208 research outputs found
Efficient and feasible state tomography of quantum many-body systems
We present a novel method to perform quantum state tomography for
many-particle systems which are particularly suitable for estimating states in
lattice systems such as of ultra-cold atoms in optical lattices. We show that
the need for measuring a tomographically complete set of observables can be
overcome by letting the state evolve under some suitably chosen random circuits
followed by the measurement of a single observable. We generalize known results
about the approximation of unitary 2-designs, i.e., certain classes of random
unitary matrices, by random quantum circuits and connect our findings to the
theory of quantum compressed sensing. We show that for ultra-cold atoms in
optical lattices established techniques like optical super-lattices, laser
speckles, and time-of-flight measurements are sufficient to perform fully
certified, assumption-free tomography. Combining our approach with tensor
network methods - in particular the theory of matrix-product states - we
identify situations where the effort of reconstruction is even constant in the
number of lattice sites, allowing in principle to perform tomography on
large-scale systems readily available in present experiments.Comment: 10 pages, 3 figures, minor corrections, discussion added, emphasizing
that no single-site addressing is needed at any stage of the scheme when
implemented in optical lattice system
Differential rotation and meridional flow in the solar supergranulation layer: Measuring the eddy viscosity
We measure the eddy viscosity in the outermost layers of the solar convection
zone by comparing the rotation law computed with the Reynolds stress resulting
from f-plane simulations of the angular momentum transport in rotating
convection with the observed differential rotation pattern. The simulations
lead to a negative vertical and a positive horizontal angular momentum
transport. The consequence is a subrotation of the outermost layers, as it is
indeed indicated both by helioseismology and the observed rotation rates of
sunspots. In order to reproduce the observed gradient of the rotation rate a
value of about 1.5 x 10^{13} cm/s for the eddy viscosity is necessary.
Comparison with the magnetic eddy diffusivity derived from the sunspot decay
yields a surprisingly large magnetic Prandtl number of 150 for the
supergranulation layer. The negative gradient of the rotation rate also drives
a surface meridional flow towards the poles, in agreement with the results from
Doppler measurements. The successful reproduction of the abnormally positive
horizontal cross correlation (on the northern hemisphere) observed for bipolar
groups then provides an independent test for the resulting eddy viscosity.Comment: 6 pages, 8 figures, Astronomy and Astrophysics (subm.
Index theory of one dimensional quantum walks and cellular automata
If a one-dimensional quantum lattice system is subject to one step of a
reversible discrete-time dynamics, it is intuitive that as much "quantum
information" as moves into any given block of cells from the left, has to exit
that block to the right. For two types of such systems - namely quantum walks
and cellular automata - we make this intuition precise by defining an index, a
quantity that measures the "net flow of quantum information" through the
system. The index supplies a complete characterization of two properties of the
discrete dynamics. First, two systems S_1, S_2 can be pieced together, in the
sense that there is a system S which locally acts like S_1 in one region and
like S_2 in some other region, if and only if S_1 and S_2 have the same index.
Second, the index labels connected components of such systems: equality of the
index is necessary and sufficient for the existence of a continuous deformation
of S_1 into S_2. In the case of quantum walks, the index is integer-valued,
whereas for cellular automata, it takes values in the group of positive
rationals. In both cases, the map S -> ind S is a group homomorphism if
composition of the discrete dynamics is taken as the group law of the quantum
systems. Systems with trivial index are precisely those which can be realized
by partitioned unitaries, and the prototypes of systems with non-trivial index
are shifts.Comment: 38 pages. v2: added examples, terminology clarifie
Fate of CMY-2-encoding plasmids introduced into the human fecal microbiota by exogenous Escherichia coli
The gut is a hot spot for transfer of antibiotic resistance genes from ingested exogenous bacteria to the indigenous microbiota. The objective of this study was to determine the fate of two nearly identical blaCMY-2-harboring plasmids introduced into the human fecal microbiota by two Escherichia coli strains isolated from human and poultry meat, respectively. The chromosome and the CMY-2-encoding plasmid of both strains were labeled with distinct fluorescent markers (mCherry and GFP), allowing Fluorescence Activated Cell Sorting (FACS)-based tracking of the strain and the resident bacteria that have acquired its plasmid. Each strain was introduced into an established in vitro gut model (CoMiniGut) inoculated with individual feces from ten healthy volunteers. Fecal samples collected 2, 6 and 24 h after strain inoculation were analyzed by FACS and plate counts. Although the human strain survived better than the poultry meat strain, both strains transferred their plasmids to the fecal microbiota at concentrations as low as 102 CFU/mL. Strain survival and plasmid transfer varied significantly depending on inoculum concentration and individual fecal microbiota. Identification of transconjugants by 16S rRNA gene sequencing and MALDI-TOF mass spectrometry revealed that the plasmids were predominantly acquired by Enterobacteriaceae such as E. coli and Hafnia alvei. Our experimental data demonstrate that exogenous E. coli of human or animal origin can readily transfer CMY-2-encoding IncI1 plasmids to the human fecal microbiota. Low amounts of exogenous strain are sufficient to ensure plasmid transfer if the strain is able to survive the gastric environment
Hemispheric Sunspot Numbers R_n and R_s: Catalogue and N-S asymmetry analysis
Sunspot drawings are provided on a regular basis at the Kanzelhoehe Solar
Observatory, Austria, and the derived relative sunspot numbers are reported to
the Sunspot Index Data Center in Brussels. From the daily sunspot drawings, we
derived the northern, R_n, and southern, R_s, relative sunspot numbers for the
time span 1975-2000. In order to accord with the International Sunspot Numbers
R_i, the R_n and R_s have been normalized to the R_i, which ensures that the
relation R_n + R_s = R_i is fulfilled. For validation, the derived R_n and R_s
are compared to the international northern and southern relative sunspot
numbers, which are available from 1992. The regression analysis performed for
the period 1992-2000 reveals good agreement with the International hemispheric
Sunspot Numbers. The monthly mean and the smoothed monthly mean hemispheric
Sunspot Numbers are compiled into a catalogue. Based on the derived hemispheric
Sunspot Numbers, we study the significance of N-S asymmetries and the
rotational behavior separately for both hemispheres. We obtain that about 60%
of the monthly N-S asymmetries are significant at a 95% level, whereas the
relative contributions of the northern and southern hemisphere are different
for different cycles. From the analysis of power spectra and autocorrelation
functions, we derive a rigid rotation with about 27 days for the northern
hemisphere, which can be followed for up to 15 periods. Contrary to that, the
southern hemisphere reveals a dominant period of about 28 days, whereas the
autocorrelation is strongly attenuated after 3 periods. These findings suggest
that the activity of the northern hemisphere is dominated by an active zone,
whereas the southern activity is mainly dominated by individual long-lived
sunspot groups.Comment: 9 pages, 8 figures, data catalogue online available at
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/70
Radiative emission of solar features in the Ca II K line: comparison of measurements and models
We study the radiative emission of various types of solar features, such as
quiet Sun, enhanced network, plage, and bright plage regions, identified on
filtergrams taken in the Ca II K line. We analysed fulldisk images obtained
with the PSPT, by using three interference filters that sample the Ca II K line
with different bandpasses. We studied the dependence of the radiative emission
of disk features on the filter bandpass. We also performed a NLTE spectral
synthesis of the Ca II K line integrated over the bandpass of PSPT filters. The
synthesis was carried out by utilizing both the PRD and CRD with the most
recent set of semi empirical atmosphere models in the literature and some
earlier atmosphere models. We measured the CLV of intensity values for various
solar features identified on PSPT images and compared the results obtained with
those derived from the synthesis. We find that CRD calculations derived using
the most recent quiet Sun model, on average, reproduce the measured values of
the quiet Sun regions slightly more accurately than PRD computations with the
same model. This may reflect that the utilized atmospheric model was computed
assuming CRD. Calculations with PRD on earlier quiet Sun model atmospheres
reproduce measured quantities with a similar accuracy as to that achieved here
by applying CRD to the recent model. We also find that the median contrast
values measured for most of the identified bright features, disk positions, and
filter widths are, on average, a factor 1.9 lower than those derived from PRD
simulations performed using the recent bright feature models. The discrepancy
between measured and modeled values decreases by 12% after taking into account
straylight effects on PSPT images. PRD computations on either the most recent
or the earlier atmosphere models of bright features reproduce measurements from
plage and bright plage regions with a similar accuracy.Comment: 14 pages, 18 figures, accepted by A&
The existence of the Lambda effect in the solar convection zone indicated by SDO observations
The empirical finding with data from the Solar Dynamics Observatory (SDO) of
positive (negative) horizontal Reynolds stress at the northern (southern)
hemisphere for solar giant cells (Hathaway et al. 2013) is discussed for its
consequences for the theory of the solar/stellar differential rotation. Solving
the nonlinear Reynolds equation for the angular velocity under neglect of the
meridional circulation we show that the horizontal Reynolds stress of the
northern hemisphere is always negative at the surface but it is positive in the
bulk of the solar convection zone by the action of the Lambda effect. The
Lambda effect, which describes the angular momentum transport of rigidly
rotating anisotropic turbulence and which avoids a rigid-body rotation of the
convection zones, is in horizontal direction of cubic power in the rotation
rate and it is always equatorwards directed. Theories without Lambda
effect which may also provide the observed solar rotation law only by the
action of a meridional circulation lead to a horizontal Reynolds stress with
the opposite sign as observed.Comment: 4 pages, 6 figure
Diversifying Anaerobic Respiration Strategies to Compete in the Rhizosphere
The rhizosphere is the interface between plant roots and soil where intense, varied interactions between plants and microbes influence plants' health and growth through their influence on biochemical cycles, such as the carbon, nitrogen, and iron cycles. The rhizosphere is also a changing environment where oxygen can be rapidly limited and anaerobic zones can be established. Microorganisms successfully colonize the rhizosphere when they possess specific traits referred to as rhizosphere competence. Anaerobic respiration flexibility contributes to the rhizosphere competence of microbes. Indeed, a wide range of compounds that are available in the rhizosphere can serve as alternative terminal electron acceptors during anaerobic respiration such as nitrates, iron, carbon compounds, sulfur, metalloids, and radionuclides. In the presence of multiple terminal electron acceptors in a complex environment such as the rhizosphere and in the absence of O2, microorganisms will first use the most energetic option to sustain growth. Anaerobic respiration has been deeply studied, and the genes involved in anaerobic respiration have been identified. However, aqueous environment and paddy soils are the most studied environments for anaerobic respiration, even if we provide evidence in this review that anaerobic respiration also occurs in the plant rhizosphere. Indeed, we provide evidence by performing a BLAST analysis on metatranscriptomic data that genes involved in iron, sulfur, arsenate and selenate anaerobic respiration are expressed in the rhizosphere, underscoring that the rhizosphere environment is suitable for the establishment of anaerobic respiration. We thus focus this review on current research concerning the different types of anaerobic respiration that occur in the rhizosphere. We also discuss the flexibility of anaerobic respiration as a fundamental trait for the microbial colonization of roots, environmental and ecological adaptation, persistence and bioremediation in the rhizosphere. Anaerobic respiration appears to be a key process for the functioning of an ecosystem and interactions between plants and microbes
Quantum Tomography via Compressed Sensing: Error Bounds, Sample Complexity, and Efficient Estimators
Intuitively, if a density operator has small rank, then it should be easier
to estimate from experimental data, since in this case only a few eigenvectors
need to be learned. We prove two complementary results that confirm this
intuition. First, we show that a low-rank density matrix can be estimated using
fewer copies of the state, i.e., the sample complexity of tomography decreases
with the rank. Second, we show that unknown low-rank states can be
reconstructed from an incomplete set of measurements, using techniques from
compressed sensing and matrix completion. These techniques use simple Pauli
measurements, and their output can be certified without making any assumptions
about the unknown state.
We give a new theoretical analysis of compressed tomography, based on the
restricted isometry property (RIP) for low-rank matrices. Using these tools, we
obtain near-optimal error bounds, for the realistic situation where the data
contains noise due to finite statistics, and the density matrix is full-rank
with decaying eigenvalues. We also obtain upper-bounds on the sample complexity
of compressed tomography, and almost-matching lower bounds on the sample
complexity of any procedure using adaptive sequences of Pauli measurements.
Using numerical simulations, we compare the performance of two compressed
sensing estimators with standard maximum-likelihood estimation (MLE). We find
that, given comparable experimental resources, the compressed sensing
estimators consistently produce higher-fidelity state reconstructions than MLE.
In addition, the use of an incomplete set of measurements leads to faster
classical processing with no loss of accuracy.
Finally, we show how to certify the accuracy of a low rank estimate using
direct fidelity estimation and we describe a method for compressed quantum
process tomography that works for processes with small Kraus rank.Comment: 16 pages, 3 figures. Matlab code included with the source file
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