1,514 research outputs found
Efficient atomic clocks operated with several atomic ensembles
Atomic clocks are typically operated by locking a local oscillator (LO) to a
single atomic ensemble. In this article we propose a scheme where the LO is
locked to several atomic ensembles instead of one. This results in an
exponential improvement compared to the conventional method and provides a
stability of the clock scaling as with being the number
of atoms in each of the ensembles and is a constant depending on
the protocol being used to lock the LOComment: 10 pages, 8 figure
Elementary test for non-classicality based on measurements of position and momentum
We generalise a non-classicality test described by Kot et al. [Phys. Rev.
Lett. 108, 233601 (2010)], which can be used to rule out any classical
description of a physical system. The test is based on measurements of
quadrature operators and works by proving a contradiction with the classical
description in terms of a probability distribution in phase space. As opposed
to the previous work, we generalise the test to include states without
rotational symmetry in phase space. Furthermore, we compare the performance of
the non-classicality test with classical tomography methods based on the
inverse Radon transform, which can also be used to establish the quantum nature
of a physical system. In particular, we consider a non-classicality test based
on the so-called filtered back-projection formula. We show that the general
non-classicality test is conceptually simpler, requires less assumptions on the
system and is statistically more reliable than the tests based on the filtered
back-projection formula. As a specific example, we derive the optimal test for
a quadrature squeezed single photon state and show that the efficiency of the
test does not change with the degree of squeezing
Fish communities in shallow coastal waters - a study of effects of season and bottom substrate
Fish communities in the outer part of Malangen fjord, Troms county were studied to identify seasonal and spatial variation. The fish species compositions differed between seasons and at the four different locations. Cod (Gadus morhua L.) dominated the trammel net catches at all months except in March, in which plaice and other flatfishes were the most numerous. Species richness and diversity were significantly positively correlated with substrate evenness, and the species richness was highest in October and lowest in March. Cod displayed a higher length at age compared with fjord populations, but lower maximum length (L∞). Plaice (Pleuronectes platessa L.) had a low annual mortality rate, and the von Bertalanffy growth coefficient (K) were higher than North Sea plaice populations. Only immature halibut (Hippoglossus hippoglossus L.) were observed, and the three locations where halibut were present are suggested to be nursery grounds for this species. Most of the flatfishes were positively associated with sand and pebble habitats whereas cod were significantly negatively correlated with sand coverage but positively correlated with high algae coverage. The present study highlights the importance of including shallow water studies for both coastal and fisheries management
Near Heisenberg limited atomic clocks in the presence of decoherence
The ultimate stability of atomic clocks is limited by the quantum noise of
the atoms. To reduce this noise it has been suggested to use entangled atomic
ensembles with reduced atomic noise. Potentially this can push the stability
all the way to the limit allowed by the Heisenberg uncertainty relation, which
is denoted the Heisenberg limit. In practice, however, entangled states are
often more prone to decoherence, which may prevent reaching this performance.
Here we present an adaptive measurement protocol that in the presence of a
realistic source of decoherence enables us to get near Heisenberg limited
stability of atomic clocks using entangled atoms. The protocol may thus realize
the full potential of entanglement for quantum metrology despite the
detrimental influence of decoherence.Comment: 13 pages, 9 figures. Note that new reference: Y. Matsuzaki, S. C.
Benjamin, and J. Fitzsimons, Phys. Rev. A 84, 012103 (2011) is adde
One- and two-axis squeezing of atomic ensembles in optical cavities
The strong light-matter coupling attainable in optical cavities enables the
generation of highly squeezed states of atomic ensembles. It was shown in
[Phys. Rev. A 66, 022314 (2002)] how an effective one-axis twisting Hamiltonian
can be realized in a cavity setup. Here, we extend this work and show how an
effective two-axis twisting Hamiltonian can be realized in a similar cavity
setup. We compare the two schemes in order to characterize their advantages. In
the absence of decoherence, the two-axis Hamiltonian leads to more squeezing
than the one-axis Hamiltonian. If limited by decoherence from spontaneous
emission and cavity decay, we find roughly the same level of squeezing for the
two schemes scaling as (NC)^(1/2) where C is the single atom cooperativity and
N is the total number of atoms. When compared to an ideal squeezing operation,
we find that for specific initial states, a dissipative version of the one-axis
scheme attains higher fidelity than the unitary one-axis scheme or the two-axis
scheme. However, the unitary one-axis and two-axis schemes perform better for
general initial states.Comment: 13 pages, 6 figure
Draft genome sequence of <i>Burkholderia sordidicola</i> S170, a potential plant growth promoter isolated from coniferous forest soil in the Czech Republic
Burkholderia species are key players in the accumulation of carbon from cellulose decomposition in coniferous forest ecosystems. We report here the draft genome of Burkholderia sordidicola strain S170, containing features associated with known genes involved in plant growth promotion, the biological control of plant diseases, and green remediation technologies
Photonic Controlled-Phase Gates Through Rydberg Blockade in Optical Cavities
We propose a novel scheme for high fidelity photonic controlled phase gates
using Rydberg blockade in an ensemble of atoms in an optical cavity. The gate
operation is obtained by first storing a photonic pulse in the ensemble and
then scattering a second pulse from the cavity, resulting in a phase change
depending on whether the first pulse contained a single photon. We show that
the combination of Rydberg blockade and optical cavities effectively enhances
the optical non-linearity created by the strong Rydberg interaction and thereby
reduces the requirements for photonic quantum gates. The resulting gate can be
implemented with cavities of moderate finesse which allows for highly efficient
processing of quantum information encoded in photons. As a particular example
of this, we show how the gate can be employed to increase the communication
rate of quantum repeaters based on atomic ensembles.Comment: main manuscript 5 pages with 11 pages of supplementary informatio
Sequencing of IncX-plasmids suggests ubiquity of mobile forms of a biofilm-promoting gene cassette recruited from <em>Klebsiella pneumoniae</em>
Plasmids are a highly effective means with which genetic traits that influence human health, such as virulence and antibiotic resistance, are disseminated through bacterial populations. The IncX-family is a hitherto sparsely populated group of plasmids that are able to thrive within Enterobacteriaceae. In this study, a replicon-centric screening method was used to locate strains from wastewater sludge containing plasmids belonging to the IncX-family. A transposon aided plasmid capture method was then employed to transport IncX-plasmids from their original hosts (and co-hosted plasmids) into a laboratory strain (Escherichia coli Genehogs®) for further study. The nucleotide sequences of the three newly isolated IncX-plasmids (pLN126_33, pMO17_54, pMO440_54) and the hitherto un-sequenced type-plasmid R485 revealed a remarkable occurrence of whole or partial gene cassettes that promote biofilm-formation in Klebsiella pneumonia or E. coli, in all four instances. Two of the plasmids (R485 and pLN126_33) were shown to directly induce biofilm formation in a crystal violet retention assay in E. coli. Sequence comparison revealed that all plasmid-borne forms of the type 3 fimbriae encoding gene cassette mrkABCDF were variations of a composite transposon Tn6011 first described in the E. coli IncX plasmid pOLA52. In conclusion, IncX-plasmids isolated from Enterobacteriaceae over almost 40 years and on three different continents have all been shown to carry a type 3 fimbriae gene cassette mrkABCDF stemming from pathogenic K. pneumoniae. Apart from contributing general knowledge about IncX-plasmids, this study also suggests an apparent ubiquity of a mobile form of an important virulence factor and is an illuminating example of the recruitment, evolution and dissemination of genetic traits through plasmid-mediated horizontal gene transfer
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