6,623 research outputs found
Doppler cooling of calcium ions using a dipole-forbidden transition
Doppler cooling of calcium ions has been experimentally demonstrated using
the S1/2 to D5/2 dipole-forbidden transition. Scattering forces and
fluorescence levels a factor of 5 smaller than for usual Doppler cooling on the
dipole allowed S1/2 to P1/2 transition have been achieved. Since the light
scattered from the ions can be monitored at (violet) wavelengths that are very
different from the excitation wavelengths, single ions can be detected with an
essentially zero background level. This, as well as other features of the
cooling scheme, can be extremely valuable for ion trap based quantum
information processing.Comment: 4 pages, 4 figures, minor changes to commentary and reference
Error tolerance in an NMR Implementation of Grover's Fixed-Point Quantum Search Algorithm
We describe an implementation of Grover's fixed-point quantum search
algorithm on a nuclear magnetic resonance (NMR) quantum computer, searching for
either one or two matching items in an unsorted database of four items. In this
new algorithm the target state (an equally weighted superposition of the
matching states) is a fixed point of the recursive search operator, and so the
algorithm always moves towards the desired state. The effects of systematic
errors in the implementation are briefly explored.Comment: 5 Pages RevTex4 including three figures. Changes made at request of
referees; now in press at Phys Rev
Aeolian transport layer
We investigate the airborne transport of particles on a granular surface by
the saltation mechanism through numerical simulation of particle motion coupled
with turbulent flow. We determine the saturated flux and show that its
behavior is consistent with a classical empirical relation obtained from wind
tunnel measurements. Our results also allow to propose a new relation valid for
small fluxes, namely, , where and
are the shear and threshold velocities of the wind, respectively, and
the scaling exponent is . We obtain an expression for the
velocity profile of the wind distorted by the particle motion and present a
dynamical scaling relation. We also find a novel expression for the dependence
of the height of the saltation layer as function of the wind velocity.Comment: 4 pages, 4 figure
Spin Squeezing in the Ising Model
We analyze the collective spin noise in interacting spin systems. General
expressions are derived for the short time behaviour of spin systems with
general spin-spin interactions, and we suggest optimum experimental conditions
for the detection of spin squeezing. For Ising models with site dependent
nearest neighbour interactions general expressions are presented for the spin
squeezing parameter for all times. The reduction of collective spin noise can
be used to verify the entangling powers of quantum computer architectures based
on interacting spins.Comment: 7 pages, including 3 figure
Density matrix algorithm for the calculation of dynamical properties of low dimensional systems
I extend the scope of the density matrix renormalization group technique
developed by White to the calculation of dynamical correlation functions. As an
application and performance evaluation I calculate the spin dynamics of the 1D
Heisenberg chain.Comment: 4 pages + 4 figures in one Latex + 4 postscript file
Non-Destructive Identification of Cold and Extremely Localized Single Molecular Ions
A simple and non-destructive method for identification of a single molecular
ion sympathetically cooled by a single laser cooled atomic ion in a linear Paul
trap is demonstrated. The technique is based on a precise determination of the
molecular ion mass through a measurement of the eigenfrequency of a common
motional mode of the two ions. The demonstrated mass resolution is sufficiently
high that a particular molecular ion species can be distinguished from other
equally charged atomic or molecular ions having the same total number of
nucleons
Entanglement and Extreme Spin Squeezing
For any mean value of a cartesian component of a spin vector we identify the
smallest possible uncertainty in any of the orthogonal components. The
corresponding states are optimal for spectroscopy and atomic clocks. We show
that the results for different spin J can be used to identify entanglement and
to quantity the depth of entanglement in systems with many particles. With the
procedure developed in this letter, collective spin measurements on an ensemble
of particles can be used as an experimental proof of multi-particle
entanglementComment: 4 pages, 2 figures, minor changes in the presentatio
Environment Assisted Metrology with Spin Qubit
We investigate the sensitivity of a recently proposed method for precision
measurement [Phys. Rev. Lett. 106, 140502 (2011)], focusing on an
implementation based on solid-state spin systems. The scheme amplifies a
quantum sensor response to weak external fields by exploiting its coupling to
spin impurities in the environment. We analyze the limits to the sensitivity
due to decoherence and propose dynamical decoupling schemes to increase the
spin coherence time. The sensitivity is also limited by the environment spin
polarization; therefore we discuss strategies to polarize the environment spins
and present a method to extend the scheme to the case of zero polarization. The
coherence time and polarization determine a figure of merit for the
environment's ability to enhance the sensitivity compared to echo-based sensing
schemes. This figure of merit can be used to engineer optimized samples for
high-sensitivity nanoscale magnetic sensing, such as diamond nanocrystals with
controlled impurity density.Comment: 9 pages, 6 figure
Persuasive Technology for Learning and Teaching – The EuroPLOT Project
The concept of persuasive design has demonstrated its benefits by changing human behavior in certain situations, but in the area of education and learning, this approach has rarely been used. To change this and to study the feasibility of persuasive technology in teaching and learning, the EuroPLOT project (PLOT = Persuasive Learning Objects and Technologies) has been funded 2010-2013 by the Education, Audiovisual and Culture Executive Agency (EACEA) in the Life-long Learning (LLL) programme. In this program two tools have been developed (PLOTMaker and PLOTLearner) which allow to create learning objects with inherently persuasive concepts embedded. These tools and the learning objects have been evaluated in four case studies: language learning (Ancient Hebrew), museum learning (Kaj Munk Museum, Denmark), chemical handling, and academic Business Computing. These case studies cover a wide range of different learning styles and learning groups, and the results obtained through the evaluation of these case studies show the wide range of success of persuasive learning. They also indicate the limitations and areas where improvements are required
Mesoscopic Cavity Quantum Electrodynamics with Quantum Dots
We describe an electrodynamic mechanism for coherent, quantum mechanical
coupling between spacially separated quantum dots on a microchip. The technique
is based on capacitive interactions between the electron charge and a
superconducting transmission line resonator, and is closely related to atomic
cavity quantum electrodynamics. We investigate several potential applications
of this technique which have varying degrees of complexity. In particular, we
demonstrate that this mechanism allows design and investigation of an on-chip
double-dot microscopic maser. Moreover, the interaction may be extended to
couple spatially separated electron spin states while only virtually populating
fast-decaying superpositions of charge states. This represents an effective,
controllable long-range interaction, which may facilitate implementation of
quantum information processing with electron spin qubits and potentially allow
coupling to other quantum systems such as atomic or superconducting qubits.Comment: 8 pages, 5 figure
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