8,665 research outputs found
Stability and structure of two coupled boson systems in an external field
The lowest adiabatic potential expressed in hyperspherical coordinates is
estimated for two boson systems in an external harmonic trap. Corresponding
conditions for stability are investigated and the related structures are
extracted for zero-range interactions. Strong repulsion between non-identical
particles leads to two new features, respectively when identical particles
attract or repel each other. For repulsion new stable structures arise with
displaced center of masses. For attraction the mean-field stability region is
restricted due to motion of the center of masses
Steady state entanglement of two superconducting qubits engineered by dissipation
We present a scheme for the dissipative preparation of an entangled steady
state of two superconducting qubits in a circuit QED setup. Combining resonator
photon loss, a dissipative process already present in the setup, with an
effective two-photon microwave drive, we engineer an effective decay mechanism
which prepares a maximally entangled state of the two qubits. This state is
then maintained as the steady state of the driven, dissipative evolution. The
performance of the dissipative state preparation protocol is studied
analytically and verified numerically. In view of the experimental
implementation of the presented scheme we investigate the effects of potential
experimental imperfections and show that our scheme is robust to small
deviations in the parameters. We find that high fidelities with the target
state can be achieved both with state-of-the-art 3D, as well as with the more
commonly used 2D transmons. The promising results of our study thus open a
route for the demonstration of an entangled steady state in circuit QED.Comment: 12 pages, 5 figures; close to published versio
Højværdiafgrøder løser problemer
Flerårige højværdiafgrøder skal levere højkvalitetsprotein og biomasse til energi og samtidig håndtere udfasning af konventionel husdyrgødning, løse ukrudtsproblemer og løfte biodiversiteten i det økologiske planteavlssædskifte
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
Kondo physics in tunable semiconductor nanowire quantum dots
We have observed the Kondo effect in strongly coupled semiconducting nanowire
quantum dots. The devices are made from indium arsenide nanowires, grown by
molecular beam epitaxy, and contacted by titanium leads. The device
transparency can be tuned by changing the potential on a gate electrode, and
for increasing transparencies the effects dominating the transport changes from
Coulomb Blockade to Universal Conductance Fluctuations with Kondo physics
appearing in the intermediate region.Comment: 4 pages, 4 figure
Bogoliubov theory of entanglement in a Bose-Einstein condensate
We consider a Bose-Einstein condensate which is illuminated by a short
resonant light pulse that coherently couples two internal states of the atoms.
We show that the subsequent time evolution prepares the atoms in an interesting
entangled state called a spin squeezed state. This evolution is analysed in
detail by developing a Bogoliubov theory which describes the entanglement of
the atoms. Our calculation is a consistent expansion in , where
is the number of particles in the condensate, and our theory predict that it is
possible to produce spin squeezing by at least a factor of . Within
the Bogoliubov approximation this result is independent of temperature.Comment: 14 pages, including 5 figures, minor changes in the presentatio
Using superlattice potentials to probe long-range magnetic correlations in optical lattices
In Pedersen et al. (2011) we proposed a method to utilize a temporally
dependent superlattice potential to mediate spin-selective transport, and
thereby probe long and short range magnetic correlations in optical lattices.
Specifically this can be used for detecting antiferromagnetic ordering in
repulsive fermionic optical lattice systems, but more generally it can serve as
a means of directly probing correlations among the atoms by measuring the mean
value of an observable, the number of double occupied sites. Here, we provide a
detailed investigation of the physical processes which limit the effectiveness
of this "conveyer belt method". Furthermore we propose a simple ways to improve
the procedure, resulting in an essentially perfect (error-free) probing of the
magnetic correlations. These results shows that suitably constructed
superlattices constitute a promising way of manipulating atoms of different
spin species as well as probing their interactions.Comment: 12 pages, 9 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
Effect of grazing white clover pasture on milk composition of Holstein and Jersey cows
Because of its high saturated fatty acid (FA) content milk fat is considered hypercholesterolemic. Intake of unsaturated FA (UFA) reduces the plasma cholesterol concentrations. Especially conjugated linoleic acids (CLA) have shown positive effects on cardiovascular diseases, prevention of cancer and obesity. The aim of our project is to investigate how grazing can enhance the content of these beneficiary FA in milk. For bith types of cow races we observed no direct effect of increased grazing in the diet on the short chain FA (SCFA) content in milk, implying that the de novo synthesis of these FA remained unaffected. Regarding the content of CLA c9,t11 there was a strong positive effect on Holstein milk (R2 = 0,88), but almost none on Jersey milk when the percentage of grazing increases in the diet, thus suggesting that the mammary gland D9-desaturase acitivities of these two cow races react differently to increasing pasture grazing
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