Electric-dipole-induced spin resonance in a lateral double quantum dot incorporating two single domain nanomagnets

On-chip magnets can be used to implement relatively large local magnetic field gradients in na- noelectronic circuits. Such field gradients provide possibilities for all-electrical control of electron spin-qubits where important coupling constants depend crucially on the detailed field distribution. We present a double quantum dot (QD) hybrid device laterally defined in a GaAs / AlGaAs het- erostructure which incorporates two single domain nanomagnets. They have appreciably different coercive fields which allows us to realize four distinct configurations of the local inhomogeneous field distribution. We perform dc transport spectroscopy in the Pauli-spin blockade regime as well as electric-dipole-induced spin resonance (EDSR) measurements to explore our hybrid nanodevice. Characterizing the two nanomagnets we find excellent agreement with numerical simulations. By comparing the EDSR measurements with a second double QD incorporating just one nanomagnet we reveal an important advantage of having one magnet per QD: It facilitates strong field gradients in each QD and allows to control the electron spins individually for instance in an EDSR experi- ment. With just one single domain nanomagnet and common QD geometries EDSR can likely be performed only in one QD

Controlled DNA compaction within chromatin: the tail-bridging effect

We study the mechanism underlying the attraction between nucleosomes, the fundamental packaging units of DNA inside the chromatin complex. We introduce a simple model of the nucleosome, the eight-tail colloid, consisting of a charged sphere with eight oppositely charged, flexible, grafted chains that represent the terminal histone tails. We demonstrate that our complexes are attracted via the formation of chain bridges and that this attraction can be tuned by changing the fraction of charged monomers on the tails. This suggests a physical mechanism of chromatin compaction where the degree of DNA condensation can be controlled via biochemical means, namely the acetylation and deacetylation of lysines in the histone tails.Comment: 4 pages, 5 figures, submitte

Landau-Zener interference at bichromatic driving

We investigate experimentally and theoretically the interference at avoided crossings which are repeatedly traversed as a consequence of an applied ac field. Our model system is a charge qubit in a serial double quantum dot connected to two leads. Our focus lies on effects caused by simultaneous driving with two different frequencies. We work out how the commensurability of the driving frequencies affects the symmetry of the interference patterns both in real space and in Fourier space. For commensurable frequencies, the symmetry depends sensitively on the relative phase between the two modes, whereas for incommensurable frequencies the symmetry of monochromatic driving is always recovered

Anderson impurity model in nonequilibrium: analytical results versus quantum Monte Carlo data

We analyze the spectral function of the single-impurity two-terminal Anderson model at finite voltage using the recently developed diagrammatic quantum Monte Carlo technique as well as perturbation theory. In the (particle-hole-)symmetric case we find an excellent agreement of the numerical data with the perturbative results of second order up to interaction strengths $U/\Gamma \approx 2$, where $\Gamma$ is the transparency of the impurity-electrode interface. The analytical results are obtained in form of the nonequilibrium self-energy for which we present explicit formulas in the closed form at arbitrary bias voltage. We observe an increase of the spectral density around zero energy brought about by the Kondo effect. Our analysis suggests that a finite applied voltage $V$ acts as an effective temperature of the system. We conclude that at voltages significantly larger than the equilibrium Kondo temperature there is a complete suppression of the Kondo effect and no resonance splitting can be observed. We confirm this scenario by comparison of the numerical data with the perturbative results.Comment: 8 pages, 6 figure

Wilson chains are not thermal reservoirs

Wilson chains, based on a logarithmic discretization of a continuous spectrum, are widely used to model an electronic (or bosonic) bath for Kondo spins and other quantum impurities within the numerical renormalization group method and other numerical approaches. In this short note we point out that Wilson chains can not serve as thermal reservoirs as their temperature changes by a number of order Delta E when a finite amount of energy Delta E is added. This proves that for a large class of non-equilibrium problems they cannot be used to predict the long-time behavior.Comment: 2 page

Heisenberg's Uncertainty Relation and Bell Inequalities in High Energy Physics

An effective formalism is developed to handle decaying two-state systems. Herewith, observables of such systems can be described by a single operator in the Heisenberg picture. This allows for using the usual framework in quantum information theory and, hence, to enlighten the quantum feature of such systems compared to non-decaying systems. We apply it to systems in high energy physics, i.e. to oscillating meson-antimeson systems. In particular, we discuss the entropic Heisenberg uncertainty relation for observables measured at different times at accelerator facilities including the effect of CP violation, i.e. the imbalance of matter and antimatter. An operator-form of Bell inequalities for systems in high energy physics is presented, i.e. a Bell-witness operator, which allows for simple analysis of unstable systems.Comment: 17 page

Centrality Dependence of Charged Particle Multiplicity in Au-Au Collisions at sqrt(s_NN)=130 GeV

We present results for the charged-particle multiplicity distribution at mid-rapidity in Au - Au collisions at sqrt(s_NN)=130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find $dN_{ch}/d\eta_{|\eta=0} = 622 \pm 1 (stat) \pm 41 (syst)$. The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.Comment: 307 authors, 43 institutions, 6 pages, 4 figures, 1 table Minor changes to figure labels and text to meet PRL requirements. One author added: M. Hibino of Waseda Universit

Mid-Rapidity Direct-Photon Production in p+p Collisions at sqrt(s) = 200 GeV

A measurement of direct photons in p+p collisions at sqrt(s)=200 GeV is presented. A photon excess above background from pi^0 --> gamma+gamma, eta --> gamma+gamma, and other decays is observed in the transverse momentum range 5.5 < p_T < 7 GeV/c. The result is compared to a next-to-leading-order perturbative QCD calculation. Within errors, good agreement is found between the QCD calculation and the measured result.Comment: 330 authors, 7 pages text, RevTeX, 2 figures, 2 tables. Submitted to Physical Review D. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm

Suppressed pi^0 Production at Large Transverse Momentum in Central Au+Au Collisions at sqrt(s_NN) = 200 GeV

Transverse momentum spectra of neutral pions in the range 1 < p_T < 10 GeV/c have been measured at mid-rapidity by the PHENIX experiment at RHIC in Au+Au collisions at sqrt(s_NN) = 200 GeV. The pi^0 multiplicity in central reactions is significantly below the yields measured at the same sqrt(s_NN) in peripheral Au+Au and p+p reactions scaled by the number of nucleon-nucleon collisions. For the most central bin, the suppression factor is ~2.5 at p_T = 2 GeV/c and increases to ~4-5 at p_T ~= 4 GeV/c. At larger p_T, the suppression remains constant within errors. The deficit is already apparent in semi-peripheral reactions and increases smoothly with centrality.Comment: 326 authors, 6 pages text, RevTeX, 3 figures, 2 tables. Submitted to PRL. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm

A Detailed Study of High-pT Neutral Pion Suppression and Azimuthal Anisotropy in Au+Au Collisions at \sqrt{s_{NN}} = 200 GeV

Measurements of neutral pion production at midrapidity in sqrt(s_NN) = 200 GeV Au+Au collisions as a function of transverse momentum, p_T, collision centrality, and angle with respect to reaction plane are presented. The data represent the final pi^0 results from the PHENIX experiment for the first RHIC Au+Au run at design center-of-mass-energy. They include additional data obtained using the PHENIX Level-2 trigger with more than a factor of three increase in statistics over previously published results for p_T > 6 GeV/c. We evaluate the suppression in the yield of high-p_T pi^0's relative to point-like scaling expectations using the nuclear modification factor R_AA. We present the p_T dependence of R_AA for nine bins in collision centrality. We separately integrate R_AA over larger p_T bins to show more precisely the centrality dependence of the high-p_T suppression. We then evaluate the dependence of the high-p_T suppression on the emission angle \Delta\phi of the pions with respect to event reaction plane for 7 bins in collision centrality. We show that the yields of high-p_T pi^0's vary strongly with \Delta\phi, consistent with prior measurements. We show that this variation persists in the most peripheral bin accessible in this analysis. For the peripheral bins we observe no suppression for neutral pions produced aligned with the reaction plane while the yield of pi^0's produced perpendicular to the reaction plane is suppressed by more than a factor of 2. We analyze the combined centrality and \Delta\phi dependence of the pi^0 suppression in different p_T bins using different possible descriptions of parton energy loss dependence on jet path-length averages to determine whether a single geometric picture can explain the observed suppression pattern.Comment: 330 authors, pages text, RevTeX4, figures, tables. Submitted to Physical Review C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm