A serial triple quantum dot ͑TQD͒ electrostatically defined in a GaAs/ AlGaAs heterostructure is characterized by using a nearby quantum point contact as charge detector. Ground-state stability diagrams demonstrate control in the regime of few electrons charging the TQD. An electrostatic model is developed to determine the ground-state charge configurations of the TQD. Numerical calculations are compared with experimental results. In addition, the tunneling conductance through all three quantum dots in series is studied. Quantum cellular automata processes are identified, which are where charge reconfiguration between two dots occurs in response to the addition of an electron in the third dot.

Charge detection utilizing a highly biased quantum point contact has become the most effective probe for studying few electron quantum dot circuits. Measurements on double and triple quantum dot circuits is performed to clarify a back action role of charge sensing on the confined electrons. The quantum point contact triggers inelastic transitions, which occur quite generally. Under specific device and measurement conditions these transitions manifest themselves as bounded regimes of telegraph noise within a stability diagram. A nonequilibrium transition from artificial atomic to molecular behavior is identified. Consequences for quantum information applications are discussed.

The paper describes the commissioning of the experimental equipment and the machine studies required for the first spin-filtering experiment with protons at a beam kinetic energy of 49.3MeV in COSY. The implementation of a low-β insertion made it possible to achieve beam lifetimes of τb=8000s in the presence of a dense polarized hydrogen storage-cell target of areal density dt=(5.5±0.2)×1013atoms/cm2. The developed techniques can be directly applied to antiproton machines and allow for the determination of the spin-dependent p¯p cross sections via spin filtering

The differential cross section for proton-proton elastic scattering has been measured at a beam energy of 1.0 GeV and in 200 MeV steps from 1.6 to 2.8 GeV for centre-of-mass angles in the range from 12 • -16 • to 25 • -30 • , depending on the energy. Absolute normalisations of typically 3% were achieved by studying the energy losses of the circulating beam of the COSY storage ring as it passed repeatedly through the windowless hydrogen target of the ANKE magnetic spectrometer. It is shown that the data have a significant impact upon a partial wave analysis. After extrapolating the differential cross sections to the forward direction, the results are broadly compatible with the predictions of forward dispersion relations.

We present transport measurements of the Kondo effect in a double quantum dot charged with only one or two electrons, respectively. For the one electron case we observe a surprising quasiperiodic oscillation of the Kondo conductance as a function of a small perpendicular magnetic field |B ⊥ | 50 mT. We discuss possible explanations of this effect and interpret it by means of a fine tuning of the energy mismatch of the single dot levels of the two quantum dots. The observed degree of control implies important consequences for applications in quantum information processing. PACS numbers: 72.15.Qm, 73.21.La 73.23.Hk,The Kondo effect describes a bound state formed by interactions between a localized magnetic impurity and itinerant conduction band electrons shielding the localized spin. This results in an increased density of localized states at the Fermi energy, causing anomalous low temperature properties. In case of a degenerate ground state of a quantum dot (QD), the Kondo effect manifests itself as an enhanced conductance within the Coulomb blockade region [1,2,3]. This was first observed on large QDs with half integer spin [4,5], and later, for a total spin of S = 1, where the triplet states of a QD are degenerate [6,7,8]. On a double quantum dot (DQD) a two-impurity Kondo effect was studied [9].In this article we present the results of Kondo effect differential conductance (KDC) measurements on a DQD charged with one or two electrons in a perpendicular magnetic field B ⊥ . For only one electron (N = 1) in the DQD we observe a quasi-periodic structure of the KDC with a characteristic scale of B 0 ∼ 10 mT. In contrast for N = 2 the KDC is found to be a monotonic function of B ⊥ . We discuss possible explanations for this effect that imply consequences in quantum information processing.Our sample is fabricated from an AlGaAs/GaAs heterostructure. It embeds a two-dimensional electron system (2DES) with carrier density n s ≃ 1.8 × 10 15 m −2 and electron mobility µ ≃ 75 m 2 /Vs (at T = 4.2 K) 120 nm below its surface. Figure 1(b) shows Ti/Au-gates created by electron beam lithography. They are used to locally deplete the 2DES to define a one electron QD. The gate design is optimized for transport measurements through a QD charged by only few electrons [10]. By decreasing the voltages applied to gates g C and g X (with respect to the 2DES) while increasing the voltages on the side gates g L and g R we deform the QD into a DQD (sketched in Fig. 1(b)) [11,12]. The DQD is tuned to the regime of strong coupling to the leads and an order of magnitude stronger interdot tunnel coupling of 2t 0 ≃ 240 µeV between the adjacent QDs [11]. Measurements are performed in a dilution refrigerator at an electron temperature T 2DES ∼ 0.1 K.A nearby quantum point contact (QPC) is used to detect the charge distribution of the DQD shown in the stability diagram in Fig. 1(a) [13]. It displays a lock-in measurement of the differential transconductance G QPC = dI QPC /dU gL as a function of the dc voltages applied to gates g L and g R . In t...