334 research outputs found
Spin Fine Structure in Optically Excited Quantum Dot Molecules
The interaction between spins in coupled quantum dots is revealed in distinct
fine structure patterns in the measured optical spectra of InAs/GaAs double
quantum dot molecules containing zero, one, or two excess holes. The fine
structure is explained well in terms of a uniquely molecular interplay of spin
exchange interactions, Pauli exclusion and orbital tunneling. This knowledge is
critical for converting quantum dot molecule tunneling into a means of
optically coupling not just orbitals, but spins.Comment: 10 pages, 7 figures, added material, (published
Optical Spin Initialization and Non-Destructive Measurement in a Quantum Dot Molecule
The spin of an electron in a self-assembled InAs/GaAs quantum dot molecule is
optically prepared and measured through the trion triplet states. A
longitudinal magnetic field is used to tune two of the trion states into
resonance, forming a superposition state through asymmetric spin exchange. As a
result, spin-flip Raman transitions can be used for optical spin
initialization, while separate trion states enable cycling transitions for
non-destructive measurement. With two-laser transmission spectroscopy we
demonstrate both operations simultaneously, something not previously
accomplished in a single quantum dot.Comment: Accepted for publication in Phys. Rev. Let
Photoluminescence Spectroscopy of the Molecular Biexciton in Vertically Stacked Quantum Dot Pairs
We present photoluminescence studies of the molecular neutral
biexciton-exciton spectra of individual vertically stacked InAs/GaAs quantum
dot pairs. We tune either the hole or the electron levels of the two dots into
tunneling resonances. The spectra are described well within a few-level,
few-particle molecular model. Their properties can be modified broadly by an
electric field and by structural design, which makes them highly attractive for
controlling nonlinear optical properties.Comment: 4 pages, 5 figures, (v2, revision based on reviewers comments,
published
Measuring Temperature Gradients over Nanometer Length Scales
When a quantum dot is subjected to a thermal gradient, the temperature of
electrons entering the dot can be determined from the dot's thermocurrent if
the conductance spectrum and background temperature are known. We demonstrate
this technique by measuring the temperature difference across a 15 nm quantum
dot embedded in a nanowire. This technique can be used when the dot's energy
states are separated by many kT and will enable future quantitative
investigations of electron-phonon interaction, nonlinear thermoelectric
effects, and the effciency of thermoelectric energy conversion in quantum dots.Comment: 6 pages, 5 figure
Electrically tunable g-factors in quantum dot molecular spin states
We present a magneto-photoluminescence study of individual vertically stacked
InAs/GaAs quantum dot pairs separated by thin tunnel barriers. As an applied
electric field tunes the relative energies of the two dots, we observe a strong
resonant increase or decrease in the g-factors of different spin states that
have molecular wavefunctions distributed over both quantum dots. We propose a
phenomenological model for the change in g-factor based on resonant changes in
the amplitude of the wavefunction in the barrier due to the formation of
bonding and antibonding orbitals.Comment: 5 pages, 5 figures, Accepted by Phys. Rev. Lett. New version reflects
response to referee comment
Sequential and co-tunneling behavior in the temperature-dependent thermopower of few-electron quantum dots
We have studied the temperature dependent thermopower of gate-defined,
lateral quantum dots in the Coulomb blockade regime using an electron heating
technique. The line shape of the thermopower oscillations depends strongly on
the contributing tunneling processes. Between 1.5 K and 40 mK a crossover from
a pure sawtooth- to an intermitted sawtooth-like line shape is observed. The
latter is attributed to the increasing dominance of cotunneling processes in
the Coulomb blockade regime at low temperatures.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Optically-controlled single-qubit rotations in self-assembled InAs quantum dots
We present a theory of the optical control of the spin of an electron in an
InAs quantum dot. We show how two Raman-detuned laser pulses can be used to
obtain arbitrary single-qubit rotations via the excitation of an intermediate
trion state. Our theory takes into account a finite in-plane hole -factor
and hole-mixing. We show that such rotations can be performed to high
fidelities with pulses lasting a few tens of picoseconds.Comment: 6 pages, 4 figures; minor changes, J-ref adde
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