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 $1/\sqrt{N}$, where $N$ 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 $1/\sqrt{N}$. 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