IBM

About: IBM is a company organization based out in Armonk, New York, United States. It is known for research contribution in the topics: Layer (electronics) & Cache. The organization has 134567 authors who have published 253905 publications receiving 7458795 citations. The organization is also known as: International Business Machines Corporation & Big Blue.

Critical-current measurements in epitaxial films of YBa2Cu

Abstract: We have grown epitaxial films of the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{x}}$ compound on ${\mathrm{SrTiO}}_{3}$ substrates. The superconducting critical current in these films at 77 K is in excess of ${10}^{5}$ A/${\mathrm{cm}}^{2}$ and at 4.2 K in excess of ${10}^{6}$ A/${\mathrm{cm}}^{2}$.

A model of a CA3 hippocampal pyramidal neuron incorporating voltage-clamp data on intrinsic conductances.

Abstract: 1. We have developed a 19-compartment cable model of a guinea pig CA3 pyramidal neuron. Each compartment is allowed to contain six active ionic conductances: gNa, gCa, gK(DR) (where DR stands for delayed rectifier), gK(A), gK(AHP), and gK(C). THe conductance gCa is of the high-voltage activated type. The model kinetics for the first five of these conductances incorporate voltage-clamp data obtained from isolated hippocampal pyramidal neurons. The kinetics of gK(C) are based on data from bullfrog sympathetic neurons. The time constant for decay of submembrane calcium derives from optical imaging of Ca signals in Purkinje cell dendrites. 2. To construct the model from available voltage-clamp data, we first reproduced current-clamp records from a model isolated neuron (soma plus proximal dendrites). We next assumed that ionic channel kinetics in the dendrites were the same as in the soma. In accord with dendritic recordings and calcium-imaging data, we also assumed that significant gCa occurs in dendrites. We then attached sections of basilar and apical dendritic cable. By trial and error, we found a distribution (not necessarily unique) of ionic conductance densities that was consistent with current-clamp records from the soma and dendrites of whole neurons and from isolated apical dendrites. 3. The resulting model reproduces the Ca(2+)-dependent spike depolarizing afterpotential (DAP) recorded after a stimulus subthreshold for burst elicitation. 4. The model also reproduces the behavior of CA3 pyramidal neurons injected with increasing somatic depolarizing currents: low-frequency (0.3-1.0 Hz) rhythmic bursting for small currents, with burst frequency increasing with current magnitude; then more irregular bursts followed by afterhyperpolarizations (AHPs) interspersed with brief bursts without AHPs; and finally, rhythmic action potentials without bursts. 5. The model predicts the existence of still another firing pattern during tonic depolarizing dendritic stimulation: brief bursts at less than 1 to approximately 12 Hz, a pattern not observed during somatic stimulation. These bursts correspond to rhythmic dendritic calcium spikes. 6. The model CA3 pyramidal neuron can be made to resemble functionally a CA1 pyramidal neuron by increasing gK(DR) and decreasing dendritic gCa and gK(C). Specifically, after these alterations, tonic depolarization of the soma leads to adapting repetitive firing, whereas stimulation of the distal dendrites leads to bursting. 7. A critical set of parameters concerns the regulation of the pool of intracellular [Ca2+] that interacts with membrane channels (gK(C) and gK(AHP)), particularly in the dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)

Pairing symmetry and flux quantization in a tricrystal superconducting ring of YBa2Cu3O7- delta.

Abstract: We have used the concept of flux quantization in superconducting $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ rings with 0, 2, and 3 grain-boundary Josephson junctions to test the pairing symmetry in high-${T}_{c}$ superconductors. The magnetic flux threading these rings at 4.2 K is measured by employing a scanning superconducting quantum interference device microscope. Spontaneous magnetization of a half magnetic flux quantum, $\frac{{\ensuremath{\Phi}}_{0}}{2}=\frac{h}{4e}$ has been observed in the 3-junction ring, but not in the 2-junction rings. These results are consistent with $d$-wave pairing symmetry.

Frequency domain data transmission using reduced computational complexity algorithms

Abstract: In this paper we describe a frequency domain data transmission method to be used for digital data transmission over analog telephone lines which exploits recently derived reduced computational complexity algorithms, such as the Winograd Fourier Transform, to achieve a significantly lower computational rate than comparable time domain QAM modems implemented digitally using signal processing techniques. In addition to the lower computational rate, the proposed method also allows for better channel bandwidth utilization by allowing optimal signal power allocation based on the channel's signal to noise versus frequency characteristics. Experimental results on this method are presented, indicating that it may be possible to send over 10,000 BPS over an unconditioned telephone line while maintaining a 10-5BER.

Error mitigation extends the computational reach of a noisy quantum processor

Abstract: Quantum computation, a paradigm of computing that is completely different from classical methods, benefits from theoretically proved speed-ups for certain problems and can be used to study the properties of quantum systems1. Yet, because of the inherently fragile nature of the physical computing elements (qubits), achieving quantum advantages over classical computation requires extremely low error rates for qubit operations, as well as substantial physical qubits, to realize fault tolerance via quantum error correction2,3. However, recent theoretical work4,5 has shown that the accuracy of computation (based on expectation values of quantum observables) can be enhanced through an extrapolation of results from a collection of experiments of varying noise. Here we demonstrate this error mitigation protocol on a superconducting quantum processor, enhancing its computational capability, with no additional hardware modifications. We apply the protocol to mitigate errors in canonical single- and two-qubit experiments and then extend its application to the variational optimization6–8 of Hamiltonians for quantum chemistry and magnetism9. We effectively demonstrate that the suppression of incoherent errors helps to achieve an otherwise inaccessible level of accuracy in the variational solutions using our noisy processor. These results demonstrate that error mitigation techniques will enable substantial improvements in the capabilities of near-term quantum computing hardware. The accuracy of computations on noisy, near-term quantum systems can be enhanced by extrapolating results from experiments with various noise levels, without requiring additional hardware modifications.