458 research outputs found
The visibility study of S-T Landau-Zener-St\"uckelberg oscillations without applied initialization
Probabilities deduced from quantum information studies are usually based on
averaging many identical experiments separated by an initialization step. Such
initialization steps become experimentally more challenging to implement as the
complexity of quantum circuits increases. To better understand the consequences
of imperfect initialization on the deduced probabilities, we study the effect
of not initializing the system between measurements. For this we utilize
Landau-Zener-St\"uckelberg oscillations in a double quantum dot circuit.
Experimental results are successfully compared to theoretical simulations.Comment: 8 pages, 5 figure
Characteristics of GaInNAsSb VCSELs operating near 1.55µm
A detailed study of the high-power pulsed operation of C-band optically-pumped GaInNAsSb vertical cavity surface emitting lasers is reported. The devices employ a resonant periodic gain structure grown by molecular beam epitaxy on a GaAs substrate with a 31-pair GaAs/AlAs bottom distributed Bragg reflector and a 4-λ, GaAs-based resonant cavity containing 10 GaInNAsSb quantum wells distributed among the 7 antinodes of the electric field. A dual-pump-band SiO2/TiO2 dielectric top mirror allows efficient optical pumping via low reflectivities at 808nm and 1064nm while providing very high reflectivity at the 1.55μm target emission wavelength. The laser characteristics were evaluated using both a Q-switched Nd:YAG 1064nm pump and a 20W-peak 180ns-pulsed 850nm diode laser. The importance of the gain-cavity detuning was evident from time-dependent spectral measurements of laser material subjected to post-growth annealing at different temperatures between 725 and 775°C. The highest annealing temperature produces the largest blue shift of the gain peak relative to the cavity resonance, resulting in the best power transfer characteristics as well as reduced temperature sensitivity
Enhanced charge detection of spin qubit readout via an intermediate state
We employ an intermediate excited charge state of a lateral quantum dot
device to increase the charge detection contrast during the qubit state readout
procedure, allowing us to increase the visibility of coherent qubit
oscillations. This approach amplifies the coherent oscillation magnitude but
has no effect on the detector noise resulting in an increase in the signal to
noise ratio. In this letter we apply this scheme to demonstrate a significant
enhancement of the fringe contrast of coherent Landau-Zener-Stuckleberg
oscillations between singlet S and triplet T+ two-spin states.Comment: 3 pages, 3 figure
Second-Order Nonlinear Mixing of Two Modes in a Planar Photonic Crystal Microcavity
Polarization-resolved second-harmonic spectra are obtained from the resonant
modes of a two-dimensional planar photonic crystal microcavity patterned in a
free-standing InP slab. The photonic crystal microcavity is comprised of a
single missing-hole defect in a hexagonal photonic crystal host formed with
elliptically-shaped holes. The cavity supports two orthogonally-polarized
resonant modes split by 60 wavenumbers. Sum-frequency data are reported from
the nonlinear interaction of the two coherently excited modes, and the
polarization dependence is explained in terms of the nonlinear susceptibility
tensor of the host InP.Comment: 7 pages, 8 Postscript figures, to be presented at Photonics West Jan.
2
Tuning the exciton g-factor in single InAs/InP quantum dots
Photoluminescence data from single, self-assembled InAs/InP quantum dots in
magnetic fields up to 7 T are presented. Exciton g-factors are obtained for
dots of varying height, corresponding to ground state emission energies ranging
from 780 meV to 1100 meV. A monotonic increase of the g-factor from -2 to +1.2
is observed as the dot height decreases. The trend is well reproduced by sp3
tight binding calculations, which show that the hole g-factor is sensitive to
confinement effects through orbital angular momentum mixing between the
light-hole and heavy-hole valence bands. We demonstrate tunability of the
exciton g-factor by manipulating the quantum dot dimensions using pyramidal InP
nanotemplates
Gate Adjustable Coherent Three and Four Level Mixing in a Vertical Quantum Dot Molecule
We study level mixing in the single particle energy spectrum of one of the
constituent quantum dots in a vertical double quantum dot by performing
magneto-resonant-tunneling spectroscopy. The device used in this study differs
from previous vertical double quantum dot devices in that the single side gate
is now split into four separate gates. Because of the presence of natural
perturbations caused by anharmonicity and anistrophy, applying different
combinations of voltages to these gates allows us to alter the effective
potential landscape of the two dots and hence influence the level mixing. We
present here preliminary results from one three level crossing and one four
level crossings high up in the energy spectrum of one of the probed quantum
dots, and demonstrate that we are able to change significantly the energy
dispersions with magnetic field in the vicinity of the crossing regions.Comment: 5 pages, 4 figures. MSS-14 conference proceedings submitted to
Physica
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