Fano-Kondo interplay in a side-coupled double quantum dot

We investigate low-temperature transport characteristics of a side-coupled double quantum dot where only one of the dots is directly connected to the leads. We observe Fano resonances, which arise from interference between discrete levels in one dot and the Kondo effect, or cotunneling in general, in the other dot, playing the role of a continuum. The Kondo resonance is partially suppressed by destructive Fano interference, reflecting novel Fano-Kondo competition. We also present a theoretical calculation based on the tight-binding model with slave boson mean field approximation, which qualitatively reproduces the experimental findings.Comment: 4 pages, 4 figure

Time-resolved charge fractionalization in inhomogeneous Luttinger liquids

The recent observation of charge fractionalization in single Tomanga-Luttinger liquids (TLLs) [Kamata et al., Nature Nanotech., 9 177 (2014)] opens new routes for a systematic investigation of this exotic quantum phenomenon. In this Letter we perform measurements on two adjacent TLLs and put forward an accurate theoretical framework to address the experiments. The theory is based on the plasmon scattering approach and can deal with injected charge pulses of arbitrary shape in TLL regions. We accurately reproduce and interpret the time-resolved multiple fractionalization events in both single and double TLLs. The effect of inter-correlations between the two TLLs is also discussed.Comment: 5 pages + Supplementary Material. To appear in Phys. Rev. B: Rapid. Com

A gate-defined silicon quantum dot molecule

We report electron transport measurements of a silicon double dot formed in multi-gated metal-oxide-semiconductor structures with a 15-nm-thick silicon-on-insulator layer. Tunable tunnel coupling enables us to observe an excitation spectrum in weakly coupled dots and an energy level anticrossing in strongly coupled ones. Such a quantum dot molecule with both charge and energy quantization provides the essential prerequisite for future implementation of silicon-based quantum computations.Comment: 11pages,3figure

Relativistic Beaming and Flux Variability in Active Galactic Nuclei

We discuss the impact of special relativistic effects on the observed light curves and variability duty cycles of AGNs. We model the properties of AGN light curves at radio wavelengths using a simulated shot noise process in which the occurrence of major flaring events in a relativistic jet is governed by Poisson statistics. We show that flaring sources whose radiation is highly beamed toward us are able to reach very high flux levels, but will in fact spend most of their time in relatively low flaring states due to relativistic contraction of flare time scales in the observer frame. The fact that highly beamed AGNs do not return to a steady-state quiescent level between flares implies that their weakly beamed counterparts should have highly stable flux densities that result from a superposition of many long-term, low-amplitude flares. The ``apparent'' quiescent flux levels of these weakly beamed AGNs (identified in many unified models as radio galaxies) will be significantly higher than their ''true'' quiescent (i.e., non-flaring) levels. We use Monte Carlo simulations to investigate flux variability bias in the selection statistics of flat-spectrum AGN samples. In the case of the Caltech-Jodrell Flat-spectrum survey, the predicted orientation bias towards jets seen end-on is weakened if the parent population is variable, since the highly beamed sources have a stronger tendency to be found in low flaring states. This effect is small, however, since highly beamed sources are relatively rare, and their fluxes tend to be boosted sufficiently above the survey limit such that they are selected regardless of their flaring level. We find that for larger flat-spectrum AGN surveys with fainter flux cutoffs, variability should not be an appreciable source of selection bias.Comment: Accepted for publication in the Astrophysical Journa

Non-markovian dynamics of double quantum dot charge qubit with static bias

The dynamics of charge qubit in double quantum dot coupled to phonons is investigated theoretically. The static bias is considered. By means of the perturbation approach based on unitary transformations, the dynamical tunneling current is obtained explicitly. The biased system displays broken symmetry and a significantly larger coherence-incoherence transition critical point $\alpha _{c}$. We also analyzed the decoherence induced by piezoelectric coupling phonons in detail. The results show that reducing the coupling between system and bath make coherence frequency increase and coherence time prolong. To maintain quantum coherence, applying static bias also is a good means.Comment: 13 pages, 5 figure

Non-equilibrium transport through a vertical quantum dot in the absence of spin-flip energy relaxation

We investigate non-equilibrium transport in the absence of spin-flip energy relaxation in a few-electron quantum dot artificial atom. Novel non-equilibrium tunneling processes involving high-spin states which cannot be excited from the ground state because of spin-blockade, and other processes involving more than two charge states are observed. These processes cannot be explained by orthodox Coulomb blockade theory. The absence of effective spin relaxation induces considerable fluctuation of the spin, charge, and total energy of the quantum dot. Although these features are revealed clearly by pulse excitation measurements, they are also observed in conventional dc current characteristics of quantum dots.Comment: accepted for publication in Phys. Rev.Let

Coherent manipulation of electronic states in a double quantum dot

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

Pauli-Spin-Blockade Transport through a Silicon Double Quantum Dot

We present measurements of resonant tunneling through discrete energy levels of a silicon double quantum dot formed in a thin silicon-on-insulator layer. In the absence of piezoelectric phonon coupling, spontaneous phonon emission with deformation-potential coupling accounts for inelastic tunneling through the ground states of the two dots. Such transport measurements enable us to observe a Pauli spin blockade due to effective two-electron spin-triplet correlations, evident in a distinct bias-polarity dependence of resonant tunneling through the ground states. The blockade is lifted by the excited-state resonance by virtue of efficient phonon emission between the ground states. Our experiment demonstrates considerable potential for investigating silicon-based spin dynamics and spin-based quantum information processing.Comment: 10 pages,3 figure