344 research outputs found
Distilling entanglement from cascades with partial "Which Path" ambiguity
We develop a framework to calculate the density matrix of a pair of photons
emitted in a decay cascade with partial "which path" ambiguity. We describe an
appropriate entanglement distillation scheme which works also for certain
random cascades. The qualitative features of the distilled entanglement are
presented in a two dimensional "phase diagram". The theory is applied to the
quantum tomography of the decay cascade of a biexciton in a semiconductor
quantum dot. Agreement with experiment is obtained
Formation of a high quality two-dimensional electron gas on cleaved GaAs
We have succeeded in fabricating a two-dimensional electron gas (2DEG) on the cleaved (110) edge of a GaAs wafer by molecular beam epitaxy (MBE). A (100) wafer previously prepared by MBE growth is reinstalled in the MBE chamber so that an in situ cleave exposes a fresh (110) GaAs edge for further MBE overgrowth. A sequence of Si-doped AlGaAs layers completes the modulation-doped structure at the cleaved edge. Mobilities as high as 6.1×10^5 cm^2/V s are measured in the 2DEG at the cleaved interface
Radiative cascade from quantum dot metastable spin-blockaded biexciton
We detect a novel radiative cascade from a neutral semiconductor quantum dot.
The cascade initiates from a metastable biexciton state in which the holes form
a spin-triplet configuration, Pauli-blockaded from relaxation to the
spin-singlet ground state. The triplet biexciton has two photon-phonon-photon
decay paths. Unlike in the singlet-ground state biexciton radiative cascade, in
which the two photons are co-linearly polarized, in the triplet biexciton
cascade they are crosslinearly polarized. We measured the two-photon
polarization density matrix and show that the phonon emitted when the
intermediate exciton relaxes from excited to ground state, preserves the
exciton's spin. The phonon, thus, does not carry with it any which-path
information other than its energy. Nevertheless, entanglement distillation by
spectral filtering was found to be rather ineffective for this cascade. This
deficiency results from the opposite sign of the anisotropic electron-hole
exchange interaction in the excited exciton relative to that in the ground
exciton.Comment: 6 pages, 4 figure
Carrier-carrier relaxation kinetics in quantum well semiconductor structures with nonparabolic energy bands
Depolarization of Electronic Spin Qubits Confined in Semiconductor Quantum Dots
Quantum dots are arguably the best interface between matter spin qubits and
flying photonic qubits. Using quantum dot devices to produce joint
spin-photonic states requires the electronic spin qubits to be stored for
extended times. Therefore, the study of the coherence of spins of various
quantum dot confined charge carriers is important both scientifically and
technologically. In this study we report on spin relaxation measurements
performed on five different forms of electronic spin qubits confined in the
very same quantum dot. In particular, we use all optical techniques to measure
the spin relaxation of the confined heavy hole and that of the dark exciton - a
long lived electron-heavy hole pair with parallel spins. Our measured results
for the spin relaxation of the electron, the heavy-hole, the dark exciton, the
negative and the positive trions, in the absence of externally applied magnetic
field, are in agreement with a central spin theory which attributes the
dephasing of the carriers' spin to their hyperfine interactions with the
nuclear spins of the atoms forming the quantum dots. We demonstrate that the
heavy hole dephases much slower than the electron. We also show, both
experimentally and theoretically, that the dark exciton dephases slower than
the heavy hole, due to the electron-hole exchange interaction, which partially
protects its spin state from dephasing.Comment: 12 pages, 5 figures, 1 tabl
Multi-Exciton Spectroscopy of a Single Self Assembled Quantum Dot
We apply low temperature confocal optical microscopy to spatially resolve,
and spectroscopically study a single self assembled quantum dot. By comparing
the emission spectra obtained at various excitation levels to a theoretical
many body model, we show that: Single exciton radiative recombination is very
weak. Sharp spectral lines are due to optical transitions between confined
multiexcitonic states among which excitons thermalize within their lifetime.
Once these few states are fully occupied, broad bands appear due to transitions
between states which contain continuum electrons.Comment: 12 pages, 4 figures, submitted for publication on Jan,28 199
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