3,824 research outputs found
Flux Qubits and Readout Device with Two Independent Flux Lines
We report measurements on two superconducting flux qubits coupled to a
readout Superconducting QUantum Interference Device (SQUID). Two on-chip flux
bias lines allow independent flux control of any two of the three elements, as
illustrated by a two-dimensional qubit flux map. The application of microwaves
yields a frequency-flux dispersion curve for 1- and 2-photon driving of the
single-qubit excited state, and coherent manipulation of the single-qubit state
results in Rabi oscillations and Ramsey fringes. This architecture should be
scalable to many qubits and SQUIDs on a single chip.Comment: 5 pages, 4 figures, higher quality figures available upon request.
Submitted to PR
A Simple, Quick, and Precise Procedure for the Determination of Water in Organic Solvents
A procedure for the UV/VIS-spectroscopic determination of water by the use of a solvatochromic pyridiniumphenolate betaine is given. The water content of organic solvents is calculated by a two parameter equation from λmax of the dye. A typical, detection limit is of the order of 1 mg in 1 ml solvent for routine spectrometers. The parameters for the determination of water are given for a number of commonly used solvents
Keeping a Quantum Bit Alive by Optimized -Pulse Sequences
A general strategy to maintain the coherence of a quantum bit is proposed.
The analytical result is derived rigorously including all memory and
back-action effects. It is based on an optimized -pulse sequence for
dynamic decoupling extending the Carr-Purcell-Meiboom-Gill (CPMG) cycle. The
optimized sequence is very efficient, in particular for strong couplings to the
environment.Comment: 4 pages, 2 figures; revised version with additional references for
better context, more stringent discussio
Lattice dynamics and electron-phonon coupling in Sr2RuO4
The lattice dynamics in SrRuO has been studied by inelastic neutron
scattering combined with shell-model calculations. The in-plane bond-stretching
modes in SrRuO exhibit a normal dispersion in contrast to all
electronically doped perovskites studied so far. Evidence for strong electron
phonon coupling is found for c-polarized phonons suggesting a close connection
with the anomalous c-axis charge transport in SrRuO.Comment: 11 pages, 8 figures 2 table
Quantum error correction benchmarks for continuous weak parity measurements
We present an experimental procedure to determine the usefulness of a
measurement scheme for quantum error correction (QEC). A QEC scheme typically
requires the ability to prepare entangled states, to carry out multi-qubit
measurements, and to perform certain recovery operations conditioned on
measurement outcomes. As a consequence, the experimental benchmark of a QEC
scheme is a tall order because it requires the conjuncture of many elementary
components. Our scheme opens the path to experimental benchmarks of individual
components of QEC. Our numerical simulations show that certain parity
measurements realized in circuit quantum electrodynamics are on the verge of
being useful for QEC
Improved magic states distillation for quantum universality
Given stabilizer operations and the ability to repeatedly prepare a
single-qubit mixed state rho, can we do universal quantum computation? As
motivation for this question, "magic state" distillation procedures can reduce
the general fault-tolerance problem to that of performing fault-tolerant
stabilizer circuits.
We improve the procedures of Bravyi and Kitaev in the Hadamard "magic"
direction of the Bloch sphere to achieve a sharp threshold between those rho
allowing universal quantum computation, and those for which any calculation can
be efficiently classically simulated. As a corollary, the ability to repeatedly
prepare any pure state which is not a stabilizer state (e.g., any single-qubit
pure state which is not a Pauli eigenstate), together with stabilizer
operations, gives quantum universality. It remains open whether there is also a
tight separation in the so-called T direction.Comment: 6 pages, 5 figure
Quantum interference effects in resonant Raman spectroscopy of single- and triple-layer MoTe from first principles
We present a combined experimental and theoretical study of resonant Raman
spectroscopy in single- and triple-layer MoTe. Raman intensities are
computed entirely from first principles by calculating finite differences of
the dielectric susceptibility. In our analysis, we investigate the role of
quantum interference effects and the electron-phonon coupling. With this
method, we explain the experimentally observed intensity inversion of the
vibrational modes in triple-layer MoTe2 with increasing laser
photon energy. Finally, we show that a quantitative comparison with
experimental data requires the proper inclusion of excitonic effects.Comment: Main Text (5 Figures, 1 Tables) + Supporting Information (6 Figures
Electron-phonon interaction in the three-band model
We study the half-breathing phonon in the three-band model of a high
temperature superconductor, allowing for vibrations of atoms and resulting
changes of hopping parameters. Two different approaches are compared. From the
three-band model a t-J model with phonons can be derived, and phonon properties
can be calculated. To make contact to density functional calculations, we also
study the three-band model in the Hartree-Fock (HF) approximation. The
paramagnetic HF solution, appropriate for the doped cuprates, has similarities
to the local-density approximation (LDA). However, in contrast to the LDA, the
existence of an antiferromagnetic insulating solution for the undoped system
makes it possible to study the softening of the half-breathing phonon under
doping. We find that although the HF approximation and the t-J model give
similar softenings, these softenings happen in quite different ways. We also
find that the HF approximation gives an incorrect doping and q dependence for
the softening and too small a width for the (half-)breathing phonon.Comment: 7 pages, RevTeX, 4 eps figure
Community Structure in Time-Dependent, Multiscale, and Multiplex Networks
Network science is an interdisciplinary endeavor, with methods and
applications drawn from across the natural, social, and information sciences. A
prominent problem in network science is the algorithmic detection of
tightly-connected groups of nodes known as communities. We developed a
generalized framework of network quality functions that allowed us to study the
community structure of arbitrary multislice networks, which are combinations of
individual networks coupled through links that connect each node in one network
slice to itself in other slices. This framework allows one to study community
structure in a very general setting encompassing networks that evolve over
time, have multiple types of links (multiplexity), and have multiple scales.Comment: 31 pages, 3 figures, 1 table. Includes main text and supporting
material. This is the accepted version of the manuscript (the definitive
version appeared in Science), with typographical corrections included her
Statistical Mechanics of Community Detection
Starting from a general \textit{ansatz}, we show how community detection can
be interpreted as finding the ground state of an infinite range spin glass. Our
approach applies to weighted and directed networks alike. It contains the
\textit{at hoc} introduced quality function from \cite{ReichardtPRL} and the
modularity as defined by Newman and Girvan \cite{Girvan03} as special
cases. The community structure of the network is interpreted as the spin
configuration that minimizes the energy of the spin glass with the spin states
being the community indices. We elucidate the properties of the ground state
configuration to give a concise definition of communities as cohesive subgroups
in networks that is adaptive to the specific class of network under study.
Further we show, how hierarchies and overlap in the community structure can be
detected. Computationally effective local update rules for optimization
procedures to find the ground state are given. We show how the \textit{ansatz}
may be used to discover the community around a given node without detecting all
communities in the full network and we give benchmarks for the performance of
this extension. Finally, we give expectation values for the modularity of
random graphs, which can be used in the assessment of statistical significance
of community structure
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