12 research outputs found
Generation of ultrabright tunable polarization entanglement without spatial, spectral, or temporal constraints
The need for spatial and spectral filtering in the generation of polarization
entanglement is eliminated by combining two coherently-driven type-II
spontaneous parametric downconverters. The resulting ultrabright source emits
photon pairs that are polarization entangled over the entire spatial cone and
spectrum of emission. We detect a flux of 12 000 polarization-entangled
pairs/s per mW of pump power at 90% quantum-interference visibility, and the
source can be temperature tuned for 5 nm around frequency degeneracy. The
output state is actively controlled by precisely adjusting the relative phase
of the two coherent pumps.Comment: 10 pages, 5 figure
High resolution coherent population trapping on a single hole spin in a semiconductor
We report high resolution coherent population trapping on a single hole spin
in a semiconductor quantum dot. The absorption dip signifying the formation of
a dark state exhibits an atomic physics-like dip width of just 10 MHz. We
observe fluctuations in the absolute frequency of the absorption dip, evidence
of very slow spin dephasing. We identify this process as charge noise by,
first, demonstrating that the hole spin g-factor in this configuration
(in-plane magnetic field) is strongly dependent on the vertical electric field,
and second, by characterizing the charge noise through its effects on the
optical transition frequency. An important conclusion is that charge noise is
an important hole spin dephasing process
A high-flux source of polarization-entangled photons from a periodically-poled KTP parametric downconverter
We have demonstrated a high-flux source of polarization-entangled photons
using a type-II phase-matched periodically-poled KTP parametric downconverter
in a collinearly propagating configuration. We have observed quantum
interference between the single-beam downconverted photons with a visibility of
99% and a measured coincidence flux of 300/s/mW of pump. The
Clauser-Horne-Shimony-Holt version of Bell's inequality was violated with a
value of 2.711 +/- 0.017.Comment: 7 pages submitted to Physical Review
Electro-elastic tuning of single particles in individual self-assembled quantum dots
We investigate the effect of uniaxial stress on InGaAs quantum dots in a
charge tunable device. Using Coulomb blockade and photoluminescence, we observe
that significant tuning of single particle energies (~ -0.5 meV/MPa) leads to
variable tuning of exciton energies (+18 to -0.9 micro-eV/MPa) under tensile
stress. Modest tuning of the permanent dipole, Coulomb interaction and
fine-structure splitting energies is also measured. We exploit the variable
exciton response to tune multiple quantum dots on the same chip into resonance.Comment: 16 pages, 4 figures, 1 table. Final versio
Basic Atomic Physics
Contains reports on five research projects.National Science Foundation Grant PHY 96-024740National Science Foundation Grant PHY 92-21489U.S. Navy - Office of Naval Research Contract N00014-96-1-0484Joint Services Electronics Program Grant DAAHO4-95-1-0038National Science Foundation Grant PHY95-14795U.S. Army Research Office Contract DAAHO4-94-G-0170U.S. Army Research Office Contract DAAG55-97-1-0236U.S. Army Research Office Contract DAAH04-95-1-0533U.S. Navy - Office of Naval Research Contract N00014-96-1-0432National Science Foundation Contract PHY92-22768David and Lucile Packard Foundation Grant 96-5158National Science Foundation Grant PHY 95-01984U.S. Army Research OfficeU.S. Navy - Office of Naval Research Contract N00014-96-1-0485AASERT N00014-94-1-080
Basic Atomic Physics
Contains reports on five research projects.Joint Services Electronics Program Grant DAAH04-95-1-0038National Science Foundation Grant PHY 92-21489U.S. Navy - Office of Naval Research Grant N00014-90-J-1322National Science Foundation Grant PHY95-14795Charles S. Draper Laboratory Contract DL-H-484775U.S. Army Research Office Contract DAAH04-94-G-0170U.S. Army Research Office Contract DAAH04-95-1-0533U.S. Navy - Office of Naval Research Contract N00014-89-J-1207U.S. Navy - Office of Naval Research Contract N000014-96-1-0432David and Lucile Packard Foundation Grant 96-5158National Science Foundation Grant PHY95-01984U.S. Army - Office of ResearchU.S. Navy - Office of Naval Research Contract N00014-96-1-0485U.S. Navy - Office of Naval Research AASERT N00014-94-1-080
Exciton fine-structure splitting of telecom-wavelength single quantum dots : Statistics and external strain tuning
In a charge tunable device, we investigate the fine structure splitting of
neutral excitons in single long-wavelength (1.1\mu m < \lambda < 1.3 \mu m)
InGaAs quantum dots as a function of external uniaxial strain. Nominal fine
structure splittings between 16 and 136 \mu eV are measured and manipulated. We
observe varied response of the splitting to the external strain, including
positive and negative tuning slopes, different tuning ranges, and linear and
parabolic dependencies, indicating that these physical parameters depend
strongly on the unique microscopic structure of the individual quantum dot. To
better understand the experimental results, we apply a phenomenological model
describing the exciton polarization and fine-structure splitting under uniaxial
strain. The model predicts that, with an increased experimental strain tuning
range, the fine-structure can be effectively canceled for select telecom
wavelength dots using uniaxial strain. These results are promising for the
generation of on-demand entangled photon pairs at telecom wavelengths.Comment: 15 pages, 3 figure