First-order nature of the ferromagnetic phase transition in (La-Ca)MnO_3 near optimal doping

Neutron scattering has been used to study the nature of the ferromagnetic transition in single crystals of La_0.7Ca_0.3MnO_3 and La_0.8Ca_0.2MnO_3, and polycrystalline samples of La_0.67Ca_0.33MnO_3 and La_5/8Ca_3/8MnO_3 where the naturally occurring O-16 can be replaced with the O-18 isotope. Small angle neutron scattering on the x=0.3 single crystal reveals a discontinuous change in the scattering at the Curie temperature for wave vectors below ~0.065 A^-1. Strong relaxation effects are observed for this domain scattering, for the magnetic order parameter, and for the quasielastic scattering, demonstrating that the transition is not continuous in nature. There is a large oxygen isotope effect observed for the T_C in the polycrystalline samples. For the optimally doped x=3/8 sample we observed T_C(O-16)=266.5 K and T_C(O-18)=261.5 K at 90% O-18 substitution. The temperature dependence of the spin-wave stiffness is found to be identical for the two samples despite changes in T_C. Hence, T_C is not solely determined by the magnetic subsystem, but instead the ferromagnetic phase is truncated by the formation of polarons which cause an abrupt transition to the paramagnetic, insulating state. Application of uniaxial stress in the x=0.3 single crystal sharply enhances the polaron scattering at room temperature. Measurements of the phonon density-of-states show only modest differences above and below T_C and between the two different isotopic samples.Comment: 13 pages, 16 figures, submitted to Phys. Rev.

Approximating Turaev-Viro 3-manifold invariants is universal for quantum computation

The Turaev-Viro invariants are scalar topological invariants of compact, orientable 3-manifolds. We give a quantum algorithm for additively approximating Turaev-Viro invariants of a manifold presented by a Heegaard splitting. The algorithm is motivated by the relationship between topological quantum computers and (2+1)-D topological quantum field theories. Its accuracy is shown to be nontrivial, as the same algorithm, after efficient classical preprocessing, can solve any problem efficiently decidable by a quantum computer. Thus approximating certain Turaev-Viro invariants of manifolds presented by Heegaard splittings is a universal problem for quantum computation. This establishes a novel relation between the task of distinguishing non-homeomorphic 3-manifolds and the power of a general quantum computer.Comment: 4 pages, 3 figure

The ground state of a class of noncritical 1D quantum spin systems can be approximated efficiently

We study families H_n of 1D quantum spin systems, where n is the number of spins, which have a spectral gap \Delta E between the ground-state and first-excited state energy that scales, asymptotically, as a constant in n. We show that if the ground state |\Omega_m> of the hamiltonian H_m on m spins, where m is an O(1) constant, is locally the same as the ground state |\Omega_n>, for arbitrarily large n, then an arbitrarily good approximation to the ground state of H_n can be stored efficiently for all n. We formulate a conjecture that, if true, would imply our result applies to all noncritical 1D spin systems. We also include an appendix on quasi-adiabatic evolutions.Comment: 9 pages, 1 eps figure, minor change

Neural superposition and oscillations in the eye of the blowfly

Neural superposition in the eye of the blowfly Calliphora erythrocephala was investigated by stimulating single photoreceptors using corneal neutralization through water immersion. Responses in Large Monopolar Cells (LMCs) in the lamina were measured, while stimulating one or more of the six photoreceptors connected to the LMC. Responses to flashes of low light intensity on individual photoreceptors add approximately linearly at the LMC. Higher intensity light flashes produce a maximum LMC response to illumination of single photoreceptors which is about half the maximum response to simultaneous illumination of the six connecting photoreceptors. This observation indicates that a saturation can occur at a stage of synaptic transmission which precedes the change in the post-synaptic membrane potential. Stimulation of single photoreceptors yields high frequency oscillations (about 200 Hz) in the LMC potential, much larger in amplitude than produced by simultaneous stimulation of the six photoreceptors connected to the LMC. It is discussed that these oscillations also arise from a mechanism that precedes the change in the postsynaptic membrane potential.

Polaronic excitations in CMR manganite films

In the colossal magnetoresistance manganites polarons have been proposed as the charge carrier state which localizes across the metal-insulator transition. The character of the polarons is still under debate. We present an assessment of measurements which identify polarons in the metallic state of La{2/3}Sr{1/3}MnO{3} (LSMO) and La{2/3}Ca{1/3}MnO{3} (LCMO) thin films. We focus on optical spectroscopy in these films which displays a pronounced resonance in the mid-infrared. The temperature dependent resonance has been previously assigned to polaron excitations. These polaronic resonances are qualitatively distinct in LSMO and LCMO and we discuss large and small polaron scenarios which have been proposed so far. There is evidence for a large polaron excitation in LSMO and small polarons in LCMO. These scenarios are examined with respect to further experimental probes, specifically charge carrier mobility (Hall-effect measurements) and high-temperature dc-resistivity.Comment: 16 pages, 10 figure

Hamiltonian Formulation of Quantum Error Correction and Correlated Noise: The Effects Of Syndrome Extraction in the Long Time Limit

We analyze the long time behavior of a quantum computer running a quantum error correction (QEC) code in the presence of a correlated environment. Starting from a Hamiltonian formulation of realistic noise models, and assuming that QEC is indeed possible, we find formal expressions for the probability of a faulty path and the residual decoherence encoded in the reduced density matrix. Systems with non-zero gate times (``long gates'') are included in our analysis by using an upper bound on the noise. In order to introduce the local error probability for a qubit, we assume that propagation of signals through the environment is slower than the QEC period (hypercube assumption). This allows an explicit calculation in the case of a generalized spin-boson model and a quantum frustration model. The key result is a dimensional criterion: If the correlations decay sufficiently fast, the system evolves toward a stochastic error model for which the threshold theorem of fault-tolerant quantum computation has been proven. On the other hand, if the correlations decay slowly, the traditional proof of this threshold theorem does not hold. This dimensional criterion bears many similarities to criteria that occur in the theory of quantum phase transitions.Comment: 19 pages, 5 figures. Includes response to arXiv:quant-ph/0702050. New title and an additional exampl

A Polymerase-chain-reaction Assay for the Specific Identification of Transcripts Encoded by Individual Carcinoembryonic Antigen (CEA)-gene-family Members

Carcinoembryonic antigen (CEA) is a tumor marker that belongs to a family of closely related molecules with variable expression patterns. We have developed sets of oligonucleotide primers for the specific amplification of transcripts from individual CEA-family members using the reverse transcriptase/ polymerase chain reaction (RT/PCR). Specific primer sets were designed for CEA, non-specific cross-reacting antigen (NCA), biliary glycoprotein (BGP), carcinoembryonic antigen gene-family members 1, 6 and 7 (CGMI, CGM6 and CGM7), and one set for all pregnancy-specific glycoprotein (PSG) transcripts. Primers were first tested for their specificity against individual cDNA clones and product-hybridization with internal, transcript-specific oligonucleotides. Total RNA from 12 brain and 63 gynecological tumors were then tested for expression of CEA-related transcripts. None were found in tumors located in the brain, including various mesenchymal and neuro-epithelial tumors. CEA and NCA transcripts were, however, present in an adenocarcinoma located in the nasal sinuses. In ovarian mucinous adenocarcinomas, we always found co-expression of CEA and NCA transcripts, and occasionally BGP mRNA. CEA-related transcripts were also found in some serous, endometrioid and clear-cell ovarian carcinomas. CEA, NCA and BGP transcripts were present in endometrial carcinomas of the uterus and cervical carcinomas, whereas uterine leiomyomas were completely negative. No transcripts were found from CGM 1, CGM6, CGM7 or from PSG genes in any of the tumors tested. The PCR data were compared with immunohistochemical investigations of ovarian tumors at the protein level using CEA (26/3/13)-, NCA-50/90 (9A6FR) and NCA-95 (80H3)-specific monoclonal antibodies

Mixed lattice and electronic states in high-temperature superconductors

Inelastic neutron scattering measurements are presented which show the abrupt development of new oxygen lattice vibrations near the doping-induced metal-insulator transition in La(2-x)Sr(x)CuO(4). A direct correlation is established between these lattice modes and the electronic susceptibility (as measured by photoemission) inferring that such modes mix strongly with charge fluctuations. This electron-lattice coupling can be characterized as a localized one-dimensional response of the lattice to short-ranged metallic charge fluctuations.Comment: 4 pages, 3 postscript figures, RevTe

Baryon Content of Massive Galaxy Clusters (0.57 < z < 1.33)

We study the stellar, Brightest Cluster Galaxy (BCG) and intracluster medium (ICM) masses of 14 South Pole Telescope (SPT) selected galaxy clusters with median redshift $z=0.9$ and median mass $M_{500}=6\times10^{14}M_{\odot}$. We estimate stellar masses for each cluster and BCG using six photometric bands spanning the range from the ultraviolet to the near-infrared observed with the VLT, HST and Spitzer. The ICM masses are derived from Chandra and XMM-Newton X-ray observations, and the virial masses are derived from the SPT Sunyaev-Zel'dovich Effect signature. At $z=0.9$ the BCG mass $M_{\star}^{\textrm{BCG}}$ constitutes $0.12\pm0.01$% of the halo mass for a $6\times10^{14}M_{\odot}$ cluster, and this fraction falls as $M_{500}^{-0.58\pm0.07}$. The cluster stellar mass function has a characteristic mass $M_{0}=10^{11.0\pm0.1}M_{\odot}$, and the number of galaxies per unit mass in clusters is larger than in the field by a factor $1.65\pm0.2$. Both results are consistent with measurements on group scales and at lower redshift. We combine our SPT sample with previously published samples at low redshift that we correct to a common initial mass function and for systematic differences in virial masses. We then explore mass and redshift trends in the stellar fraction (fstar), the ICM fraction (fICM), the cold baryon fraction (fc) and the baryon fraction (fb). At a pivot mass of $6\times10^{14}M_{\odot}$ and redshift $z=0.9$, the characteristic values are fstar=$1.1\pm0.1$%, fICM=$9.6\pm0.5$%, fc=$10.4\pm1.2$% and fb=$10.7\pm0.6$%. These fractions all vary with cluster mass at high significance, indicating that higher mass clusters have lower fstar and fc and higher fICM and fb. When accounting for a 15% systematic virial mass uncertainty, there is no statistically significant redshift trend at fixed mass in these baryon fractions. (abridged)Comment: Accepted for publication in MNRA