Resonant Plasmon-Assisted Tunneling in a Double Quantum Dot Coupled to a Quantum Hall Plasmon Resonator.

Edge magnetoplasmon is an emergent chiral bosonic mode promising for studying electronic quantum optics. While the plasmon transport has been investigated with various techniques for decades, its coupling to a mesoscopic device remained unexplored. Here, we demonstrate the coupling between a single plasmon mode in a quantum Hall plasmon resonator and a double quantum dot (DQD).

Quantized charge fractionalization at quantum Hall Y junctions in the disorder dominated regime.

Fractionalization is a phenomenon where an elementary excitation partitions into several pieces. This picture explains non-trivial transport through a junction of one-dimensional edge channels defined by topologically distinct quantum Hall states, for example, a hole-conjugate state at Landau-level filling factor ν = 2/3. Here we employ a time-resolved scheme to identify an elementary fractionalization process; injection of charge q from a non-interaction region into an interacting and scattering region of one-dimensional channels results in the formation of a collective excitation with charge (1-r)q by reflecting fractionalized charge rq.

Electronic energy spectroscopy of monochromatic edge magnetoplasmons in the quantum Hall regime.

We investigate electronic excitation in a quantum Hall edge channel when a monochromatic plasmon wave is excited by applying a radio-frequency voltage to a long surface gate on an AlGaAs/GaAs heterostructure. A quantum-dot energy spectrometer is employed to evaluate the amplitude of the potential wave and possible electronic heating. The potential wave is analyzed with a capacitance model.

Signatures of a Nonthermal Metastable State in Copropagating Quantum Hall Edge Channels.

A Tomonaga-Luttinger (TL) liquid is known as an integrable system, in which a nonequilibrium many-body state survives without relaxing to a thermalized state. This intriguing characteristic is tested experimentally in copropagating quantum Hall edge channels at bulk filling factor ν=2. The unidirectional transport allows us to investigate the time evolution by measuring the spatial evolution of the electronic states.

Shot-noise evidence of fractional quasiparticle creation in a local fractional quantum Hall state.

We experimentally identify fractional quasiparticle creation in a tunneling process through a local fractional quantum Hall (FQH) state. The local FQH state is prepared in a low-density region near a quantum point contact in an integer quantum Hall (IQH) system. Shot-noise measurements reveal a clear transition from elementary-charge tunneling at low bias to fractional-charge tunneling at high bias.

Cross-correlation measurement of quantum shot noise using homemade transimpedance amplifiers.

We report a cross-correlation measurement system, based on a new approach, which can be used to measure shot noise in a mesoscopic conductor at milliKelvin temperatures. In contrast to other measurement systems in which high-speed low-noise voltage amplifiers are commonly used, our system employs homemade transimpedance amplifiers (TAs). The low input impedance of the TAs significantly reduces the crosstalk caused by unavoidable parasitic capacitance between wires.

Correlated coherent oscillations in coupled semiconductor charge qubits.

We study coherent dynamics of two spatially separated electrons in a coupled semiconductor double quantum dot (DQD). Coherent oscillations in one DQD are strongly influenced by electronic states of the other DQD, or the two electrons simultaneously tunnel in a correlated manner. The observed coherent oscillations are interpreted as various two-qubit operations.

Voltage-pulse-induced electromigration.

We propose and demonstrate a voltage-pulse-induced electromigration technique, in which electromigration in a gold nanowire is induced for a short period of about 10 µs by applying a voltage pulse. A local temperature analysis and a controlled electromigration experiment in the presence of voltage pulses indicate successful control of this voltage-pulsed-induced electromigration. We also measured the current-voltage characteristics of the nanowire after the application of each single voltage pulse to investigate the stochastic behavior of electromigration.

Direct measurement of the binding energy and bohr radius of a single hydrogenic defect in a semiconductor quantum well.

Low-temperature scanning tunneling spectroscopy under ultrahigh vacuum was used to study donor point defects located at the epitaxial surface of an In(0.53)Ga(0.47)As quantum well.

Bidirectional counting of single electrons.

A bidirectional single-electron counting device is demonstrated. Individual electrons flowing in forward and reverse directions through a double quantum dot are detected with a quantum point contact acting as a charge sensor. A comprehensive statistical analysis in the frequency and time domains and of higher order moments of noise reveals antibunching correlation in single-electron transport through the device itself.

Allowed and forbidden transitions in artificial hydrogen and helium atoms.

The strength of radiative transitions in atoms is governed by selection rules that depend on the occupation of atomic orbitals with electrons. Experiments have shown similar electron occupation of the quantized energy levels in semiconductor quantum dots--often described as artificial atoms. But unlike real atoms, the confinement potential of quantum dots is anisotropic, and the electrons can easily couple with phonons of the material.