1,052 research outputs found
Prospects for a European welfare state: Lessons from welfare state development in six OECD-Federations
This paper uses the findings of a very recent major international research collaboration on the impact of federal arrangements on the development of the welfare state to explore the possibilities of progress beyond Europe's present diversity of nation-state welfare standards. These findings - based on the longterm historical experience of the OECD's oldest federations - suggest that federal arrangements tend to slow down welfare state consolidation, but that much depends on the context of historical development. The emergence of bypass mechanisms circumventing federal veto-points is located as the key to welfare progress, and the role of regulation in European integration and the special role of the ECJ as well as that of "the open method of co-ordination" are tentatively identified as possible EU bypass equivalents. --
Pulsed force sequences for fast phase-insensitive quantum gates in trapped ions
We show how to create quantum gates of arbitrary speed between trapped ions,
using a laser walking wave, with complete insensitivity to drift of the optical
phase, and requiring cooling only to the Lamb-Dicke regime. We present pulse
sequences that satisfy the requirements and are easy to produce in the
laboratory.Comment: 11 pages, 3 figure
Comparing the states of many quantum systems
We investigate how to determine whether the states of a set of quantum
systems are identical or not. This paper treats both error-free comparison, and
comparison where errors in the result are allowed. Error-free comparison means
that we aim to obtain definite answers, which are known to be correct, as often
as possible. In general, we will have to accept also inconclusive results,
giving no information. To obtain a definite answer that the states of the
systems are not identical is always possible, whereas, in the situation
considered here, a definite answer that they are identical will not be
possible. The optimal universal error-free comparison strategy is a projection
onto the totally symmetric and the different non-symmetric subspaces, invariant
under permutations and unitary transformations. We also show how to construct
optimal comparison strategies when allowing for some errors in the result,
minimising either the error probability, or the average cost of making an
error. We point out that it is possible to realise universal error-free
comparison strategies using only linear elements and particle detectors, albeit
with less than ideal efficiency. Also minimum-error and minimum-cost strategies
may sometimes be realised in this way. This is of great significance for
practical applications of quantum comparison.Comment: 13 pages, 2 figures. Corrected a misprint on p. 7 and added a few
references. Accepted for publication in J Mod Op
Investigating the magnetovolume effect in isotropic body-centered-cubic iron using spin-lattice dynamics simulations
published_or_final_versio
Prospects for a European welfare state : lessons from welfare state development in six OECD-Federations
This paper uses the findings of a very recent major international research collaboration on the impact of federal arrangements on the development of the welfare state to explore the possibilities of progress beyond Europeâs present diversity of nation-state welfare standards. These findings â based on the longterm historical experience of the OECDâs oldest federations â suggest that federal arrangements tend to slow down welfare state consolidation, but that much depends on the context of historical development. The emergence of bypass mechanisms circumventing federal veto-points is located as the key to welfare progress, and the role of regulation in European integration and the special role of the ECJ as well as that of âthe open method of co-ordinationâ are tentatively identified as possible EU bypass equivalents
Laser cooling with electromagnetically induced transparency: Application to trapped samples of ions or neutral atoms
A novel method of ground state laser cooling of trapped atoms utilizes the
absorption profile of a three (or multi-) level system which is tailored by a
quantum interference. With cooling rates comparable to conventional sideband
cooling, lower final temperatures may be achieved. The method was
experimentally implemented to cool a single Ca ion to its vibrational
ground state. Since a broad band of vibrational frequencies can be cooled
simultaneously, the technique will be particularly useful for the cooling of
larger ion strings, thereby being of great practical importance for
initializing a quantum register based on trapped ions. We also discuss its
application to different level schemes and for ground state cooling of neutral
atoms trapped by a far detuned standing wave laser field.Comment: 9 pages, 13 figures, submitted to Appl Phys B 200
Estimating mixed quantum states
We discuss single adaptive measurements for the estimation of mixed quantum
states of qubits. The results are compared to the optimal estimation schemes
using collective measurements. We also demonstrate that the advantage of
collective measurements increases when the degree of mixing of the quantum
states increases.Comment: RevTeX, 7 pages, 4 figure
Experiments towards quantum information with trapped Calcium ions
Ground state cooling and coherent manipulation of ions in an rf-(Paul) trap
is the prerequisite for quantum information experiments with trapped ions. With
resolved sideband cooling on the optical S1/2 - D5/2 quadrupole transition we
have cooled one and two 40Ca+ ions to the ground state of vibration with up to
99.9% probability. With a novel cooling scheme utilizing electromagnetically
induced transparency on the S1/2 - P1/2 manifold we have achieved simultaneous
ground state cooling of two motional sidebands 1.7 MHz apart. Starting from the
motional ground state we have demonstrated coherent quantum state manipulation
on the S1/2 - D5/2 quadrupole transition at 729 nm. Up to 30 Rabi oscillations
within 1.4 ms have been observed in the motional ground state and in the n=1
Fock state. In the linear quadrupole rf-trap with 700 kHz trap frequency along
the symmetry axis (2 MHz in radial direction) the minimum ion spacing is more
than 5 micron for up to 4 ions. We are able to cool two ions to the ground
state in the trap and individually address the ions with laser pulses through a
special optical addressing channel.Comment: Proceedings of the ICAP 2000, Firenz
A trapped-ion local field probe
We introduce a measurement scheme that utilizes a single ion as a local field
probe. The ion is confined in a segmented Paul trap and shuttled around to
reach different probing sites. By the use of a single atom probe, it becomes
possible characterizing fields with spatial resolution of a few nm within an
extensive region of millimeters. We demonstrate the scheme by accurately
investigating the electric fields providing the confinement for the ion. For
this we present all theoretical and practical methods necessary to generate
these potentials. We find sub-percent agreement between measured and calculated
electric field values
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