457 research outputs found
Experimental quantum information processing with 43Ca+ ions
For quantum information processing (QIP) with trapped ions, the isotope 43Ca+
offers the combined advantages of a quantum memory with long coherence time, a
high fidelity read out and the possibility of performing two qubit gates on a
quadrupole transition with a narrow-band laser. Compared to other ions used for
quantum computing, 43Ca+ has a relatively complicated level structure. In this
paper we discuss how to meet the basic requirements for QIP and demonstrate
ground state cooling, robust state initialization and efficient read out for
the hyperfine qubit with a single 43Ca+ ion. A microwave field and a Raman
light field are used to drive qubit transitions, and the coherence times for
both fields are compared. Phase errors due to interferometric instabilities in
the Raman field generation do not limit the experiments on a time scale of 100
ms. We find a quantum information storage time of many seconds for the
hyperfine qubit.Comment: 9 pages, 10 figure
Measurement of the hyperfine structure of the S1/2-D5/2 transition in 43Ca+
The hyperfine structure of the S1/2-D5/2 quadrupole transition at 729 nm in
43Ca+ has been investigated by laser spectroscopy using a single trapped 43Ca+
ion. We determine the hyperfine structure constants of the metastable level as
A=-3.8931(2) MHz and B=-4.241(4) MHz. The isotope shift of the transition with
respect to 40Ca+ was measured to be 4134.713(5) MHz. We demonstrate the
existence of transitions that become independent of the first-order Zeeman
shift at non-zero low magnetic fields. These transitions might be better suited
for building a frequency standard than the well-known 'clock transitions'
between m=0 levels at zero magnetic field.Comment: corrected for sign errors in the hyperfine constants. No corrections
to were made to the data analysi
Characterization of low loss microstrip resonators as a building block for circuit QED in a 3D waveguide
Here we present the microwave characterization of microstrip resonators made
from aluminum and niobium inside a 3D microwave waveguide. In the low
temperature, low power limit internal quality factors of up to one million were
reached. We found a good agreement to models predicting conductive losses and
losses to two level systems for increasing temperature. The setup presented
here is appealing for testing materials and structures, as it is free of wire
bonds and offers a well controlled microwave environment. In combination with
transmon qubits, these resonators serve as a building block for a novel circuit
QED architecture inside a rectangular waveguide
Quantum communication between trapped ions through a dissipative environment
We study two trapped ions coupled to the axial phonon modes of a
one-dimensional Coulomb crystal. This system is formally equivalent to the "two
spin-boson" model. We propose a scheme to dynamically generate a maximally
entangled state of two ions within a decoherence-free subspace. Here the
phononic environment of the trapped ions, whatever its temperature and number
of modes, serves as the entangling bus. The efficient production of the pure
singlet state can be exploited to perform short-ranged quantum communication
which is essential in building up a large-scale quantum computer.Comment: 4 pages, 2 figure
Entangled states of trapped ions allow measuring the magnetic field gradient of a single atomic spin
Using trapped ions in an entangled state we propose detecting a magnetic
dipole of a single atom at distance of a few m. This requires a
measurement of the magnetic field gradient at a level of about 10
Tesla/m. We discuss applications e.g. in determining a wide variation of
ionic magnetic moments, for investigating the magnetic substructure of ions
with a level structure not accessible for optical cooling and detection,and for
studying exotic or rare ions, and molecular ions. The scheme may also be used
for measureing spin imbalances of neutral atoms or atomic ensembles trapped by
optical dipole forces. As the proposed method relies on techniques well
established in ion trap quantum information processing it is within reach of
current technology.Comment: 4 pages, 2 fi
Entanglement at the quantum phase transition in a harmonic lattice
The entanglement properties of the phase transition in a two dimensional
harmonic lattice, similar to the one observed in recent ion trap experiments,
are discussed both, for finite number of particles and thermodynamical limit.
We show that for the ground state at the critical value of the trapping
potential two entanglement measures, the negativity between two neighbouring
sites and the block entropy for blocks of size 1, 2 and 3, change abruptly.
Entanglement thus indicates quantum phase transitions in general; not only in
the finite dimensional case considered in [Phys. Rev. Lett. {\bf 93}, 250404
(2004)]. Finally, we consider the thermal state and compare its exact
entanglement with a temperature entanglement witness introduced in [Phys. Rev.
A {\bf 77} 062102 (2008)].Comment: extended published versio
First record of a plasmodiophorid parasite in grapevine
In the context of an interdisciplinary project on grape pests and pathogens in Rheingau (Germany), the fine root system of grafted rootstocks has been screened for pathogenic fungi associated with root galls induced by grape phylloxera (Daktulosphaira vitifoliae (Fitch)). In several insect-induced galls, masses of resting spores of a plasmodiophorid could be seen. An additional selective screening revealed the occurrence of the plasmodiophorid parasite also in samples of gall-free rootlets: cortical cells of small necrotic areas were crowded with resting spores or other developmental stages of its life cycle. According to current taxonomic concepts, this plasmodiophorid could be identified as a member of the genus Sorosphaera Schroeter, resembling S. veronicae Schroeter. This is the first record of a plasmodiophorid parasite in grapevine
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