1,317 research outputs found
Dark-time decay of the retrieval efficiency of light stored as a Rydberg excitation in a noninteracting ultracold gas
We study the dark-time decay of the retrieval efficiency for light stored in
a Rydberg state in an ultracold gas of Rb atoms based on
electromagnetically induced transparency (EIT). Using low atomic density to
avoid dephasing caused by atom-atom interactions, we measure a time of 30
s for the state in free expansion. One of the dominant limitations
is the combination of photon recoil and thermal atomic motion at 0.2 K. If
the 1064-nm dipole trap is left on, then the time is reduced to 13
s, in agreement with a model taking differential light shifts and
gravitational sag into account. To characterize how coherent the retrieved
light is, we overlap it with reference light and measure the visibility of
the resulting interference pattern, obtaining for short dark time.
Our experimental work is accompanied by a detailed model for the dark-time
decay of the retrieval efficiency of light stored in atomic ensembles. The
model is generally applicable for photon storage in Dicke states, such as in
EIT with -type or ladder-type level schemes and in
Duan-Lukin-Cirac-Zoller single-photon sources. The model includes a treatment
of the dephasing caused by thermal atomic motion combined with net photon
recoil, as well as the influence of trapping potentials. It takes into account
that the signal light field is typically not a plane wave. The model maps the
retrieval efficiency to single-atom properties and shows that the retrieval
efficiency is related to the decay of fringe visibility in Ramsey spectroscopy
and to the spatial first-order coherence function of the gas.Comment: List of changes: (i) The role of separable and entangled states was
clarified. In the process, a new appendix C was added. (ii) More detail was
added in the supplemental material in sections II.E and II.F, that discuss
the relation to Ramsey spectroscopy and to the spatial coherence function.
(iii) A new figure 1 was added. (iv) Various smaller revisions were mad
On the direction of transcription of cloned genes in Neurospora crassa.
On the direction of transcription of cloned genes in Neurospora crassa
Patterns of Sympathetic Responses Induced by Different Stress Tasks
Stress tasks are used to induce sympathetic nervous system (SNS) arousal. However, the efficacy and the patterns of SNS activation have not been systematically compared between different tasks
Superacid resin-based heterogeneous catalysts for the selective acylation of 1,2-methylenedioxybenzene
In this work, we firstly report on the use of highly active and selective Aquivion superacid resins as heterogeneous catalysts for the acylation of 1,2-methylenedioxybenzene (MDB) with propionic anhydride (AP). The reaction was investigated and optimized using solvent-free conditions to selectively produce 3,4-methylenedioxypropiophenone (MDP1P), a key intermediate for the manufacture of active ingredients used in insecticide formulations with a volume of production of roughly 3000 t/y. Interestingly, Aquivion-based catalysts allows to work in mild reaction conditions (i. e. 80 °C), obtaining MDP1P yields as high as 44 % after only 1 h of reaction (selectivity 83 %). A detailed study of the AP reactivity demonstrated its tendency to promote oligomerization reactions that, as confirmed by ex-situ and in-situ FT-ATR analyses, caused the deactivation of the catalyst forming surficial carbonaceous residues. In this context, a fast oxidation of the resin surface organic residues using a diluted HNO3 (or H2O2) solution was proven to be an efficient method to regenerate the catalyst, which can be reused for several reaction cycles. The results obtained in preliminary scale-up tests were basically unaffected by the reaction volume (up to 800 mL), paving the way for possible future applications of the process
Demonstration of a quantum-enhanced fiber Sagnac interferometer
The injection of squeezed light can be used to improve the sensitivity of an interferometer beyond the limit imposed by the zero-point fluctuation of the electromagnetic field. Here, we report on the realization of such a quantum-enhanced interferometer with a fiber-based Sagnac topology. Continuous wave squeezed states at 1550 nm with a noise reduction of 6.4 dB below shot noise were produced by type I optical parametric amplification and subsequently injected into the dark port of the interferometer. A reduction of the interferometer shot noise by 4.5 dB was observed, and the enhancement of the signal-to-noise ratio for a phase modulation signal generated within the interferometer could be demonstrated. We achieved a 95% fiber transmission for the squeezed states, which suggests that corresponding fiber-based quantum metrology and communication systems are feasible
Upper estimate of martingale dimension for self-similar fractals
We study upper estimates of the martingale dimension of diffusion
processes associated with strong local Dirichlet forms. By applying a general
strategy to self-similar Dirichlet forms on self-similar fractals, we prove
that for natural diffusions on post-critically finite self-similar sets
and that is dominated by the spectral dimension for the Brownian motion
on Sierpinski carpets.Comment: 49 pages, 7 figures; minor revision with adding a referenc
Fusion algebra of critical percolation
We present an explicit conjecture for the chiral fusion algebra of critical
percolation considering Virasoro representations with no enlarged or extended
symmetry algebra. The representations we take to generate fusion are countably
infinite in number. The ensuing fusion rules are quasi-rational in the sense
that the fusion of a finite number of these representations decomposes into a
finite direct sum of these representations. The fusion rules are commutative,
associative and exhibit an sl(2) structure. They involve representations which
we call Kac representations of which some are reducible yet indecomposable
representations of rank 1. In particular, the identity of the fusion algebra is
a reducible yet indecomposable Kac representation of rank 1. We make detailed
comparisons of our fusion rules with the recent results of Eberle-Flohr and
Read-Saleur. Notably, in agreement with Eberle-Flohr, we find the appearance of
indecomposable representations of rank 3. Our fusion rules are supported by
extensive numerical studies of an integrable lattice model of critical
percolation. Details of our lattice findings and numerical results will be
presented elsewhere.Comment: 12 pages, v2: comments and references adde
Acquired demyelination but not genetic developmental defects in myelination leads to brain tissue stiffness changes
Changes in axonal myelination are an important hallmark of aging and a number of neurological diseases. Demyelinated axons are impaired in their function and degenerate over time. Oligodendrocytes, the cells responsible for myelination of axons, are sensitive to mechanical properties of their environment. Growing evidence indicates that mechanical properties of demyelinating lesions are different from the healthy state and thus have the potential to affect myelinating potential of oligodendrocytes. We performed a high-resolution spatial mapping of the mechanical heterogeneity of demyelinating lesions using atomic force microscope-enabled indentation. Our results indicate that the stiffness of specific regions of mouse brain tissue is influenced by age and degree of myelination. Here we specifically demonstrate that acquired acute but not genetic demyelination leads to decreased tissue stiffness, which could influence the remyelination potential of oligodendrocytes. We also demonstrate that specific brain regions have unique ranges of stiffness in white and grey matter. Our ex vivo findings may help the design of future in vitro models to mimic the mechanical environment of the brain in healthy and diseased states. The mechanical properties of demyelinating lesions reported here may facilitate novel approaches in treating demyelinating diseases such as multiple sclerosis
Ab-initio Quantum Enhanced Optical Phase Estimation Using Real-time Feedback Control
Optical phase estimation is a vital measurement primitive that is used to
perform accurate measurements of various physical quantities like length,
velocity and displacements. The precision of such measurements can be largely
enhanced by the use of entangled or squeezed states of light as demonstrated in
a variety of different optical systems. Most of these accounts however deal
with the measurement of a very small shift of an already known phase, which is
in stark contrast to ab-initio phase estimation where the initial phase is
unknown. Here we report on the realization of a quantum enhanced and fully
deterministic phase estimation protocol based on real-time feedback control.
Using robust squeezed states of light combined with a real-time Bayesian
estimation feedback algorithm, we demonstrate deterministic phase estimation
with a precision beyond the quantum shot noise limit. The demonstrated protocol
opens up new opportunities for quantum microscopy, quantum metrology and
quantum information processing.Comment: 5 figure
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