We investigate coherent time evolution of charge states (pseudospin qubit) in a semiconductor double quantum dot. This fully tunable qubit is manipulated with high-speed voltage pulse that controls the energy and decoherence system. Coherent oscillations are observed for several combinations many-body ground excited dots. Possible mechanisms present device also discussed.

A bidirectional single-electron counting device is demonstrated. Individual electrons flowing in forward and reverse directions through a double quantum dot are detected with point contact acting as charge sensor. comprehensive statistical analysis the frequency time domains of higher order moments noise reveals antibunching correlation transport itself. The can also be used to investigate current flow attoampere range, which cannot measured by existing meters.

Using scanning tunneling spectroscopy in an ultrahigh vacuum at low temperature (T=0.3 K) and high magnetic fields (B<or=12 T), we directly probe electronic wave functions across integer quantum Hall transition. In accordance with theoretical predictions, observe the evolution from localized drift states insulating phases to branched extended critical point. The observed microscopic behavior close state indicates points of tunneling, which are considered be decisive for a quantitative description

A method is proposed for obtaining the spectrum noise that causes phase decoherence of a qubit directly from experimentally available data. The based on simple relationship between and coherence time in presence π pulse sequence. found to hold every system interacting with classical-noise, bosonic, spin baths.

We study interactions between electrons and nuclear spins by using the resistance ( Rxx) peak which develops near Landau-level filling factor nu = 2/3 as a probe. Temporarily tuning to different value, nu(temp), with gate demonstrates that Rxx regenerates even after complete depletion nu(temp) 0), while it rapidly relaxes on either side of 1. This indicates domain morphology is memorized can be depolarized Skyrmions. An additional enhancement in spin relaxation around 1/2 3/2 suggests Fermi...

The valley splitting, which lifts the degeneracy of lowest two states in a SiO(2)/Si(100)/SiO(2) quantum well, is examined through transport measurements. We demonstrate that splitting can be observed directly as step conductance defining boundary between valley-unpolarized and -polarized regions. This persists to well above liquid helium temperature shows no dependence on magnetic field, indicating single-particle polarization exist (100) silicon even at zero field.

Single-electron tunneling through a quantum dot is detected by means of radio-frequency single-electron transistor. Poisson statistics events are observed from frequency domain measurements, and individual in the time-domain measurements. Counting gives an accurate current measurement saturated regime, where electrons tunnel into only one electrode out to other electrode.

We present measurements of resonant tunneling through discrete energy levels a silicon double quantum dot formed in thin silicon-on-insulator layer. In the absence piezoelectric phonon coupling, spontaneous emission with deformation-potential coupling accounts for inelastic ground states two dots. Such transport enable us to observe Pauli spin blockade due effective two-electron spin-triplet correlations, evident distinct bias-polarity dependence states. The is lifted by excited-state...

A quantum-well wire was fabricated with use of local intermixing a GaAs-${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As single-quantum-well epitaxial layer induced by Ga focused-ion-beam implantation. Fine structures were observed in low temperature photoluminescence and excitation spectra. These fine are explained the density states specific to two-dimensionally confined carrier system.

The local density of states (LDOS) at the epitaxially grown InAs surface on a GaAs(111) A substrate were characterized using low-temperature scanning tunneling microscopy. Using dI/dV signal mapping, LDOS standing waves clearly imaged point defects and within nanostructures. Measurement wavelength as function bias voltage showed nonparabolic dispersion relation for conduction band. observed wave features originate from Friedel oscillations two-dimensional electron gas in semiconductor...

Lateral dimensions of ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs double-barrier diodes were restricted by use focused Ga ion-beam implantation. The diode with a lateral dimension exhibited series resonant-tunneling current peaks corresponding to the laterally confined one-dimensional levels superimposed on ground state heterojunctions. resonant more pronounced in smaller and consequently stronger confinement. spectral feature suggests mixing even-...

Transient current spectroscopy is proposed and demonstrated in order to investigate the energy relaxation inside a quantum dot Coulomb blockade regime. We employ fast pulse signal excite an AlGaAs/GaAs excited state, analyze non-equilibrium transient as function of length. The amplitude time-constant are sensitive ground spin states. find that time longer than, at least, few microsecond.

The interdiffusion coefficients of Ga and Al were measured for GaAs-AlAs superlattices ion-implanted with Be, B, F, Si, Ar As. degree enhancement was in the order Si&gt;F&gt;As&gt;B no effects observed Be Ar. Except impurities large diffusion have a tendency to enhance impurity-induced compositional disordering.

We observed negative Coulomb drag for parallel coupled quantum wires, in which electrons flow the opposite directions between wires. This only occurred under conditions of strong correlation that is, low density, high magnetic field, and temperature, cannot be addressed by a standard theory momentum transfer. propose model formation Wigner crystal state wire particle-like drive is taken into account.

Using a focused ion beam technology, Ga is implanted into GaAs-Al x 1- As superlattice epitaxial wafer. The compositional disordering of the occurs during an annealing after ion-implantation. Interdiffusion coefficient and Al measured from photoluminescence peak energy shift as function time result shows that it large for Si superlattice. By line-and-space scan beam, submicron periodic structure mixed crystal fabricated over epi-wafer examined by low temperature cathodo-luminescence topography.

We investigate background charge fluctuation in a GaAs quantum dot device by measuring 1/f noise the single-electron tunneling current through dot. The is understood as fluctuations of confinement potential and barriers. estimated increases almost linearly with temperature, which consistent simple model noise. find that very slightly when electrons are injected into excited states

Radio-frequency (rf)-operated single-electron transistors (SETs) are high-sensitivity, fast-response electrometers, which valuable for developing new insights into single-charge dynamics. We investigate high-frequency (up to 1 MHz) charge noise in an AlGaAs/GaAs quantum dot using a transmission-type rf SET technique. The electron capture and emission kinetics on trap the vicinity of dominated by Poisson process. maximum bandwidth measuring single trapping events is about MHz, same as that...

We study charge excitations in quantum Hall ferromagnets realized a symmetric well. Landau levels (LLs) with different subband and orbital indices crossing at the Fermi level act as up down pseudospin levels. The activation energy measured function of Zeeman energy, Delta(Z), reveals easy-plane easy-axis ferromagnetism for LL filling nu = 3 4, respectively, which have parallel antiparallel spin. For we observe sharp reduction gap Delta(Z)-->0, discuss terms topological excitation domain...

Very short and narrow channels are fabricated by use of focused-ion-beam implantation into a ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As/GaAs modulation-doped epilayer. The constricted highly resistive Ga-implanted regions. electron transport experiments exhibited prominent quantization conductance characteristics, which is peculiar to ballistic through one-dimensional subbands. These quantized characteristics observed until the temperature raised...

Heteroepitaxy of high-quality InSb films was performed directly on GaAs surfaces by using molecular beam epitaxy. Despite the 14.6% lattice mismatch, two-dimensionally grown GaAs(111)A substrates were obtained from initial stage, but not (001) substrates. A conductive layer formed early stage growth (111)A surface, and mobilities carrier concentrations suggested a low defect density due to confinement dislocations interface.

We investigate nonequilibrium transport in the absence of spin-flip energy relaxation a few-electron quantum dot artificial atom. Novel tunneling processes involving high-spin states, which cannot be excited from ground state because spin blockade, and other more than two charge states are observed. These explained by orthodox Coulomb blockade theory. The effective induces considerable fluctuation spin, charge, total dot. Although these features revealed clearly pulse excitation...

We review electrical pulse experiments carried out to probe inelastic energy relaxation processes and related non-equilibrium transport characteristics of quantum dots (QDs) in the Coulomb blockade (CB) regime. In contrast relatively short momentum time (∼10 ns) that can be understood on basis acoustic phonon emission, spin-flip is found extremely long (∼200 µs). The spin process our QDs actually dominated by a cotunnelling process, thus intrinsic should have longer time. discussed terms...