arXiv subjects

Tomohiro Otsuka

Publications and source records attributed to Tomohiro Otsuka.

43 records · Page 3Linked to original sources

arXiv2014

Single to quadruple quantum dots with tunable tunnel couplings

We prepare a gate-defined quadruple quantum dot to study the gate-tunability of single to quadruple quantum dots with finite inter-dot tunnel couplings. The measured charging energies of various double dots suggest that the dot size is governed by gate geometry. For the triple and quadruple dots we study gate-tunable inter-dot tunnel couplings. Particularly for the triple dot we find that the effective tunnel coupling between side dots significantly depends on the alignment of the center dot potential. These results imply that the present quadruple dot device has gate performance relevant for implementing spin-based four-qubit systems with controllable exchange couplings.

cond-mat.mes-hall↗

arXiv2012

Detection of spin polarization utilizing singlet and triplet states in a single-lead quantum dot

We propose and demonstrate a new method to probe local spin polarization in semiconductor micro devices at low and zero magnetic fields. By connecting a single-lead quantum dot to a semiconductor micro device and monitoring electron tunneling into singlet and triplet states in the dot, we can detect the local spin polarization formed in the target device. We confirm the validity of this detection scheme utilizing spin split quantum Hall edge states. We also observe non-zero local spin polarization at the device edge in low magnetic fields, which is not detectable with conventional macroscopic probes.

cond-mat.mes-hall↗

arXiv2010

Probing local electronic states in the quantum Hall regime with a side coupled quantum dot

We demonstrate a new method for locally probing the edge states in the quantum Hall regime utilizing a side coupled quantum dot positioned at an edge of a Hall bar. By measuring the tunneling of electrons from the edge states into the dot, we acquire information on the local electrochemical potential and electron temperature of the edge states. Furthermore, this method allows us to observe the spatial modulation of the electrostatic potential at the edge state due to many-body screening effect.

cond-mat.mes-hall↗

arXiv2009

Detection of spin polarization with a side coupled quantum dot

We propose realistic methods to detect local spin polarization, which utilize a quantum dot side coupled to the target system. By choosing appropriate states in the dot, we can put spin selectivity to the dot and detect spins in the target with small disturbance. We also present an experiment which realizes one of the proposed spin detection schemes in magnetic fields.

cond-mat.mes-hall↗

arXiv2008

Excited-state spectroscopy on a quantum dot side-coupled to a quantum wire

We report excited-state spectroscopy on a quantum dot side-coupled to a quantum wire with accurate energy estimation. Our method utilizes periodic voltage pulses on the dot, and the energy calibration is performed with reference to the bias voltage across the wire. We demonstrate the observation of the orbital excited state and the Zeeman splitting in a single dot.

cond-mat.mes-hall↗

arXiv2007

Fano Effect in a Few-Electron Quantum Dot

We have studied the Fano effect in a few-electron quantum dot side-coupled to a quantum wire. The conductance of the wire, which shows an ordinal staircase-like quantization without the dot, is modified through the interference (the Fano effect) and the charging effects. These effects are utilized to verify the exhaustion of electrons in the dot. The "addition energy spectrum" of the dot shows a shell structure, indicating that the electron confinement potential is fairly circular. A rapid sign inversion of the Fano parameter on the first conductance plateau with the change of the wire gate voltage has been observed, and explained by introducing a finite width of dot-wire coupling.

cond-mat.mes-hall↗

arXiv2005

Breakdown of `phase rigidity' and variations of the Fano effect in closed Aharonov-Bohm interferometers

Although the conductance of a closed Aharonov-Bohm interferometer, with a quantum dot on one branch, obeys the Onsager symmetry under magnetic field reversal, it needs not be a periodic function of this field: the conductance maxima move with both the field and the gate voltage on the dot, in an apparent breakdown of `phase rigidity'. These experimental findings are explained theoretically as resulting from multiple electronic paths around the interferometer ring. Data containing several Coulomb blockade peaks, whose shapes change with the magnetic flux, are fitted to a simple model, in which each resonant level on the dot couples to a different path around the ring.

cond-mat.mes-hall↗