3-0.5eV, and an anomalous enhancement of the width of the LDA-based CuO2 band extending to energies of ~ 2 eV. Besides their universal behavior over the families, we find that all of these three dispersion anomalies also show clear doping dependence over the doping range presented., Comment: 7 pages, 6 figures

We have measured the superconducting critical temperature (Tc) and the diamagnetic susceptibility of La2-xSrxCuO4 single crystals in various magnetic fields. We observed a field-induced evolution from an apparent Tc phase to an intrinsic Tc1 = 15 K or Tc2 = 30 K phase characterized by "magic" hole concentration which is commensurate with that of a two dimensional electronic lattice. The onset Tc of the intrinsic superconducting phases remains robust up to H = 5 Tesla. We suggest that the intrinsic superconducting phases at "magic" doping concentrations are the pristine electronic phases of high temperature superconductivity., Comment: 17 pages, 4 figures, submitted to Phys. Rev. Lett

By using thermal and Lorentz force, the vortex motion is successfully manipulated in the mixed state of underdoped La$_{2 - x}$Sr$_{x}$CuO$_{4}$ single crystals and optimally doped YBa$_{2}$Cu$_{3}$O$_{7 - \delta}$ thin films. A conclusion is drawn that the strong Nernst signal above $T_{c}$ is induced by vortex motion. In the normal state, in order to reduce the dissipative contribution from the quasiparticle scattering and enhance the signal due to the possible vortex motion, a new measurement configuration is proposed. It is found that the in-plane Nernst signal ($H$ $| | $ $c$) can be measurable up to a high temperature in the pseudogap region, while the Abrikosov flux flow dissipation can only be measured up to $T_{c}$. This may point to different vortices below and above $T_{c}$ if we attribute the strong Nernst signal in the pseudogap region to the vortex motion. Below $T_{c}$ the dissipation is induced by the motion of the Abrikosov vortices. Above $T_{c}$ the dissipation may be caused by the motion of the spontaneously generated unbinded vortex-antivortex pairs., Comment: 6 pages, 8 figures; to be published in Physical Review B

We used point-contact tunnelling spectroscopy to study the superconducting pairing symmetry of electron-doped $Nd_{1.85}Ce_{0.15}CuO_{4-y}$ (NCCO) and hole-doped $La_{1.89}Sr_{0.11}CuO_{4}$ (LSCO). Nearly identical spectra without zero bias conductance peak (ZBCP) were obtained on the (110) and (100) oriented surfaces (the so-called nodal and anti-nodal directions) of NCCO. In contrast, LSCO showed a remarkable ZBCP in the nodal direction as expected from a d-wave superconductor. Detailed analysis reveals an s-wave component in the pairing symmetry of the NCCO sample with $\Delta/k_BT_c=1.66$, a value remarkable close to that of a weakly coupled BCS superconductor. We argue that this s-wave component is formed at the Fermi surface pockets centered at ($\pm\pi$,0) and (0,$\pm\pi$) although a d-wave component may also exist., Comment: 4 pages, 4 figures

We study magnetically stabilized nematic order for spin-one bosons in optical lattices. We show that the Zeeman field-driven quantum transitions between non-nematic Mott states and quantum spin nematic states in the weak hopping limit are in the universality class of the ferromagnetic XXZ (S=1/2) spin model. We further discuss these transitions as condensation of interacting magnons. The development of O(2) nematic order when external fields are applied corresponds to condensation of magnons, which breaks a U(1) symmetry. Microscopically, this results from a coherent superposition of two non-nematic states at each individual site. Nematic order and spin wave excitations around critical points are studied and critical behaviors are obtained in a dilute gas approximation. We also find that spin singlet states are unstable with respect to quadratic Zeeman effects and Ising nematic order appears in the presence of any finite quadratic Zeeman coupling. All discussions are carried out for states in three dimensional bipartite lattices., Comment: 16 pages, 3 figures

We have observed the plasma edge in the normal state c-axis far-infrared (far-IR) reflectivity of La2-xSrxCuO4 (LSCO) single crystals at an unlikely Sr-doping concentration x = 0.07 but not in x = 0.09. We find that the c-axis scattering rate (Gc) is surprisingly small, Gc = 13 (+_) 2 cm-1 for x = 0.07 and Gc = 24 (+_) 1 cm-1 for x = 0.09 and nearly temperature independent but increases linearly with doping up to x = 0.16. We suggest that the apparent absence of the normal state plasma edge in the previous measurements is due to the larger Gc than the screened plasma frequency of the coherent free carriers. We conclude that the c-axis charge transport in LSCO in the underdoped regime is intrinsically coherent., Comment: 4 pages, 4 figures. to appear in PRB71

High resolution angle-resolved photoemission spectroscopy data along the (0,0)-($\pi$,$\pi$) nodal direction with significantly improved statistics reveal fine structure in the electron self-energy of the underdoped (La$_{2-x}$Sr$_x$)CuO$_4$ samples in the normal state. Fine structure at energies of (40$\sim$46) meV and (58$\sim$63)meV, and possible fine structure at energies of (23$\sim$29)meV and (75$\sim$85)meV, have been identified. These observations indicate that, in LSCO, more than one bosonic modes are involved in the coupling with electrons., Comment: 4 pages, 3 figures, Fig. 2 updated

We report on a significant failure of LDA and GGA to reproduce the phase stability and thermodynamics of mixed-valence Li$_x$FePO$_4$ compounds. Experimentally, Li$_x$FePO$_4$ compositions ($0 \leq x \leq 1$) are known to be unstable and phase separate into Li FePO$_4$ and FePO$_4$. However, first-principles calculations with LDA/GGA yield energetically favorable intermediate compounds an d hence no phase separation. This qualitative failure of LDA/GGA seems to have its origin in the LDA/GGA self-interaction which de localizes charge over the mixed-valence Fe ions, and is corrected by explicitly considering correlation effects in this material. This is demonstrated with LDA+U calculations which correctly predict phase separation in Li$_x$FePO$_4$ for $U-J \gtrsim 3.5$eV. T he origin of the destabilization of intermediate compounds is identified as electron localization and charge ordering at different iron sites. Introduction of correlation also yields more accurate electrochemical reaction energies between FePO$_4$/Li$_x$FePO$_ 4$ and Li/Li$^+$ electrodes., Comment: 12 pages, 5 figures, Phys. Rev. B 201101R, 2004

High resolution angle-resolved photoemission measurements on underdoped (La$_{2-x}$Sr$_x$)CuO$_4$ system show that, at energies below 70 meV, the quasiparticle peak is well defined around the ($\pi$/2,$\pi$/2) nodal region and disappears rather abruptly when the momentum is changed from the nodal point to the ($\pi$,0) antinodal point along the underlying ``Fermi surface''. It indicates that there is an extra low energy scattering mechanism acting upon the antinodal quasiparticles. We propose that this mechanism is the scattering of quasiparticles across the nearly parallel segments of the Fermi surface near the antinodes., Comment: to appear in Phys. Rev. Lett

A series of high-quality under-doped La2-xSrxCuO4 superconductor crystals with x = 0.063 - 0.125 were prepared by traveling-solvent floating-zone (TSFZ) technique. We found by dc magnetic measurements that, in this series of crystals, the superconducting transition was quite sharp in the vicinity of the hole densities of x = 1/16 and x = 1/9 while it was much broader away from these two "magic numbers", and the Meissner fraction showed a remarkable minimum near x = 1/9. We concluded that these phenomena are reflections of intrinsic properties of this cuprate system. Our observations are discussed in light of recently proposed composite charge model together with charge inhomogeneity and electronic phase separations., Comment: 4 pages, 4 figures; Presented at the 7th Intl. Conf. M2S.(Rio de Janeiro, May 2003)

Through far-infrared studies of La2-xSrxCuO4 single crystals for x = 0.063, 0.07, 0.09, and 0.11, we found that only ~ 0.2 % of the total holes participated in the nearly dissipationless normal state charge transport and superconductivity. We have also observed characteristic collective modes at w ~ 18 cm-1 and 22 cm-1 due to the bound carriers in an electronic lattice (EL) state and the free carriers are massively screened by the EL. Our findings lead us to propose a composite picture of the charge system where the free carriers are coupled to and riding on the EL. This unique composite system of charge carriers may provide further insights into the understanding of the cuprate physics., Comment: 10 pages, 4 figures

Nernst effect has been measured for an underdoped and an optimally doped $La_{2-x}Sr_xCuO_4$ single crystal with the magnetic field applied along different directions. For both samples, when $H \|$ c, a significant Nernst voltage appears above $T_c$ and keeps measurable up to a high temperature (100 K) as reported by Xu et al.[ Nature 406, 486(2000) ]. However, when $H \|$ a-b plane the Nernst signal drops below the noise level quickly above $T_c$ for the underdoped sample. Moreover, the in-plane Nernst data with field at different angles shows a nice scaling behavior with the c-axis component of the field. All these give strong indication for strictly in-plane vortex-like excitations in pseudo-gap region., Comment: 5 Pages, 4 Figures, Revised Feb.4, 2003

A series of high-quality La2-xSrxCuO4 (LSCO) superconductor crystals in the under-doping region with x = 0.063, 0.07, 0.09, 0.10, 0.111 and 0.125 has been successfully prepared by traveling-solvent floating-zone (TSFZ) technique. The crystals are large and free of sub-grains and foreign phases. The high crystal quality has been revealed by double-crystal x-ray rocking curves and Rutherford backscattering spectrometry combined with ion-beam channeling effect. We find that the evolutions of the superconducting transition width and volume fraction as a function of carrier concentration exhibit interesting anomalies in the vicinity of some magic number doping levels such as x =1/4^2 (=0.0625) and 1/3^2 (=0.111). We argue that these behaviours are of intrinsic electronic origin., Comment: 4 pages, 4 figures, to be published on Superconductor Science and Technology

We analyze the strong coupling limit of spin-one bosons in low dimensional Mott insulating states. In 1D lattices, for an odd number of bosons per site ($N_0$), the ground state is a dimerized valence bond crystal state with a two-fold degeneracy; the low lying elementary spin excitations carry spin one. For an even number of bosons per site, the ground state is a nondegenerate spin singlet Mott state. We also argue that in a square lattice in a quantum disordered limit the ground states should be dimerized valence bond crystals for an odd integer $N_0$. Finally, we briefly report results for non-integer numbers of bosons per site in one-dimensional lattices., Comment: 5 pages; discussions on non-integer case have been shortened

Bunches of high charge (up to 10 nC) are compressed in length in the CTF II magnetic chicane to less than 0.2 mm rms. The short bunches radiate coherently in the chicane magnetic field, and the horizontal and longitudinal phase space density distributions are affected. This paper reports the results of beam emittance and momentum measurements. Horizontal and vertical emittances and momentum spectra were measured for different bunch compression factors and bunch charges. In particular, for 10 nC bunches, the mean beam momentum decreased by about 5% while the FWHM momentum spread increased from 5% to 19%. The experimental results are compared with simulations made with the code TraFiC4., Comment: 5 pages, 6 figures, submitted to the LINAC 2000 Conference

The CLIC Test Facility (CTF3) is an intermediate step to demonstrate the technical feasibility of the key concepts of the new RF power source for CLIC. CTF3 will use electron beams with an energy range adjustable from 170 MeV (3.5 A) to 380 MeV (with low current). The injector is based on a thermionic gun followed by a classical bunching system embedded in a long solenoidal field. As an alternative, an RF photo-injector is also being studied. The beam dynamics studies on how to reach the stringent beam parameters at the exit of the injector are presented. Simulations performed with the EGUN code showed that a current of 7 A can be obtained with an emittance less than 10 mm.mrad at the gun exit. PARMELA results are presented and compared to the requested beam performance at the injector exit. Sub-Harmonic Bunchers (SHB) are foreseen, to switch the phase of the bunch trains by 180 degrees from even to odd RF buckets. Specific issues of the thermionic gun and of the SHB with fast phase switch are discussed., Comment: MOB02, 3 pages, 3 figures, Linac 2000 conference

Using density functional theory, we investigate fluctuations of the ground state energy of spin-polarized, disordered quantum dots in the metallic regime. To compare to experiment, we evaluate the distribution of addition energies and find a convolution of the Wigner-Dyson distribution, expected for noniteracting electrons, with a narrower Gaussian distribution due to interactions. The tird moment of the total distribution is independent of interactions, and so is predicted to decrease by a factor of 0.405 upon application of a magnetic field which transforms from the Gaussian orthogonal to the Gaussian unitary ensemble., Comment: 13 pages, 2 figures

We consider adiabatic charge transport through mesoscopic metallic samples caused by a periodically changing external potential. We find that both the amplitude and the sign of the charge transferred through a sample per period are random sample specific quantities. The characteristic magnitude of the charge is determined by the quantum interference., Comment: 4 pages, 2 figures

We find the spin polarized disordered Fermi liquids are unstable to the nucleation of superconducting pairing states at mesoscopic scales even when magnetic fields which polarize the spins are substantially higher than the critical one. We study the probability of finding superconducting pairing states at mesoscopic scales in this limit. We find that the distribution function depends only on the film conductance. The typical length scale at which pairing takes place is universal, and decreases when the magnetic field is increased. The number density of these states determines the strength of the random exchange interactions between mesoscopic pairing states., Comment: 11 pages, no figures

We show that above the critical temperature of superconductor - metal phase transitions, both the longitudinal and Hall conductivity exhibit strong temperature dependent mesoscopic fluctuations, with amplitudes much larger than the mesoscopic fluctuations in noninteracting normal metals. Such an enhancement of the mesoscopic fluctuations arises from pairing correlations and is strongly dependent on dimensions., Comment: 10 pages, 1 figure

In this paper we develop a theory of mesoscopic fluctuations in disordered thin superconducting films in a parallel magnetic field. At zero temperature and sufficiently strong magnetic field the system undergoes a phase transition into a state characterized by a superfluid density, which is random in sign. Consequently, in this region, random supercurrents are spontaneously created in the ground state of the system, and it belongs to the same universality class as the two dimensional XY spin glass with a random sign of the exchange interaction., Comment: 12 Latex pages, 2 eps figures, submitted to Phys. Rev. Lett

We consider the chi_0 dependence of the density of states inside the normal metal of a superconductor - normal metal - superconductor (SNS) junction.Here chi_0 is the phase difference of two superconductors of the junction. It is shown that in the absence of electron-electron interaction the energy dependence of the density of states has a gap which decreases as chi_0 increases and closes at chi_0= pi. Both the analytical expressions for the chi_0 dependence of the density of states and the results of numerical simulations are presented., Comment: 7 pages with 4 included epsf figures, published version with small changes

Hall effect in SN and SNS junctions is considered. It is shown that at small temperature the Hall voltage is significantly suppressed as compared to its normal metal value. The time dependence of the Hall voltage in SNS junctions has a form of narrow pulses with the Josephson frequency., Comment: Latex file, 5 pages, 2 figures

Using a Dirac-Heisenberg Hamiltonian with biquadratic exchange interactions, we study the effect of iron disproportionation on the magnetic ordering, and describe the first-order magnetic transition occurring in the perovskite Sr_{2}LaFe_{3}O_{9}. Upon fitting the experimental data, we give an estimate of the exchange integrals for the antiferromagntic and ferromagnetic interactions, in agreement with previous works on kindered compounds. Spin-wave theory yields a magnon spectrum with a gapless antiferromagnetic mode together with two gapped ferromagnetic ones., Comment: 8 pages of RevTex, 5 figures (available upon request), submitted to J. Mag. Mag. Mat

It is shown that the conductance of a superconductor-normal metal-superconductor junction can exhibit a significant dependence on the phase of the superconducting order parameter in the situation when the size of the normal region of the junction is much larger than the normal metal coherence length and the critical current of the junction is already exponentially small. The period of the conductance oscillations as a function of the phase can be equal to $\pi$ or $2\pi$ depending on parameters of the system., Comment: 5 pages, Latex, Submitted to Phys. Rev. Lett. Figures available upon request