arXiv subjects

H. Qin

Publications and source records attributed to H. Qin.

25 records · Page 2Linked to original sources

arXiv2013

The Hamiltonian structure and Euler-Poincaré formulation of the Vlasov-Maxwell and gyrokinetic systems

We present a new variational principle for the gyrokinetic system, similar to the Maxwell-Vlasov action presented in Ref. 1. The variational principle is in the Eulerian frame and based on constrained variations of the phase space fluid velocity and particle distribution function. Using a Legendre transform, we explicitly derive the field theoretic Hamiltonian structure of the system. This is carried out with a modified Dirac theory of constraints, which is used to construct meaningful brackets from those obtained directly from Euler-Poincaré theory. Possible applications of these formulations include continuum geometric integration techniques, large-eddy simulation models and Casimir type stability methods. [1] H. Cendra et. al., Journal of Mathematical Physics 39, 3138 (1998)

physics.plasm-ph↗

arXiv2012

Probing and modelling the localized self-mixing in a GaN/AlGaN field-effect terahertz detector

In a GaN/AlGaN field-effect terahertz detector, the directional photocurrent is mapped in the two-dimensional space of the gate voltage and the drain/source bias. It is found that not only the magnitude, but also the polarity, of the photocurrent can be tuned. A quasistatic self-mixing model taking into account the localized terahertz field provides a quantitative description of the detector characteristics. Strongly localized self-mixing is confirmed. It is therefore important to engineer the spatial distribution of the terahertz field and its coupling to the field-effect channel on the sub-micron scale.

cond-mat.mes-hall↗

arXiv2008

Physics at BES-III

This physics book provides detailed discussions on important topics in $τ$-charm physics that will be explored during the next few years at \bes3 . Both theoretical and experimental issues are covered, including extensive reviews of recent theoretical developments and experimental techniques. Among the subjects covered are: innovations in Partial Wave Analysis (PWA), theoretical and experimental techniques for Dalitz-plot analyses, analysis tools to extract absolute branching fractions and measurements of decay constants, form factors, and CP-violation and \DzDzb-oscillation parameters. Programs of QCD studies and near-threshold tau-lepton physics measurements are also discussed.

hep-ex↗

arXiv2002

Spin blockade in ground state resonance of a quantum dot

We present measurements on spin blockade in a laterally integrated quantum dot. The dot is tuned into the regime of strong Coulomb blockade, confining ~ 50 electrons. At certain electronic states we find an additional mechanism suppressing electron transport. This we identify as spin blockade at zero bias, possibly accompanied by a change in orbital momentum in subsequent dot ground states. We support this by probing the bias, magnetic field and temperature dependence of the transport spectrum. Weak violation of the blockade is modelled by detailed calculations of non-linear transport taking into account forbidden transitions.

cond-mat.mes-hall↗

arXiv2001

Superposition of photon- and phonon- assisted tunneling in coupled quantum dots

We report on electron transport through an artificial molecule formed by two tunnel coupled quantum dots, which are laterally confined in a two-dimensional electron system of an Al$_x$Ga$_{1-x}$As/GaAs heterostructure. Coherent molecular states in the coupled dots are probed by photon-assisted tunneling (PAT). Above 10 GHz, we observe clear PAT as a result of the resonance between the microwave photons and the molecular states. Below 8 GHz, a pronounced superposition of phonon- and photon-assisted tunneling is observed. Coherent superposition of molecular states persists under excitation of acoustic phonons.

cond-mat.mes-hall↗

arXiv2000

Determination of the complex microwave photoconductance of a single quantum dot

A small quantum dot containing approximately 20 electrons is realized in a two-dimensional electron system of an AlGaAs/GaAs heterostructure. Conventional transport and microwave spectroscopy reveal the dot's electronic structure. By applying a coherently coupled two-source technique, we are able to determine the complex microwave induced tunnel current. The amplitude of this photoconductance resolves photon-assisted tunneling (PAT) in the non-linear regime through the ground state and an excited state as well. The out-of-phase component (susceptance) allows to study charge relaxation within the quantum dot on a time scale comparable to the microwave beat period.

cond-mat.mes-hall↗

arXiv2000

Microwave spectroscopy on a double quantum dot with an on-chip Josephson oscillator

We present measurements on microwave spectroscopy on a double quantum dot with an on-chip microwave source. The quantum dots are realized in the two-dimensional electron gas of an AlGaAs/GaAs heterostructure and are weakly coupled in series by a tunnelling barrier forming an 'ionic' molecular state. We employ a Josephson oscillator formed by a long Nb/Al-AlO$_x$/Nb junction as a microwave source. We find photon-assisted tunnelling sidebands induced by the Josephson oscillator, and compare the results with those obtained using an externally operated microwave source.

cond-mat.mes-hall↗