61 research outputs found
Atom-molecule Rabi oscillations in a Mott insulator
We observe large-amplitude Rabi oscillations between an atomic and a
molecular state near a Feshbach resonance. The experiment uses 87Rb in an
optical lattice and a Feshbach resonance near 414 G. The frequency and
amplitude of the oscillations depend on magnetic field in a way that is well
described by a two-level model. The observed density dependence of the
oscillation frequency agrees with the theoretical expectation. We confirmed
that the state produced after a half-cycle contains exactly one molecule at
each lattice site. In addition, we show that for energies in a gap of the
lattice band structure, the molecules cannot dissociate
Controlling a magnetic Feshbach resonance with laser light
The capability to tune the strength of the elastic interparticle interaction
is crucial for many experiments with ultracold gases. Magnetic Feshbach
resonances are a tool widely used for this purpose, but future experiments
would benefit from additional flexibility such as spatial modulation of the
interaction strength on short length scales. Optical Feshbach resonances offer
this possibility in principle, but suffer from fast particle loss due to
light-induced inelastic collisions. Here we show that light near-resonant with
a molecular bound-to-bound transition can be used to shift the magnetic field
at which a magnetic Feshbach resonance occurs. This makes it possible to tune
the interaction strength with laser light and at the same time induce
considerably less loss than an optical Feshbach resonance would do
Strong dissipation inhibits losses and induces correlations in cold molecular gases
Atomic quantum gases in the strong-correlation regime offer unique
possibilities to explore a variety of many-body quantum phenomena. Reaching
this regime has usually required both strong elastic and weak inelastic
interactions, as the latter produce losses. We show that strong inelastic
collisions can actually inhibit particle losses and drive a system into a
strongly-correlated regime. Studying the dynamics of ultracold molecules in an
optical lattice confined to one dimension, we show that the particle loss rate
is reduced by a factor of 10. Adding a lattice along the one dimension
increases the reduction to a factor of 2000. Our results open up the
possibility to observe exotic quantum many-body phenomena with systems that
suffer from strong inelastic collisions
An Elementary Quantum Network of Single Atoms in Optical Cavities
Quantum networks are distributed quantum many-body systems with tailored
topology and controlled information exchange. They are the backbone of
distributed quantum computing architectures and quantum communication. Here we
present a prototype of such a quantum network based on single atoms embedded in
optical cavities. We show that atom-cavity systems form universal nodes capable
of sending, receiving, storing and releasing photonic quantum information.
Quantum connectivity between nodes is achieved in the conceptually most
fundamental way: by the coherent exchange of a single photon. We demonstrate
the faithful transfer of an atomic quantum state and the creation of
entanglement between two identical nodes in independent laboratories. The
created nonlocal state is manipulated by local qubit rotation. This efficient
cavity-based approach to quantum networking is particularly promising as it
offers a clear perspective for scalability, thus paving the way towards
large-scale quantum networks and their applications.Comment: 8 pages, 5 figure
Photonic quantum state transfer between a cold atomic gas and a crystal
Interfacing fundamentally different quantum systems is key to build future
hybrid quantum networks. Such heterogeneous networks offer superior
capabilities compared to their homogeneous counterparts as they merge
individual advantages of disparate quantum nodes in a single network
architecture. However, only very few investigations on optical
hybrid-interconnections have been carried out due to the high fundamental and
technological challenges, which involve e.g. wavelength and bandwidth matching
of the interfacing photons. Here we report the first optical quantum
interconnection between two disparate matter quantum systems with photon
storage capabilities. We show that a quantum state can be faithfully
transferred between a cold atomic ensemble and a rare-earth doped crystal via a
single photon at telecommunication wavelength, using cascaded quantum frequency
conversion. We first demonstrate that quantum correlations between a photon and
a single collective spin excitation in the cold atomic ensemble can be
transferred onto the solid-state system. We also show that single-photon
time-bin qubits generated in the cold atomic ensemble can be converted, stored
and retrieved from the crystal with a conditional qubit fidelity of more than
. Our results open prospects to optically connect quantum nodes with
different capabilities and represent an important step towards the realization
of large-scale hybrid quantum networks
Candida albicans AGE3, the Ortholog of the S. cerevisiae ARF-GAP-Encoding Gene GCS1, Is Required for Hyphal Growth and Drug Resistance
BACKGROUND: Hyphal growth and multidrug resistance of C. albicans are important features for virulence and antifungal therapy of this pathogenic fungus. METHODOLOGY/PRINCIPAL FINDINGS: Here we show by phenotypic complementation analysis that the C. albicans gene AGE3 is the functional ortholog of the yeast ARF-GAP-encoding gene GCS1. The finding that the gene is required for efficient endocytosis points to an important functional role of Age3p in endosomal compartments. Most C. albicans age3Delta mutant cells which grew as cell clusters under yeast growth conditions showed defects in filamentation under different hyphal growth conditions and were almost completely disabled for invasive filamentous growth. Under hyphal growth conditions only a fraction of age3Delta cells shows a wild-type-like polarization pattern of the actin cytoskeleton and lipid rafts. Moreover, age3Delta cells were highly susceptible to several unrelated toxic compounds including antifungal azole drugs. Irrespective of the AGE3 genotype, C-terminal fusions of GFP to the drug efflux pumps Cdr1p and Mdr1p were predominantly localized in the plasma membrane. Moreover, the plasma membranes of wild-type and age3Delta mutant cells contained similar amounts of Cdr1p, Cdr2p and Mdr1p. CONCLUSIONS/SIGNIFICANCE: The results indicate that the defect in sustaining filament elongation is probably caused by the failure of age3Delta cells to polarize the actin cytoskeleton and possibly of inefficient endocytosis. The high susceptibility of age3Delta cells to azoles is not caused by inefficient transport of efflux pumps to the cell membrane. A possible role of a vacuolar defect of age3Delta cells in drug susceptibility is proposed and discussed. In conclusion, our study shows that the ARF-GAP Age3p is required for hyphal growth which is an important virulence factor of C. albicans and essential for detoxification of azole drugs which are routinely used for antifungal therapy. Thus, it represents a promising antifungal drug target
Insulin resistance, lipotoxicity, type 2 diabetes and atherosclerosis: the missing links. The Claude Bernard Lecture 2009
Insulin resistance is a hallmark of type 2 diabetes mellitus and is associated with a metabolic and cardiovascular cluster of disorders (dyslipidaemia, hypertension, obesity [especially visceral], glucose intolerance, endothelial dysfunction), each of which is an independent risk factor for cardiovascular disease (CVD). Multiple prospective studies have documented an association between insulin resistance and accelerated CVD in patients with type 2 diabetes, as well as in non-diabetic individuals. The molecular causes of insulin resistance, i.e. impaired insulin signalling through the phosphoinositol-3 kinase pathway with intact signalling through the mitogen-activated protein kinase pathway, are responsible for the impairment in insulin-stimulated glucose metabolism and contribute to the accelerated rate of CVD in type 2 diabetes patients. The current epidemic of diabetes is being driven by the obesity epidemic, which represents a state of tissue fat overload. Accumulation of toxic lipid metabolites (fatty acyl CoA, diacylglycerol, ceramide) in muscle, liver, adipocytes, beta cells and arterial tissues contributes to insulin resistance, beta cell dysfunction and accelerated atherosclerosis, respectively, in type 2 diabetes. Treatment with thiazolidinediones mobilises fat out of tissues, leading to enhanced insulin sensitivity, improved beta cell function and decreased atherogenesis. Insulin resistance and lipotoxicity represent the missing links (beyond the classical cardiovascular risk factors) that help explain the accelerated rate of CVD in type 2 diabetic patients
Niche separation in common prostome freshwater ciliates: the effect of food and temperature
We characterized the ecological niches of several planktonic prostome ciliates with respect to their food demand and temperature. We found intergeneric differences between Balanion planctonicum and the 2 Urotricha spp., U. furcata and U. farcta. There were also significant interspecific differences within the genus Urotricha and intraspecific differences between 2 Balanion spp. and 3 U, furcata isolates from distant lakes. Relative to Urotricha spp., Balanion appeared to be the superior competitor at low to medium food concentrations and reached high growth rates at moderate temperatures. The threshold prey concentration for positive population growth of B. planctonicum was lower than that obtained for the 2 Urotricha spp., but higher than that reported earlier for the marine species, B. comatum. A third Urotricha species, U. castalia, was investigated for its temperature response only, The temperature response revealed species-specific temperature adaptation between B. planctonicum and the sympatric U. furcata, and further differences within the genus Urotricha: U, farcta grew fastest at high temperatures; U. castalia was adapted to low temperatures; and U, furcata peaked at moderately warm temperature
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