1,401 research outputs found
A deterministic cavity-QED source of polarization entangled photon pairs
We present two cavity quantum electrodynamics proposals that, sharing the
same basic elements, allow for the deterministic generation of entangled
photons pairs by means of a three-level atom successively coupled to two single
longitudinal mode high-Q optical resonators presenting polarization degeneracy.
In the faster proposal, the three-level atom yields a polarization entangled
photon pair via two truncated Rabi oscillations, whereas in the adiabatic
proposal a counterintuitive Stimulated Raman Adiabatic Passage process is
considered. Although slower than the former process, this second method is very
efficient and robust under fluctuations of the experimental parameters and,
particularly interesting, almost completely insensitive to atomic decay.Comment: 5 pages, 5 figure
Deterministic single-photon source from a single ion
We realize a deterministic single-photon source from one and the same calcium
ion interacting with a high-finesse optical cavity. Photons are created in the
cavity with efficiency (88 +- 17)%, a tenfold improvement over previous
cavity-ion sources. Results of the second-order correlation function are
presented, demonstrating a high suppression of two-photon events limited only
by background counts. The cavity photon pulse shape is obtained, with good
agreement between experiment and simulation. Moreover, theoretical analysis of
the temporal evolution of the atomic populations provides relevant information
about the dynamics of the process and opens the way to future investigations of
a coherent atom-photon interface
Raman spectroscopy of a single ion coupled to a high-finesse cavity
We describe an ion-based cavity-QED system in which the internal dynamics of
an atom is coupled to the modes of an optical cavity by vacuum-stimulated Raman
transitions. We observe Raman spectra for different excitation polarizations
and find quantitative agreement with theoretical simulations. Residual motion
of the ion introduces motional sidebands in the Raman spectrum and leads to ion
delocalization. The system offers prospects for cavity-assisted
resolved-sideband ground-state cooling and coherent manipulation of ions and
photons.Comment: 8 pages, 6 figure
Integrated fiber-mirror ion trap for strong ion-cavity coupling
We present and characterize fiber mirrors and a miniaturized ion-trap design developed to integrate a fiber-based Fabry-Perot cavity (FFPC) with a linear Paul trap for use in cavity-QED experiments with trapped ions. Our fiber-mirror fabrication process not only enables the construction of FFPCs with small mode volumes, but also allows us to minimize the influence of the dielectric fiber mirrors on the trapped-ion pseudopotential. We discuss the effect of clipping losses for long FFPCs and the effect of angular and lateral displacements on the coupling efficiencies between cavity and fiber. Optical profilometry allows us to determine the radii of curvature and ellipticities of the fiber mirrors. From finesse measurements, we infer a single-atom cooperativity of up to 12 for FFPCs longer than 200 μm in length; comparison to cavities constructed with reference substrate mirrors produced in the same coating run indicates that our FFPCs have similar scattering losses. We characterize the birefringence of our fiber mirrors, finding that careful fiber-mirror selection enables us to construct FFPCs with degenerate polarization modes. As FFPCs are novel devices, we describe procedures developed for handling, aligning, and cleaning them. We discuss experiments to anneal fiber mirrors and explore the influence of the atmosphere under which annealing occurs on coating losses, finding that annealing under vacuum increases the losses for our reference substrate mirrors. X-ray photoelectron spectroscopy measurements indicate that these losses may be attributable to oxygen depletion in the mirror coating. Special design considerations enable us to introduce a FFPC into a trapped ion setup. Our unique linear Paul trap design provides clearance for such a cavity and is miniaturized to shield trapped ions from the dielectric fiber mirrors. We numerically calculate the trap potential in the absence of fibers. In the experiment additional electrodes can be used to compensate distortions of the potential due to the fibers. Home-built fiber feedthroughs connect the FFPC to external optics, and an integrated nanopositioning system affords the possibility of retracting or realigning the cavity without breaking vacuum
Run 2 Upgrades to the CMS Level-1 Calorimeter Trigger
The CMS Level-1 calorimeter trigger is being upgraded in two stages to
maintain performance as the LHC increases pile-up and instantaneous luminosity
in its second run. In the first stage, improved algorithms including
event-by-event pile-up corrections are used. New algorithms for heavy ion
running have also been developed. In the second stage, higher granularity
inputs and a time-multiplexed approach allow for improved position and energy
resolution. Data processing in both stages of the upgrade is performed with
new, Xilinx Virtex-7 based AMC cards.Comment: 10 pages, 7 figure
Highway Construction Materials From the Consolidated Rocks of Southwestern Iowa
Southwestern Iowa, unlike other parts of the State, does not have plentiful near-surface supplies of stone available for highway construction purposes. The long and intensive search for such road material by quarrymen, highway engineers, geologists, and others interested in all phases of stone use resulted in a growing conviction that the only hope of locating new and significant deposits lay in a regional geological survey. Further, such a survey would result in the delineation of areas where exploration should be economically feasible as well as those areas where exploration would have little or no chance of success. These views formed the foundation for de-veloping the project covered by this report under a cooperative agreement with the Iowa Highway Research Board of the Iowa State Highway Commission. The aims of the project were (1) to locate and describe all consolidated rocks found in place at the surface, or penetrated by drilling or other means; (2) to correlate these rocks geologically; (3) to assemble this information and the valid geological inferences from it into cross sections and maps showing the type of bedrock, thickness of overburden and rock structure; and (4) to write appropriate comments so that the potential usefulness and the most promising sites for future exploration or expansion for stone quarries can be readily seen and be of maximum value. The report was prepared with the knowledge that its chief immediate use would be by highway engineers and geologists, county engineers, materials producers, and prospectors. To facilitate their use of the report, certain phases were stressed and some standard methods of presentation and arrangement were not rigidly followed. The scientific integrity of the report is not compromised by these deviations from the formal scientific writing practices, nor is the value of the report for other uses thereby lessened
Bostonia: The Boston University Alumni Magazine. Volume 9
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
Modeling the series of (n x 2) Si-rich reconstructions of beta-SiC(001): a prospective atomic wire?
We perform ab initio plane wave supercell density functional calculations on
three candidate models of the (3 x 2) reconstruction of the beta-SiC(001)
surface. We find that the two-adlayer asymmetric-dimer model (TAADM) is
unambiguously favored for all reasonable values of Si chemical potential. We
then use structures derived from the TAADM parent to model the silicon lines
that are observed when the (3 x 2) reconstruction is annealed (the (n x 2)
series of reconstructions), using a tight-binding method. We find that as we
increase n, and so separate the lines, a structural transition occurs in which
the top addimer of the line flattens. We also find that associated with the
separation of the lines is a large decrease in the HOMO-LUMO gap, and that the
HOMO state becomes quasi-one-dimensional. These properties are qualititatively
and quantitatively different from the electronic properties of the original (3
x 2) reconstruction.Comment: 22 pages, including 6 EPS figure
Topological Qubits with Majorana Fermions in Trapped Ions
We propose a method of encoding a topologically-protected qubit using
Majorana fermions in a trapped-ion chain. This qubit is protected against major
sources of decoherence, while local operations and measurements can be
realized. Furthermore, we show that an efficient quantum interface and memory
for arbitrary multiqubit photonic states can be built, encoding them into a set
of entangled Majorana-fermion qubits inside cavities.Comment: 9 pages, 2 figure
Fundamental research questions in subterranean biology
Five decades ago, a landmark paper inSciencetitledThe Cave Environmentheralded caves as ideal natural experimental laboratories in which to develop and address general questions in geology, ecology, biogeography, and evolutionary biology. Although the 'caves as laboratory' paradigm has since been advocated by subterranean biologists, there are few examples of studies that successfully translated their results into general principles. The contemporary era of big data, modelling tools, and revolutionary advances in genetics and (meta)genomics provides an opportunity to revisit unresolved questions and challenges, as well as examine promising new avenues of research in subterranean biology. Accordingly, we have developed a roadmap to guide future research endeavours in subterranean biology by adapting a well-established methodology of 'horizon scanning' to identify the highest priority research questions across six subject areas. Based on the expert opinion of 30 scientists from around the globe with complementary expertise and of different academic ages, we assembled an initial list of 258 fundamental questions concentrating on macroecology and microbial ecology, adaptation, evolution, and conservation. Subsequently, through online surveys, 130 subterranean biologists with various backgrounds assisted us in reducing our list to 50 top-priority questions. These research questions are broad in scope and ready to be addressed in the next decade. We believe this exercise will stimulate research towards a deeper understanding of subterranean biology and foster hypothesis-driven studies likely to resonate broadly from the traditional boundaries of this field.Peer reviewe
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