Heavy Quark Physics From Lattice QCD

We review the application of lattice QCD to the phenomenology of b- and c-quarks. After a short discussion of the lattice techniques used to evaluate hadronic matrix elements and the corresponding systematic uncertainties, we summarise results for leptonic decay constants, B--Bbar mixing, semileptonic and rare radiative decays. A discussion of the determination of heavy quark effective theory parameters is followed by an explanation of the difficulty in applying lattice methods to exclusive nonleptonic decays.Comment: 52 pages LaTeX with 10 eps files. Requires: hfsprocl.sty (included) plus axodraw.sty, rotating.sty and array.sty. To appear in Heavy Flavours (2nd edition) edited by A J Buras and M Lindner (World Scientific, Singapore). Revised version corrects typo in axis labelling of Fig 1

Coulomb and Spin blockade of two few-electrons quantum dots in series in the co-tunneling regime

We present Coulomb Blockade measurements of two few-electron quantum dots in series which are configured such that the electrochemical potential of one of the two dots is aligned with spin-selective leads. The charge transfer through the system requires co-tunneling through the second dot which is $not$ in resonance with the leads. The observed amplitude modulation of the resulting current is found to reflect spin blockade events occurring through either of the two dots. We also confirm that charge redistribution events occurring in the off-resonance dot are detected indirectly via changes in the electrochemical potential of the aligned dot.Comment: 6 pages, 5 figures, submitted to Phys. Rev.

The influence of the long-lived quantum Hall potential on the characteristics of quantum devices

Novel hysteretic effects are reported in magneto-transport experiments on lateral quantum devices. The effects are characterized by two vastly different relaxation times (minutes and days). It is shown that the observed phenomena are related to long-lived eddy currents. This is confirmed by torsion-balance magnetometry measurements of the same 2-dimensional electron gas (2DEG) material. These observations show that the induced quantum Hall potential at the edges of the 2DEG reservoirs influences transport through the devices, and have important consequences for the magneto-transport of all lateral quantum devices.Comment: 5 pages, 4 figure

Suppression of compressible edge channels and spatial spin polarization in the integer quantum Hall regime

We perform systematic numerical studies of the structure of spin-resolved compressible strips in split-gate quantum wires taking into account the exchange and correlation interactions within the density functional theory in the local spin-density approximation. We find that for realistic parameters of the wire the exchange interaction can completely suppress the formation of the compressible strips. As the depletion length or magnetic field are increased, the compressible strips starts to form first for the spin-down and then for spin-up edge channels. We demonstrate that the widths of these strips plus the spatial separation between them caused by the exchange interaction are equal to the width of the compressible strip calculated in the Hartree approximation for spinless electrons. We also discuss the effect of electron density on the suppression of the compressible strips in quantum wires.Comment: 5 pages, 4 figures, submitted to Phys. Rev.

Non-Perturbative Renormalisation of the Lattice Δs=2\Delta s=2 Four-Fermion Operator

We compute the renormalised four-fermion operator $O^{\Delta S=2}$ using a non-perturbative method recently introduced for determining the renormalisation constants of generic lattice composite operators. Because of the presence of the Wilson term, $O^{\Delta S=2}$ mixes with operators of different chiralities. A projection method to determine the mixing coefficients is implemented. The numerical results for the renormalisation constants have been obtained from a simulation performed using the SW-Clover quark action, on a $16^3 \times 32$ lattice, at $\beta=6.0$. We show that the use of the constants determined non-perturbatively improves the chiral behaviour of the lattice kaon matrix element \_{\latt}.Comment: LaTeX, 16 pages, 2 postscript figure

Few-electron quantum dots in III-V ternary alloys: role of fluctuations

We study experimentally the electron transport properties of gated quantum dots formed in InGaAs/InP and InAsP/InP quantum well structures grown by chemical-beam epitaxy. For the case of the InGaAs quantum well, quantum dots form directly underneath narrow gate electrodes due to potential fluctuations. We measure the Coulomb-blockade diamonds in the few-electron regime of a single quantum dot and observe photon-assisted tunneling peaks under microwave irradiation. A singlet-triplet transition at high magnetic field and Coulomb-blockade effects in the quantum Hall regime are also observed. For the InAsP quantum well, an incidental triple quantum dot forms also due to potential fluctuations within a single dot layout. Tunable quadruple points are observed via transport measurements.Comment: 3.3 pages, 3 figures. Added two new subfigures, new references, and improved the tex

A Tuneable Few Electron Triple Quantum Dot

In this paper we report on a tuneable few electron lateral triple quantum dot design. The quantum dot potentials are arranged in series. The device is aimed at studies of triple quantum dot properties where knowing the exact number of electrons is important as well as quantum information applications involving electron spin qubits. We demonstrate tuning strategies for achieving required resonant conditions such as quadruple points where all three quantum dots are on resonance. We find that in such a device resonant conditions at specific configurations are accompanied by novel charge transfer behaviour.Comment: 11 pages, 4 figure

Tunable Negative Differential Resistance controlled by Spin Blockade in Single Electron Transistors

We demonstrate a tunable negative differential resistance controlled by spin blockade in single electron transistors. The single electron transistors containing a few electrons and spin polarized source and drain contacts were formed in GaAs/GaAlAs heterojunctions using metallic gates. Coulomb blockade measurements performed as a function of applied source-drain bias, electron number and magnetic field reveal well defined regimes where a decrease in the current is observed with increasing bias. We establish that the origin of the negative differential regime is the spin-polarized detection of electrons combined with a long spin relaxation time in the dot. These results indicate new functionalities that may be utilized in nano-spintronic devices in which the spin state is electro-statically controlled via the electron occupation number.Comment: 8 pages, 4 figure