386 research outputs found
Magnetic excitations in the S = 1/2 antiferromagnetic-ferromagnetic chain compound BaCu2V2O8 at zero and finite temperature
Unlike most quantum systems which rapidly become incoherent as temperature is
raised, strong correlations persist at elevated temperatures in dimer
magnets, as revealed by the unusual asymmetric lineshape of their excitations
at finite temperatures. Here we quantitatively explore and parameterize the
strongly correlated magnetic excitations at finite temperatures using the high
resolution inelastic neutron scattering on the model compound
BaCuVO which we show to be an alternating
antiferromagnetic-ferromagnetic spin chain. Comparison to state of the
art computational techniques shows excellent agreement over a wide temperature
range. Our findings hence demonstrate the possibility to quantitatively predict
coherent behavior at elevated temperatures in quantum magnets.Comment: 5 pages + 6 pages supplement; problems with list of references are
fixe
Fermionic symmetry-protected topological state in strained graphene
The low-energy physics of graphene is described by relativistic Dirac
fermions with spin and valley degrees of freedom. Mechanical strain can be used
to create a pseudo magnetic field pointing to opposite directions in the two
valleys. We study interacting electrons in graphene exposed to both an external
real magnetic field and a strain-induced pseudo magnetic field. For a certain
ratio between these two fields, it is proposed that a fermionic
symmetry-protected topological state can be realized. The state is
characterized in detail using model wave functions, Chern-Simons field theory,
and numerical calculations. Our paper suggests that graphene with artificial
gauge fields may host a rich set of topological states.Comment: 8 pages, 4 figure
Position-dependent correlation function from the SDSS-III Baryon Oscillation Spectroscopic Survey Data Release 10 CMASS Sample
We report on the first measurement of the three-point function with the
position-dependent correlation function from the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS) Data Release 10 CMASS sample. This new observable
measures the correlation between two-point functions of galaxy pairs within
different subvolumes, , where is the
location of a subvolume, and the corresponding mean overdensities,
. This correlation, which we call the "integrated
three-point function", , measures a three-point function of two
short- and one long-wavelength modes, and is generated by nonlinear
gravitational evolution and possibly also by the physics of inflation. The
measured from the BOSS data lies within the scatter of those from
the mock galaxy catalogs in redshift space, yielding a ten-percent-level
determination of the amplitude of . The tree-level perturbation
theory in redshift space predicts how this amplitude depends on the linear and
quadratic nonlinear galaxy bias parameters ( and ), as well as on the
amplitude and linear growth rate of matter fluctuations ( and ).
Combining with the constraints on and
from the global two-point correlation function and that on from the
weak lensing signal of BOSS galaxies, we measure (68% C.L.)
assuming standard perturbation theory at the tree level and the local bias
model.Comment: 30 pages, 11 figures. revised version submitted to JCA
On-chip generation and dynamic piezo-optomechanical rotation of single photons
Integrated photonic circuits are key components for photonic quantum
technologies and for the implementation of chip-based quantum devices. Future
applications demand flexible architectures to overcome common limitations of
many current devices, for instance the lack of tuneabilty or built-in quantum
light sources. Here, we report on a dynamically reconfigurable integrated
photonic circuit comprising integrated quantum dots (QDs), a Mach-Zehnder
interferometer (MZI) and surface acoustic wave (SAW) transducers directly
fabricated on a monolithic semiconductor platform. We demonstrate on-chip
single photon generation by the QD and its sub-nanosecond dynamic on-chip
control. Two independently applied SAWs piezo-optomechanically rotate the
single photon in the MZI or spectrally modulate the QD emission wavelength. In
the MZI, SAWs imprint a time-dependent optical phase and modulate the qubit
rotation to the output superposition state. This enables dynamic single photon
routing with frequencies exceeding one gigahertz. Finally, the combination of
the dynamic single photon control and spectral tuning of the QD realizes
wavelength multiplexing of the input photon state and demultiplexing it at the
output. Our approach is scalable to multi-component integrated quantum photonic
circuits and is compatible with hybrid photonic architectures and other key
components for instance photonic resonators or on-chip detectors
Scale dependence of galaxy biasing investigated by weak gravitational lensing: An assessment using semi-analytic galaxies and simulated lensing data
Galaxies are biased tracers of the matter density on cosmological scales. For
future tests of galaxy models, we refine and assess a method to measure galaxy
biasing as function of physical scale with weak gravitational lensing. This
method enables us to reconstruct the galaxy bias factor as well as the
galaxy-matter correlation on spatial scales between for redshift-binned lens galaxies below redshift .
In the refinement, we account for an intrinsic alignment of source
ellipticities, and we correct for the magnification bias of the lens galaxies,
relevant for the galaxy-galaxy lensing signal, to improve the accuracy of the
reconstructed . For simulated data, the reconstructions achieve an
accuracy of (68\% confidence level) over the above -range for a
survey area and a typical depth of contemporary ground-based surveys.
Realistically the accuracy is, however, probably reduced to about ,
mainly by systematic uncertainties in the assumed intrinsic source alignment,
the fiducial cosmology, and the redshift distributions of lens and source
galaxies (in that order). Furthermore, our reconstruction technique employs
physical templates for and that elucidate the impact of central
galaxies and the halo-occupation statistics of satellite galaxies on the
scale-dependence of galaxy bias, which we discuss in the paper. In a first
demonstration, we apply this method to previous measurements in the
Garching-Bonn-Deep Survey and give a physical interpretation of the lens
population.Comment: 31 pages, 16 figures; corrected typos in Eqs. (31), (34), and (36
Dynamical Quasicondensation of Hard-Core Bosons at Finite Momenta
Long-range order in quantum many-body systems is usually associated with
equilibrium situations. Here, we experimentally investigate the
quasicondensation of strongly-interacting bosons at finite momenta in a
far-from-equilibrium case. We prepare an inhomogeneous initial state consisting
of one-dimensional Mott insulators in the center of otherwise empty
one-dimensional chains in an optical lattice with a lattice constant . After
suddenly quenching the trapping potential to zero, we observe the onset of
coherence in spontaneously forming quasicondensates in the lattice. Remarkably,
the emerging phase order differs from the ground-state order and is
characterized by peaks at finite momenta in the
momentum distribution function.Comment: See also Viewpoint: Emerging Quantum Order in an Expanding Gas,
Physics 8, 99 (2015
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