Tunable few electron quantum dots in InAs nanowires

Quantum dots realized in InAs are versatile systems to study the effect of spin-orbit interaction on the spin coherence, as well as the possibility to manipulate single spins using an electric field. We present transport measurements on quantum dots realized in InAs nanowires. Lithographically defined top-gates are used to locally deplete the nanowire and to form tunneling barriers. By using three gates, we can form either single quantum dots, or two quantum dots in series along the nanowire. Measurements of the stability diagrams for both cases show that this method is suitable for producing high quality quantum dots in InAs.Comment: 8 pages, 4 figure

Experimental set-up for detecting blood pressure, heart rate, and lymphocyte redistribution in the running rat

An experimental set--up for detecting lymphocyte redistribution blood pressureand heart rate in the running rat is presented.The design is based 011 caterisation of the carotid anery which previously has been described. The design offers direct access to the blood stream making it possible to examine different cells and biochemical parameters.Furthermore, eontinnusly monitorering of blood pressure and heart rate both at rest and during exercise is described

Magnetic excitations in coupled Haldane spin chains near the quantum critical point

Two quasi-1-dimensional S=1 quantum antiferromagnetic materials, PbNi2V2O8 and SrNi2V2O8, are studied by inelastic neutron scattering on powder samples. While magnetic interactions in the two systems are found to be very similar, subtle differences in inter-chain interaction strengths and magnetic anisotropy are detected. The latter are shown to be responsible for qualitatively different ground state properties: magnetic long-range order in SrNi2V2O8 and disordered ``spin liquid'' Haldane-gap state in PbNi2V2O8.Comment: 15 figures, Figs. 5,9, and 10 in color. Some figures in JPEG format. Complete PostScript and PDF available from http://papillon.phy.bnl.gov/publicat.ht

Calorons, instantons and constituent monopoles in SU(3) lattice gauge theory

We analyze the zero-modes of the Dirac operator in quenched SU(3) gauge configurations at non-zero temperature and compare periodic and anti-periodic temporal boundary conditions for the fermions. It is demonstrated that for the different boundary conditions often the modes are localized at different space-time points and have different sizes. Our observations are consistent with patterns expected for Kraan - van Baal solutions of the classical Yang-Mills equations. These solutions consist of constituent monopoles and the zero-modes are localized on different constituents for different boundary conditions. Our findings indicate that the excitations of the QCD vacuum are more structured than simple instanton-like lumps.Comment: Remarks added. To appear in Phys. Rev.

Testing the self-duality of topological lumps in SU(3) lattice gauge theory

We discuss a simple formula which connects the field-strength tensor to a spectral sum over certain quadratic forms of the eigenvectors of the lattice Dirac operator. We analyze these terms for the near zero-modes and find that they give rise to contributions which are essentially either self-dual or anti self-dual. Modes with larger eigenvalues in the bulk of the spectrum are more dominated by quantum fluctuations and are less (anti) self-dual. In the high temperature phase of QCD we find considerably reduced (anti) self-duality for the modes near the edge of the spectral gap.Comment: Remarks added, to appear in Phys. Rev. Let

Electronic Structure of Atoms in Magnetic Quadrupole Traps

We investigate the electronic structure and properties of atoms exposed to a magnetic quadrupole field. The spin-spatial as well as generalized time reversal symmetries are established and shown to lead to a two-fold degeneracy of the electronic states in the presence of the field. Low-lying as well as highly excited Rydberg states are computed and analyzed for a broad regime of field gradients. The delicate interplay between the Coulomb and various magnetic interactions leads to complex patterns of the spatial spin polarization of individual excited states. Electromagnetic transitions in the quadrupole field are studied in detail thereby providing the selection rules and in particular the transition wavelengths and corresponding dipole strengths. The peculiar property that the quadrupole magnetic field induces permanent electric dipole moments of the atoms is derived and discussed.Comment: 17 pages, 13 figures, accepted for publication in PR

Locality and topology with fat link overlap actions

We study the locality and topological properties of fat link clover overlap (FCO) actions. We find that a small amount of fattening (2-4 steps of APE or 1 step of HYP) already results in greatly improved properties compared to the Wilson overlap (WO). We present a detailed study of the localisation of the FCO and its connection to the density of low modes of $A^\dagger A$. In contrast to the Wilson overlap, on quenched gauge backgrounds we do not find any dependence of the localization of the FCO on the gauge coupling. This suggests that the FCO remains local in the continuum limit. The FCO also faithfully reproduces the zero mode wave functions of typical lattice instantons, not like the Wilson overlap. After a general discussion of different lattice definitions of the topological charge we also show that the FCO together with the Boulder charge are likely to satisfy the index theorem in the continuum limit. Finally, we present a high statistics computation of the quenched topological susceptibility with the FCO action.Comment: 19 pages, LaTe

Numerical Study of the S=1S=1 Antiferrromagnetic Spin Chain with Bond Alternation

We study the $S=1$ quantum spin chain with bond alternation {\cal H}=\sum _i (1-(-1)^i\delta)\vect{S}_i\cdot \vect{S}_{i+1} by the density matrix renormalization group method recently proposed by Steven R. White (\PRL{69}{3844}{1993}). We find a massless point at $\delta _c =0.25 \pm 0.01$. We also find the edge states in the region $\delta <\delta_c$ under the open boundary condition, which disappear in the region $\delta >\delta _{c}$. At the massless point, the spin wave velocity $v_s$ is $3.66 \pm 0.10$ and the central charge $c$ is $1.0\pm 0.15$. Our results indicate that a continuous phase transition occurs at the massless point $\delta =\delta_c$ accompanying breaking of the hidden $Z_2\times Z_2$ symmetry.Comment: 9 pages and 1 PostScript figure, Revtex 3.0 (Minor corrections in TEX-file format to remove possible compilatory troubles.