Abstract
This thesis presents the study of solid-state quantum emitters in two dierent forms. The
rst part of the thesis deals with quantum dot based single-photon sources with an emphasis
on ecient photon extraction into an optical ber. The second part of the thesis covers a
theoretical study of optical refrigeration with coupled quantum wells.
Many photonic quantum information processing applications would benet from a highbrightness,
ber-coupled source of triggered single photons. This thesis presents a study
of such sources based on quantum dots coupled to unidirectional photonic-crystal waveguide
devices, where the out-coupling section of the device is separated from the strong
emitter-waveguide coupling section. Two out-coupling methods are investigated. The rst
method, end-re coupling from a tapered waveguide to a lensed ber, yields a chip-to-ber
coupling eciency of 16.6 %, which is calculated through the characterization of single
quantum dots. The second method, evanescent coupling from a tapered waveguide to a
microber, demonstrates a chip-to-ber coupling eciency exceeding 80 % in passive re-
ection measurements. The characterization of quantum dots from this device establishes
a ber-coupled source eciency of 15.6 %. This latter method opens a promising future
for increasing the eciency and reliability of planar chip-based single-photon sources.
Refrigeration of a solid-state system with light has potential applications for cooling
small-scale electronic and photonic circuits. We show theoretically that two coupled
semiconductor quantum wells are ecient cooling media because they support long-lived
indirect electron-hole pairs. These pairs can be thermally excited to distinct higher-energy
states with faster radiative recombination, thereby creating an ecient escape channel to
remove thermal energy from the system. From band-diagram calculations along with an
experimentally realistic level scheme we calculate the cooling eciency and cooling yield
of dierent devices with coupled quantum wells embedded in a suspended nanomembrane
rst part of the thesis deals with quantum dot based single-photon sources with an emphasis
on ecient photon extraction into an optical ber. The second part of the thesis covers a
theoretical study of optical refrigeration with coupled quantum wells.
Many photonic quantum information processing applications would benet from a highbrightness,
ber-coupled source of triggered single photons. This thesis presents a study
of such sources based on quantum dots coupled to unidirectional photonic-crystal waveguide
devices, where the out-coupling section of the device is separated from the strong
emitter-waveguide coupling section. Two out-coupling methods are investigated. The rst
method, end-re coupling from a tapered waveguide to a lensed ber, yields a chip-to-ber
coupling eciency of 16.6 %, which is calculated through the characterization of single
quantum dots. The second method, evanescent coupling from a tapered waveguide to a
microber, demonstrates a chip-to-ber coupling eciency exceeding 80 % in passive re-
ection measurements. The characterization of quantum dots from this device establishes
a ber-coupled source eciency of 15.6 %. This latter method opens a promising future
for increasing the eciency and reliability of planar chip-based single-photon sources.
Refrigeration of a solid-state system with light has potential applications for cooling
small-scale electronic and photonic circuits. We show theoretically that two coupled
semiconductor quantum wells are ecient cooling media because they support long-lived
indirect electron-hole pairs. These pairs can be thermally excited to distinct higher-energy
states with faster radiative recombination, thereby creating an ecient escape channel to
remove thermal energy from the system. From band-diagram calculations along with an
experimentally realistic level scheme we calculate the cooling eciency and cooling yield
of dierent devices with coupled quantum wells embedded in a suspended nanomembrane
| Original language | English |
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| Publisher | The Niels Bohr Institute, Faculty of Science, University of Copenhagen |
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| Publication status | Published - 2016 |