arXiv subjects

F. Minami

Publications and source records attributed to F. Minami.

6 recordsLinked to original sources

arXiv2008

Photon correlation in GaAs self-assembled quantum dots

We report on photon coincidence measurement in a single GaAs self-assembled quantum dot (QD) using a pulsed excitation light source. At low excitation, when a neutral exciton line was present in the photoluminescence (PL) spectrum, we observed nearly perfect single photon emission from an isolated QD at 670 nm wavelength. For higher excitation, multiple PL lines appeared on the spectra, reflecting the formation of exciton complexes. Cross-correlation functions between these lines showed either bunching or antibunching behavior, depending on whether the relevant emission was from a biexciton cascade or a charged exciton recombination.

cond-mat.other↗

arXiv2006

Self-assembly of laterally aligned GaAs quantum dot pairs

We report the fabrication of self-assembled, strain-free GaAs/Al$_{0.27}$Ga$_{0.73}$As quantum dot pairs which are laterally aligned in the growth plane, utilizing the droplet epitaxy technique and the anisotropic surface potentials of the GaAs (100) surface for the migration of Ga adatoms. Photoluminescence spectra from a single quantum dot pair, consisting of a doublet, have been observed. Finite element energy level calculations of a model quantum dot pair are also presented.

cond-mat.mtrl-sci↗

arXiv2004

Theory of multiwave mixing and decoherence control in qubit array system

We develop a theory to analyze the decoherence effect in a charged qubit array system with photon echo signals in the multiwave mixing configuration. We present how the decoherence suppression effect by the {\it bang-bang} control with the $π$ pulses can be demonstrated in laboratory by using a bulk ensemble of exciton qubits and optical pulses whose pulse area is even smaller than $π$. Analysis is made on the time-integated multiwave mixing signals diffracted into certain phase matching directions from a bulk ensemble. Depending on the pulse interval conditions, the cross over from the decoherence acceleration regime to the decoherence suppression regime, which is a peculiar feature of the coherent interaction between a qubit and the reservoir bosons, may be observed in the time-integated multiwave mixing signals in the realistic case including inhomogeneous broadening effect. Our analysis will successfully be applied to precise estimation of the reservoir parameters from experimental data of the direction resolved signal intensities obtained in the multiwave mixing technique.

quant-ph↗

arXiv2003

Photo-induced spin dynamics in ferromagnetic semiconductor $p$-(Ga,Mn)As

Spin dynamics in ferromagnetic $p$-(Ga,Mn)As ($x$ = 0.011, $T_{C}$ = 30 K) has been studied by carefully comparing the decay time of the photo-induced reflectivity change with the transient behavior of polar Kerr rotation induced by photo-generated carrier spins with a femtosecond light pulse of various polarizations. As to the rising process, the rate of Kerr rotation is found comparable to the generation rate of spin-polarized carriers. For the decay process, the Kerr rotation and reflectivity signal both show the same decay rate at above the $T_{C}$, whereas, below the $T_{C}$, the former becomes slower than the latter. The magnitude of Kerr rotation suggests that 10$^{2}$ Mn spins are revolved by injecting one hole spin. On the basis of these observations, collective rotation of ferromagnetically coupled Mn spins is discussed in terms of $p$-$d$ exchange interaction and successive transverse spin relaxation. Development of another long-lived behavior under external perpendicular magnetic fields is also disclosed.

cond-mat.mtrl-sci↗

arXiv2003

Nonlinear Rabi Oscillations of Excitons in Dense Quantum Dot System

Nonlinear optical response and optical coherence of excitons in semiconductor dense quantum dots in GaAs single quantum wells has been studied by using photon echo techniques. At low temperatures, the optical coherence is estimated to be 2 ns from the decay curve in the photon echo signal. Rabi oscillations are also observed. Unlike the results for a single quantum dot in the literature to date, the oscillation shows nonlinear behavior affected strongly by the pre-excited carrier density. The results can be explained by the theory of the local field correction originating from exciton-exciton interaction between the inter dots.

cond-mat.mtrl-sci↗

arXiv2002

Picosecond Nonlinear Relaxation of Photoinjected Carriers in a Single GaAs/AlGaAs Quantum Dot

Photoemission from a single self-organized GaAs/AlGaAs quantum dot (QD) is temporally resolved with picosecond time resolution. The emission spectra consisting of the multiexciton structures are observed to depend on the delay time and the excitation intensity. Quantitative agreement is found between the experimental data and the calculation based on a model which characterizes the successive relaxation of multiexcitons. Through the analysis we can determine the carrier relaxation time as a function of population of photoinjected carriers. Enhancement of the intra-dot carrier relaxation is demonstrated to be due to the carrier-carrier scattering inside a single QD.

cond-mat.mtrl-sci↗