544 research outputs found
Economic (In)Security: The Experience of the African-American and Latino Middle Classes
As the next installment in the By a Thread series, Economic (In)Security uses the Middle Class Security Index to provide the first comprehensive portrait of the level of financial security enjoyed by African-American and Latino middle-class families. The findings show that, in the wake of fading economic opportunity, these two rapidly growing groups face mounting obstacles in becoming part of, and remaining securely in, America's middle class
From Middle to Shaky Ground: The Economic Decline of America's Middle Class
A middle-class standard of living requires that families have adequate financial security to meet current obligations, invest in the future, and access opportunities. The most recent findings from the Middle Class Security Index show that between 2000 and 2006--even before the most recent economic downturn--the economic well-being of middle-class families slipped noticeably.Between 2000 and 2006 an estimated 4 million middle-class families lost their financial security, bringing the total number of middle-income families on shaky ground to 23 million.These worrisome changes in the overall financial health of the middle class were driven by a decline in assets, rising housing costs, and a growing lack of health insurance
Ultra-sensitive surface absorption spectroscopy using sub-wavelength diameter optical fibers
The guided modes of sub-wavelength diameter air-clad optical fibers exhibit a
pronounced evanescent field. The absorption of particles on the fiber surface
is therefore readily detected via the fiber transmission. We show that the
resulting absorption for a given surface coverage can be orders of magnitude
higher than for conventional surface spectroscopy. As a demonstration, we
present measurements on sub-monolayers of 3,4,9,10-perylene-tetracarboxylic
dianhydride (PTCDA) molecules at ambient conditions, revealing the
agglomeration dynamics on a second to minutes timescale.Comment: 4 pages, Fig.1a corrected y-axis, p.2 minor text changes to
facilitate the understanding of eq. 4 and
Cold Atom Physics Using Ultra-Thin Optical Fibers: Light-Induced Dipole Forces and Surface Interactions
The strong evanescent field around ultra-thin unclad optical fibers bears a
high potential for detecting, trapping, and manipulating cold atoms.
Introducing such a fiber into a cold atom cloud, we investigate the interaction
of a small number of cold Caesium atoms with the guided fiber mode and with the
fiber surface. Using high resolution spectroscopy, we observe and analyze
light-induced dipole forces, van der Waals interaction, and a significant
enhancement of the spontaneous emission rate of the atoms. The latter can be
assigned to the modification of the vacuum modes by the fiber.Comment: 4 pages, 4 figure
A neutral atom quantum register
We demonstrate the realization of a quantum register using a string of single
neutral atoms which are trapped in an optical dipole trap. The atoms are
selectively and coherently manipulated in a magnetic field gradient using
microwave radiation. Our addressing scheme operates with a high spatial
resolution and qubit rotations on individual atoms are performed with 99%
contrast. In a final read-out operation we analyze each individual atomic
state. Finally, we have measured the coherence time and identified the
predominant dephasing mechanism for our register.Comment: 4 pages, 4 figure
Precision preparation of strings of trapped neutral atoms
We have recently demonstrated the creation of regular strings of neutral
caesium atoms in a standing wave optical dipole trap using optical tweezers [Y.
Miroshnychenko et al., Nature, in press (2006)]. The rearrangement is realized
atom-by-atom, extracting an atom and re-inserting it at the desired position
with sub-micrometer resolution. We describe our experimental setup and present
detailed measurements as well as simple analytical models for the resolution of
the extraction process, for the precision of the insertion, and for heating
processes. We compare two different methods of insertion, one of which permits
the placement of two atoms into one optical micropotential. The theoretical
models largely explain our experimental results and allow us to identify the
main limiting factors for the precision and efficiency of the manipulations.
Strategies for future improvements are discussed.Comment: 25 pages, 18 figure
Adiabatic Quantum State Manipulation of Single Trapped Atoms
We use microwave induced adiabatic passages for selective spin flips within a
string of optically trapped individual neutral Cs atoms. We
position-dependently shift the atomic transition frequency with a magnetic
field gradient. To flip the spin of a selected atom, we optically measure its
position and sweep the microwave frequency across its respective resonance
frequency. We analyze the addressing resolution and the experimental robustness
of this scheme. Furthermore, we show that adiabatic spin flips can also be
induced with a fixed microwave frequency by deterministically transporting the
atoms across the position of resonance.Comment: 4 pages, 4 figure
Coherence properties and quantum state transportation in an optical conveyor belt
We have prepared and detected quantum coherences with long dephasing times at
the level of single trapped cesium atoms. Controlled transport by an "optical
conveyor belt" over macroscopic distances preserves the atomic coherence with
slight reduction of coherence time. The limiting dephasing effects are
experimentally identified and are of technical rather than fundamental nature.
We present an analytical model of the reversible and irreversible dephasing
mechanisms. Coherent quantum bit operations along with quantum state transport
open the route towards a "quantum shift register" of individual neutral atoms.Comment: 4 pages, 3 figure
Quantum bit detector
We propose and analyze an experimental scheme of quantum nondemolition
detection of monophotonic and vacuum states in a superconductive toroidal
cavity by means of Rydberg atoms.Comment: 4 pages, 3 figure
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