8,362 research outputs found
Numerical Analysis of Boosting Scheme for Scalable NMR Quantum Computation
Among initialization schemes for ensemble quantum computation beginning at
thermal equilibrium, the scheme proposed by Schulman and Vazirani [L. J.
Schulman and U. V. Vazirani, in Proceedings of the 31st ACM Symposium on Theory
of Computing (STOC'99) (ACM Press, New York, 1999), pp. 322-329] is known for
the simple quantum circuit to redistribute the biases (polarizations) of qubits
and small time complexity. However, our numerical simulation shows that the
number of qubits initialized by the scheme is rather smaller than expected from
the von Neumann entropy because of an increase in the sum of the binary
entropies of individual qubits, which indicates a growth in the total classical
correlation. This result--namely, that there is such a significant growth in
the total binary entropy--disagrees with that of their analysis.Comment: 14 pages, 18 figures, RevTeX4, v2,v3: typos corrected, v4: minor
changes in PROGRAM 1, conforming it to the actual programs used in the
simulation, v5: correction of a typographical error in the inequality sign in
PROGRAM 1, v6: this version contains a new section on classical correlations,
v7: correction of a wrong use of terminology, v8: Appendix A has been added,
v9: published in PR
T/B scaling without quasiparticle mass divergence: YbCo2Ge4
YbCoGe is a clean paramagnetic Kondo lattice which displays non-Fermi
liquid behavior. We report a detailed investigation of the specific heat,
magnetic Gr\"uneisen parameter () and temperature derivative
of the magnetization () on a high-quality single crystal at temperatures
down to ~K and magnetic fields up to 7~T. and
display a divergence upon cooling and obey scaling. Similar behavior has
previously been found in several other Yb-based Kondo lattices and related to a
zero-field quantum critical point without fine tuning of pressure or
composition. However, in the approach of the electronic heat
capacity coefficient of YbCoGe saturates at low , excluding
ferromagnetic quantum criticality. This indicates that scaling is
insufficient to prove a zero-field quantum critical point.Comment: 6 pages, 6 figures (including supplemental material
Crossover from commensurate to incommensurate antiferromagnetism in stoichiometric NaFeAs revealed by single-crystal 23Na,75As-NMR experiments
We report results of 23Na and 75As nuclear magnetic resonance (NMR)
experiments on a self-flux grown high-quality single crystal of stoichiometric
NaFeAs. The NMR spectra revealed a tetragonal to twinned-orthorhombic
structural phase transition at T_O = 57 K and an antiferromagnetic (AF)
transition at T_AF = 45 K. The divergent behavior of nuclear relaxation rate
near T_AF shows significant anisotropy, indicating that the critical slowing
down of stripe-type AF fluctuations are strongly anisotropic in spin space. The
NMR spectra at low enough temperatures consist of sharp peaks showing a
commensurate stripe AF order with a small moment \sim 0.3 muB. However, the
spectra just below T_AF exhibits highly asymmetric broadening pointing to an
incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs
shows a certain similarity to the behavior of SrFe2As2 under high pressure.Comment: 5 pages, 5 figures, revised version to appear in J. Phys. Soc. Jp
Enhanced grain boundary sliding during reversed creep of lead
Grain boundary migration in lead after repeated creep stress reversal
Topological characterization of periodically-driven quantum systems
Topological properties of physical systems can lead to robust behaviors that
are insensitive to microscopic details. Such topologically robust phenomena are
not limited to static systems but can also appear in driven quantum systems. In
this paper, we show that the Floquet operators of periodically driven systems
can be divided into topologically distinct (homotopy) classes, and give a
simple physical interpretation of this classification in terms of the spectra
of Floquet operators. Using this picture, we provide an intuitive understanding
of the well-known phenomenon of quantized adiabatic pumping. Systems whose
Floquet operators belong to the trivial class simulate the dynamics generated
by time-independent Hamiltonians, which can be topologically classified
according to the schemes developed for static systems. We demonstrate these
principles through an example of a periodically driven two--dimensional
hexagonal lattice model which exhibits several topological phases. Remarkably,
one of these phases supports chiral edge modes even though the bulk is
topologically trivial.Comment: 9 Pages + Appendi
Phase sensitive measurements of order parameters for ultracold atoms through two particles interferometry
Nontrivial symmetry of order parameters is crucial in some of the most
interesting quantum many-body states of ultracold atoms and condensed matter
systems. Examples in cold atoms include p-wave Feshbach molecules and d-wave
paired states of fermions that could be realized in optical lattices in the
Hubbard regime. Identifying these states in experiments requires measurements
of the relative phase of different components of the entangled pair
wavefunction.
We propose and discuss two schemes for such phase sensitive measurements,
based on two-particle interference revealed in atom-atom or atomic density
correlations. Our schemes can also be used for relative phase measurements for
non-trivial particle-hole order parameters, such as d-density wave order.Comment: 4 pages, 4 figure
Observation of Jonscher Law in AC Hopping Conduction of Electron-Doped Nanoporous Crystal 12CaO7Al2O3 in THz Frequency Range
We have performed terahertz time-domain spectroscopy of carrier-doped
nanoporous crystal 12CaO7Al2O3 showing the Mott variable range hopping at room
temperature. The real part of the dielectric constant clearly demonstrates the
nature of localized carriers. The frequency dependence of both the real and
imaginary parts of the dielectric constant can be simply explained by assuming
two contributions: a dielectric response by the parent compound with no
carriers and an AC hopping conduction with the Jonscher law generally reported
up to GHz range. The possible obedience to the Jonscher law in the THz range
suggests a relaxation time of the hopping carriers much faster than 1ps in the
carrier-doped 12CaO7Al2O3.Comment: 4pages 3figures. to be published in Phys. Rev.
Magnetic and superconducting properties on S-type single-crystal CeCuSi probed by Cu nuclear magnetic resonance and nuclear quadrupole resonance
We have performed Cu nuclear magnetic resonance/nuclear quadrupole
resonance measurements to investigate the magnetic and superconducting (SC)
properties on a "superconductivity dominant" (-type) single crystal of
CeCuSi. Although the development of antiferromagnetic (AFM)
fluctuations down to 1~K indicated that the AFM criticality was close, Korringa
behavior was observed below 0.8~K, and no magnetic anomaly was observed above
0.6 K. These behaviors were expected in -type
CeCuSi. The temperature dependence of the nuclear spin-lattice
relaxation rate at zero field was almost identical to that in the
previous polycrystalline samples down to 130~mK, but the temperature dependence
deviated downward below 120~mK. In fact, in the SC state could be
fitted with the two-gap -wave rather than the two-gap -wave
model down to 90~mK. Under magnetic fields, the spin susceptibility in both
directions clearly decreased below , indicative of the formation of
spin singlet pairing. The residual part of the spin susceptibility was
understood by the field-induced residual density of states evaluated from
, which was ascribed to the effect of the vortex cores. No magnetic
anomaly was observed above the upper critical field , but the
development of AFM fluctuations was observed, indicating that superconductivity
was realized in strong AFM fluctuations.Comment: 10 pages, 8 figure
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